Title: | Community Ecology Package |
---|---|
Description: | Ordination methods, diversity analysis and other functions for community and vegetation ecologists. |
Authors: | Jari Oksanen [aut, cre], Gavin L. Simpson [aut], F. Guillaume Blanchet [aut], Roeland Kindt [aut], Pierre Legendre [aut], Peter R. Minchin [aut], R.B. O'Hara [aut], Peter Solymos [aut], M. Henry H. Stevens [aut], Eduard Szoecs [aut], Helene Wagner [aut], Matt Barbour [aut], Michael Bedward [aut], Ben Bolker [aut], Daniel Borcard [aut], Tuomas Borman [aut], Gustavo Carvalho [aut], Michael Chirico [aut], Miquel De Caceres [aut], Sebastien Durand [aut], Heloisa Beatriz Antoniazi Evangelista [aut], Rich FitzJohn [aut], Michael Friendly [aut], Brendan Furneaux [aut], Geoffrey Hannigan [aut], Mark O. Hill [aut], Leo Lahti [aut], Dan McGlinn [aut], Marie-Helene Ouellette [aut], Eduardo Ribeiro Cunha [aut], Tyler Smith [aut], Adrian Stier [aut], Cajo J.F. Ter Braak [aut], James Weedon [aut] |
Maintainer: | Jari Oksanen <[email protected]> |
License: | GPL-2 |
Version: | 2.7-0 |
Built: | 2024-11-21 08:27:04 UTC |
Source: | https://github.com/vegandevs/vegan |
The vegan package provides tools for descriptive community ecology. It has most basic functions of diversity analysis, community ordination and dissimilarity analysis. Most of its multivariate tools can be used for other data types as well.
The functions in the vegan package contain tools for diversity analysis, ordination methods and tools for the analysis of dissimilarities. Together with the labdsv package, the vegan package provides most standard tools of descriptive community analysis. Package ade4 provides an alternative comprehensive package, and several other packages complement vegan and provide tools for deeper analysis in specific fields. Package BiodiversityR provides a GUI for a large subset of vegan functionality.
The vegan package is developed at GitHub (https://github.com/vegandevs/vegan/). GitHub provides up-to-date information and forums for bug reports.
Most important changes in vegan documents can be read with
news(package="vegan")
and vignettes can be browsed with
browseVignettes("vegan")
. The vignettes include a vegan
FAQ, discussion on design decisions, short introduction to ordination
and discussion on diversity methods.
To see the preferable citation of the package, type
citation("vegan")
.
The vegan development team is Jari Oksanen, F. Guillaume Blanchet, Roeland Kindt, Pierre Legendre, Peter R. Minchin, R. B. O'Hara, Gavin L. Simpson, Peter Solymos, M. Henry H. Stevens, Helene Wagner. Many other people have contributed to individual functions: see credits in function help pages.
### Example 1: Unconstrained ordination ## NMDS data(varespec) data(varechem) ord <- metaMDS(varespec) plot(ord, type = "t") ## Fit environmental variables ef <- envfit(ord, varechem) ef plot(ef, p.max = 0.05) ### Example 2: Constrained ordination (RDA) ## The example uses formula interface to define the model data(dune) data(dune.env) ## No constraints: PCA mod0 <- rda(dune ~ 1, dune.env) mod0 plot(mod0) ## All environmental variables: Full model mod1 <- rda(dune ~ ., dune.env) mod1 plot(mod1) ## Automatic selection of variables by permutation P-values mod <- ordistep(mod0, scope=formula(mod1)) mod plot(mod) ## Permutation test for all variables anova(mod) ## Permutation test of "type III" effects, or significance when a term ## is added to the model after all other terms anova(mod, by = "margin") ## Plot only sample plots, use different symbols and draw SD ellipses ## for Managemenet classes plot(mod, display = "sites", type = "n") with(dune.env, points(mod, disp = "si", pch = as.numeric(Management))) with(dune.env, legend("topleft", levels(Management), pch = 1:4, title = "Management")) with(dune.env, ordiellipse(mod, Management, label = TRUE)) ## add fitted surface of diversity to the model ordisurf(mod, diversity(dune), add = TRUE) ### Example 3: analysis of dissimilarites a.k.a. non-parametric ### permutational anova adonis2(dune ~ ., dune.env) adonis2(dune ~ Management + Moisture, dune.env)
### Example 1: Unconstrained ordination ## NMDS data(varespec) data(varechem) ord <- metaMDS(varespec) plot(ord, type = "t") ## Fit environmental variables ef <- envfit(ord, varechem) ef plot(ef, p.max = 0.05) ### Example 2: Constrained ordination (RDA) ## The example uses formula interface to define the model data(dune) data(dune.env) ## No constraints: PCA mod0 <- rda(dune ~ 1, dune.env) mod0 plot(mod0) ## All environmental variables: Full model mod1 <- rda(dune ~ ., dune.env) mod1 plot(mod1) ## Automatic selection of variables by permutation P-values mod <- ordistep(mod0, scope=formula(mod1)) mod plot(mod) ## Permutation test for all variables anova(mod) ## Permutation test of "type III" effects, or significance when a term ## is added to the model after all other terms anova(mod, by = "margin") ## Plot only sample plots, use different symbols and draw SD ellipses ## for Managemenet classes plot(mod, display = "sites", type = "n") with(dune.env, points(mod, disp = "si", pch = as.numeric(Management))) with(dune.env, legend("topleft", levels(Management), pch = 1:4, title = "Management")) with(dune.env, ordiellipse(mod, Management, label = TRUE)) ## add fitted surface of diversity to the model ordisurf(mod, diversity(dune), add = TRUE) ### Example 3: analysis of dissimilarites a.k.a. non-parametric ### permutational anova adonis2(dune ~ ., dune.env) adonis2(dune ~ Management + Moisture, dune.env)
Compute all single terms that can be added to or dropped from a constrained ordination model.
## S3 method for class 'cca' add1(object, scope, test = c("none", "permutation"), permutations = how(nperm=199), ...) ## S3 method for class 'cca' drop1(object, scope, test = c("none", "permutation"), permutations = how(nperm=199), ...)
## S3 method for class 'cca' add1(object, scope, test = c("none", "permutation"), permutations = how(nperm=199), ...) ## S3 method for class 'cca' drop1(object, scope, test = c("none", "permutation"), permutations = how(nperm=199), ...)
object |
A constrained ordination object from
|
scope |
A formula giving the terms to be considered for adding
or dropping; see |
test |
Should a permutation test be added using |
permutations |
a list of control values for the permutations
as returned by the function |
... |
Other arguments passed to |
With argument test = "none"
the functions will only call
add1.default
or drop1.default
. With
argument test = "permutation"
the functions will add test
results from anova.cca
. Function drop1.cca
will
call anova.cca
with argument by = "margin"
.
Function add1.cca
will implement a test for single term
additions that is not directly available in anova.cca
.
Functions are used implicitly in step
,
ordiR2step
and ordistep
. The
deviance.cca
and deviance.rda
used in
step
have no firm basis, and setting argument test
= "permutation"
may help in getting useful insight into validity of
model building. Function ordistep
calls alternately
drop1.cca
and add1.cca
with argument
test = "permutation"
and selects variables by their permutation
-values. Meticulous use of
add1.cca
and
drop1.cca
will allow more judicious model building.
The default number of permutations
is set to a low value, because
permutation tests can take a long time. It should be sufficient to
give a impression on the significances of the terms, but higher
values of permutations
should be used if values really
are important.
Returns a similar object as add1
and drop1
.
Jari Oksanen
add1
, drop1
and
anova.cca
for basic methods. You probably need these
functions with step
and ordistep
. Functions
deviance.cca
and extractAIC.cca
are used
to produce the other arguments than test results in the
output.
data(dune) data(dune.env) ## Automatic model building based on AIC but with permutation tests step(cca(dune ~ 1, dune.env), reformulate(names(dune.env)), test="perm") ## see ?ordistep to do the same, but based on permutation P-values ## Not run: ordistep(cca(dune ~ 1, dune.env), reformulate(names(dune.env))) ## End(Not run) ## Manual model building ## -- define the maximal model for scope mbig <- rda(dune ~ ., dune.env) ## -- define an empty model to start with m0 <- rda(dune ~ 1, dune.env) ## -- manual selection and updating add1(m0, scope=formula(mbig), test="perm") m0 <- update(m0, . ~ . + Management) add1(m0, scope=formula(mbig), test="perm") m0 <- update(m0, . ~ . + Moisture) ## -- included variables still significant? drop1(m0, test="perm") add1(m0, scope=formula(mbig), test="perm")
data(dune) data(dune.env) ## Automatic model building based on AIC but with permutation tests step(cca(dune ~ 1, dune.env), reformulate(names(dune.env)), test="perm") ## see ?ordistep to do the same, but based on permutation P-values ## Not run: ordistep(cca(dune ~ 1, dune.env), reformulate(names(dune.env))) ## End(Not run) ## Manual model building ## -- define the maximal model for scope mbig <- rda(dune ~ ., dune.env) ## -- define an empty model to start with m0 <- rda(dune ~ 1, dune.env) ## -- manual selection and updating add1(m0, scope=formula(mbig), test="perm") m0 <- update(m0, . ~ . + Management) add1(m0, scope=formula(mbig), test="perm") m0 <- update(m0, . ~ . + Moisture) ## -- included variables still significant? drop1(m0, test="perm") add1(m0, scope=formula(mbig), test="perm")
In additive diversity partitioning, mean values of alpha diversity at lower levels of a sampling
hierarchy are compared to the total diversity in the entire data set (gamma diversity).
In hierarchical null model testing, a statistic returned by a function is evaluated
according to a nested hierarchical sampling design (hiersimu
).
adipart(...) ## Default S3 method: adipart(y, x, index=c("richness", "shannon", "simpson"), weights=c("unif", "prop"), relative = FALSE, nsimul=99, method = "r2dtable", ...) ## S3 method for class 'formula' adipart(formula, data, index=c("richness", "shannon", "simpson"), weights=c("unif", "prop"), relative = FALSE, nsimul=99, method = "r2dtable", ...) hiersimu(...) ## Default S3 method: hiersimu(y, x, FUN, location = c("mean", "median"), relative = FALSE, drop.highest = FALSE, nsimul=99, method = "r2dtable", ...) ## S3 method for class 'formula' hiersimu(formula, data, FUN, location = c("mean", "median"), relative = FALSE, drop.highest = FALSE, nsimul=99, method = "r2dtable", ...)
adipart(...) ## Default S3 method: adipart(y, x, index=c("richness", "shannon", "simpson"), weights=c("unif", "prop"), relative = FALSE, nsimul=99, method = "r2dtable", ...) ## S3 method for class 'formula' adipart(formula, data, index=c("richness", "shannon", "simpson"), weights=c("unif", "prop"), relative = FALSE, nsimul=99, method = "r2dtable", ...) hiersimu(...) ## Default S3 method: hiersimu(y, x, FUN, location = c("mean", "median"), relative = FALSE, drop.highest = FALSE, nsimul=99, method = "r2dtable", ...) ## S3 method for class 'formula' hiersimu(formula, data, FUN, location = c("mean", "median"), relative = FALSE, drop.highest = FALSE, nsimul=99, method = "r2dtable", ...)
y |
A community matrix. |
x |
A matrix with same number of rows as in |
formula |
A two sided model formula in the form |
data |
A data frame where to look for variables defined in the
right hand side of |
index |
Character, the diversity index to be calculated (see Details). |
weights |
Character, |
relative |
Logical, if |
nsimul |
Number of permutations to use. If |
method |
Null model method: either a name (character string) of
a method defined in |
FUN |
A function to be used by |
location |
Character, identifies which function (mean or median) is to be used to calculate location of the samples. |
drop.highest |
Logical, to drop the highest level or not. When
|
... |
Other arguments passed to functions, e.g. base of
logarithm for Shannon diversity, or |
Additive diversity partitioning means that mean alpha and beta
diversities add up to gamma diversity, thus beta diversity is measured
in the same dimensions as alpha and gamma (Lande 1996). This additive
procedure is then extended across multiple scales in a hierarchical
sampling design with levels of sampling
(Crist et al. 2003). Samples in lower hierarchical levels are nested
within higher level units, thus from
to
grain size
is increasing under constant survey extent. At each level
,
denotes average diversity found within samples.
At the highest sampling level, the diversity components are calculated as
For each lower sampling level as
Then, the additive partition of diversity is
Average alpha components can be weighted uniformly
(weight="unif"
) to calculate it as simple average, or
proportionally to sample abundances (weight="prop"
) to
calculate it as weighted average as follows
where
is the diversity index and
is the weight
calculated for the
th sample at the
th sampling level.
The implementation of additive diversity partitioning in
adipart
follows Crist et al. 2003. It is based on species
richness (, not
), Shannon's and Simpson's diversity
indices stated as the
index
argument.
The expected diversity components are calculated nsimul
times
by individual based randomisation of the community data matrix. This
is done by the "r2dtable"
method in oecosimu
by
default.
hiersimu
works almost in the same way as adipart
, but
without comparing the actual statistic values returned by FUN
to the highest possible value (cf. gamma diversity). This is so,
because in most of the cases, it is difficult to ensure additive
properties of the mean statistic values along the hierarchy.
An object of class "adipart"
or "hiersimu"
with same
structure as oecosimu
objects.
Péter Sólymos, [email protected]
Crist, T.O., Veech, J.A., Gering, J.C. and Summerville,
K.S. (2003). Partitioning species diversity across landscapes and
regions: a hierarchical analysis of ,
, and
-diversity. Am. Nat., 162, 734–743.
Lande, R. (1996). Statistics and partitioning of species diversity, and similarity among multiple communities. Oikos, 76, 5–13.
See oecosimu
for permutation settings and
calculating -values.
multipart
for multiplicative
diversity partitioning.
## NOTE: 'nsimul' argument usually needs to be >= 99 ## here much lower value is used for demonstration data(mite) data(mite.xy) data(mite.env) ## Function to get equal area partitions of the mite data cutter <- function (x, cut = seq(0, 10, by = 2.5)) { out <- rep(1, length(x)) for (i in 2:(length(cut) - 1)) out[which(x > cut[i] & x <= cut[(i + 1)])] <- i return(out)} ## The hierarchy of sample aggregation levsm <- with(mite.xy, data.frame( l1=1:nrow(mite), l2=cutter(y, cut = seq(0, 10, by = 2.5)), l3=cutter(y, cut = seq(0, 10, by = 5)), l4=rep(1, nrow(mite)))) ## Let's see in a map par(mfrow=c(1,3)) plot(mite.xy, main="l1", col=as.numeric(levsm$l1)+1, asp = 1) plot(mite.xy, main="l2", col=as.numeric(levsm$l2)+1, asp = 1) plot(mite.xy, main="l3", col=as.numeric(levsm$l3)+1, asp = 1) par(mfrow=c(1,1)) ## Additive diversity partitioning adipart(mite, index="richness", nsimul=19) ## the next two define identical models adipart(mite, levsm, index="richness", nsimul=19) adipart(mite ~ l2 + l3, levsm, index="richness", nsimul=19) ## Hierarchical null model testing ## diversity analysis (similar to adipart) hiersimu(mite, FUN=diversity, relative=TRUE, nsimul=19) hiersimu(mite ~ l2 + l3, levsm, FUN=diversity, relative=TRUE, nsimul=19) ## Hierarchical testing with the Morisita index morfun <- function(x) dispindmorisita(x)$imst hiersimu(mite ~., levsm, morfun, drop.highest=TRUE, nsimul=19)
## NOTE: 'nsimul' argument usually needs to be >= 99 ## here much lower value is used for demonstration data(mite) data(mite.xy) data(mite.env) ## Function to get equal area partitions of the mite data cutter <- function (x, cut = seq(0, 10, by = 2.5)) { out <- rep(1, length(x)) for (i in 2:(length(cut) - 1)) out[which(x > cut[i] & x <= cut[(i + 1)])] <- i return(out)} ## The hierarchy of sample aggregation levsm <- with(mite.xy, data.frame( l1=1:nrow(mite), l2=cutter(y, cut = seq(0, 10, by = 2.5)), l3=cutter(y, cut = seq(0, 10, by = 5)), l4=rep(1, nrow(mite)))) ## Let's see in a map par(mfrow=c(1,3)) plot(mite.xy, main="l1", col=as.numeric(levsm$l1)+1, asp = 1) plot(mite.xy, main="l2", col=as.numeric(levsm$l2)+1, asp = 1) plot(mite.xy, main="l3", col=as.numeric(levsm$l3)+1, asp = 1) par(mfrow=c(1,1)) ## Additive diversity partitioning adipart(mite, index="richness", nsimul=19) ## the next two define identical models adipart(mite, levsm, index="richness", nsimul=19) adipart(mite ~ l2 + l3, levsm, index="richness", nsimul=19) ## Hierarchical null model testing ## diversity analysis (similar to adipart) hiersimu(mite, FUN=diversity, relative=TRUE, nsimul=19) hiersimu(mite ~ l2 + l3, levsm, FUN=diversity, relative=TRUE, nsimul=19) ## Hierarchical testing with the Morisita index morfun <- function(x) dispindmorisita(x)$imst hiersimu(mite ~., levsm, morfun, drop.highest=TRUE, nsimul=19)
Analysis of variance using distance matrices — for
partitioning distance matrices among sources of variation and fitting
linear models (e.g., factors, polynomial regression) to distance
matrices; uses a permutation test with pseudo- ratios.
adonis2(formula, data, permutations = 999, method = "bray", sqrt.dist = FALSE, add = FALSE, by = NULL, parallel = getOption("mc.cores"), na.action = na.fail, strata = NULL, ...)
adonis2(formula, data, permutations = 999, method = "bray", sqrt.dist = FALSE, add = FALSE, by = NULL, parallel = getOption("mc.cores"), na.action = na.fail, strata = NULL, ...)
formula |
Model formula. The left-hand side (LHS) of the formula
must be either a community data matrix or a dissimilarity matrix,
e.g., from |
data |
the data frame for the independent variables, with rows
in the same order as the community data matrix or dissimilarity
matrix named on the LHS of |
permutations |
a list of control values for the permutations
as returned by the function |
method |
the name of any method used in |
sqrt.dist |
Take square root of dissimilarities. This often euclidifies dissimilarities. |
add |
Add a constant to the non-diagonal dissimilarities such
that all eigenvalues are non-negative in the underlying Principal
Co-ordinates Analysis (see |
by |
|
parallel |
Number of parallel processes or a predefined socket
cluster. With |
na.action |
Handling of missing values on the right-hand-side
of the formula (see |
strata |
Groups within which to constrain permutations. The traditional non-movable strata are set as Blocks in the permute package, but some more flexible alternatives may be more appropriate. |
... |
Other arguments passed to |
adonis2
is a function for the analysis and partitioning sums of
squares using dissimilarities. The function is based on the principles
of McArdle & Anderson (2001) and can perform sequential, marginal and
overall tests. The function also allows using additive constants or
squareroot of dissimilarities to avoid negative eigenvalues, but can
also handle semimetric indices (such as Bray-Curtis) that produce
negative eigenvalues. The adonis2
tests are identical to
anova.cca
of dbrda
. With Euclidean
distances, the tests are also identical to anova.cca
of
rda
.
The function partitions sums of squares of a multivariate data set,
and they are directly analogous to MANOVA (multivariate analysis of
variance). McArdle and Anderson (2001) and Anderson (2001) refer to
the method as “permutational MANOVA” (formerly
“nonparametric MANOVA”). Further, as the inputs are linear
predictors, and a response matrix of an arbitrary number of columns,
they are a robust alternative to both parametric MANOVA and to
ordination methods for describing how variation is attributed to
different experimental treatments or uncontrolled covariates. The
method is also analogous to distance-based redundancy analysis and
algorithmically similar to dbrda
(Legendre and Anderson
1999), and provides an alternative to AMOVA (nested analysis of
molecular variance, Excoffier, Smouse, and Quattro, 1992; amova
in the ade4 package) for both crossed and nested factors.
The function returns an anova.cca
result object with a
new column for partial : This is the proportion
of sum of squares from the total, and in marginal models
(
by = "margin"
) the terms do not add up to
1.
Anderson (2001, Fig. 4) warns that the method may confound
location and dispersion effects: significant differences may be caused
by different within-group variation (dispersion) instead of different
mean values of the groups (see Warton et al. 2012 for a general
analysis). However, it seems that adonis2
is less sensitive to
dispersion effects than some of its alternatives (anosim
,
mrpp
). Function betadisper
is a sister
function to adonis2
to study the differences in dispersion
within the same geometric framework.
Martin Henry H. Stevens and Jari Oksanen.
Anderson, M.J. 2001. A new method for non-parametric multivariate analysis of variance. Austral Ecology, 26: 32–46.
Excoffier, L., P.E. Smouse, and J.M. Quattro. 1992. Analysis of molecular variance inferred from metric distances among DNA haplotypes: Application to human mitochondrial DNA restriction data. Genetics, 131:479–491.
Legendre, P. and M.J. Anderson. 1999. Distance-based redundancy analysis: Testing multispecies responses in multifactorial ecological experiments. Ecological Monographs, 69:1–24.
McArdle, B.H. and M.J. Anderson. 2001. Fitting multivariate models to community data: A comment on distance-based redundancy analysis. Ecology, 82: 290–297.
Warton, D.I., Wright, T.W., Wang, Y. 2012. Distance-based multivariate analyses confound location and dispersion effects. Methods in Ecology and Evolution, 3, 89–101.
mrpp
, anosim
,
mantel
, varpart
.
data(dune) data(dune.env) ## default is overall (omnibus) test adonis2(dune ~ Management*A1, data = dune.env) ## sequential tests adonis2(dune ~ Management*A1, data = dune.env, by = "terms") ### Example of use with strata, for nested (e.g., block) designs. dat <- expand.grid(rep=gl(2,1), NO3=factor(c(0,10)),field=gl(3,1) ) dat Agropyron <- with(dat, as.numeric(field) + as.numeric(NO3)+2) +rnorm(12)/2 Schizachyrium <- with(dat, as.numeric(field) - as.numeric(NO3)+2) +rnorm(12)/2 total <- Agropyron + Schizachyrium dotplot(total ~ NO3, dat, jitter.x=TRUE, groups=field, type=c('p','a'), xlab="NO3", auto.key=list(columns=3, lines=TRUE) ) Y <- data.frame(Agropyron, Schizachyrium) mod <- metaMDS(Y, trace = FALSE) plot(mod) ### Ellipsoid hulls show treatment with(dat, ordiellipse(mod, NO3, kind = "ehull", label = TRUE)) ### Spider shows fields with(dat, ordispider(mod, field, lty=3, col="red", label = TRUE)) ### Incorrect (no strata) adonis2(Y ~ NO3, data = dat, permutations = 199) ## Correct with strata with(dat, adonis2(Y ~ NO3, data = dat, permutations = 199, strata = field))
data(dune) data(dune.env) ## default is overall (omnibus) test adonis2(dune ~ Management*A1, data = dune.env) ## sequential tests adonis2(dune ~ Management*A1, data = dune.env, by = "terms") ### Example of use with strata, for nested (e.g., block) designs. dat <- expand.grid(rep=gl(2,1), NO3=factor(c(0,10)),field=gl(3,1) ) dat Agropyron <- with(dat, as.numeric(field) + as.numeric(NO3)+2) +rnorm(12)/2 Schizachyrium <- with(dat, as.numeric(field) - as.numeric(NO3)+2) +rnorm(12)/2 total <- Agropyron + Schizachyrium dotplot(total ~ NO3, dat, jitter.x=TRUE, groups=field, type=c('p','a'), xlab="NO3", auto.key=list(columns=3, lines=TRUE) ) Y <- data.frame(Agropyron, Schizachyrium) mod <- metaMDS(Y, trace = FALSE) plot(mod) ### Ellipsoid hulls show treatment with(dat, ordiellipse(mod, NO3, kind = "ehull", label = TRUE)) ### Spider shows fields with(dat, ordispider(mod, field, lty=3, col="red", label = TRUE)) ### Incorrect (no strata) adonis2(Y ~ NO3, data = dat, permutations = 199) ## Correct with strata with(dat, adonis2(Y ~ NO3, data = dat, permutations = 199, strata = field))
Analysis of similarities (ANOSIM) provides a way to test statistically whether there is a significant difference between two or more groups of sampling units.
anosim(x, grouping, permutations = 999, distance = "bray", strata = NULL, parallel = getOption("mc.cores"))
anosim(x, grouping, permutations = 999, distance = "bray", strata = NULL, parallel = getOption("mc.cores"))
x |
Data matrix or data frame in which rows are samples and columns are response variable(s), or a dissimilarity object or a symmetric square matrix of dissimilarities. |
grouping |
Factor for grouping observations. |
permutations |
a list of control values for the permutations
as returned by the function |
distance |
Choice of distance metric that measures the
dissimilarity between two observations. See |
strata |
An integer vector or factor specifying the strata for permutation. If supplied, observations are permuted only within the specified strata. |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
Analysis of similarities (ANOSIM) provides a way to test statistically
whether there is a significant difference between two or more groups
of sampling units. Function anosim
operates directly on a
dissimilarity matrix. A suitable dissimilarity matrix is produced by
functions dist
or vegdist
. The
method is philosophically allied with NMDS ordination
(monoMDS
), in that it uses only the rank order of
dissimilarity values.
If two groups of sampling units are really different in their species
composition, then compositional dissimilarities between the groups
ought to be greater than those within the groups. The anosim
statistic is based on the difference of mean ranks between
groups (
) and within groups (
):
The divisor is chosen so that will be in the interval
, value
indicating completely random
grouping.
The statistical significance of observed is assessed by
permuting the grouping vector to obtain the empirical distribution
of
under null-model. See
permutations
for
additional details on permutation tests in Vegan. The distribution
of simulated values can be inspected with the permustats
function.
The function has summary
and plot
methods. These both
show valuable information to assess the validity of the method: The
function assumes that all ranked dissimilarities within groups
have about equal median and range. The plot
method uses
boxplot
with options notch=TRUE
and
varwidth=TRUE
.
The function returns a list of class "anosim"
with following
items:
call |
Function call. |
statistic |
The value of ANOSIM statistic |
signif |
Significance from permutation. |
perm |
Permutation values of |
class.vec |
Factor with value |
dis.rank |
Rank of dissimilarity entry. |
dissimilarity |
The name of the dissimilarity index: the
|
control |
A list of control values for the permutations
as returned by the function |
The anosim
function can confound the differences between groups
and dispersion within groups and the results can be difficult to
interpret (cf. Warton et al. 2012). The function returns a lot of
information to ease studying its performance. Most anosim
models could be analysed with adonis2
which seems to be a
more robust alternative.
Jari Oksanen, with a help from Peter R. Minchin.
Clarke, K. R. (1993). Non-parametric multivariate analysis of changes in community structure. Australian Journal of Ecology 18, 117–143.
Warton, D.I., Wright, T.W., Wang, Y. 2012. Distance-based multivariate analyses confound location and dispersion effects. Methods in Ecology and Evolution, 3, 89–101
mrpp
for a similar function using original
dissimilarities instead of their ranks.
dist
and vegdist
for obtaining
dissimilarities, and rank
for ranking real values. For
comparing dissimilarities against continuous variables, see
mantel
. Function adonis2
is a more robust
alternative that should preferred.
data(dune) data(dune.env) dune.dist <- vegdist(dune) dune.ano <- with(dune.env, anosim(dune.dist, Management)) summary(dune.ano) plot(dune.ano)
data(dune) data(dune.env) dune.dist <- vegdist(dune) dune.ano <- with(dune.env, anosim(dune.dist, Management)) summary(dune.ano) plot(dune.ano)
The function performs an ANOVA like permutation test for Constrained
Correspondence Analysis (cca
), Redundancy Analysis
(rda
) or distance-based Redundancy Analysis (dbRDA,
dbrda
) to assess the significance of constraints.
## S3 method for class 'cca' anova(object, ..., permutations = how(nperm=999), by = NULL, model = c("reduced", "direct", "full"), parallel = getOption("mc.cores"), strata = NULL, cutoff = 1, scope = NULL) ## S3 method for class 'cca' permutest(x, permutations = how(nperm = 99), model = c("reduced", "direct", "full"), by = NULL, first = FALSE, strata = NULL, parallel = getOption("mc.cores"), ...)
## S3 method for class 'cca' anova(object, ..., permutations = how(nperm=999), by = NULL, model = c("reduced", "direct", "full"), parallel = getOption("mc.cores"), strata = NULL, cutoff = 1, scope = NULL) ## S3 method for class 'cca' permutest(x, permutations = how(nperm = 99), model = c("reduced", "direct", "full"), by = NULL, first = FALSE, strata = NULL, parallel = getOption("mc.cores"), ...)
object |
One or several result objects from |
x |
A single ordination result object. |
permutations |
a list of control values for the permutations
as returned by the function |
by |
Setting |
model |
Permutation model: |
parallel |
Use parallel processing with the given number of cores. |
strata |
An integer vector or factor specifying the strata for
permutation. If supplied, observations are permuted only within
the specified strata. It is an error to use this when
|
cutoff |
Only effective with |
scope |
Only effective with |
first |
Analyse only significance of the first axis. |
... |
Parameters passed to other functions. |
Functions anova.cca
and permutest.cca
implement ANOVA
like permutation tests for the joint effect of constraints in
cca
, rda
, dbrda
or
capscale
. Function anova
is intended as a more
user-friendly alternative to permutest
(that is the real
workhorse).
Function anova
can analyse a sequence of constrained
ordination models. The analysis is based on the differences in
residual deviance in permutations of nested models.
The default test is for the sum of all constrained eigenvalues.
Setting first = TRUE
will perform a test for the first
constrained eigenvalue. Argument first
can be set either in
anova.cca
or in permutest.cca
. It is also possible to
perform significance tests for each axis or for each term
(constraining variable) using argument by
in anova.cca
.
Setting by = "axis"
will perform separate significance tests
for each constrained axis. All previous constrained axes will be used
as conditions (“partialled out”) and a test for the first
constrained eigenvalues is performed (Legendre et al. 2011). You can
stop permutation tests after exceeding a given significance level with
argument cutoff
to speed up calculations in large
models. Setting by = "terms"
will perform separate significance
test for each term (constraining variable). The terms are assessed
sequentially from first to last, and the order of the terms will
influence their significances. Setting by = "onedf"
will
perform a similar sequential test for one-degree-of-freedom effects,
where multi-level factors are split in their contrasts. Setting
by = "margin"
will perform separate significance test for each
marginal term in a model with all other terms. The marginal test also
accepts a scope
argument for the drop.scope
which
can be a character vector of term labels that are analysed, or a
fitted model of lower scope. The marginal effects are also known as
“Type III” effects, but the current function only evaluates
marginal terms. It will, for instance, ignore main effects that are
included in interaction terms. In calculating pseudo-, all
terms are compared to the same residual of the full model.
Community data are permuted with choice model="direct"
, and
residuals after partial CCA/ RDA/ dbRDA with choice
model="reduced"
(default). If there is no partial CCA/ RDA/
dbRDA stage, model="reduced"
simply permutes the data and is
equivalent to model="direct"
. The test statistic is
“pseudo-”, which is the ratio of constrained and
unconstrained total Inertia (Chi-squares, variances or something
similar), each divided by their respective degrees of freedom. If
there are no conditions (“partial” terms), the sum of all
eigenvalues remains constant, so that pseudo-
and eigenvalues
would give equal results. In partial CCA/ RDA/ dbRDA, the effect of
conditioning variables (“covariables”) is removed before
permutation, and the total Chi-square is not fixed, and test based on
pseudo-
would differ from the test based on plain
eigenvalues.
The function anova.cca
calls permutest.cca
and fills an
anova
table. Additional attributes are
Random.seed
(the random seeds used),
control
(the permutation design, see how) and
F.perm
(the permuted test statistics).
Jari Oksanen
Legendre, P. and Legendre, L. (2012). Numerical Ecology. 3rd English ed. Elsevier.
Legendre, P., Oksanen, J. and ter Braak, C.J.F. (2011). Testing the significance of canonical axes in redundancy analysis. Methods in Ecology and Evolution 2, 269–277.
anova.cca
, cca
,
rda
, dbrda
to get something to
analyse. Function drop1.cca
calls anova.cca
with by = "margin"
, and add1.cca
an analysis
for single terms additions, which can be used in automatic or
semiautomatic model building (see deviance.cca
).
data(dune, dune.env) mod <- cca(dune ~ Moisture + Management, dune.env) ## overall test anova(mod) ## tests for individual terms anova(mod, by="term") anova(mod, by="margin") ## sequential test for contrasts anova(mod, by = "onedf") ## test for adding all environmental variables anova(mod, cca(dune ~ ., dune.env))
data(dune, dune.env) mod <- cca(dune ~ Moisture + Management, dune.env) ## overall test anova(mod) ## tests for individual terms anova(mod, by="term") anova(mod, by="margin") ## sequential test for contrasts anova(mod, by = "onedf") ## test for adding all environmental variables anova(mod, cca(dune ~ ., dune.env))
The function computes the dissimilarity matrix of a dataset multiple
times using vegdist
while randomly subsampling the
dataset each time. All of the subsampled iterations are then averaged
(mean) to provide a distance matrix that represents the average of
multiple subsampling iterations. This emulates the behavior of the
distance matrix calculator within the Mothur microbial ecology toolkit.
avgdist(x, sample, distfun = vegdist, meanfun = mean, transf = NULL, iterations = 100, dmethod = "bray", diag = TRUE, upper = TRUE, ...)
avgdist(x, sample, distfun = vegdist, meanfun = mean, transf = NULL, iterations = 100, dmethod = "bray", diag = TRUE, upper = TRUE, ...)
x |
Community data matrix. |
sample |
The subsampling depth to be used in each iteration. Samples that do not meet this threshold will be removed from the analysis, and their identity returned to the user in stdout. |
distfun |
The dissimilarity matrix function to be used. Default is the
vegan |
meanfun |
The calculation to use for the average (mean or median). |
transf |
Option for transforming the count data before calculating the
distance matrix. Any base transformation option can be used (e.g.
|
iterations |
The number of random iterations to perform before averaging. Default is 100 iterations. |
dmethod |
Dissimilarity index to be used with the specified dissimilarity matrix function. Default is Bray-Curtis |
diag , upper
|
Return dissimilarities with diagonal and upper
triangle. NB. the default differs from |
... |
Any additional arguments to add to the distance function or mean/median function specified. |
The function builds on the function rrarefy
and and
additional distance matrix function (e.g. vegdist
) to
add more meaningful representations of distances among randomly
subsampled datasets by presenting the average of multiple random
iterations. This function runs using the vegdist
. This
functionality has been utilized in the Mothur standalone microbial
ecology toolkit here.
Geoffrey Hannigan, with some minor tweaks by Gavin L. Simpson.
This function utilizes the vegdist
and rrarefy
functions.
# Import an example count dataset data(BCI) # Test the base functionality mean.avg.dist <- avgdist(BCI, sample = 50, iterations = 10) # Test the transformation function mean.avg.dist.t <- avgdist(BCI, sample = 50, iterations = 10, transf = sqrt) # Test the median functionality median.avg.dist <- avgdist(BCI, sample = 50, iterations = 10, meanfun = median) # Print the resulting tables head(as.matrix(mean.avg.dist)) head(as.matrix(mean.avg.dist.t)) head(as.matrix(median.avg.dist)) # Run example to illustrate low variance of mean, median, and stdev results # Mean and median std dev are around 0.05 sdd <- avgdist(BCI, sample = 50, iterations = 100, meanfun = sd) summary(mean.avg.dist) summary(median.avg.dist) summary(sdd) # Test for when subsampling depth excludes some samples # Return samples that are removed for not meeting depth filter depth.avg.dist <- avgdist(BCI, sample = 450, iterations = 10) # Print the result depth.avg.dist
# Import an example count dataset data(BCI) # Test the base functionality mean.avg.dist <- avgdist(BCI, sample = 50, iterations = 10) # Test the transformation function mean.avg.dist.t <- avgdist(BCI, sample = 50, iterations = 10, transf = sqrt) # Test the median functionality median.avg.dist <- avgdist(BCI, sample = 50, iterations = 10, meanfun = median) # Print the resulting tables head(as.matrix(mean.avg.dist)) head(as.matrix(mean.avg.dist.t)) head(as.matrix(median.avg.dist)) # Run example to illustrate low variance of mean, median, and stdev results # Mean and median std dev are around 0.05 sdd <- avgdist(BCI, sample = 50, iterations = 100, meanfun = sd) summary(mean.avg.dist) summary(median.avg.dist) summary(sdd) # Test for when subsampling depth excludes some samples # Return samples that are removed for not meeting depth filter depth.avg.dist <- avgdist(BCI, sample = 450, iterations = 10) # Print the result depth.avg.dist
Tree counts in 1-hectare plots in the Barro Colorado Island and associated site information.
data(BCI) data(BCI.env)
data(BCI) data(BCI.env)
A data frame with 50 plots (rows) of 1 hectare with counts of trees on
each plot with total of 225 species (columns). Full Latin names are
used for tree species. The names were updated against
http://www.theplantlist.org and Kress et al. (2009) which allows
matching 207 of species against doi:10.5061/dryad.63q27 (Zanne et
al., 2014). The original species names are available as attribute
original.names
of BCI
. See Examples for changed names.
For BCI.env
, a data frame with 50 plots (rows) and nine site
variables derived from Pyke et al. (2001) and Harms et al. (2001):
UTM.EW
: UTM coordinates (zone 17N) East-West.
UTM.NS
: UTM coordinates (zone 17N) North-South.
Precipitation
: Precipitation in mm per year.
Elevation
: Elevation in m above sea level.
Age.cat
: Forest age category.
Geology
: The Underlying geological formation.
Habitat
: Dominant habitat type based on the map of
habitat types in 25 grid cells in each plot (Harms et al. 2001,
excluding streamside habitat). The habitat types are Young
forests (ca. 100 years), old forests on > 7 degree slopes
(OldSlope
), old forests under 152 m elevation
(OldLow
) and at higher elevation (OldHigh
) and
Swamp
forests.
River
: "Yes"
if there is streamside habitat
in the plot.
EnvHet
: Environmental Heterogeneity assessed as the
Simpson diversity of frequencies of Habitat
types in 25
grid cells in the plot.
Data give the numbers of trees at least 10 cm in diameter at breast
height (DBH) in each one hectare quadrat in the 1982 BCI
plot. Within each plot, all individuals were tallied and are
recorded in this table. The full survey included smaller trees with
DBH 1 cm or larger, but the BCI
dataset is a subset of larger
trees as compiled by Condit et al. (2002). The full data with
thinner trees has densities above 4000 stems per hectare, or about
ten times more stems than these data. The dataset BCI
was
provided (in 2003) to illustrate analysis methods in
vegan. For scientific research on ecological issues we
strongly recommend to access complete and more modern data (Condit
et al. 2019) with updated taxonomy (Condit et al. 2020).
The data frame contains only the Barro Colorado Island subset of the full data table of Condit et al. (2002).
The quadrats are located in a regular grid. See BCI.env
for the
coordinates.
A full description of the site information in BCI.env
is
given in Pyke et al. (2001) and Harms et al. (2001). N.B.
Pyke et al. (2001) and Harms et al. (2001) give conflicting
information about forest age categories and elevation.
https://www.science.org/doi/10.1126/science.1066854 for community data and References for environmental data. For updated complete data (incl. thinner trees down to 1 cm), see Condit et al. (2019).
Condit, R, Pitman, N, Leigh, E.G., Chave, J., Terborgh, J., Foster, R.B., Nuñez, P., Aguilar, S., Valencia, R., Villa, G., Muller-Landau, H.C., Losos, E. & Hubbell, S.P. (2002). Beta-diversity in tropical forest trees. Science 295, 666–669.
Condit R., Pérez, R., Aguilar, S., Lao, S., Foster, R. & Hubbell, S. (2019). Complete data from the Barro Colorado 50-ha plot: 423617 trees, 35 years [Dataset]. Dryad. doi:10.15146/5xcp-0d46
Condit, R., Aguilar, S., Lao, S., Foster, R., Hubbell, S. (2020). BCI 50-ha Plot Taxonomy [Dataset]. Dryad. doi:10.15146/R3FH61
Harms K.E., Condit R., Hubbell S.P. & Foster R.B. (2001) Habitat associations of trees and shrubs in a 50-ha neotropical forest plot. J. Ecol. 89, 947–959.
Kress W.J., Erickson D.L, Jones F.A., Swenson N.G, Perez R., Sanjur O. & Bermingham E. (2009) Plant DNA barcodes and a community phylogeny of a tropical forest dynamics plot in Panama. PNAS 106, 18621–18626.
Pyke, C. R., Condit, R., Aguilar, S., & Lao, S. (2001). Floristic composition across a climatic gradient in a neotropical lowland forest. Journal of Vegetation Science 12, 553–566. doi:10.2307/3237007
Zanne A.E., Tank D.C., Cornwell, W.K., Eastman J.M., Smith, S.A., FitzJohn, R.G., McGlinn, D.J., O’Meara, B.C., Moles, A.T., Reich, P.B., Royer, D.L., Soltis, D.E., Stevens, P.F., Westoby, M., Wright, I.J., Aarssen, L., Bertin, R.I., Calaminus, A., Govaerts, R., Hemmings, F., Leishman, M.R., Oleksyn, J., Soltis, P.S., Swenson, N.G., Warman, L. & Beaulieu, J.M. (2014) Three keys to the radiation of angiosperms into freezing environments. Nature 506, 89–92. doi:10.1038/nature12872 (published online Dec 22, 2013).
Extra-CRAN package natto
(https://github.com/jarioksa/natto) has data set
BCI.env2
with original grid data of Harms et al. (2001)
habitat classification, and data set BCI.taxon
of APG III
classification of tree species.
data(BCI, BCI.env) head(BCI.env) ## see changed species names oldnames <- attr(BCI, "original.names") taxa <- cbind("Old Names" = oldnames, "Current Names" = names(BCI)) noquote(taxa[taxa[,1] != taxa[,2], ])
data(BCI, BCI.env) head(BCI.env) ## see changed species names oldnames <- attr(BCI, "original.names") taxa <- cbind("Old Names" = oldnames, "Current Names" = names(BCI)) noquote(taxa[taxa[,1] != taxa[,2], ])
Beals smoothing replaces each entry in the community data with a probability of a target species occurring in that particular site, based on the joint occurrences of the target species with the species that actually occur in the site. Swan's (1970) degree of absence applies Beals smoothing to zero items so long that all zeros are replaced with smoothed values.
beals(x, species = NA, reference = x, type = 0, include = TRUE) swan(x, maxit = Inf, type = 0)
beals(x, species = NA, reference = x, type = 0, include = TRUE) swan(x, maxit = Inf, type = 0)
x |
Community data frame or matrix. |
species |
Column index used to compute Beals function for a single species.
The default ( |
reference |
Community data frame or matrix to be used to compute
joint occurrences. By default, |
type |
Numeric. Specifies if and how abundance values have to be
used in function |
include |
This logical flag indicates whether the target species has to be
included when computing the mean of the conditioned probabilities. The
original Beals (1984) definition is equivalent to |
maxit |
Maximum number of iterations. The default |
Beals smoothing is the estimated probability that
species
occurs at site
. It is defined as
, where
is the number of
species at site
,
is the number of joint
occurrences of species
and
,
is the
number of occurrences of species
, and
is the incidence
(0 or 1) of species (this last term is usually omitted from the
equation, but it is necessary). As
can be
interpreted as a mean of conditional probability, the
beals
function can be interpreted as a mean of conditioned probabilities (De
Cáceres & Legendre 2008). The present function is
generalized to abundance values (De Cáceres & Legendre
2008).
The type
argument specifies if and how abundance values have to be
used. type = 0
presence/absence mode. type = 1
abundances in reference
(or x
) are used to compute
conditioned probabilities. type = 2
abundances in x
are
used to compute weighted averages of conditioned
probabilities. type = 3
abundances are used to compute both
conditioned probabilities and weighted averages.
Beals smoothing was originally suggested as a method of data
transformation to remove excessive zeros (Beals 1984, McCune 1994).
However, it is not a suitable method for this purpose since it does
not maintain the information on species presences: a species may have
a higher probability of occurrence at a site where it does not occur
than at sites where it occurs. Moreover, it regularizes data too
strongly. The method may be useful in identifying species that belong
to the species pool (Ewald 2002) or to identify suitable unoccupied
patches in metapopulation analysis (Münzbergová &
Herben 2004). In this case, the function should be called with
include=FALSE
for cross-validation smoothing for species;
argument species
can be used if only one species is studied.
Swan (1970) suggested replacing zero values with degrees of absence of
a species in a community data matrix. Swan expressed the method in
terms of a similarity matrix, but it is equivalent to applying Beals
smoothing to zero values, at each step shifting the smallest initially
non-zero item to value one, and repeating this so many times that
there are no zeros left in the data. This is actually very similar to
extended dissimilarities (implemented in function
stepacross
), but very rarely used.
The function returns a transformed data matrix or a vector if Beals smoothing is requested for a single species.
Miquel De Cáceres and Jari Oksanen
Beals, E.W. 1984. Bray-Curtis ordination: an effective strategy for analysis of multivariate ecological data. Pp. 1–55 in: MacFadyen, A. & E.D. Ford [eds.] Advances in Ecological Research, 14. Academic Press, London.
De Cáceres, M. & Legendre, P. 2008. Beals smoothing revisited. Oecologia 156: 657–669.
Ewald, J. 2002. A probabilistic approach to estimating species pools from large compositional matrices. J. Veg. Sci. 13: 191–198.
McCune, B. 1994. Improving community ordination with the Beals smoothing function. Ecoscience 1: 82–86.
Münzbergová, Z. & Herben, T. 2004. Identification of suitable unoccupied habitats in metapopulation studies using co-occurrence of species. Oikos 105: 408–414.
Swan, J.M.A. 1970. An examination of some ordination problems by use of simulated vegetational data. Ecology 51: 89–102.
decostand
for proper standardization methods,
specpool
for an attempt to assess the size of species
pool. Function indpower
assesses the power of each species
to estimate the probabilities predicted by beals
.
data(dune) ## Default x <- beals(dune) ## Remove target species x <- beals(dune, include = FALSE) ## Smoothed values against presence or absence of species pa <- decostand(dune, "pa") boxplot(as.vector(x) ~ unlist(pa), xlab="Presence", ylab="Beals") ## Remove the bias of tarbet species: Yields lower values. beals(dune, type =3, include = FALSE) ## Uses abundance information. ## Vector with beals smoothing values corresponding to the first species ## in dune. beals(dune, species=1, include=TRUE)
data(dune) ## Default x <- beals(dune) ## Remove target species x <- beals(dune, include = FALSE) ## Smoothed values against presence or absence of species pa <- decostand(dune, "pa") boxplot(as.vector(x) ~ unlist(pa), xlab="Presence", ylab="Beals") ## Remove the bias of tarbet species: Yields lower values. beals(dune, type =3, include = FALSE) ## Uses abundance information. ## Vector with beals smoothing values corresponding to the first species ## in dune. beals(dune, species=1, include=TRUE)
Implements Marti Anderson's PERMDISP2 procedure for the analysis of
multivariate homogeneity of group dispersions (variances).
betadisper
is a multivariate analogue of Levene's test for
homogeneity of variances. Non-euclidean distances between objects and
group centres (centroids or medians) are handled by reducing the
original distances to principal coordinates. This procedure has
latterly been used as a means of assessing beta diversity. There are
anova
, scores
, plot
and boxplot
methods.
TukeyHSD.betadisper
creates a set of confidence intervals on
the differences between the mean distance-to-centroid of the levels of
the grouping factor with the specified family-wise probability of
coverage. The intervals are based on the Studentized range statistic,
Tukey's 'Honest Significant Difference' method.
betadisper(d, group, type = c("median","centroid"), bias.adjust = FALSE, sqrt.dist = FALSE, add = FALSE) ## S3 method for class 'betadisper' anova(object, ...) ## S3 method for class 'betadisper' scores(x, display = c("sites", "centroids"), choices = c(1,2), ...) ## S3 method for class 'betadisper' eigenvals(x, ...) ## S3 method for class 'betadisper' plot(x, axes = c(1,2), cex = 0.7, pch = seq_len(ng), col = NULL, lty = "solid", lwd = 1, hull = TRUE, ellipse = FALSE, conf, segments = TRUE, seg.col = "grey", seg.lty = lty, seg.lwd = lwd, label = TRUE, label.cex = 1, ylab, xlab, main, sub, ...) ## S3 method for class 'betadisper' boxplot(x, ylab = "Distance to centroid", ...) ## S3 method for class 'betadisper' TukeyHSD(x, which = "group", ordered = FALSE, conf.level = 0.95, ...) ## S3 method for class 'betadisper' print(x, digits = max(3, getOption("digits") - 3), neigen = 8, ...)
betadisper(d, group, type = c("median","centroid"), bias.adjust = FALSE, sqrt.dist = FALSE, add = FALSE) ## S3 method for class 'betadisper' anova(object, ...) ## S3 method for class 'betadisper' scores(x, display = c("sites", "centroids"), choices = c(1,2), ...) ## S3 method for class 'betadisper' eigenvals(x, ...) ## S3 method for class 'betadisper' plot(x, axes = c(1,2), cex = 0.7, pch = seq_len(ng), col = NULL, lty = "solid", lwd = 1, hull = TRUE, ellipse = FALSE, conf, segments = TRUE, seg.col = "grey", seg.lty = lty, seg.lwd = lwd, label = TRUE, label.cex = 1, ylab, xlab, main, sub, ...) ## S3 method for class 'betadisper' boxplot(x, ylab = "Distance to centroid", ...) ## S3 method for class 'betadisper' TukeyHSD(x, which = "group", ordered = FALSE, conf.level = 0.95, ...) ## S3 method for class 'betadisper' print(x, digits = max(3, getOption("digits") - 3), neigen = 8, ...)
d |
a distance structure such as that returned by
|
group |
vector describing the group structure, usually a factor
or an object that can be coerced to a factor using
|
type |
the type of analysis to perform. Use the spatial median or the group centroid? The spatial median is now the default. |
bias.adjust |
logical: adjust for small sample bias in beta diversity estimates? |
sqrt.dist |
Take square root of dissimilarities. This often euclidifies dissimilarities. |
add |
Add a constant to the non-diagonal dissimilarities such
that all eigenvalues are non-negative in the underlying Principal
Co-ordinates Analysis (see |
display |
character; partial match to access scores for
|
object , x
|
an object of class |
choices , axes
|
the principal coordinate axes wanted. |
hull |
logical; should the convex hull for each group be plotted? |
ellipse |
logical; should the standard deviation data ellipse for each group be plotted? |
conf |
Expected fractions of data coverage for data ellipses,
e.g. 0.95. The default is to draw a 1 standard deviation data
ellipse, but if supplied, |
pch |
plot symbols for the groups, a vector of length equal to the number of groups. |
col |
colors for the plot symbols and centroid labels for the groups, a vector of length equal to the number of groups. |
lty , lwd
|
linetype, linewidth for convex hulls and confidence ellipses. |
segments |
logical; should segments joining points to their centroid be drawn? |
seg.col |
colour to draw segments between points and their centroid. Can be a vector, in which case one colour per group. |
seg.lty , seg.lwd
|
linetype and line width for segments. |
label |
logical; should the centroids by labelled with their respective factor label? |
label.cex |
numeric; character expansion for centroid labels. |
cex , ylab , xlab , main , sub
|
graphical parameters. For details,
see |
which |
A character vector listing terms in the fitted model for which the intervals should be calculated. Defaults to the grouping factor. |
ordered |
logical; see |
conf.level |
A numeric value between zero and one giving the family-wise confidence level to use. |
digits , neigen
|
numeric; for the |
... |
arguments, including graphical parameters (for
|
One measure of multivariate dispersion (variance) for a group of samples is to calculate the average distance of group members to the group centroid or spatial median (both referred to as 'centroid' from now on unless stated otherwise) in multivariate space. To test if the dispersions (variances) of one or more groups are different, the distances of group members to the group centroid are subject to ANOVA. This is a multivariate analogue of Levene's test for homogeneity of variances if the distances between group members and group centroids is the Euclidean distance.
However, better measures of distance than the Euclidean distance are available for ecological data. These can be accommodated by reducing the distances produced using any dissimilarity coefficient to principal coordinates, which embeds them within a Euclidean space. The analysis then proceeds by calculating the Euclidean distances between group members and the group centroid on the basis of the principal coordinate axes rather than the original distances.
Non-metric dissimilarity coefficients can produce principal coordinate axes that have negative Eigenvalues. These correspond to the imaginary, non-metric part of the distance between objects. If negative Eigenvalues are produced, we must correct for these imaginary distances.
The distance to its centroid of a point is
where
is the squared Euclidean distance between
, the principal coordinate for the
th
point in the
th group, and
, the
coordinate of the centroid for the
th group. The
super-scripted ‘
’ and ‘
’ indicate the
real and imaginary parts respectively. This is equation (3) in
Anderson (2006). If the imaginary part is greater in magnitude than
the real part, then we would be taking the square root of a negative
value, resulting in NaN, and these cases are changed to zero distances
(with a warning). This is in line with the behaviour of Marti Anderson's
PERMDISP2 programme.
To test if one or more groups is more variable than the others, ANOVA
of the distances to group centroids can be performed and parametric
theory used to interpret the significance of . An alternative is to
use a permutation test.
permutest.betadisper
permutes model
residuals to generate a permutation distribution of under the Null
hypothesis of no difference in dispersion between groups.
Pairwise comparisons of group mean dispersions can also be performed
using permutest.betadisper
. An alternative to the classical
comparison of group dispersions, is to calculate Tukey's Honest
Significant Differences between groups, via
TukeyHSD.betadisper
. This is a simple wrapper to
TukeyHSD
. The user is directed to read the help file
for TukeyHSD
before using this function. In particular,
note the statement about using the function with
unbalanced designs.
The results of the analysis can be visualised using the plot
and boxplot
methods. The distances of points to all centroids
(group
) can be found with function centredist
.
One additional use of these functions is in assessing beta diversity
(Anderson et al 2006). Function betadiver
provides some popular dissimilarity measures for this purpose.
As noted in passing by Anderson (2006) and in a related
context by O'Neill (2000), estimates of dispersion around a
central location (median or centroid) that is calculated from the same data
will be biased downward. This bias matters most when comparing diversity
among treatments with small, unequal numbers of samples. Setting
bias.adjust=TRUE
when using betadisper
imposes a
correction (Stier et al. 2013).
The anova
method returns an object of class "anova"
inheriting from class "data.frame"
.
The scores
method returns a list with one or both of the
components "sites"
and "centroids"
.
The plot
function invisibly returns an object of class
"ordiplot"
, a plotting structure which can be used by
identify.ordiplot
(to identify the points) or other
functions in the ordiplot
family.
The boxplot
function invisibly returns a list whose components
are documented in boxplot
.
eigenvals.betadisper
returns a named vector of eigenvalues.
TukeyHSD.betadisper
returns a list. See TukeyHSD
for further details.
betadisper
returns a list of class "betadisper"
with the
following components:
eig |
numeric; the eigenvalues of the principal coordinates analysis. |
vectors |
matrix; the eigenvectors of the principal coordinates analysis. |
distances |
numeric; the Euclidean distances in principal coordinate space between the samples and their respective group centroid or median. |
group |
factor; vector describing the group structure |
centroids |
matrix; the locations of the group centroids or medians on the principal coordinates. |
group.distances |
numeric; the mean distance to each group centroid or median. |
call |
the matched function call. |
Stewart Schultz noticed that the permutation test for
type="centroid"
had the wrong type I error and was
anti-conservative. As such, the default for type
has been
changed to "median"
, which uses the spatial median as the group
centroid. Tests suggests that the permutation test for this type of
analysis gives the correct error rates.
If group
consists of a single level or group, then the
anova
and permutest
methods are not appropriate and if
used on such data will stop with an error.
Missing values in either d
or group
will be removed
prior to performing the analysis.
Gavin L. Simpson; bias correction by Adrian Stier and Ben Bolker.
Anderson, M.J. (2006) Distance-based tests for homogeneity of multivariate dispersions. Biometrics 62, 245–253.
Anderson, M.J., Ellingsen, K.E. & McArdle, B.H. (2006) Multivariate dispersion as a measure of beta diversity. Ecology Letters 9, 683–693.
O'Neill, M.E. (2000) A Weighted Least Squares Approach to Levene's Test of Homogeneity of Variance. Australian & New Zealand Journal of Statistics 42, 81-–100.
Stier, A.C., Geange, S.W., Hanson, K.M., & Bolker, B.M. (2013) Predator density and timing of arrival affect reef fish community assembly. Ecology 94, 1057–1068.
permutest.betadisper
, centredist
,
anova.lm
,
scores
, boxplot
,
TukeyHSD
. Further measure of beta diversity
can be found in betadiver
.
data(varespec) ## Bray-Curtis distances between samples dis <- vegdist(varespec) ## First 16 sites grazed, remaining 8 sites ungrazed groups <- factor(c(rep(1,16), rep(2,8)), labels = c("grazed","ungrazed")) ## Calculate multivariate dispersions mod <- betadisper(dis, groups) mod ## Perform test anova(mod) ## Permutation test for F permutest(mod, pairwise = TRUE, permutations = 99) ## Tukey's Honest Significant Differences (mod.HSD <- TukeyHSD(mod)) plot(mod.HSD) ## Plot the groups and distances to centroids on the ## first two PCoA axes plot(mod) ## with data ellipses instead of hulls plot(mod, ellipse = TRUE, hull = FALSE) # 1 sd data ellipse plot(mod, ellipse = TRUE, hull = FALSE, conf = 0.90) # 90% data ellipse # plot with manual colour specification my_cols <- c("#1b9e77", "#7570b3") plot(mod, col = my_cols, pch = c(16,17), cex = 1.1) ## can also specify which axes to plot, ordering respected plot(mod, axes = c(3,1), seg.col = "forestgreen", seg.lty = "dashed") ## Draw a boxplot of the distances to centroid for each group boxplot(mod) ## `scores` and `eigenvals` also work scrs <- scores(mod) str(scrs) head(scores(mod, 1:4, display = "sites")) # group centroids/medians scores(mod, 1:4, display = "centroids") # eigenvalues from the underlying principal coordinates analysis eigenvals(mod) ## try out bias correction; compare with mod3 (mod3B <- betadisper(dis, groups, type = "median", bias.adjust=TRUE)) anova(mod3B) permutest(mod3B, permutations = 99) ## should always work for a single group group <- factor(rep("grazed", NROW(varespec))) (tmp <- betadisper(dis, group, type = "median")) (tmp <- betadisper(dis, group, type = "centroid")) ## simulate missing values in 'd' and 'group' ## using spatial medians groups[c(2,20)] <- NA dis[c(2, 20)] <- NA mod2 <- betadisper(dis, groups) ## messages mod2 permutest(mod2, permutations = 99) anova(mod2) plot(mod2) boxplot(mod2) plot(TukeyHSD(mod2)) ## Using group centroids mod3 <- betadisper(dis, groups, type = "centroid") mod3 permutest(mod3, permutations = 99) anova(mod3) plot(mod3) boxplot(mod3) plot(TukeyHSD(mod3))
data(varespec) ## Bray-Curtis distances between samples dis <- vegdist(varespec) ## First 16 sites grazed, remaining 8 sites ungrazed groups <- factor(c(rep(1,16), rep(2,8)), labels = c("grazed","ungrazed")) ## Calculate multivariate dispersions mod <- betadisper(dis, groups) mod ## Perform test anova(mod) ## Permutation test for F permutest(mod, pairwise = TRUE, permutations = 99) ## Tukey's Honest Significant Differences (mod.HSD <- TukeyHSD(mod)) plot(mod.HSD) ## Plot the groups and distances to centroids on the ## first two PCoA axes plot(mod) ## with data ellipses instead of hulls plot(mod, ellipse = TRUE, hull = FALSE) # 1 sd data ellipse plot(mod, ellipse = TRUE, hull = FALSE, conf = 0.90) # 90% data ellipse # plot with manual colour specification my_cols <- c("#1b9e77", "#7570b3") plot(mod, col = my_cols, pch = c(16,17), cex = 1.1) ## can also specify which axes to plot, ordering respected plot(mod, axes = c(3,1), seg.col = "forestgreen", seg.lty = "dashed") ## Draw a boxplot of the distances to centroid for each group boxplot(mod) ## `scores` and `eigenvals` also work scrs <- scores(mod) str(scrs) head(scores(mod, 1:4, display = "sites")) # group centroids/medians scores(mod, 1:4, display = "centroids") # eigenvalues from the underlying principal coordinates analysis eigenvals(mod) ## try out bias correction; compare with mod3 (mod3B <- betadisper(dis, groups, type = "median", bias.adjust=TRUE)) anova(mod3B) permutest(mod3B, permutations = 99) ## should always work for a single group group <- factor(rep("grazed", NROW(varespec))) (tmp <- betadisper(dis, group, type = "median")) (tmp <- betadisper(dis, group, type = "centroid")) ## simulate missing values in 'd' and 'group' ## using spatial medians groups[c(2,20)] <- NA dis[c(2, 20)] <- NA mod2 <- betadisper(dis, groups) ## messages mod2 permutest(mod2, permutations = 99) anova(mod2) plot(mod2) boxplot(mod2) plot(TukeyHSD(mod2)) ## Using group centroids mod3 <- betadisper(dis, groups, type = "centroid") mod3 permutest(mod3, permutations = 99) anova(mod3) plot(mod3) boxplot(mod3) plot(TukeyHSD(mod3))
The function estimates any of the 24 indices of beta diversity reviewed by Koleff et al. (2003). Alternatively, it finds the co-occurrence frequencies for triangular plots (Koleff et al. 2003).
betadiver(x, method = NA, order = FALSE, help = FALSE, ...) ## S3 method for class 'betadiver' plot(x, ...) ## S3 method for class 'betadiver' scores(x, triangular = TRUE, ...)
betadiver(x, method = NA, order = FALSE, help = FALSE, ...) ## S3 method for class 'betadiver' plot(x, ...) ## S3 method for class 'betadiver' scores(x, triangular = TRUE, ...)
x |
Community data matrix, or the |
method |
The index of beta diversity as defined in Koleff et al.
(2003), Table 1. You can use either the subscript of |
order |
Order sites by increasing number of species. This will influence the configuration in the triangular plot and non-symmetric indices. |
help |
Show the numbers, subscript names and the defining equations of the indices and exit. |
triangular |
Return scores suitable for triangular plotting of
proportions. If |
... |
Other arguments to functions. |
The most commonly used index of beta diversity is
, where
is the total number of
species, and
is the average number of species per site
(Whittaker 1960). A drawback of this model is that
increases
with sample size, but the expectation of
remains
constant, and so the beta diversity increases with sample size. A
solution to this problem is to study the beta diversity of pairs of
sites (Marion et al. 2017). If we denote the number of species
shared between two sites as
and the numbers of unique
species (not shared) as
and
, then
and
so that
. This is the Sørensen
dissimilarity as defined in vegan function
vegdist
with argument binary = TRUE
. Many other
indices are dissimilarity indices as well.
Function betadiver
finds all indices reviewed by Koleff et
al. (2003). All these indices could be found with function
designdist
, but the current function provides a
conventional shortcut. The function only finds the indices. The proper
analysis must be done with functions such as betadisper
,
adonis2
or mantel
.
The indices are directly taken from Table 1 of Koleff et al. (2003),
and they can be selected either by the index number or the subscript
name used by Koleff et al. The numbers, names and defining equations
can be seen using betadiver(help = TRUE)
. In all cases where
there are two alternative forms, the one with the term is
used. There are several duplicate indices, and the number of distinct
alternatives is much lower than 24 formally provided. The formulations
used in functions differ occasionally from those in Koleff et
al. (2003), but they are still mathematically equivalent. With
method = NA
, no index is calculated, but instead an object of
class betadiver
is returned. This is a list of elements
a
, b
and c
. Function plot
can be used to
display the proportions of these elements in triangular plot as
suggested by Koleff et al. (2003), and scores
extracts the
triangular coordinates or the raw scores. Function plot
returns
invisibly the triangular coordinates as an "ordiplot"
object.
With method = NA
, the function returns an object of class
"betadisper"
with elements a
, b
, and c
. If
method
is specified, the function returns a "dist"
object which can be used in any function analysing
dissimilarities. For beta diversity, particularly useful functions are
betadisper
to study the betadiversity in groups,
adonis2
for any model, and mantel
to
compare beta diversities to other dissimilarities or distances
(including geographical distances). Although betadiver
returns
a "dist"
object, some indices are similarities and cannot be
used as such in place of dissimilarities, but that is a user
error. Functions 10 ("j"
), 11 ("sor"
) and 21
("rlb"
) are similarity indices. Function sets argument
"maxdist"
similarly as vegdist
, using NA
when there is no fixed upper limit, and 0 for similarities.
Some indices return similarities instead of dissimilarities.
Jari Oksanen
Baselga, A. (2010) Partitioning the turnover and nestedness components of beta diversity. Global Ecology and Biogeography 19, 134–143.
Koleff, P., Gaston, K.J. and Lennon, J.J. (2003) Measuring beta diversity for presence-absence data. Journal of Animal Ecology 72, 367–382.
Marion, Z.H., Fordyce, J.A. and Fitzpatrick, B.M. (2017) Pairwise beta diversity resolves an underappreciated source of confusion in calculating species turnover. Ecology 98, 933–939.
Whittaker, R.H. (1960) Vegetation of Siskiyou mountains, Oregon and California. Ecological Monographs 30, 279–338.
designdist
can be used to implement all these
functions, and also allows using notation with alpha
and
gamma
diversities. vegdist
has some canned
alternatives. Functions betadisper
,
adonis2
and mantel
can be used for
analysing beta diversity objects. The returned dissimilarities can
be used in any distance-based methods, such as
metaMDS
, capscale
and
dbrda
. Functions nestedbetasor
and
nestedbetajac
implement decomposition beta diversity
measures (Sørensen and Jaccard) into turnover and
nestedness components following Baselga (2010).
## Raw data and plotting data(sipoo) m <- betadiver(sipoo) plot(m) ## The indices betadiver(help=TRUE) ## The basic Whittaker index d <- betadiver(sipoo, "w") ## This should be equal to Sorensen index (binary Bray-Curtis in ## vegan) range(d - vegdist(sipoo, binary=TRUE))
## Raw data and plotting data(sipoo) m <- betadiver(sipoo) plot(m) ## The indices betadiver(help=TRUE) ## The basic Whittaker index d <- betadiver(sipoo, "w") ## This should be equal to Sorensen index (binary Bray-Curtis in ## vegan) range(d - vegdist(sipoo, binary=TRUE))
This function computes coefficients of dispersal direction between geographically connected areas, as defined by Legendre and Legendre (1984), and also described in Legendre and Legendre (2012, section 13.3.4).
bgdispersal(mat, PAonly = FALSE, abc = FALSE)
bgdispersal(mat, PAonly = FALSE, abc = FALSE)
mat |
Data frame or matrix containing a community composition data table (species presence-absence or abundance data). |
PAonly |
|
abc |
If |
The signs of the DD coefficients indicate the direction of dispersal, provided that the asymmetry is significant. A positive sign indicates dispersal from the first (row in DD tables) to the second region (column); a negative sign indicates the opposite. A McNemar test of asymmetry is computed from the presence-absence data to test the hypothesis of a significant asymmetry between the two areas under comparison.
In the input data table, the rows are sites or
areas, the columns are taxa. Most often, the taxa
are species, but the coefficients can be computed
from genera or families as well. DD1 and DD2 only
are computed for presence-absence data. The four
types of coefficients are computed for
quantitative data, which are converted to
presence-absence for the computation of DD1 and
DD2. PAonly = FALSE
indicates that the four types
of coefficients are requested. PAonly = TRUE
if DD1
and DD2 only are sought.
Function bgdispersal
returns a list containing the following matrices:
DD1 |
|
DD2 |
|
DD3 |
|
DD4 |
|
McNemar |
McNemar chi-square statistic of asymmetry (Sokal and
Rohlf 1995):
|
prob.McNemar |
probabilities associated
with McNemar statistics, chi-square test. H0: no
asymmetry in |
The function uses a more powerful alternative for the McNemar test
than the classical formula. The classical formula was constructed in
the spirit of Pearson's Chi-square, but the formula in this function
was constructed in the spirit of Wilks Chi-square or the
statistic. Function
mcnemar.test
uses the classical
formula. The new formula was introduced in vegan version
1.10-11, and the older implementations of bgdispersal
used the
classical formula.
Pierre Legendre, Departement de Sciences Biologiques, Universite de Montreal
Legendre, P. and V. Legendre. 1984. Postglacial dispersal of freshwater fishes in the Québec peninsula. Can. J. Fish. Aquat. Sci. 41: 1781-1802.
Legendre, P. and L. Legendre. 2012. Numerical ecology, 3rd English edition. Elsevier Science BV, Amsterdam.
Sokal, R. R. and F. J. Rohlf. 1995. Biometry. The principles and practice of statistics in biological research. 3rd edn. W. H. Freeman, New York.
mat <- matrix(c(32,15,14,10,70,30,100,4,10,30,25,0,18,0,40, 0,0,20,0,0,0,0,4,0,30,20,0,0,0,0,25,74,42,1,45,89,5,16,16,20), 4, 10, byrow=TRUE) bgdispersal(mat)
mat <- matrix(c(32,15,14,10,70,30,100,4,10,30,25,0,18,0,40, 0,0,20,0,0,0,0,4,0,30,20,0,0,0,0,25,74,42,1,45,89,5,16,16,20), 4, 10, byrow=TRUE) bgdispersal(mat)
Function finds the best subset of environmental variables, so that the Euclidean distances of scaled environmental variables have the maximum (rank) correlation with community dissimilarities.
## Default S3 method: bioenv(comm, env, method = "spearman", index = "bray", upto = ncol(env), trace = FALSE, partial = NULL, metric = c("euclidean", "mahalanobis", "manhattan", "gower"), parallel = getOption("mc.cores"), ...) ## S3 method for class 'formula' bioenv(formula, data, ...) bioenvdist(x, which = "best")
## Default S3 method: bioenv(comm, env, method = "spearman", index = "bray", upto = ncol(env), trace = FALSE, partial = NULL, metric = c("euclidean", "mahalanobis", "manhattan", "gower"), parallel = getOption("mc.cores"), ...) ## S3 method for class 'formula' bioenv(formula, data, ...) bioenvdist(x, which = "best")
comm |
Community data frame or a dissimilarity object or a square matrix that can be interpreted as dissimilarities. |
env |
Data frame of continuous environmental variables. |
method |
The correlation method used in |
index |
The dissimilarity index used for community data ( |
upto |
Maximum number of parameters in studied subsets. |
formula , data
|
Model |
trace |
Trace the calculations |
partial |
Dissimilarities partialled out when inspecting
variables in |
metric |
Metric used for distances of environmental distances. See Details. |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
x |
|
which |
The number of the model for which the environmental
distances are evaluated, or the |
... |
Other arguments passed to |
The function calculates a community dissimilarity matrix using
vegdist
. Then it selects all possible subsets of
environmental variables, scale
s the variables, and
calculates Euclidean distances for this subset using
dist
. The function finds the correlation between
community dissimilarities and environmental distances, and for each
size of subsets, saves the best result. There are
subsets of
variables, and an exhaustive search may take a
very, very, very long time (parameter
upto
offers a partial
relief).
The argument metric
defines distances in the given set of
environmental variables. With metric = "euclidean"
, the
variables are scaled to unit variance and Euclidean distances are
calculated. With metric = "mahalanobis"
, the Mahalanobis
distances are calculated: in addition to scaling to unit variance,
the matrix of the current set of environmental variables is also
made orthogonal (uncorrelated). With metric = "manhattan"
,
the variables are scaled to unit range and Manhattan distances are
calculated, so that the distances are sums of differences of
environmental variables. With metric = "gower"
, the Gower
distances are calculated using function
daisy
. This allows also using factor
variables, but with continuous variables the results are equal to
metric = "manhattan"
.
The function can be called with a model formula
where
the LHS is the data matrix and RHS lists the environmental variables.
The formula interface is practical in selecting or transforming
environmental variables.
With argument partial
you can perform “partial”
analysis. The partializing item must be a dissimilarity object of
class dist
. The
partial
item can be used with any correlation method
,
but it is strictly correct only for Pearson.
Function bioenvdist
recalculates the environmental distances
used within the function. The default is to calculate distances for
the best model, but the number of any model can be given.
Clarke & Ainsworth (1993) suggested this method to be used for selecting the best subset of environmental variables in interpreting results of nonmetric multidimensional scaling (NMDS). They recommended a parallel display of NMDS of community dissimilarities and NMDS of Euclidean distances from the best subset of scaled environmental variables. They warned against the use of Procrustes analysis, but to me this looks like a good way of comparing these two ordinations.
Clarke & Ainsworth wrote a computer program BIO-ENV giving the name to the current function. Presumably BIO-ENV was later incorporated in Clarke's PRIMER software (available for Windows). In addition, Clarke & Ainsworth suggested a novel method of rank correlation which is not available in the current function.
The function returns an object of class bioenv
with a
summary
method.
If you want to study the ‘significance’ of bioenv
results, you can use function mantel
or
mantel.partial
which use the same definition of
correlation. However, bioenv
standardizes environmental
variables depending on the used metric, and you must do the same in
mantel
for comparable results (the standardized data are
returned as item x
in the result object). It is safest to use
bioenvdist
to extract the environmental distances that really
were used within bioenv
. NB., bioenv
selects variables
to maximize the Mantel correlation, and significance tests based on
a priori selection of variables are biased.
Jari Oksanen
Clarke, K. R & Ainsworth, M. 1993. A method of linking multivariate community structure to environmental variables. Marine Ecology Progress Series, 92, 205–219.
vegdist
, dist
, cor
for underlying routines, monoMDS
and
metaMDS
for ordination, procrustes
for
Procrustes analysis, protest
for an alternative, and
rankindex
for studying alternatives to the default
Bray-Curtis index.
# The method is very slow for large number of possible subsets. # Therefore only 6 variables in this example. data(varespec) data(varechem) sol <- bioenv(wisconsin(varespec) ~ log(N) + P + K + Ca + pH + Al, varechem) sol ## IGNORE_RDIFF_BEGIN summary(sol) ## IGNORE_RDIFF_END
# The method is very slow for large number of possible subsets. # Therefore only 6 variables in this example. data(varespec) data(varechem) sol <- bioenv(wisconsin(varespec) ~ log(N) + P + K + Ca + pH + Al, varechem) sol ## IGNORE_RDIFF_BEGIN summary(sol) ## IGNORE_RDIFF_END
Draws a PCA biplot with species scores indicated by biplot arrows
## S3 method for class 'rda' biplot(x, choices = c(1, 2), scaling = "species", display = c("sites", "species"), type, xlim, ylim, col = c(1,2), const, correlation = FALSE, ...)
## S3 method for class 'rda' biplot(x, choices = c(1, 2), scaling = "species", display = c("sites", "species"), type, xlim, ylim, col = c(1,2), const, correlation = FALSE, ...)
x |
A |
choices |
Axes to show. |
scaling |
Scaling for species and site scores. Either species
( The type of scores can also be specified as one of |
correlation |
logical; if |
display |
Scores shown. These must some of the alternatives
|
type |
Type of plot: partial match to |
xlim , ylim
|
the x and y limits (min, max) of the plot. |
col |
Colours used for sites and species (in this order). If only one colour is given, it is used for both. |
const |
General scaling constant for |
... |
Other parameters for plotting functions. |
Produces a plot or biplot of the results of a call to
rda
. It is common for the "species" scores in a PCA to
be drawn as biplot arrows that point in the direction of increasing
values for that variable. The biplot.rda
function provides a
wrapper to plot.cca
to allow the easy production of such a
plot.
biplot.rda
is only suitable for unconstrained models. If
used on an ordination object with constraints, an error is issued.
If species scores are drawn using "text"
, the arrows are drawn
from the origin to 0.85 * species score, whilst the labels are
drawn at the species score. If the type used is "points"
, then
no labels are drawn and therefore the arrows are drawn from the origin
to the actual species score.
The plot
function returns invisibly a plotting structure which
can be used by identify.ordiplot
to identify
the points or other functions in the ordiplot
family.
Gavin Simpson, based on plot.cca
by Jari Oksanen.
plot.cca
, rda
for something to
plot, ordiplot
for an alternative plotting routine
and more support functions, and text
,
points
and arrows
for the basic routines.
data(dune) mod <- rda(dune, scale = TRUE) biplot(mod, scaling = "symmetric") ## plot.cca can do the same plot(mod, scaling = "symmetric", spe.par = list(arrows=TRUE)) ## different type for species and site scores biplot(mod, scaling = "symmetric", type = c("text", "points")) ## We can use ordiplot pipes to build similar plots with flexible ## control plot(mod, scaling = "symmetric", type="n") |> points("sites", cex=0.7) |> text("species", arrows=TRUE, length=0.05, col=2, cex=0.7, font=3)
data(dune) mod <- rda(dune, scale = TRUE) biplot(mod, scaling = "symmetric") ## plot.cca can do the same plot(mod, scaling = "symmetric", spe.par = list(arrows=TRUE)) ## different type for species and site scores biplot(mod, scaling = "symmetric", type = c("text", "points")) ## We can use ordiplot pipes to build similar plots with flexible ## control plot(mod, scaling = "symmetric", type="n") |> points("sites", cex=0.7) |> text("species", arrows=TRUE, length=0.05, col=2, cex=0.7, font=3)
This function is a wrapper for the kmeans
function. It creates
several partitions forming a cascade from a small to a large number of
groups.
cascadeKM(data, inf.gr, sup.gr, iter = 100, criterion = "calinski", parallel = getOption("mc.cores")) cIndexKM(y, x, index = "all") ## S3 method for class 'cascadeKM' plot(x, min.g, max.g, grpmts.plot = TRUE, sortg = FALSE, gridcol = NA, ...)
cascadeKM(data, inf.gr, sup.gr, iter = 100, criterion = "calinski", parallel = getOption("mc.cores")) cIndexKM(y, x, index = "all") ## S3 method for class 'cascadeKM' plot(x, min.g, max.g, grpmts.plot = TRUE, sortg = FALSE, gridcol = NA, ...)
data |
The data matrix. The objects (samples) are the rows. |
inf.gr |
The number of groups for the partition with the smallest number of groups of the cascade (min). |
sup.gr |
The number of groups for the partition with the largest number of groups of the cascade (max). |
iter |
The number of random starting configurations for each value
of |
criterion |
The criterion that will be used to select the best
partition. The default value is |
y |
Object of class |
x |
Data matrix where columns correspond to variables and rows to
observations, or the plotting object in |
index |
The available indices are: |
min.g , max.g
|
The minimum and maximum numbers of groups to be displayed. |
grpmts.plot |
Show the plot ( |
sortg |
Sort the objects as a function of their group membership
to produce a more easily interpretable graph. See Details. The
original object names are kept; they are used as labels in the
output table |
gridcol |
The colour of the grid lines in the plots. |
... |
Other parameters to the functions (ignored). |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
The function creates several partitions forming a cascade from a small
to a large number of groups formed by kmeans
. Most
of the work is performed by function cIndex
which is based on the
clustIndex
in package cclust).
Some of the criteria were removed from this version because computation
errors were generated when only one object was found in a group.
The default value is "calinski"
, which refers to the well-known
Calinski-Harabasz (1974) criterion. The other available index is the
simple structure index "ssi"
(Dolnicar et al. 1999).
In the case of groups of equal
sizes, "calinski"
is generally a good criterion to indicate the
correct number of groups. Users should not take its indications
literally when the groups are not equal in size. Type "all"
to
obtain both indices. The indices are defined as:
, where
is the
number of data points and
is the number of clusters.
is the sum of squares within the clusters while
is the sum of squares among the clusters. This index
is simply an
(ANOVA) statistic.
the “Simple Structure Index” multiplicatively combines several elements which influence the interpretability of a partitioning solution. The best partition is indicated by the highest SSI value.
In a simulation study, Milligan and Cooper (1985) found
that the Calinski-Harabasz criterion recovered the correct number of
groups the most often. We recommend this criterion because, if the
groups are of equal sizes, the maximum value of "calinski"
usually indicates the correct number of groups. Another available
index is the simple structure index "ssi"
. Users should not
take the indications of these indices literally when the groups are
not equal in size and explore the groups corresponding to other values
of .
Function cascadeKM
has a plot
method. Two plots are
produced. The graph on the left has the objects in
abscissa and the number of groups in ordinate. The groups are
represented by colours. The graph on the right shows the values of the
criterion ("calinski"
or "ssi"
) for determining the best
partition. The highest value of the criterion is marked in red. Points
marked in orange, if any, indicate partitions producing an increase in
the criterion value as the number of groups increases; they may
represent other interesting partitions.
If sortg=TRUE
, the objects are reordered by the following
procedure: (1) a simple matching distance matrix is computed among the
objects, based on the table of K-means assignments to groups, from
=
min.g
to =
max.g
. (2) A principal
coordinate analysis (PCoA, Gower 1966) is computed on the centred
distance matrix. (3) The first principal coordinate is used as the new
order of the objects in the graph. A simplified algorithm is used to
compute the first principal coordinate only, using the iterative
algorithm described in Legendre & Legendre (2012). The
full distance matrix among objects is never computed; this avoids
the problem of storing it when the number of objects is
large. Distance values are computed as they are needed by the
algorithm.
Function cascadeKM
returns an object of class
cascadeKM
with items:
partition |
Table with the partitions found for different numbers
of groups |
results |
Values of the criterion to select the best partition. |
criterion |
The name of the criterion used. |
size |
The number of objects found in each group, for all partitions (columns). |
Function cIndex
returns a vector with the index values. The
maximum value of these indices is supposed to indicate the best
partition. These indices work best with groups of equal sizes. When
the groups are not of equal sizes, one should not put too much faith
in the maximum of these indices, and also explore the groups
corresponding to other values of .
Marie-Helene Ouellette [email protected], Sebastien Durand [email protected] and Pierre Legendre [email protected]. Parallel processing by Virgilio Gómez-Rubio. Edited for vegan by Jari Oksanen.
Calinski, T. and J. Harabasz. 1974. A dendrite method for cluster analysis. Commun. Stat. 3: 1–27.
Dolnicar, S., K. Grabler and J. A. Mazanec. 1999. A tale of three cities: perceptual charting for analyzing destination images. Pp. 39-62 in: Woodside, A. et al. [eds.] Consumer psychology of tourism, hospitality and leisure. CAB International, New York.
Gower, J. C. 1966. Some distance properties of latent root and vector methods used in multivariate analysis. Biometrika 53: 325–338.
Legendre, P. & L. Legendre. 2012. Numerical ecology, 3rd English edition. Elsevier Science BV, Amsterdam.
Milligan, G. W. & M. C. Cooper. 1985. An examination of procedures for determining the number of clusters in a data set. Psychometrika 50: 159–179.
Weingessel, A., Dimitriadou, A. and Dolnicar, S. 2002. An examination of indexes for determining the number of clusters in binary data sets. Psychometrika 67: 137–160.
# Partitioning a (10 x 10) data matrix of random numbers mat <- matrix(runif(100),10,10) res <- cascadeKM(mat, 2, 5, iter = 25, criterion = 'calinski') toto <- plot(res) # Partitioning an autocorrelated time series vec <- sort(matrix(runif(30),30,1)) res <- cascadeKM(vec, 2, 5, iter = 25, criterion = 'calinski') toto <- plot(res) # Partitioning a large autocorrelated time series # Note that we remove the grid lines vec <- sort(matrix(runif(1000),1000,1)) res <- cascadeKM(vec, 2, 7, iter = 10, criterion = 'calinski') toto <- plot(res, gridcol=NA)
# Partitioning a (10 x 10) data matrix of random numbers mat <- matrix(runif(100),10,10) res <- cascadeKM(mat, 2, 5, iter = 25, criterion = 'calinski') toto <- plot(res) # Partitioning an autocorrelated time series vec <- sort(matrix(runif(30),30,1)) res <- cascadeKM(vec, 2, 5, iter = 25, criterion = 'calinski') toto <- plot(res) # Partitioning a large autocorrelated time series # Note that we remove the grid lines vec <- sort(matrix(runif(1000),1000,1)) res <- cascadeKM(vec, 2, 7, iter = 10, criterion = 'calinski') toto <- plot(res, gridcol=NA)
Function cca
performs correspondence analysis, or optionally
constrained correspondence analysis (a.k.a. canonical correspondence
analysis), or optionally partial constrained correspondence
analysis. Function rda
performs redundancy analysis, or
optionally principal components analysis.
These are all very popular ordination techniques in community ecology.
## S3 method for class 'formula' cca(formula, data, na.action = na.fail, subset = NULL, ...) ## S3 method for class 'formula' rda(formula, data, scale=FALSE, na.action = na.fail, subset = NULL, ...) ## Default S3 method: cca(X, Y, Z, ...) ## Default S3 method: rda(X, Y, Z, scale=FALSE, ...) ca(X, ...) pca(X, scale=FALSE, ...)
## S3 method for class 'formula' cca(formula, data, na.action = na.fail, subset = NULL, ...) ## S3 method for class 'formula' rda(formula, data, scale=FALSE, na.action = na.fail, subset = NULL, ...) ## Default S3 method: cca(X, Y, Z, ...) ## Default S3 method: rda(X, Y, Z, scale=FALSE, ...) ca(X, ...) pca(X, scale=FALSE, ...)
formula |
Model formula, where the left hand side gives the
community data matrix, right hand side gives the constraining variables,
and conditioning variables can be given within a special function
|
data |
Data frame containing the variables on the right hand side of the model formula. |
X |
Community data matrix. |
Y |
Constraining matrix, typically of environmental variables.
Can be missing. If this is a |
Z |
Conditioning matrix, the effect of which is removed
(“partialled out”) before next step. Can be missing. If this is a
|
scale |
Scale species to unit variance (like correlations). |
na.action |
Handling of missing values in constraints or
conditions. The default ( |
subset |
Subset of data rows. This can be a logical vector which
is |
... |
Other arguments for |
Since their introduction (ter Braak 1986), constrained, or canonical,
correspondence analysis and its spin-off, redundancy analysis, have
been the most popular ordination methods in community ecology.
Functions cca
and rda
are similar to popular
proprietary software Canoco
, although the implementation is
completely different. The functions are based on Legendre &
Legendre's (2012) algorithm: in cca
Chi-square transformed data matrix is subjected to weighted linear
regression on constraining variables, and the fitted values are
submitted to correspondence analysis performed via singular value
decomposition (svd
). Function rda
is similar, but uses
ordinary, unweighted linear regression and unweighted SVD. Legendre &
Legendre (2012), Table 11.5 (p. 650) give a skeleton of the RDA
algorithm of vegan. The algorithm of CCA is similar, but
involves standardization by row and column weights.
The functions cca()
and rda()
can be called either with
matrix-like entries for community data and constraints, or with formula
interface. In general, the formula interface is preferred, because it
allows a better control of the model and allows factor constraints. Some
analyses of ordination results are only possible if model was fitted
with formula (e.g., most cases of anova.cca
, automatic
model building).
In the following sections, X
, Y
and Z
, although
referred to as matrices, are more commonly data frames.
In the matrix interface, the
community data matrix X
must be given, but the other data
matrices may be omitted, and the corresponding stage of analysis is
skipped. If matrix Z
is supplied, its effects are removed from
the community matrix, and the residual matrix is submitted to the next
stage. This is called partial correspondence or redundancy
analysis. If matrix
Y
is supplied, it is used to constrain the ordination,
resulting in constrained or canonical correspondence analysis, or
redundancy analysis.
Finally, the residual is submitted to ordinary correspondence
analysis (or principal components analysis). If both matrices
Z
and Y
are missing, the
data matrix is analysed by ordinary correspondence analysis (or
principal components analysis).
Instead of separate matrices, the model can be defined using a model
formula
. The left hand side must be the
community data matrix (X
). The right hand side defines the
constraining model.
The constraints can contain ordered or unordered factors,
interactions among variables and functions of variables. The defined
contrasts
are honoured in factor
variables. The constraints can also be matrices (but not data
frames).
The formula can include a special term Condition
for conditioning variables (“covariables”) partialled out before
analysis. So the following commands are equivalent:
cca(X, Y, Z)
, cca(X ~ Y + Condition(Z))
, where Y
and Z
refer to constraints and conditions matrices respectively.
Constrained correspondence analysis is indeed a constrained method:
CCA does not try to display all variation in the
data, but only the part that can be explained by the used constraints.
Consequently, the results are strongly dependent on the set of
constraints and their transformations or interactions among the
constraints. The shotgun method is to use all environmental variables
as constraints. However, such exploratory problems are better
analysed with
unconstrained methods such as correspondence analysis
(decorana
, corresp
) or non-metric
multidimensional scaling (metaMDS
) and
environmental interpretation after analysis
(envfit
, ordisurf
).
CCA is a good choice if the user has
clear and strong a priori hypotheses on constraints and is not
interested in the major structure in the data set.
CCA is able to correct the curve artefact commonly found in correspondence analysis by forcing the configuration into linear constraints. However, the curve artefact can be avoided only with a low number of constraints that do not have a curvilinear relation with each other. The curve can reappear even with two badly chosen constraints or a single factor. Although the formula interface makes it easy to include polynomial or interaction terms, such terms often produce curved artefacts (that are difficult to interpret), these should probably be avoided.
According to folklore, rda
should be used with “short
gradients” rather than cca
. However, this is not based
on research which finds methods based on Euclidean metric as uniformly
weaker than those based on Chi-squared metric. However, standardized
Euclidean distance may be an appropriate measures (see Hellinger
standardization in decostand
in particular).
Partial CCA (pCCA; or alternatively partial RDA) can be used to remove
the effect of some
conditioning or background or random variables or
covariables before CCA proper. In fact, pCCA compares models
cca(X ~ Z)
and cca(X ~ Y + Z)
and attributes their
difference to the effect of Y
cleansed of the effect of
Z
. Some people have used the method for extracting
“components of variance” in CCA. However, if the effect of
variables together is stronger than sum of both separately, this can
increase total Chi-square after partialling out some
variation, and give negative “components of variance”. In general,
such components of “variance” are not to be trusted due to
interactions between two sets of variables.
The unconstrained ordination methods, Principal Components Analysis (PCA) and
Correspondence Analysis (CA), may be performed using pca()
and
ca()
, which are simple wrappers around rda()
and cca()
,
respectively. Functions pca()
and ca()
can only be called with
matrix-like objects.
The functions have summary
and plot
methods which are
documented separately (see plot.cca
, summary.cca
).
Function cca
returns a huge object of class cca
, which
is described separately in cca.object
.
Function rda
returns an object of class rda
which
inherits from class cca
and is described in cca.object
.
The scaling used in rda
scores is described in a separate
vignette with this package.
Functions pca()
and ca()
return objects of class
"vegan_pca"
and "vegan_ca"
respectively to avoid
clashes with other packages. These classes inherit from "rda"
and "cca"
respectively.
The responsible author was Jari Oksanen, but the code borrows heavily from Dave Roberts (Montana State University, USA).
The original method was by ter Braak, but the current implementation follows Legendre and Legendre.
Legendre, P. and Legendre, L. (2012) Numerical Ecology. 3rd English ed. Elsevier.
McCune, B. (1997) Influence of noisy environmental data on canonical correspondence analysis. Ecology 78, 2617-2623.
Palmer, M. W. (1993) Putting things in even better order: The advantages of canonical correspondence analysis. Ecology 74,2215-2230.
Ter Braak, C. J. F. (1986) Canonical Correspondence Analysis: a new eigenvector technique for multivariate direct gradient analysis. Ecology 67, 1167-1179.
This help page describes two constrained ordination functions,
cca
and rda
and their corresponding unconstrained
ordination functions, ca
and pca
. A related method,
distance-based redundancy analysis (dbRDA) is described separately
(capscale
), as is dbRDA's unconstrained variant,
principal coordinates analysis (PCO). All these functions return
similar objects (described in cca.object
). There are
numerous support functions that can be used to access the result object.
In the list below, functions of type cca
will handle all three
constrained ordination objects, and functions of rda
only handle
rda
and capscale
results.
The main plotting functions are plot.cca
for all
methods, and biplot.rda
for RDA and dbRDA. However,
generic vegan plotting functions can also handle the results.
The scores can be accessed and scaled with scores.cca
,
and summarized with summary.cca
. The eigenvalues can
be accessed with eigenvals.cca
and the regression
coefficients for constraints with coef.cca
. The
eigenvalues can be plotted with screeplot.cca
, and the
(adjusted) can be found with
RsquareAdj.rda
. The scores can be also calculated for
new data sets with predict.cca
which allows adding
points to ordinations. The values of constraints can be inferred
from ordination and community composition with
calibrate.cca
.
Diagnostic statistics can be found with goodness.cca
,
inertcomp
, spenvcor
,
intersetcor
, tolerance.cca
, and
vif.cca
. Function as.mlm.cca
refits the
result object as a multiple lm
object, and this allows
finding influence statistics (lm.influence
,
cooks.distance
etc.).
Permutation based significance for the overall model, single
constraining variables or axes can be found with
anova.cca
. Automatic model building with R
step
function is possible with
deviance.cca
, add1.cca
and
drop1.cca
. Functions ordistep
and
ordiR2step
(for RDA) are special functions for
constrained ordination. Randomized data sets can be generated with
simulate.cca
.
Separate methods based on constrained ordination model are principal
response curves (prc
) and variance partitioning between
several components (varpart
).
Design decisions are explained in vignette
on “Design decisions” which can be accessed with
browseVignettes("vegan")
.
data(varespec) data(varechem) ## Common but bad way: use all variables you happen to have in your ## environmental data matrix vare.cca <- cca(varespec, varechem) vare.cca plot(vare.cca) ## Formula interface and a better model vare.cca <- cca(varespec ~ Al + P*(K + Baresoil), data=varechem) vare.cca plot(vare.cca) ## Partialling out and negative components of variance cca(varespec ~ Ca, varechem) cca(varespec ~ Ca + Condition(pH), varechem) ## RDA data(dune) data(dune.env) dune.Manure <- rda(dune ~ Manure, dune.env) plot(dune.Manure)
data(varespec) data(varechem) ## Common but bad way: use all variables you happen to have in your ## environmental data matrix vare.cca <- cca(varespec, varechem) vare.cca plot(vare.cca) ## Formula interface and a better model vare.cca <- cca(varespec ~ Al + P*(K + Baresoil), data=varechem) vare.cca plot(vare.cca) ## Partialling out and negative components of variance cca(varespec ~ Ca, varechem) cca(varespec ~ Ca + Condition(pH), varechem) ## RDA data(dune) data(dune.env) dune.Manure <- rda(dune ~ Manure, dune.env) plot(dune.Manure)
Ordination methods cca
, rda
,
dbrda
and capscale
return similar result
objects. All these methods use the same internal function
ordConstrained
. They differ only in (1) initial
transformation of the data and in defining inertia, (2) weighting,
and (3) the use of rectangular rows columns data or
symmetric rows
rows dissimilarities:
rda
initializes data to give variance or correlations
as inertia, cca
is based on double-standardized data
to give Chi-square inertia and uses row and column weights,
capscale
maps the real part of dissimilarities to
rectangular data and performs RDA, and dbrda
performs
an RDA-like analysis directly on symmetric dissimilarities.
Function ordConstrained
returns the same result components
for all these methods, and the calling function may add some more
components to the final result. However, you should not access these
result components directly (using $
): the internal structure
is not regarded as stable application interface (API), but it can
change at any release. If you access the results components
directly, you take a risk of breakage at any vegan release.
The vegan provides a wide set of accessor functions to those
components, and these functions are updated when the result object
changes. This documentation gives an overview of accessor functions
to the cca
result object.
ordiYbar(x, model = c("CCA", "CA", "pCCA", "partial", "initial")) ## S3 method for class 'cca' model.frame(formula, ...) ## S3 method for class 'cca' model.matrix(object, ...) ## S3 method for class 'cca' weights(object, display = "sites", ...)
ordiYbar(x, model = c("CCA", "CA", "pCCA", "partial", "initial")) ## S3 method for class 'cca' model.frame(formula, ...) ## S3 method for class 'cca' model.matrix(object, ...) ## S3 method for class 'cca' weights(object, display = "sites", ...)
object , x , formula
|
|
model |
Show constrained ( |
display |
Display either |
... |
Other arguments passed to the the function. |
The internal (“working”) form of the dependent (community)
data can be accessed with function ordiYbar
. The form depends
on the ordination method: for instance, in cca
the
data are weighted and Chi-square transformed, and in
dbrda
they are Gower-centred dissimilarities. The
input data in the original (“response”) form can be accessed
with fitted.cca
and residuals.cca
.
Function predict.cca
can return either working or
response data, and also their lower-rank approximations.
The model matrix of independent data (“Constraints” and
“Conditions”) can be extracted with model.matrix
. In
partial analysis, the function returns a list of design matrices
called Conditions
and Constraints
. If either component
was missing, a single matrix is returned. The redundant (aliased)
terms do not appear in the model matrix. These terms can be found
with alias.cca
. Function model.frame
tries to
reconstruct the data frame from which the model matrices were
derived. This is only possible if the original model was fitted with
formula
and data
arguments, and still fails if the
data
are unavailable.
The number of observations can be accessed with
nobs.cca
, and the residual degrees of freedom with
df.residual.cca
. The information on observations with
missing values can be accessed with na.action
. The
terms and formula of the fitted model can be accessed with
formula
and terms
.
The weights used in cca
can be accessed with
weights
. In unweighted methods (rda
) all
weights are equal.
The ordination results are saved in separate components for partial terms, constraints and residual unconstrained ordination. There is no guarantee that these components will have the same internal names as currently, and you should be cautious when developing scripts and functions that directly access these components.
The constrained ordination algorithm is based on QR decomposition of
constraints and conditions (environmental data), and the QR
component is saved separately for partial and constrained
components. The QR decomposition of constraints can be accessed
with qr.cca
. This will also include the residual
effects of partial terms (Conditions), and it should be used
together with ordiYbar(x, "partial")
. The environmental data
are first centred in rda
or weighted and centred in
cca
. The QR decomposition is used in many functions that
access cca
results, and it can be used to find many items
that are not directly stored in the object. For examples, see
coef.cca
, coef.rda
,
vif.cca
, permutest.cca
,
predict.cca
, predict.rda
,
calibrate.cca
. See qr
for other possible
uses of this component. For instance, the rank of the constraints
can be found from the QR decomposition.
The eigenvalues of the solution can be accessed with
eigenvals.cca
. Eigenvalues are not evaluated for
partial component, and they will only be available for constrained
and residual components.
The ordination scores are internally stored as (weighted)
orthonormal scores matrices. These results can be accessed with
scores.cca
and scores.rda
functions. The
ordination scores are scaled when accessed with scores
functions, but internal (weighted) orthonormal scores can be
accessed by setting scaling = FALSE
. Unconstrained residual
component has species and site scores, and constrained component has
also fitted site scores or linear combination scores for sites and
biplot scores and centroids for constraint variables. The biplot
scores correspond to the model.matrix
, and centroids
are calculated for factor variables when they were used. The scores
can be selected by defining the axes, and there is no direct way of
accessing all scores of a certain component. The number of dimensions
can be assessed from eigenvals
. In addition, some
other types can be derived from the results although not saved in
the results. For instance, regression scores and model coefficients
can be accessed with scores
and coef
functions. Partial component will have no scores.
Distance-based methods (dbrda
, capscale
)
can have negative eigenvalues and associated imaginary axis scores. In
addition, species scores are initially missing in dbrda
and they are accessory and found after analysis in
capscale
(and may be misleading). Function
sppscores
can be used to add species scores or replace
them with more meaningful ones.
The latest large change of result object was made in release 2.5-1 in
2016. You can modernize ancient stray results with
modernobject <- update(ancientobject)
.
Jari Oksanen
Legendre, P. and Legendre, L. (2012) Numerical Ecology. 3rd English ed. Elsevier.
The core function is ordConstrained
which is called by
cca
, rda
, dbrda
and
capscale
. The basic class is "cca"
for all
methods, and the following functions are defined for this class:
RsquareAdj.cca
, SSD.cca
, add1.cca
, alias.cca
, anova.cca
, as.mlm.cca
, biplot.cca
, bstick.cca
, calibrate.cca
, centredist.cca
, coef.cca
, cooks.distance.cca
, deviance.cca
, df.residual.cca
, drop1.cca
, eigenvals.cca
, extractAIC.cca
, fitted.cca
, goodness.cca
, hatvalues.cca
, labels.cca
, model.frame.cca
, model.matrix.cca
, nobs.cca
, permutest.cca
, plot.cca
, points.cca
, predict.cca
, print.cca
, qr.cca
, residuals.cca
, rstandard.cca
, rstudent.cca
, scores.cca
, screeplot.cca
, sigma.cca
, simulate.cca
, stressplot.cca
, summary.cca
, text.cca
, tolerance.cca
, vcov.cca
, weights.cca
.
Other functions handling "cca"
objects include inertcomp
,
intersetcor
, mso
, ordiresids
,
ordistep
and ordiR2step
.
Canonical correlation analysis, following Brian McArdle's unpublished graduate course notes, plus improvements to allow the calculations in the case of very sparse and collinear matrices, and permutation test of Pillai's trace statistic.
CCorA(Y, X, stand.Y=FALSE, stand.X=FALSE, permutations = 0, ...) ## S3 method for class 'CCorA' biplot(x, plot.type="ov", xlabs, plot.axes = 1:2, int=0.5, col.Y="red", col.X="blue", cex=c(0.7,0.9), ...)
CCorA(Y, X, stand.Y=FALSE, stand.X=FALSE, permutations = 0, ...) ## S3 method for class 'CCorA' biplot(x, plot.type="ov", xlabs, plot.axes = 1:2, int=0.5, col.Y="red", col.X="blue", cex=c(0.7,0.9), ...)
Y |
Left matrix (object class: |
X |
Right matrix (object class: |
stand.Y |
Logical; should |
stand.X |
Logical; should |
permutations |
a list of control values for the permutations
as returned by the function |
x |
|
plot.type |
A character string indicating which of the following
plots should be produced: |
xlabs |
Row labels. The default is to use row names, |
plot.axes |
A vector with 2 values containing the order numbers of the canonical axes to be plotted. Default: first two axes. |
int |
Radius of the inner circles plotted as visual references in
the plots of the variables. Default: |
col.Y |
Color used for objects and variables in the first data table (Y) plots. In biplots, the objects are in black. |
col.X |
Color used for objects and variables in the second data table (X) plots. |
cex |
A vector with 2 values containing the size reduction factors
for the object and variable names, respectively, in the plots.
Default values: |
... |
Other arguments passed to these functions. The function
|
Canonical correlation analysis (Hotelling 1936) seeks linear
combinations of the variables of Y
that are maximally
correlated to linear combinations of the variables of X
. The
analysis estimates the relationships and displays them in graphs.
Pillai's trace statistic is computed and tested parametrically (F-test);
a permutation test is also available.
Algorithmic note –
The blunt approach would be to read the two matrices, compute the
covariance matrices, then the matrix
S12 %*% inv(S22) %*% t(S12) %*% inv(S11)
.
Its trace is Pillai's trace statistic.
This approach may fail, however, when there is heavy multicollinearity
in very sparse data matrices. The safe approach is to replace all data
matrices by their PCA object scores.
The function can produce different types of plots depending on the option
chosen:
"objects"
produces two plots of the objects, one in the space
of Y, the second in the space of X;
"variables"
produces two plots of the variables, one of the variables
of Y in the space of Y, the second of the variables of X in the space of X;
"ov"
produces four plots, two of the objects and two of the variables;
"biplots"
produces two biplots, one for the first matrix (Y) and
one for second matrix (X) solutions. For biplots, the function passes all arguments
to biplot.default
; consult its help page for configuring biplots.
Function CCorA
returns a list containing the following elements:
Pillai |
Pillai's trace statistic = sum of the canonical eigenvalues. |
Eigenvalues |
Canonical eigenvalues. They are the squares of the canonical correlations. |
CanCorr |
Canonical correlations. |
Mat.ranks |
Ranks of matrices |
RDA.Rsquares |
Bimultivariate redundancy coefficients (R-squares) of RDAs of Y|X and X|Y. |
RDA.adj.Rsq |
|
nperm |
Number of permutations. |
p.Pillai |
Parametric probability value associated with Pillai's trace. |
p.perm |
Permutational probability associated with Pillai's trace. |
Cy |
Object scores in Y biplot. |
Cx |
Object scores in X biplot. |
corr.Y.Cy |
Scores of Y variables in Y biplot, computed as cor(Y,Cy). |
corr.X.Cx |
Scores of X variables in X biplot, computed as cor(X,Cx). |
corr.Y.Cx |
cor(Y,Cy) available for plotting variables Y in space of X manually. |
corr.X.Cy |
cor(X,Cx) available for plotting variables X in space of Y manually. |
control |
A list of control values for the permutations
as returned by the function |
call |
Call to the CCorA function. |
Pierre Legendre, Departement de Sciences Biologiques, Universite de Montreal. Implemented in vegan with the help of Jari Oksanen.
Hotelling, H. 1936. Relations between two sets of variates. Biometrika 28: 321-377.
Legendre, P. 2005. Species associations: the Kendall coefficient of concordance revisited. Journal of Agricultural, Biological, and Environmental Statistics 10: 226-245.
# Example using two mite groups. The mite data are available in vegan data(mite) # Two mite species associations (Legendre 2005, Fig. 4) group.1 <- c(1,2,4:8,10:15,17,19:22,24,26:30) group.2 <- c(3,9,16,18,23,25,31:35) # Separate Hellinger transformations of the two groups of species mite.hel.1 <- decostand(mite[,group.1], "hel") mite.hel.2 <- decostand(mite[,group.2], "hel") rownames(mite.hel.1) = paste("S",1:nrow(mite),sep="") rownames(mite.hel.2) = paste("S",1:nrow(mite),sep="") out <- CCorA(mite.hel.1, mite.hel.2) out biplot(out, "ob") # Two plots of objects biplot(out, "v", cex=c(0.7,0.6)) # Two plots of variables biplot(out, "ov", cex=c(0.7,0.6)) # Four plots (2 for objects, 2 for variables) biplot(out, "b", cex=c(0.7,0.6)) # Two biplots biplot(out, xlabs = NA, plot.axes = c(3,5)) # Plot axes 3, 5. No object names biplot(out, plot.type="biplots", xlabs = NULL) # Replace object names by numbers # Example using random numbers. No significant relationship is expected mat1 <- matrix(rnorm(60),20,3) mat2 <- matrix(rnorm(100),20,5) out2 = CCorA(mat1, mat2, permutations=99) out2 biplot(out2, "b")
# Example using two mite groups. The mite data are available in vegan data(mite) # Two mite species associations (Legendre 2005, Fig. 4) group.1 <- c(1,2,4:8,10:15,17,19:22,24,26:30) group.2 <- c(3,9,16,18,23,25,31:35) # Separate Hellinger transformations of the two groups of species mite.hel.1 <- decostand(mite[,group.1], "hel") mite.hel.2 <- decostand(mite[,group.2], "hel") rownames(mite.hel.1) = paste("S",1:nrow(mite),sep="") rownames(mite.hel.2) = paste("S",1:nrow(mite),sep="") out <- CCorA(mite.hel.1, mite.hel.2) out biplot(out, "ob") # Two plots of objects biplot(out, "v", cex=c(0.7,0.6)) # Two plots of variables biplot(out, "ov", cex=c(0.7,0.6)) # Four plots (2 for objects, 2 for variables) biplot(out, "b", cex=c(0.7,0.6)) # Two biplots biplot(out, xlabs = NA, plot.axes = c(3,5)) # Plot axes 3, 5. No object names biplot(out, plot.type="biplots", xlabs = NULL) # Replace object names by numbers # Example using random numbers. No significant relationship is expected mat1 <- matrix(rnorm(60),20,3) mat2 <- matrix(rnorm(100),20,5) out2 = CCorA(mat1, mat2, permutations=99) out2 biplot(out2, "b")
Function finds Euclidean or squared Mahalanobis distances of points
to class centroids in betadisper
or ordination results.
## Default S3 method: centredist(x, group, distance = c("euclidean", "mahalanobis"), display = "sites", w, ...) ## S3 method for class 'betadisper' centredist(x, ...) ## S3 method for class 'cca' centredist(x, group, distance = c("euclidean", "mahalanobis"), display = c("sites", "species"), rank = 2, ...) ## S3 method for class 'rda' centredist(x, group, distance = c("euclidean", "mahalanobis"), display = "sites", rank = 2, ...) ## S3 method for class 'dbrda' centredist(x, group, distance = c("euclidean","mahalanobis"), display = "sites", rank = 2, ...) ## S3 method for class 'wcmdscale' centredist(x, group, distance= c("euclidean","mahalanobis"), display = "sites", rank = 2, ...)
## Default S3 method: centredist(x, group, distance = c("euclidean", "mahalanobis"), display = "sites", w, ...) ## S3 method for class 'betadisper' centredist(x, ...) ## S3 method for class 'cca' centredist(x, group, distance = c("euclidean", "mahalanobis"), display = c("sites", "species"), rank = 2, ...) ## S3 method for class 'rda' centredist(x, group, distance = c("euclidean", "mahalanobis"), display = "sites", rank = 2, ...) ## S3 method for class 'dbrda' centredist(x, group, distance = c("euclidean","mahalanobis"), display = "sites", rank = 2, ...) ## S3 method for class 'wcmdscale' centredist(x, group, distance= c("euclidean","mahalanobis"), display = "sites", rank = 2, ...)
x |
An ordination result object, or a matrix for the default
method or a |
group |
Factor to define classes for which centroids are found. |
distance |
Use either simple Euclidean distance or squared Mahalanobis distances that take into account the shape of covariance ellipses. |
display |
Kind of |
w |
Weights. If |
rank |
Number of axes used in ordination methods. |
... |
Other arguments to functions (ignored). |
Function finds either simple Euclidean distances of all points to
their centroid as given by argument group
or squared
Mahalanobis distances of points to the centroid. In addition to the
distances, it returns information of the original group and the
nearest group for each point.
Currently the distances are scaled so that the sum of squared
Euclidean distance will give the residual (unexplained) eigenvalue
in constrained ordination with given group. The distances may not
correspond to the distances in ordination plots with specific
scaling
and setting argument scaling
gives an
error. Due to restriction of this scaling, Euclidean distances for
species scores are only allowed in ca
and
cca
. These restrictions may be relaxed in the future
versions of the method.
Squared Mahalanobis distances (mahalanobis
) are scaled
by the within group covariance matrix, and they are consistent with
ordiellipse
.
Mahalanobis distances can only be calculated for group
that
are larger than rank
. For rank = 2
, minimum
permissible group
has three points. However, even this can
fail in degenerate cases, such as three points on a line. Euclidean
distances can be calculated for any rank
. With rank = "full"
distance-based methods wcmdscale
, pco
,
dbrda
and betadisper
will handle
negative eigenvalues and associated eigenvectors, but with numeric
rank they will only use real eigenvectors with positive eigenvalues.
There are specific methods for some ordination models, but many will
be handled by the default method (including metaMDS
and monoMDS
).
The specific method for betadisper
ignores most
arguments and calculates the distances as specified in model
fitting. The betadisper
result with argument
type = "centroid"
is equal to wcmdscale
,
pco
or dbrda
with the same
group
and rank = "full"
.
Function returns a list with components
centre |
Centre to which a point was originally allocated. |
nearest |
Nearest centre to a point. |
distances |
Distance matrix where each observation point is a row, and column gives the distance of the point to that centre. |
centerdist
is a synonym of centredist
.
Jari Oksanen
betadisper
, goodness.cca
,
mahalanobis
and various ordination methods.
data(dune, dune.env) d <- vegdist(dune) # Bray-Curtis mod <- with(dune.env, betadisper(d, Management)) centredist(mod) ## equal to metric scaling when using centroids instead of medians modc <- with(dune.env, betadisper(d, Management, type = "centroid")) ord <- pco(d) all.equal(centredist(modc), centredist(ord, dune.env$Management, rank="full"), check.attributes = FALSE)
data(dune, dune.env) d <- vegdist(dune) # Bray-Curtis mod <- with(dune.env, betadisper(d, Management)) centredist(mod) ## equal to metric scaling when using centroids instead of medians modc <- with(dune.env, betadisper(d, Management, type = "centroid")) ord <- pco(d) all.equal(centredist(modc), centredist(ord, dune.env$Management, rank="full"), check.attributes = FALSE)
The CLAM statistical approach for classifying generalists and specialists in two distinct habitats is described in Chazdon et al. (2011).
clamtest(comm, groups, coverage.limit = 10, specialization = 2/3, npoints = 20, alpha = 0.05/20) ## S3 method for class 'clamtest' summary(object, ...) ## S3 method for class 'clamtest' plot(x, xlab, ylab, main, pch = 21:24, col.points = 1:4, col.lines = 2:4, lty = 1:3, position = "bottomright", ...)
clamtest(comm, groups, coverage.limit = 10, specialization = 2/3, npoints = 20, alpha = 0.05/20) ## S3 method for class 'clamtest' summary(object, ...) ## S3 method for class 'clamtest' plot(x, xlab, ylab, main, pch = 21:24, col.points = 1:4, col.lines = 2:4, lty = 1:3, position = "bottomright", ...)
comm |
Community matrix, consisting of counts. |
groups |
A vector identifying the two habitats. Must have exactly
two unique values or levels. Habitat IDs in the grouping vector
must match corresponding rows in the community matrix |
coverage.limit |
Integer, the sample coverage based correction
is applied to rare species with counts below this limit.
Sample coverage is calculated separately
for the two habitats. Sample relative abundances are used for species
with higher than or equal to |
specialization |
Numeric, specialization threshold value between 0 and 1.
The value of |
npoints |
Integer, number of points used to determine the boundary lines in the plots. |
alpha |
Numeric, nominal significance level for individual
tests. The default value reduces the conventional limit of
|
x , object
|
Fitted model object of class |
xlab , ylab
|
Labels for the plot axes. |
main |
Main title of the plot. |
pch , col.points
|
Symbols and colors used in plotting species groups. |
lty , col.lines
|
Line types and colors for boundary lines in plot to separate species groups. |
position |
Position of figure legend, see |
... |
Additional arguments passed to methods. |
The method uses a multinomial model based on estimated
species relative abundance in two habitats (A, B). It minimizes bias
due to differences in sampling intensities between two habitat types
as well as bias due to insufficient sampling within each
habitat. The method permits a robust statistical classification of
habitat specialists and generalists, without excluding rare species
a priori (Chazdon et al. 2011). Based on a user-defined
specialization
threshold, the model classifies species into
one of four groups: (1) generalists; (2) habitat A specialists; (3)
habitat B specialists; and (4) too rare to classify with confidence.
A data frame (with class attribute "clamtest"
),
with columns:
Species: |
species name (column names from |
Total_*A*: |
total count in habitat A, |
Total_*B*: |
total count in habitat B, |
Classes: |
species classification, a factor with
levels |
*A*
and *B*
are placeholders for habitat names/labels found in the
data.
The summary
method returns descriptive statistics of the results.
The plot
method returns values invisibly and produces a bivariate
scatterplot of species total abundances in the two habitats. Symbols and
boundary lines are shown for species groups.
The code was tested against standalone CLAM software provided on the website of Anne Chao (which were then at http://chao.stat.nthu.edu.tw/wordpress); minor inconsistencies were found, especially for finding the threshold for 'too rare' species. These inconsistencies are probably due to numerical differences between the two implementation. The current R implementation uses root finding for iso-lines instead of iterative search.
The original method (Chazdon et al. 2011) has two major problems:
It assumes that the error distribution is multinomial. This is a justified choice if individuals are freely distributed, and there is no over-dispersion or clustering of individuals. In most ecological data, the variance is much higher than multinomial assumption, and therefore test statistic are too optimistic.
The original authors suggest that multiple testing adjustment
for multiple testing should be based on the number of points
(npoints
) used to draw the critical lines on the plot,
whereas the adjustment should be based on the number of tests (i.e.,
tested species). The function uses the same numerical values as
the original paper, but there is no automatic connection between
npoints
and alpha
arguments, but you must work out
the adjustment yourself.
Peter Solymos [email protected]
Chazdon, R. L., Chao, A., Colwell, R. K., Lin, S.-Y., Norden, N., Letcher, S. G., Clark, D. B., Finegan, B. and Arroyo J. P.(2011). A novel statistical method for classifying habitat generalists and specialists. Ecology 92, 1332–1343.
data(mite) data(mite.env) sol <- with(mite.env, clamtest(mite, Shrub=="None", alpha=0.005)) summary(sol) head(sol) plot(sol)
data(mite) data(mite.env) sol <- with(mite.env, clamtest(mite, Shrub=="None", alpha=0.005)) summary(sol) head(sol) plot(sol)
The commsim
function can be used to feed Null Model algorithms into
nullmodel
analysis.
The make.commsim
function returns various predefined algorithm types
(see Details).
These functions represent low level interface for community null model
infrastructure in vegan with the intent of extensibility,
and less emphasis on direct use by users.
commsim(method, fun, binary, isSeq, mode) make.commsim(method) ## S3 method for class 'commsim' print(x, ...)
commsim(method, fun, binary, isSeq, mode) make.commsim(method) ## S3 method for class 'commsim' print(x, ...)
method |
Character, name of the algorithm. |
fun |
A function. For possible formal arguments of this function see Details. |
binary |
Logical, if the algorithm applies to presence-absence or count matrices. |
isSeq |
Logical, if the algorithm is sequential (needs burnin and thinning) or not. |
mode |
Character, storage mode of the community matrix, either
|
x |
An object of class |
... |
Additional arguments. |
The function fun
must return an array of dim(nr, nc, n)
,
and must take some of the following arguments:
x
: input matrix,
n
: number of permuted matrices in output,
nr
: number of rows,
nc
: number of columns,
rs
: vector of row sums,
cs
: vector of column sums,
rf
: vector of row frequencies (non-zero cells),
cf
: vector of column frequencies (non-zero cells),
s
: total sum of x
,
fill
: matrix fill (non-zero cells),
thin
: thinning value for sequential algorithms,
...
: additional arguments.
You can define your own null model, but
several null model algorithm are pre-defined and can be called by
their name. The predefined algorithms are described in detail in the
following chapters. The binary null models produce matrices of zeros
(absences) and ones (presences) also when input matrix is
quantitative. There are two types of quantitative data: Counts are
integers with a natural unit so that individuals can be shuffled, but
abundances can have real (floating point) values and do not have a
natural subunit for shuffling. All quantitative models can handle
counts, but only some are able to handle real values. Some of the null
models are sequential so that the next matrix is derived from the
current one. This makes models dependent from previous models, and usually
you must thin these matrices and study the sequences for stability:
see oecosimu
for details and instructions.
See Examples for structural constraints imposed by each algorithm and defining your own null model.
An object of class commsim
with elements
corresponding to the arguments (method
, binary
,
isSeq
, mode
, fun
).
If the input of make.comsimm
is a commsim
object,
it is returned without further evaluation. If this is not the case,
the character method
argument is matched against
predefined algorithm names. An error message is issued
if none such is found. If the method
argument is missing,
the function returns names of all currently available
null model algorithms as a character vector.
All binary null models preserve fill: number of presences or
conversely the number of absences. The classic models may also
preserve column (species) frequencies (c0
) or row frequencies
or species richness of each site (r0
) and take into account
commonness and rarity of species (r1
, r2
). Algorithms
swap
, tswap
, curveball
, quasiswap
and
backtracking
preserve both row and column frequencies. Three
first ones are sequential but the two latter are non-sequential
and produce independent matrices. Basic algorithms are reviewed by
Wright et al. (1998).
"r00"
: non-sequential algorithm for binary matrices that only preserves the number of presences (fill).
"r0"
: non-sequential algorithm for binary matrices that preserves the site (row) frequencies.
"r1"
: non-sequential algorithm for binary matrices that preserves the site (row) frequencies, but uses column marginal frequencies as probabilities of selecting species.
"r2"
: non-sequential algorithm for binary matrices that preserves the site (row) frequencies, and uses squared column marginal frequencies as as probabilities of selecting species.
"c0"
: non-sequential algorithm for binary matrices that preserves species frequencies (Jonsson 2001).
"swap"
: sequential algorithm for binary matrices that
changes the matrix structure, but does not influence marginal sums
(Gotelli & Entsminger 2003). This inspects submatrices so long that a swap can be done.
"tswap"
: sequential algorithm for binary matrices.
Same as the "swap"
algorithm, but it tries a fixed
number of times and performs zero to many swaps at one step
(according to the thin argument in the call). This
approach was suggested by Miklós & Podani (2004)
because they found that ordinary swap may lead to biased
sequences, since some columns or rows are more easily swapped.
"curveball"
: sequential method for binary matrices that implements the ‘Curveball’ algorithm of Strona et al. (2014). The algorithm selects two random rows and finds the set of unique species that occur only in one of these rows. The algorithm distributes the set of unique species to rows preserving the original row frequencies. Zero to several species are swapped in one step, and usually the matrix is perturbed more strongly than in other sequential methods.
"quasiswap"
: non-sequential algorithm for binary
matrices that implements a method where matrix is first filled
honouring row and column totals, but with integers that may be
larger than one. Then the method inspects random
matrices and performs a quasiswap on
them. In addition to ordinary swaps, quasiswap can reduce numbers
above one to ones preserving marginal totals (Miklós &
Podani 2004). The method is non-sequential, but it accepts
thin
argument: the convergence is checked at every
thin
steps. This allows performing several ordinary swaps in
addition to fill changing swaps which helps in reducing or removing
the bias.
"greedyqswap"
: A greedy variant of quasiswap. In
greedy step, one element of the matrix is
taken from
elements. The greedy steps are biased, but
the method can be thinned, and only the first of
thin
steps is greedy. Even modest thinning (say thin = 20
)
removes or reduces the bias, and thin = 100
(1% greedy
steps) looks completely safe and still speeds up simulation. The
code is experimental and it is provided here for further scrutiny,
and should be tested for bias before use.
"backtracking"
: non-sequential algorithm for binary matrices that implements a filling method with constraints both for row and column frequencies (Gotelli & Entsminger 2001). The matrix is first filled randomly, but typically row and column sums are reached before all incidences are filled in. After this begins "backtracking", where some of the incidences are removed, and filling is started again, and this backtracking is done so many times that all incidences will be filled into matrix. The results may be biased and should be inspected carefully before use.
These models shuffle individuals of counts and keep marginal sums
fixed, but marginal frequencies are not preserved. Algorithm
r2dtable
uses standard R function r2dtable
also
used for simulated -values in
chisq.test
.
Algorithm quasiswap_count
uses the same, but preserves the
original fill. Typically this means increasing numbers of zero cells
and the result is zero-inflated with respect to r2dtable
.
"r2dtable"
: non-sequential algorithm for count
matrices. This algorithm keeps matrix sum and row/column sums
constant. Based on r2dtable
.
"quasiswap_count"
: non-sequential algorithm for count
matrices. This algorithm is similar as Carsten Dormann's
swap.web
function in the package
bipartite. First, a random matrix is generated by the
r2dtable
function preserving row and column sums. Then
the original matrix fill is reconstructed by sequential steps to
increase or decrease matrix fill in the random matrix. These steps
are based on swapping submatrices (see
"swap_count"
algorithm for details) to maintain row and
column totals.
Quantitative swap models are similar to binary swap
, but they
swap the largest permissible value. The models in this section all
maintain the fill and perform a quantitative swap only if this can
be done without changing the fill. Single step of swap often changes
the matrix very little. In particular, if cell counts are variable,
high values change very slowly. Checking the chain stability and
independence is even more crucial than in binary swap, and very
strong thin
ning is often needed. These models should never be
used without inspecting their properties for the current data. These
null models can also be defined using permatswap
function.
"swap_count"
: sequential algorithm for count matrices.
This algorithm find submatrices that can be
swapped leaving column and row totals and fill unchanged. The
algorithm finds the largest value in the submatrix that can be
swapped (
). Swap means that the values in diagonal or
antidiagonal positions are decreased by
, while remaining
cells are increased by
. A swap is made only if fill does not
change.
"abuswap_r"
: sequential algorithm for count or
nonnegative real valued matrices with fixed row frequencies (see
also permatswap
). The algorithm is similar to
swap_count
, but uses different swap value for each row of the
submatrix. Each step changes the the
corresponding column sums, but honours matrix fill, row sums, and
row/column frequencies (Hardy 2008; randomization scheme 2x).
"abuswap_c"
: sequential algorithm for count or
nonnegative real valued matrices with fixed column frequencies
(see also permatswap
). The algorithm is similar as
the previous one, but operates on columns. Each step changes the
the corresponding row sums, but honours matrix fill, column sums,
and row/column frequencies (Hardy 2008; randomization scheme 3x).
Quantitative Swap and Shuffle methods (swsh
methods) preserve
fill and column and row frequencies, and also either row or column
sums. The methods first perform a binary quasiswap
and then
shuffle original quantitative data to non-zero cells. The
samp
methods shuffle original non-zero cell values and can be
used also with non-integer data. The both
methods
redistribute individuals randomly among non-zero cells and can only
be used with integer data. The shuffling is either free over the
whole matrix, or within rows (r
methods) or within columns
(c
methods). Shuffling within a row preserves row sums, and
shuffling within a column preserves column sums. These models can
also be defined with permatswap
.
"swsh_samp"
: non-sequential algorithm for quantitative data (either integer counts or non-integer values). Original non-zero values values are shuffled.
"swsh_both"
: non-sequential algorithm for count data. Individuals are shuffled freely over non-zero cells.
"swsh_samp_r"
: non-sequential algorithm for quantitative data. Non-zero values (samples) are shuffled separately for each row.
"swsh_samp_c"
: non-sequential algorithm for quantitative data. Non-zero values (samples) are shuffled separately for each column.
"swsh_both_r"
: non-sequential algorithm for count matrices. Individuals are shuffled freely for non-zero values within each row.
"swsh_both_c"
: non-sequential algorithm for count matrices. Individuals are shuffled freely for non-zero values with each column.
Quantitative shuffle methods are generalizations of binary models
r00
, r0
and c0
. The _ind
methods
shuffle individuals so that the grand sum, row sum or column sums
are preserved. These methods are similar as r2dtable
but
with still slacker constraints on marginal sums. The _samp
and _both
methods first apply the corresponding binary model
with similar restriction on marginal frequencies and then distribute
quantitative values over non-zero cells. The _samp
models
shuffle original cell values and can therefore handle also non-count
real values. The _both
models shuffle individuals among
non-zero values. The shuffling is over the whole matrix in
r00_
, and within row in r0_
and within column in
c0_
in all cases.
"r00_ind"
: non-sequential algorithm for count matrices. This algorithm preserves grand sum and individuals are shuffled among cells of the matrix.
"r0_ind"
: non-sequential algorithm for count matrices. This algorithm preserves row sums and individuals are shuffled among cells of each row of the matrix.
"c0_ind"
: non-sequential algorithm for count matrices. This algorithm preserves column sums and individuals are shuffled among cells of each column of the matrix.
"r00_samp"
: non-sequential algorithm for count
or nonnegative real valued (mode = "double"
) matrices.
This algorithm preserves grand sum and
cells of the matrix are shuffled.
"r0_samp"
: non-sequential algorithm for count
or nonnegative real valued (mode = "double"
) matrices.
This algorithm preserves row sums and
cells within each row are shuffled.
"c0_samp"
: non-sequential algorithm for count
or nonnegative real valued (mode = "double"
) matrices.
This algorithm preserves column sums constant and
cells within each column are shuffled.
"r00_both"
: non-sequential algorithm for count matrices. This algorithm preserves grand sum and cells and individuals among cells of the matrix are shuffled.
"r0_both"
: non-sequential algorithm for count matrices. This algorithm preserves grand sum and cells and individuals among cells of each row are shuffled.
"c0_both"
: non-sequential algorithm for count matrices. This algorithm preserves grand sum and cells and individuals among cells of each column are shuffled.
Jari Oksanen and Peter Solymos
Gotelli, N.J. & Entsminger, N.J. (2001). Swap and fill algorithms in null model analysis: rethinking the knight's tour. Oecologia 129, 281–291.
Gotelli, N.J. & Entsminger, N.J. (2003). Swap algorithms in null model analysis. Ecology 84, 532–535.
Hardy, O. J. (2008) Testing the spatial phylogenetic structure of local communities: statistical performances of different null models and test statistics on a locally neutral community. Journal of Ecology 96, 914–926.
Jonsson, B.G. (2001) A null model for randomization tests of nestedness in species assemblages. Oecologia 127, 309–313.
Miklós, I. & Podani, J. (2004). Randomization of presence-absence matrices: comments and new algorithms. Ecology 85, 86–92.
Patefield, W. M. (1981) Algorithm AS159. An efficient method of generating r x c tables with given row and column totals. Applied Statistics 30, 91–97.
Strona, G., Nappo, D., Boccacci, F., Fattorini, S. & San-Miguel-Ayanz, J. (2014). A fast and unbiased procedure to randomize ecological binary matrices with fixed row and column totals. Nature Communications 5:4114 doi:10.1038/ncomms5114.
Wright, D.H., Patterson, B.D., Mikkelson, G.M., Cutler, A. & Atmar, W. (1998). A comparative analysis of nested subset patterns of species composition. Oecologia 113, 1–20.
See permatfull
, permatswap
for
alternative specification of quantitative null models. Function
oecosimu
gives a higher-level interface for applying null
models in hypothesis testing and analysis of models. Function
nullmodel
and simulate.nullmodel
are used to
generate arrays of simulated null model matrices.
## write the r00 algorithm f <- function(x, n, ...) array(replicate(n, sample(x)), c(dim(x), n)) (cs <- commsim("r00", fun=f, binary=TRUE, isSeq=FALSE, mode="integer")) ## retrieving the sequential swap algorithm (cs <- make.commsim("swap")) ## feeding a commsim object as argument make.commsim(cs) ## making the missing c1 model using r1 as a template ## non-sequential algorithm for binary matrices ## that preserves the species (column) frequencies, ## but uses row marginal frequencies ## as probabilities of selecting sites f <- function (x, n, nr, nc, rs, cs, ...) { out <- array(0L, c(nr, nc, n)) J <- seq_len(nc) storage.mode(rs) <- "double" for (k in seq_len(n)) for (j in J) out[sample.int(nr, cs[j], prob = rs), j, k] <- 1L out } cs <- make.commsim("r1") cs$method <- "c1" cs$fun <- f ## structural constraints diagfun <- function(x, y) { c(sum = sum(y) == sum(x), fill = sum(y > 0) == sum(x > 0), rowSums = all(rowSums(y) == rowSums(x)), colSums = all(colSums(y) == colSums(x)), rowFreq = all(rowSums(y > 0) == rowSums(x > 0)), colFreq = all(colSums(y > 0) == colSums(x > 0))) } evalfun <- function(meth, x, n) { m <- nullmodel(x, meth) y <- simulate(m, nsim=n) out <- rowMeans(sapply(1:dim(y)[3], function(i) diagfun(attr(y, "data"), y[,,i]))) z <- as.numeric(c(attr(y, "binary"), attr(y, "isSeq"), attr(y, "mode") == "double")) names(z) <- c("binary", "isSeq", "double") c(z, out) } x <- matrix(rbinom(10*12, 1, 0.5)*rpois(10*12, 3), 12, 10) algos <- make.commsim() a <- t(sapply(algos, evalfun, x=x, n=10)) print(as.table(ifelse(a==1,1,0)), zero.print = ".")
## write the r00 algorithm f <- function(x, n, ...) array(replicate(n, sample(x)), c(dim(x), n)) (cs <- commsim("r00", fun=f, binary=TRUE, isSeq=FALSE, mode="integer")) ## retrieving the sequential swap algorithm (cs <- make.commsim("swap")) ## feeding a commsim object as argument make.commsim(cs) ## making the missing c1 model using r1 as a template ## non-sequential algorithm for binary matrices ## that preserves the species (column) frequencies, ## but uses row marginal frequencies ## as probabilities of selecting sites f <- function (x, n, nr, nc, rs, cs, ...) { out <- array(0L, c(nr, nc, n)) J <- seq_len(nc) storage.mode(rs) <- "double" for (k in seq_len(n)) for (j in J) out[sample.int(nr, cs[j], prob = rs), j, k] <- 1L out } cs <- make.commsim("r1") cs$method <- "c1" cs$fun <- f ## structural constraints diagfun <- function(x, y) { c(sum = sum(y) == sum(x), fill = sum(y > 0) == sum(x > 0), rowSums = all(rowSums(y) == rowSums(x)), colSums = all(colSums(y) == colSums(x)), rowFreq = all(rowSums(y > 0) == rowSums(x > 0)), colFreq = all(colSums(y > 0) == colSums(x > 0))) } evalfun <- function(meth, x, n) { m <- nullmodel(x, meth) y <- simulate(m, nsim=n) out <- rowMeans(sapply(1:dim(y)[3], function(i) diagfun(attr(y, "data"), y[,,i]))) z <- as.numeric(c(attr(y, "binary"), attr(y, "isSeq"), attr(y, "mode") == "double")) names(z) <- c("binary", "isSeq", "double") c(z, out) } x <- matrix(rbinom(10*12, 1, 0.5)*rpois(10*12, 3), 12, 10) algos <- make.commsim() a <- t(sapply(algos, evalfun, x=x, n=10)) print(as.table(ifelse(a==1,1,0)), zero.print = ".")
The contribution diversity approach is based in the differentiation of within-unit and among-unit diversity by using additive diversity partitioning and unit distinctiveness.
contribdiv(comm, index = c("richness", "simpson"), relative = FALSE, scaled = TRUE, drop.zero = FALSE) ## S3 method for class 'contribdiv' plot(x, sub, xlab, ylab, ylim, col, ...)
contribdiv(comm, index = c("richness", "simpson"), relative = FALSE, scaled = TRUE, drop.zero = FALSE) ## S3 method for class 'contribdiv' plot(x, sub, xlab, ylab, ylim, col, ...)
comm |
The community data matrix with samples as rows and species as column. |
index |
Character, the diversity index to be calculated. |
relative |
Logical, if |
scaled |
Logical, if |
drop.zero |
Logical, should empty rows dropped from the result?
If empty rows are not dropped, their corresponding results will be |
x |
An object of class |
sub , xlab , ylab , ylim , col
|
Graphical arguments passed to plot. |
... |
Other arguments passed to plot. |
This approach was proposed by Lu et al. (2007).
Additive diversity partitioning (see adipart
for more references)
deals with the relation of mean alpha and the total (gamma) diversity. Although
alpha diversity values often vary considerably. Thus, contributions of the sites
to the total diversity are uneven. This site specific contribution is measured by
contribution diversity components. A unit that has e.g. many unique species will
contribute more to the higher level (gamma) diversity than another unit with the
same number of species, but all of which common.
Distinctiveness of species can be defined as the number of sites where it
occurs (
), or the sum of its relative frequencies (
). Relative
frequencies are computed sitewise and
s at site
sum up
to
.
The contribution of site to the total diversity is given by
when dealing with richness and
for the Simpson index.
The unit distinctiveness of site is the average of the species
distinctiveness, averaging only those species which occur at site
.
For species richness:
(in the paper, the second
equation contains a typo,
is without index). For the Simpson index:
.
The Lu et al. (2007) gives an in-depth description of the different indices.
An object of class "contribdiv"
inheriting from data frame.
Returned values are alpha, beta and gamma components for each sites (rows)
of the community matrix. The "diff.coef"
attribute gives the
differentiation coefficient (see Examples).
Péter Sólymos, [email protected]
Lu, H. P., Wagner, H. H. and Chen, X. Y. 2007. A contribution diversity approach to evaluate species diversity. Basic and Applied Ecology, 8, 1–12.
## Artificial example given in ## Table 2 in Lu et al. 2007 x <- matrix(c( 1/3,1/3,1/3,0,0,0, 0,0,1/3,1/3,1/3,0, 0,0,0,1/3,1/3,1/3), 3, 6, byrow = TRUE, dimnames = list(LETTERS[1:3],letters[1:6])) x ## Compare results with Table 2 contribdiv(x, "richness") contribdiv(x, "simpson") ## Relative contribution (C values), compare with Table 2 (cd1 <- contribdiv(x, "richness", relative = TRUE, scaled = FALSE)) (cd2 <- contribdiv(x, "simpson", relative = TRUE, scaled = FALSE)) ## Differentiation coefficients attr(cd1, "diff.coef") # D_ST attr(cd2, "diff.coef") # D_DT ## BCI data set data(BCI) opar <- par(mfrow=c(2,2)) plot(contribdiv(BCI, "richness"), main = "Absolute") plot(contribdiv(BCI, "richness", relative = TRUE), main = "Relative") plot(contribdiv(BCI, "simpson")) plot(contribdiv(BCI, "simpson", relative = TRUE)) par(opar)
## Artificial example given in ## Table 2 in Lu et al. 2007 x <- matrix(c( 1/3,1/3,1/3,0,0,0, 0,0,1/3,1/3,1/3,0, 0,0,0,1/3,1/3,1/3), 3, 6, byrow = TRUE, dimnames = list(LETTERS[1:3],letters[1:6])) x ## Compare results with Table 2 contribdiv(x, "richness") contribdiv(x, "simpson") ## Relative contribution (C values), compare with Table 2 (cd1 <- contribdiv(x, "richness", relative = TRUE, scaled = FALSE)) (cd2 <- contribdiv(x, "simpson", relative = TRUE, scaled = FALSE)) ## Differentiation coefficients attr(cd1, "diff.coef") # D_ST attr(cd2, "diff.coef") # D_DT ## BCI data set data(BCI) opar <- par(mfrow=c(2,2)) plot(contribdiv(BCI, "richness"), main = "Absolute") plot(contribdiv(BCI, "richness", relative = TRUE), main = "Relative") plot(contribdiv(BCI, "simpson")) plot(contribdiv(BCI, "simpson", relative = TRUE)) par(opar)
Distance-based redundancy analysis (dbRDA) is an ordination method
similar to Redundancy Analysis (rda
), but it allows
non-Euclidean dissimilarity indices, such as Manhattan or
Bray-Curtis distance. Despite this non-Euclidean feature, the
analysis is strictly linear and metric. If called with Euclidean
distance, the results are identical to rda
, but dbRDA
will be less efficient. Functions dbrda
is constrained
versions of metric scaling, a.k.a. principal coordinates analysis,
which are based on the Euclidean distance but can be used, and are
more useful, with other dissimilarity measures. Function
capscale
is a simplified version based on Euclidean
approximation of dissimilarities. The functions can also perform
unconstrained principal coordinates analysis (PCO), optionally using
extended dissimilarities. pco()
is a wrapper to dbrda()
,
which performs PCO.
dbrda(formula, data, distance = "euclidean", sqrt.dist = FALSE, add = FALSE, dfun = vegdist, metaMDSdist = FALSE, na.action = na.fail, subset = NULL, ...) capscale(formula, data, distance = "euclidean", sqrt.dist = FALSE, comm = NULL, add = FALSE, dfun = vegdist, metaMDSdist = FALSE, na.action = na.fail, subset = NULL, ...) pco(X, ...)
dbrda(formula, data, distance = "euclidean", sqrt.dist = FALSE, add = FALSE, dfun = vegdist, metaMDSdist = FALSE, na.action = na.fail, subset = NULL, ...) capscale(formula, data, distance = "euclidean", sqrt.dist = FALSE, comm = NULL, add = FALSE, dfun = vegdist, metaMDSdist = FALSE, na.action = na.fail, subset = NULL, ...) pco(X, ...)
formula |
Model formula. The function can be called only with the
formula interface. Most usual features of |
X |
Community data matrix. |
data |
Data frame containing the variables on the right hand side of the model formula. |
distance |
The name of the dissimilarity (or distance) index if
the LHS of the |
sqrt.dist |
Take square roots of dissimilarities. See section
|
comm |
Community data frame which will be used for finding
species scores when the LHS of the |
add |
Add a constant to the non-diagonal dissimilarities such
that all eigenvalues are non-negative in the underlying Principal
Co-ordinates Analysis (see |
dfun |
Distance or dissimilarity function used. Any function
returning standard |
metaMDSdist |
Use |
na.action |
Handling of missing values in constraints or
conditions. The default ( |
subset |
Subset of data rows. This can be a logical vector
which is |
... |
Other parameters passed to underlying functions (e.g.,
|
Functions dbrda
and capscale
provide two alternative
implementations of dbRDA. Function dbrda
is based on McArdle
& Anderson (2001) and directly decomposes dissimilarities. With
Euclidean distances results are identical to rda
.
Non-Euclidean dissimilarities may give negative eigenvalues
associated with imaginary axes. Function capscale
is based on
Legendre & Anderson (1999): the dissimilarity data are first
ordinated using metric scaling, and the ordination results are
analysed as rda
. capscale
ignores the imaginary
component and will not give negative eigenvalues (but will report
the magnitude on imaginary component).
If the user supplied a community data frame instead of
dissimilarities, the functions will find dissimilarities using
vegdist
or distance function given in dfun
with
specified distance
. The functions will accept distance
objects from vegdist
, dist
, or any other
method producing compatible objects. The constraining variables can be
continuous or factors or both, they can have interaction terms, or
they can be transformed in the call. Moreover, there can be a
special term Condition
just like in rda
and
cca
so that “partial” analysis can be performed.
Function dbrda
does not return species scores, and they can
also be missing in capscale
, but they can be added after the
analysis using function sppscores
.
Non-Euclidean dissimilarities can produce negative eigenvalues
(Legendre & Anderson 1999, McArdle & Anderson 2001). If there are
negative eigenvalues, the printed output of capscale
will add
a column with sums of positive eigenvalues and an item of sum of
negative eigenvalues, and dbrda
will add a column giving the
number of real dimensions with positive eigenvalues. If negative
eigenvalues are disturbing, functions let you distort the
dissimilarities so that only non-negative eigenvalues will be
produced with argument add = TRUE
. Alternatively, with
sqrt.dist = TRUE
, square roots of dissimilarities can be
used which may help in avoiding negative eigenvalues (Legendre &
Anderson 1999).
The functions can be also used to perform ordinary metric scaling
a.k.a. principal coordinates analysis by using a formula with only a
constant on the right hand side, or comm ~ 1
. The new function
pco()
implements principal coordinates analysis via
dbrda()
directly, using this formula. With
metaMDSdist = TRUE
, the function can do automatic data
standardization and use extended dissimilarities using function
stepacross
similarly as in non-metric multidimensional
scaling with metaMDS
.
The functions return an object of class dbrda
or
capscale
which inherit from rda
. See
cca.object
for description of the result object. Function
pco()
returns an object of class "vegan_pco"
(which
inherits from class "dbrda"
) to avoid clashes with other packages.
Function dbrda
implements real distance-based RDA and is
preferred over capscale
. capscale
was originally
developed as a variant of constrained analysis of proximities
(Anderson & Willis 2003), but these developments made it more
similar to dbRDA. However, it discards the imaginary dimensions with
negative eigenvalues and ordination and significance tests area only
based on real dimensions and positive eigenvalues. capscale
may be removed from vegan in the future. It has been in
vegan
since 2003 (CRAN release 1.6-0) while dbrda
was
first released in 2016 (version 2.4-0), and removal of
capscale
may be disruptive to historical examples and
scripts, but in modern times dbrda
should be used.
The inertia is named after the dissimilarity index as defined in the
dissimilarity data, or as unknown distance
if such
information is missing. If the largest original dissimilarity was
larger than 4, capscale
handles input similarly as rda
and bases its analysis on variance instead of sum of
squares. Keyword mean
is added to the inertia in these cases,
e.g. with Euclidean and Manhattan distances. Inertia is based on
squared index, and keyword squared
is added to the name of
distance, unless data were square root transformed (argument
sqrt.dist=TRUE
). If an additive constant was used with
argument add
, Lingoes
or Cailliez adjusted
is
added to the the name of inertia, and the value of the constant is
printed.
Jari Oksanen
Anderson, M.J. & Willis, T.J. (2003). Canonical analysis of principal coordinates: a useful method of constrained ordination for ecology. Ecology 84, 511–525.
Gower, J.C. (1985). Properties of Euclidean and non-Euclidean distance matrices. Linear Algebra and its Applications 67, 81–97.
Legendre, P. & Anderson, M. J. (1999). Distance-based redundancy analysis: testing multispecies responses in multifactorial ecological experiments. Ecological Monographs 69, 1–24.
Legendre, P. & Legendre, L. (2012). Numerical Ecology. 3rd English Edition. Elsevier.
McArdle, B.H. & Anderson, M.J. (2001). Fitting multivariate models to community data: a comment on distance-based redundancy analysis. Ecology 82, 290–297.
rda
, cca
, plot.cca
,
anova.cca
, vegdist
,
dist
, cmdscale
, wcmdscale
for underlying and related functions. Function sppscores
can add species scores or replace existing species scores.
The function returns similar result object as rda
(see
cca.object
). This section for rda
gives a
more complete list of functions that can be used to access and
analyse dbRDA results.
data(varespec, varechem) ## dbrda dbrda(varespec ~ N + P + K + Condition(Al), varechem, dist="bray") ## avoid negative eigenvalues with sqrt distances dbrda(varespec ~ N + P + K + Condition(Al), varechem, dist="bray", sqrt.dist = TRUE) ## avoid negative eigenvalues also with Jaccard distances (m <- dbrda(varespec ~ N + P + K + Condition(Al), varechem, dist="jaccard")) ## add species scores sppscores(m) <- wisconsin(varespec) ## pco pco(varespec, dist = "bray", sqrt.dist = TRUE)
data(varespec, varechem) ## dbrda dbrda(varespec ~ N + P + K + Condition(Al), varechem, dist="bray") ## avoid negative eigenvalues with sqrt distances dbrda(varespec ~ N + P + K + Condition(Al), varechem, dist="bray", sqrt.dist = TRUE) ## avoid negative eigenvalues also with Jaccard distances (m <- dbrda(varespec ~ N + P + K + Condition(Al), varechem, dist="jaccard")) ## add species scores sppscores(m) <- wisconsin(varespec) ## pco pco(varespec, dist = "bray", sqrt.dist = TRUE)
Performs detrended correspondence analysis and basic reciprocal averaging or orthogonal correspondence analysis.
decorana(veg, iweigh=0, iresc=4, ira=0, mk=26, short=0, before=NULL, after=NULL) ## S3 method for class 'decorana' plot(x, choices=c(1,2), origin=TRUE, display=c("both","sites","species","none"), cex = 0.7, cols = c(1,2), type, xlim, ylim, ...) ## S3 method for class 'decorana' text(x, display = c("sites", "species"), labels, choices = 1:2, origin = TRUE, select, ...) ## S3 method for class 'decorana' points(x, display = c("sites", "species"), choices=1:2, origin = TRUE, select, ...) ## S3 method for class 'decorana' scores(x, display="sites", choices=1:4, origin=TRUE, tidy=FALSE, ...) downweight(veg, fraction = 5)
decorana(veg, iweigh=0, iresc=4, ira=0, mk=26, short=0, before=NULL, after=NULL) ## S3 method for class 'decorana' plot(x, choices=c(1,2), origin=TRUE, display=c("both","sites","species","none"), cex = 0.7, cols = c(1,2), type, xlim, ylim, ...) ## S3 method for class 'decorana' text(x, display = c("sites", "species"), labels, choices = 1:2, origin = TRUE, select, ...) ## S3 method for class 'decorana' points(x, display = c("sites", "species"), choices=1:2, origin = TRUE, select, ...) ## S3 method for class 'decorana' scores(x, display="sites", choices=1:4, origin=TRUE, tidy=FALSE, ...) downweight(veg, fraction = 5)
veg |
Community data, a matrix-like object. |
iweigh |
Downweighting of rare species (0: no). |
iresc |
Number of rescaling cycles (0: no rescaling). |
ira |
Type of analysis (0: detrended, 1: basic reciprocal averaging). |
mk |
Number of segments in rescaling. |
short |
Shortest gradient to be rescaled. |
before |
Hill's piecewise transformation: values before transformation. |
after |
Hill's piecewise transformation: values after
transformation – these must correspond to values in |
x |
A |
choices |
Axes shown. |
origin |
Use true origin even in detrended correspondence analysis. |
display |
Display only sites, only species, both or neither. |
cex |
Plot character size. |
cols |
Colours used for sites and species. |
type |
Type of plots, partial match to |
labels |
Optional text to be used instead of row names. |
select |
Items to be displayed. This can either be a logical
vector which is |
xlim , ylim
|
the x and y limits (min,max) of the plot. |
fraction |
Abundance fraction where downweighting begins. |
tidy |
Return scores that are compatible with ggplot2:
all scores are in a single |
... |
Other arguments for |
In late 1970s, correspondence analysis became the method of choice for ordination in vegetation science, since it seemed better able to cope with non-linear species responses than principal components analysis. However, even correspondence analysis can produce an arc-shaped configuration of a single gradient. Mark Hill developed detrended correspondence analysis to correct two assumed ‘faults’ in correspondence analysis: curvature of straight gradients and packing of sites at the ends of the gradient.
The curvature is removed by replacing the orthogonalization of axes
with detrending. In orthogonalization successive axes are made
non-correlated, but detrending should remove all systematic dependence
between axes. Detrending is performed using a smoothing window on
mk
segments. The packing of sites at the ends of the gradient
is undone by rescaling the axes after extraction. After rescaling,
the axis is supposed to be scaled by ‘SD’ units, so that the
average width of Gaussian species responses is supposed to be one over
whole axis. Other innovations were the piecewise linear transformation
of species abundances and downweighting of rare species which were
regarded to have an unduly high influence on ordination axes.
It seems that detrending actually works by twisting the ordination
space, so that the results look non-curved in two-dimensional
projections (‘lolly paper effect’). As a result, the points
usually have an easily recognized triangular or diamond shaped
pattern, obviously an artefact of detrending. Rescaling works
differently than commonly presented, too. decorana
does not
use, or even evaluate, the widths of species responses. Instead, it
tries to equalize the weighted standard deviation of species scores on
axis segments (parameter mk
has no effect, since
decorana
finds the segments internally). Function
tolerance
returns this internal criterion and can be
used to assess the success of rescaling.
The plot
method plots species and site scores. Classical
decorana
scaled the axes so that smallest site score was 0 (and
smallest species score was negative), but summary
, plot
and scores
use the true origin, unless origin = FALSE
.
In addition to proper eigenvalues, the function reports
‘decorana values’ in detrended analysis. These ‘decorana
values’ are the values that the legacy code of decorana
returns
as eigenvalues. They are estimated during iteration, and describe the
joint effects of axes and detrending. The ‘decorana values’ are
estimated before rescaling and do not show its effect on
eigenvalues. The proper eigenvalues are estimated after extraction of
the axes and they are the ratio of weighted sum of squares of site and
species scores even in detrended and rescaled solutions. These
eigenvalues are estimated for each axis separately, but they are not
additive, because higher decorana
axes can show effects already
explained by prior axes. ‘Additive eigenvalues’ are cleansed
from the effects of prior axes, and they can be assumed to add up to
total inertia (scaled Chi-square). For proportions and cumulative
proportions explained you can use eigenvals.decorana
.
decorana
returns an object of class "decorana"
, which
has print
, summary
, scores
, plot
,
points
and text
methods, and support functions
eigenvals
, bstick
, screeplot
,
predict
and tolerance
. downweight
is an
independent function that can also be used with other methods than
decorana
.
decorana
uses the central numerical engine of the
original Fortran code (which is in the public domain), or about 1/3 of
the original program. I have tried to implement the original
behaviour, although a great part of preparatory steps were written in
R language, and may differ somewhat from the original code. However,
well-known bugs are corrected and strict criteria used (Oksanen &
Minchin 1997).
Please note that there really is no need for piecewise transformation
or even downweighting within decorana
, since there are more
powerful and extensive alternatives in R, but these options are
included for compliance with the original software. If a different
fraction of abundance is needed in downweighting, function
downweight
must be applied before decorana
. Function
downweight
indeed can be applied prior to correspondence
analysis, and so it can be used together with cca
, too.
Github package natto has an R implementation of
decorana
which allows easier inspection of the
algorithm and also easier development of the function.
vegan 2.6-6 and earlier had a summary
method, but it did
nothing useful and is now defunct. All its former information can be
extracted with scores
or weights.decorana
.
Mark O. Hill wrote the original Fortran code, the R port was by Jari Oksanen.
Hill, M.O. and Gauch, H.G. (1980). Detrended correspondence analysis: an improved ordination technique. Vegetatio 42, 47–58.
Oksanen, J. and Minchin, P.R. (1997). Instability of ordination results under changes in input data order: explanations and remedies. Journal of Vegetation Science 8, 447–454.
For unconstrained ordination, non-metric multidimensional scaling in
monoMDS
may be more robust (see also
metaMDS
). Constrained (or ‘canonical’)
correspondence analysis can be made with cca
.
Orthogonal correspondence analysis can be made with decorana
or
cca
, but the scaling of results vary (and the one in
decorana
corresponds to scaling = "sites"
and hill
= TRUE
in cca
.). See predict.decorana
for adding new points to an ordination.
data(varespec) vare.dca <- decorana(varespec) vare.dca plot(vare.dca) ### the detrending rationale: gaussresp <- function(x,u) exp(-(x-u)^2/2) x <- seq(0,6,length=15) ## The gradient u <- seq(-2,8,len=23) ## The optima pack <- outer(x,u,gaussresp) matplot(x, pack, type="l", main="Species packing") opar <- par(mfrow=c(2,2)) plot(scores(prcomp(pack)), asp=1, type="b", main="PCA") plot(scores(decorana(pack, ira=1)), asp=1, type="b", main="CA") plot(scores(decorana(pack)), asp=1, type="b", main="DCA") plot(scores(cca(pack ~ x), dis="sites"), asp=1, type="b", main="CCA") ### Let's add some noise: noisy <- (0.5 + runif(length(pack)))*pack par(mfrow=c(2,1)) matplot(x, pack, type="l", main="Ideal model") matplot(x, noisy, type="l", main="Noisy model") par(mfrow=c(2,2)) plot(scores(prcomp(noisy)), type="b", main="PCA", asp=1) plot(scores(decorana(noisy, ira=1)), type="b", main="CA", asp=1) plot(scores(decorana(noisy)), type="b", main="DCA", asp=1) plot(scores(cca(noisy ~ x), dis="sites"), asp=1, type="b", main="CCA") par(opar)
data(varespec) vare.dca <- decorana(varespec) vare.dca plot(vare.dca) ### the detrending rationale: gaussresp <- function(x,u) exp(-(x-u)^2/2) x <- seq(0,6,length=15) ## The gradient u <- seq(-2,8,len=23) ## The optima pack <- outer(x,u,gaussresp) matplot(x, pack, type="l", main="Species packing") opar <- par(mfrow=c(2,2)) plot(scores(prcomp(pack)), asp=1, type="b", main="PCA") plot(scores(decorana(pack, ira=1)), asp=1, type="b", main="CA") plot(scores(decorana(pack)), asp=1, type="b", main="DCA") plot(scores(cca(pack ~ x), dis="sites"), asp=1, type="b", main="CCA") ### Let's add some noise: noisy <- (0.5 + runif(length(pack)))*pack par(mfrow=c(2,1)) matplot(x, pack, type="l", main="Ideal model") matplot(x, noisy, type="l", main="Noisy model") par(mfrow=c(2,2)) plot(scores(prcomp(noisy)), type="b", main="PCA", asp=1) plot(scores(decorana(noisy, ira=1)), type="b", main="CA", asp=1) plot(scores(decorana(noisy)), type="b", main="DCA", asp=1) plot(scores(cca(noisy ~ x), dis="sites"), asp=1, type="b", main="CCA") par(opar)
The function provides some popular (and effective) standardization methods for community ecologists.
decostand(x, method, MARGIN, range.global, logbase = 2, na.rm=FALSE, ...) wisconsin(x) decobackstand(x, zap = TRUE)
decostand(x, method, MARGIN, range.global, logbase = 2, na.rm=FALSE, ...) wisconsin(x) decobackstand(x, zap = TRUE)
x |
Community data, a matrix-like object. For
|
method |
Standardization method. See Details for available options. |
MARGIN |
Margin, if default is not acceptable. |
range.global |
Matrix from which the range is found in
|
logbase |
The logarithm base used in |
na.rm |
Ignore missing values in row or column
standardizations. The |
zap |
Make near-zero values exact zeros to avoid negative values and exaggerated estimates of species richness. |
... |
Other arguments to the function (ignored). |
The function offers following standardization methods for community data:
total
: divide by margin total (default MARGIN = 1
).
max
: divide by margin maximum (default MARGIN = 2
).
frequency
: divide by margin total and multiply by the
number of non-zero items, so that the average of non-zero entries is
one (Oksanen 1983; default MARGIN = 2
).
normalize
: make margin sum of squares equal to one (default
MARGIN = 1
).
range
: standardize values into range 0 ... 1 (default
MARGIN = 2
). If all values are constant, they will be
transformed to 0.
rank, rrank
: rank
replaces abundance values by
their increasing ranks leaving zeros unchanged, and rrank
is
similar but uses relative ranks with maximum 1 (default
MARGIN = 1
). Average ranks are used for tied values.
standardize
: scale x
to zero mean and unit variance
(default MARGIN = 2
).
pa
: scale x
to presence/absence scale (0/1).
chi.square
: divide by row sums and square root of
column sums, and adjust for square root of matrix total
(Legendre & Gallagher 2001). When used with the Euclidean
distance, the distances should be similar to the
Chi-square distance used in correspondence analysis. However, the
results from cmdscale
would still differ, since
CA is a weighted ordination method (default MARGIN = 1
).
hellinger
: square root of method = "total"
(Legendre & Gallagher 2001).
log
: logarithmic transformation as suggested by
Anderson et al. (2006): for
, where
is the base of the logarithm; zeros are
left as zeros. Higher bases give less weight to quantities and more
to presences, and
logbase = Inf
gives the presence/absence
scaling. Please note this is not .
Anderson et al. (2006) suggested this for their (strongly) modified
Gower distance (implemented as
method = "altGower"
in
vegdist
), but the standardization can be used
independently of distance indices.
alr
: Additive log ratio ("alr") transformation
(Aitchison 1986) reduces data skewness and compositionality
bias. The transformation assumes positive values, pseudocounts can
be added with the argument pseudocount
. One of the
rows/columns is a reference that can be given by reference
(name of index). The first row/column is used by default
(reference = 1
). Note that this transformation drops one
row or column from the transformed output data. The alr
transformation is defined formally as follows:
where the denominator sample can be chosen
arbitrarily. This transformation is often used with pH and other
chemistry measurenments. It is also commonly used as multinomial
logistic regression. Default
MARGIN = 1
uses row as the
reference
.
clr
: centered log ratio ("clr") transformation proposed by
Aitchison (1986) and it is used to reduce data skewness and compositionality bias.
This transformation has frequent applications in microbial ecology
(see e.g. Gloor et al., 2017). The clr transformation is defined as:
where is a single value, and g(x) is the geometric mean of
.
The method can operate only with positive data;
a common way to deal with zeroes is to add pseudocount
(e.g. the smallest positive value in the data), either by
adding it manually to the input data, or by using the argument
pseudocount
as in
decostand(x, method = "clr", pseudocount = 1)
. Adding
pseudocount will inevitably introduce some bias; see
the rclr
method for one available solution.
rclr
: robust clr ("rclr") is similar to regular clr
(see above) but allows data that contains zeroes. This method
does not use pseudocounts, unlike the standard clr.
The robust clr (rclr) divides the values by geometric mean
of the observed features; zero values are kept as zeroes, and not
taken into account. In high dimensional data,
the geometric mean of rclr approximates the true
geometric mean; see e.g. Martino et al. (2019)
The rclr
transformation is defined formally as follows:
where is a single value, and
is the geometric
mean of sample-wide values
that are positive (> 0).
Standardization, as contrasted to transformation, means that the entries are transformed relative to other entries.
All methods have a default margin. MARGIN=1
means rows (sites
in a normal data set) and MARGIN=2
means columns (species in a
normal data set).
Command wisconsin
is a shortcut to common Wisconsin double
standardization where species (MARGIN=2
) are first standardized
by maxima (max
) and then sites (MARGIN=1
) by
site totals (tot
).
Most standardization methods will give nonsense results with
negative data entries that normally should not occur in the community
data. If there are empty sites or species (or constant with
method = "range"
), many standardization will change these into
NaN
.
Function decobackstand
can be used to transform standardized
data back to original. This is not possible for all standardization
and may not be implemented to all cases where it would be
possible. There are round-off errors and back-transformation is not
exact, and it is wise not to overwrite the original data. With
zap=TRUE
original zeros should be exact.
Returns the standardized data frame, and adds an attribute
"decostand"
giving the name of applied standardization
"method"
and attribute "parameters"
with appropriate
transformation parameters.
Common transformations can be made with standard R functions.
Jari Oksanen, Etienne Laliberté
(method = "log"
), Leo Lahti (alr
,
"clr"
and "rclr"
).
Aitchison, J. The Statistical Analysis of Compositional Data (1986). London, UK: Chapman & Hall.
Anderson, M.J., Ellingsen, K.E. & McArdle, B.H. (2006) Multivariate dispersion as a measure of beta diversity. Ecology Letters 9, 683–693.
Egozcue, J.J., Pawlowsky-Glahn, V., Mateu-Figueras, G., Barcel'o-Vidal, C. (2003) Isometric logratio transformations for compositional data analysis. Mathematical Geology 35, 279–300.
Gloor, G.B., Macklaim, J.M., Pawlowsky-Glahn, V. & Egozcue, J.J. (2017) Microbiome Datasets Are Compositional: And This Is Not Optional. Frontiers in Microbiology 8, 2224.
Legendre, P. & Gallagher, E.D. (2001) Ecologically meaningful transformations for ordination of species data. Oecologia 129, 271–280.
Martino, C., Morton, J.T., Marotz, C.A., Thompson, L.R., Tripathi, A., Knight, R. & Zengler, K. (2019) A novel sparse compositional technique reveals microbial perturbations. mSystems 4, 1.
Oksanen, J. (1983) Ordination of boreal heath-like vegetation with principal component analysis, correspondence analysis and multidimensional scaling. Vegetatio 52, 181–189.
data(varespec) sptrans <- decostand(varespec, "max") apply(sptrans, 2, max) sptrans <- wisconsin(varespec) # CLR transformation for rows, with pseudocount varespec.clr <- decostand(varespec, "clr", pseudocount=1) # ALR transformation for rows, with pseudocount and reference sample varespec.alr <- decostand(varespec, "alr", pseudocount=1, reference=1) ## Chi-square: PCA similar but not identical to CA. ## Use wcmdscale for weighted analysis and identical results. sptrans <- decostand(varespec, "chi.square") plot(procrustes(rda(sptrans), cca(varespec)))
data(varespec) sptrans <- decostand(varespec, "max") apply(sptrans, 2, max) sptrans <- wisconsin(varespec) # CLR transformation for rows, with pseudocount varespec.clr <- decostand(varespec, "clr", pseudocount=1) # ALR transformation for rows, with pseudocount and reference sample varespec.alr <- decostand(varespec, "alr", pseudocount=1, reference=1) ## Chi-square: PCA similar but not identical to CA. ## Use wcmdscale for weighted analysis and identical results. sptrans <- decostand(varespec, "chi.square") plot(procrustes(rda(sptrans), cca(varespec)))
Function designdist
lets you define your own dissimilarities
using terms for shared and total quantities, number of rows and number
of columns. The shared and total quantities can be binary, quadratic
or minimum terms. In binary terms, the shared component is number of
shared species, and totals are numbers of species on sites. The
quadratic terms are cross-products and sums of squares, and minimum
terms are sums of parallel minima and row totals. Function
designdist2
is similar, but finds dissimilarities among two
data sets. Function chaodist
lets you define your own
dissimilarities using terms that are supposed to take into account the
“unseen species” (see Chao et al., 2005 and Details in
vegdist
).
designdist(x, method = "(A+B-2*J)/(A+B)", terms = c("binary", "quadratic", "minimum"), abcd = FALSE, alphagamma = FALSE, name, maxdist) designdist2(x, y, method = "(A+B-2*J)/(A+B)", terms = c("binary", "quadratic", "minimum"), abcd = FALSE, alphagamma = FALSE, name, maxdist) chaodist(x, method = "1 - 2*U*V/(U+V)", name)
designdist(x, method = "(A+B-2*J)/(A+B)", terms = c("binary", "quadratic", "minimum"), abcd = FALSE, alphagamma = FALSE, name, maxdist) designdist2(x, y, method = "(A+B-2*J)/(A+B)", terms = c("binary", "quadratic", "minimum"), abcd = FALSE, alphagamma = FALSE, name, maxdist) chaodist(x, method = "1 - 2*U*V/(U+V)", name)
x |
Input data. |
y |
Another input data set: dissimilarities will be calculated
among rows of |
method |
Equation for your dissimilarities. This can use terms
|
terms |
How shared and total components are found. For vectors
|
abcd |
Use 2x2 contingency table notation for binary data:
|
alphagamma |
Use beta diversity notation with terms
|
name |
The name you want to use for your index. The default is to
combine the |
maxdist |
Theoretical maximum of the dissimilarity, or |
Most popular dissimilarity measures in ecology can be expressed with
the help of terms J
, A
and B
, and some also involve
matrix dimensions N
and P
. Some examples you can define in
designdist
are:
A+B-2*J |
"quadratic" |
squared Euclidean |
A+B-2*J |
"minimum" |
Manhattan |
(A+B-2*J)/(A+B) |
"minimum" |
Bray-Curtis |
(A+B-2*J)/(A+B) |
"binary" |
Sørensen |
(A+B-2*J)/(A+B-J) |
"binary" |
Jaccard |
(A+B-2*J)/(A+B-J) |
"minimum" |
Ružička |
(A+B-2*J)/(A+B-J) |
"quadratic" |
(dis)similarity ratio |
1-J/sqrt(A*B) |
"binary" |
Ochiai |
1-J/sqrt(A*B) |
"quadratic" |
cosine complement |
1-phyper(J-1, A, P-A, B) |
"binary" |
Raup-Crick (but see raupcrick )
|
The function designdist
can implement most dissimilarity
indices in vegdist
or elsewhere, and it can also be
used to implement many other indices, amongst them, most of those
described in Legendre & Legendre (2012). It can also be used to
implement all indices of beta diversity described in Koleff et
al. (2003), but there also is a specific function
betadiver
for the purpose.
If you want to implement binary dissimilarities based on the 2x2
contingency table notation, you can set abcd = TRUE
. In this
notation a = J
, b = A-J
, c = B-J
, d = P-A-B+J
.
This notation is often used instead of the more more
tangible default notation for reasons that are opaque to me.
With alphagamma = TRUE
it is possible to use beta diversity
notation with terms alpha
for average alpha diversity and
gamma
for gamma diversity in two compared sites. The terms
are calculated as alpha = (A+B)/2
, gamma = A+B-J
and
delta = abs(A-B)/2
. Terms A
and B
are also
available and give the alpha diversities of the individual compared
sites. The beta diversity terms may make sense only for binary
terms (so that diversities are expressed in numbers of species), but
they are calculated for quadratic and minimum terms as well (with a
warning).
Function chaodist
is similar to designgist
, but uses
terms U
and V
of Chao et al. (2005). These terms are
supposed to take into account the effects of unseen species. Both
U
and V
are scaled to range . They take
the place of
A
and B
and the product U*V
is used
in the place of J
of designdist
. Function
chaodist
can implement any commonly used Chao et al. (2005)
style dissimilarity:
1 - 2*U*V/(U+V) |
Sørensen type |
1 - U*V/(U+V-U*V) |
Jaccard type |
1 - sqrt(U*V) |
Ochiai type |
(pmin(U,V) - U*V)/pmin(U,V) |
Simpson type |
Function vegdist
implements Jaccard-type Chao distance,
and its documentation contains more complete discussion on the
calculation of the terms.
designdist
returns an object of class dist
.
designdist
does not use compiled code, but it is based on
vectorized R code. The designdist
function can be much
faster than vegdist
, although the latter uses compiled
code. However, designdist
cannot skip missing values and uses
much more memory during calculations.
The use of sum terms can be numerically unstable. In particularly,
when these terms are large, the precision may be lost. The risk is
large when the number of columns is high, and particularly large with
quadratic terms. For precise calculations it is better to use
functions like dist
and vegdist
which are
more robust against numerical problems.
Jari Oksanen
Chao, A., Chazdon, R. L., Colwell, R. K. and Shen, T. (2005) A new statistical approach for assessing similarity of species composition with incidence and abundance data. Ecology Letters 8, 148–159.
Koleff, P., Gaston, K.J. and Lennon, J.J. (2003) Measuring beta diversity for presence–absence data. J. Animal Ecol. 72, 367–382.
Legendre, P. and Legendre, L. (2012) Numerical Ecology. 3rd English ed. Elsevier
vegdist
, betadiver
, dist
,
raupcrick
.
data(BCI) ## Four ways of calculating the same Sørensen dissimilarity d0 <- vegdist(BCI, "bray", binary = TRUE) d1 <- designdist(BCI, "(A+B-2*J)/(A+B)") d2 <- designdist(BCI, "(b+c)/(2*a+b+c)", abcd = TRUE) d3 <- designdist(BCI, "gamma/alpha - 1", alphagamma = TRUE) ## Arrhenius dissimilarity: the value of z in the species-area model ## S = c*A^z when combining two sites of equal areas, where S is the ## number of species, A is the area, and c and z are model parameters. ## The A below is not the area (which cancels out), but number of ## species in one of the sites, as defined in designdist(). dis <- designdist(BCI, "(log(A+B-J)-log(A+B)+log(2))/log(2)") ## This can be used in clustering or ordination... ordiplot(cmdscale(dis)) ## ... or in analysing beta diversity (without gradients) summary(dis)
data(BCI) ## Four ways of calculating the same Sørensen dissimilarity d0 <- vegdist(BCI, "bray", binary = TRUE) d1 <- designdist(BCI, "(A+B-2*J)/(A+B)") d2 <- designdist(BCI, "(b+c)/(2*a+b+c)", abcd = TRUE) d3 <- designdist(BCI, "gamma/alpha - 1", alphagamma = TRUE) ## Arrhenius dissimilarity: the value of z in the species-area model ## S = c*A^z when combining two sites of equal areas, where S is the ## number of species, A is the area, and c and z are model parameters. ## The A below is not the area (which cancels out), but number of ## species in one of the sites, as defined in designdist(). dis <- designdist(BCI, "(log(A+B-J)-log(A+B)+log(2))/log(2)") ## This can be used in clustering or ordination... ordiplot(cmdscale(dis)) ## ... or in analysing beta diversity (without gradients) summary(dis)
The functions extract statistics that resemble deviance and AIC from the
result of constrained correspondence analysis cca
or
redundancy analysis rda
. These functions are rarely
needed directly, but they are called by step
in
automatic model building. Actually, cca
and
rda
do not have AIC
and these functions
are certainly wrong.
## S3 method for class 'cca' deviance(object, ...) ## S3 method for class 'cca' extractAIC(fit, scale = 0, k = 2, ...)
## S3 method for class 'cca' deviance(object, ...) ## S3 method for class 'cca' extractAIC(fit, scale = 0, k = 2, ...)
object |
|
fit |
fitted model from constrained ordination. |
scale |
optional numeric specifying the scale parameter of the model,
see |
k |
numeric specifying the "weight" of the equivalent degrees of
freedom (=: |
... |
further arguments. |
The functions find statistics that
resemble deviance
and AIC
in constrained
ordination. Actually, constrained ordination methods do not have a
log-Likelihood, which means that they cannot have AIC and deviance.
Therefore you should not use these functions, and if you use them, you
should not trust them. If you use these functions, it remains as your
responsibility to check the adequacy of the result.
The deviance of cca
is equal to the Chi-square of
the residual data matrix after fitting the constraints. The deviance
of rda
is defined as the residual sum of squares. The
deviance function of rda
is also used for distance-based RDA
dbrda
. Function extractAIC
mimics
extractAIC.lm
in translating deviance to AIC.
There is little need to call these functions directly. However, they
are called implicitly in step
function used in automatic
selection of constraining variables. You should check the resulting
model with some other criteria, because the statistics used here are
unfounded. In particular, the penalty k
is not properly
defined, and the default k = 2
is not justified
theoretically. If you have only continuous covariates, the step
function will base the model building on magnitude of eigenvalues, and
the value of k
only influences the stopping point (but the
variables with the highest eigenvalues are not necessarily the most
significant in permutation tests in anova.cca
). If you
also have multi-class factors, the value of k
will have a
capricious effect in model building. The step
function
will pass arguments to add1.cca
and
drop1.cca
, and setting test = "permutation"
will provide permutation tests of each deletion and addition which
can help in judging the validity of the model building.
The deviance
functions return “deviance”, and
extractAIC
returns effective degrees of freedom and “AIC”.
These functions are unfounded and untested and they should not be used
directly or implicitly. Moreover, usual caveats in using
step
are very valid.
Jari Oksanen
Godínez-Domínguez, E. & Freire, J. (2003) Information-theoretic approach for selection of spatial and temporal models of community organization. Marine Ecology Progress Series 253, 17–24.
cca
, rda
, anova.cca
,
step
, extractAIC
,
add1.cca
, drop1.cca
.
# The deviance of correspondence analysis equals Chi-square data(dune) data(dune.env) chisq.test(dune) deviance(cca(dune)) # Stepwise selection (forward from an empty model "dune ~ 1") ord <- cca(dune ~ ., dune.env) step(cca(dune ~ 1, dune.env), scope = formula(ord))
# The deviance of correspondence analysis equals Chi-square data(dune) data(dune.env) chisq.test(dune) deviance(cca(dune)) # Stepwise selection (forward from an empty model "dune ~ 1") ord <- cca(dune ~ ., dune.env) step(cca(dune ~ 1, dune.env), scope = formula(ord))
Calculates the Morisita index of dispersion, standardized index values, and the so called clumpedness and uniform indices.
dispindmorisita(x, unique.rm = FALSE, crit = 0.05, na.rm = FALSE)
dispindmorisita(x, unique.rm = FALSE, crit = 0.05, na.rm = FALSE)
x |
community data matrix, with sites (samples) as rows and species as columns. |
unique.rm |
logical, if |
crit |
two-sided p-value used to calculate critical Chi-squared values. |
na.rm |
logical.
Should missing values (including |
The Morisita index of dispersion is defined as (Morisita 1959, 1962):
Imor = n * (sum(xi^2) - sum(xi)) / (sum(xi)^2 - sum(xi))
where is the count of individuals in sample
, and
is the number of samples (
).
has values from 0 to
. In uniform (hyperdispersed)
patterns its value falls between 0 and 1, in clumped patterns it falls
between 1 and
. For increasing sample sizes (i.e. joining
neighbouring quadrats),
goes to
as the
quadrat size approaches clump size. For random patterns,
and counts in the samples follow Poisson
frequency distribution.
The deviation from random expectation (null hypothesis)
can be tested using critical values of the Chi-squared
distribution with degrees of freedom.
Confidence intervals around 1 can be calculated by the clumped
and uniform
indices (Hairston et al. 1971, Krebs
1999) (Chi2Lower and Chi2Upper refers to e.g. 0.025 and 0.975 quantile
values of the Chi-squared distribution with
degrees of
freedom, respectively, for
crit = 0.05
):
Mclu = (Chi2Lower - n + sum(xi)) / (sum(xi) - 1)
Muni = (Chi2Upper - n + sum(xi)) / (sum(xi) - 1)
Smith-Gill (1975) proposed scaling of Morisita index from [0, n]
interval into [-1, 1], and setting up -0.5 and 0.5 values as
confidence limits around random distribution with rescaled value 0. To
rescale the Morisita index, one of the following four equations apply
to calculate the standardized index :
(a) Imor >= Mclu > 1
: Imst = 0.5 + 0.5 (Imor - Mclu) / (n - Mclu)
,
(b) Mclu > Imor >= 1
: Imst = 0.5 (Imor - 1) / (Mclu - 1)
,
(c) 1 > Imor > Muni
: Imst = -0.5 (Imor - 1) / (Muni - 1)
,
(d) 1 > Muni > Imor
: Imst = -0.5 + 0.5 (Imor - Muni) / Muni
.
Returns a data frame with as many rows as the number of columns
in the input data, and with four columns. Columns are: imor
the
unstandardized Morisita index, mclu
the clumpedness index,
muni
the uniform index, imst
the standardized Morisita
index, pchisq
the Chi-squared based probability for the null
hypothesis of random expectation.
A common error found in several papers is that when standardizing
as in the case (b), the denominator is given as Muni - 1
. This
results in a hiatus in the [0, 0.5] interval of the standardized
index. The root of this typo is the book of Krebs (1999), see the Errata
for the book (Page 217,
https://www.zoology.ubc.ca/~krebs/downloads/errors_2nd_printing.pdf).
Péter Sólymos, [email protected]
Morisita, M. 1959. Measuring of the dispersion of individuals and analysis of the distributional patterns. Mem. Fac. Sci. Kyushu Univ. Ser. E 2, 215–235.
Morisita, M. 1962. Id-index, a measure of dispersion of individuals. Res. Popul. Ecol. 4, 1–7.
Smith-Gill, S. J. 1975. Cytophysiological basis of disruptive pigmentary patterns in the leopard frog, Rana pipiens. II. Wild type and mutant cell specific patterns. J. Morphol. 146, 35–54.
Hairston, N. G., Hill, R. and Ritte, U. 1971. The interpretation of aggregation patterns. In: Patil, G. P., Pileou, E. C. and Waters, W. E. eds. Statistical Ecology 1: Spatial Patterns and Statistical Distributions. Penn. State Univ. Press, University Park.
Krebs, C. J. 1999. Ecological Methodology. 2nd ed. Benjamin Cummings Publishers.
data(dune) x <- dispindmorisita(dune) x y <- dispindmorisita(dune, unique.rm = TRUE) y dim(x) ## with unique species dim(y) ## unique species removed
data(dune) x <- dispindmorisita(dune) x y <- dispindmorisita(dune, unique.rm = TRUE) y dim(x) ## with unique species dim(y) ## unique species removed
Transform abundance data downweighting species that are overdispersed to the Poisson error.
dispweight(comm, groups, nsimul = 999, nullmodel = "c0_ind", plimit = 0.05) gdispweight(formula, data, plimit = 0.05) ## S3 method for class 'dispweight' summary(object, ...)
dispweight(comm, groups, nsimul = 999, nullmodel = "c0_ind", plimit = 0.05) gdispweight(formula, data, plimit = 0.05) ## S3 method for class 'dispweight' summary(object, ...)
comm |
Community data matrix. |
groups |
Factor describing the group structure. If missing, all
sites are regarded as belonging to one group. |
nsimul |
Number of simulations. |
nullmodel |
The |
plimit |
Downweight species if their |
formula , data
|
Formula where the left-hand side is the
community data frame and right-hand side gives the explanatory
variables. The explanatory variables are found in the data frame
given in |
object |
Result object from |
... |
Other parameters passed to functions. |
The dispersion index () is calculated as ratio between variance
and expected value for each species. If the species abundances follow
Poisson distribution, expected dispersion is
, and if
, the species is overdispersed. The inverse
can
be used to downweight species abundances. Species are only
downweighted when overdispersion is judged to be statistically
significant (Clarke et al. 2006).
Function dispweight
implements the original procedure of Clarke
et al. (2006). Only one factor can be used to group the sites and to
find the species means. The significance of overdispersion is assessed
freely distributing individuals of each species within factor
levels. This is achieved by using nullmodel
"c0_ind"
(which accords to Clarke et al. 2006), but other
nullmodels can be used, though they may not be meaningful (see
commsim
for alternatives). If a species is absent in
some factor level, the whole level is ignored in calculation of
overdispersion, and the number of degrees of freedom can vary among
species. The reduced number of degrees of freedom is used as a divisor
for overdispersion , and such species have higher dispersion
and hence lower weights in transformation.
Function gdispweight
is a generalized parametric version of
dispweight
. The function is based on glm
with
quasipoisson
error family
. Any
glm
model can be used, including several factors or
continuous covariates. Function gdispweight
uses the same test
statistic as dispweight
(Pearson Chi-square), but it does not
ignore factor levels where species is absent, and the number of
degrees of freedom is equal for all species. Therefore transformation
weights can be higher than in dispweight
. The
gdispweight
function evaluates the significance of
overdispersion parametrically from Chi-square distribution
(pchisq
).
Functions dispweight
and gdispweight
transform data, but
they add information on overdispersion and weights as attributes of
the result. The summary
can be used to extract and print that
information.
Function returns transformed data with the following new attributes:
D |
Dispersion statistic. |
df |
Degrees of freedom for each species. |
p |
|
weights |
weights applied to community data. |
nsimul |
Number of simulations used to assess the |
nullmodel |
The name of |
Eduard Szöcs [email protected] wrote the original
dispweight
, Jari Oksanen significantly modified the code,
provided support functions and developed gdispweight
.
Clarke, K. R., M. G. Chapman, P. J. Somerfield, and H. R. Needham. 2006. Dispersion-based weighting of species counts in assemblage analyses. Marine Ecology Progress Series, 320, 11–27.
data(mite, mite.env) ## dispweight and its summary mite.dw <- with(mite.env, dispweight(mite, Shrub, nsimul = 99)) ## IGNORE_RDIFF_BEGIN summary(mite.dw) ## IGNORE_RDIFF_END ## generalized dispersion weighting mite.dw <- gdispweight(mite ~ Shrub + WatrCont, data = mite.env) rda(mite.dw ~ Shrub + WatrCont, data = mite.env)
data(mite, mite.env) ## dispweight and its summary mite.dw <- with(mite.env, dispweight(mite, Shrub, nsimul = 99)) ## IGNORE_RDIFF_BEGIN summary(mite.dw) ## IGNORE_RDIFF_END ## generalized dispersion weighting mite.dw <- gdispweight(mite ~ Shrub + WatrCont, data = mite.env) rda(mite.dw ~ Shrub + WatrCont, data = mite.env)
Function distconnected
finds groups that are connected
disregarding dissimilarities that are at or above a threshold or
NA
. The function can be used to find groups that can be
ordinated together or transformed by
stepacross
. Function no.shared
returns a logical
dissimilarity object, where TRUE
means that sites have no
species in common. This is a minimal structure for
distconnected
or can be used to set missing values to
dissimilarities.
distconnected(dis, toolong = 1, trace = TRUE) no.shared(x)
distconnected(dis, toolong = 1, trace = TRUE) no.shared(x)
dis |
Dissimilarity data inheriting from class |
toolong |
Shortest dissimilarity regarded as |
trace |
Summarize results of |
x |
Community data. |
Data sets are disconnected if they have sample plots or groups of
sample plots which share no species with other sites or groups of
sites. Such data sets cannot be sensibly ordinated by any
unconstrained method because these subsets cannot be related to each
other. For instance, correspondence analysis will polarize these
subsets with eigenvalue 1. Neither can such dissimilarities be
transformed with stepacross
, because there is no path
between all points, and result will contain NA
s. Function
distconnected
will find such subsets in dissimilarity
matrices. The function will return a grouping vector that can be used
for sub-setting the data. If data are connected, the result vector will
be all s. The connectedness between two points can be defined
either by a threshold
toolong
or using input dissimilarities
with NA
s.
Function no.shared
returns a dist
structure having value
TRUE
when two sites have nothing in common, and value
FALSE
when they have at least one shared species. This is a
minimal structure that can be analysed with distconnected
. The
function can be used to select dissimilarities with no shared species
in indices which do not have a fixed upper limit.
Function distconnected
uses depth-first search
(Sedgewick 1990).
Function distconnected
returns a vector for
observations using integers to identify connected groups. If the data
are connected, values will be all 1
. Function no.shared
returns an object of class dist
.
Jari Oksanen
Sedgewick, R. (1990). Algorithms in C. Addison Wesley.
vegdist
or dist
for getting
dissimilarities, stepacross
for a case where you may need
distconnected
, and for connecting points spantree
.
## There are no disconnected data in vegan, and the following uses an ## extremely low threshold limit for connectedness. This is for ## illustration only, and not a recommended practice. data(dune) dis <- vegdist(dune) gr <- distconnected(dis, toolong=0.4) # Make sites with no shared species as NA in Manhattan dissimilarities dis <- vegdist(dune, "manhattan") is.na(dis) <- no.shared(dune)
## There are no disconnected data in vegan, and the following uses an ## extremely low threshold limit for connectedness. This is for ## illustration only, and not a recommended practice. data(dune) dis <- vegdist(dune) gr <- distconnected(dis, toolong=0.4) # Make sites with no shared species as NA in Manhattan dissimilarities dis <- vegdist(dune, "manhattan") is.na(dis) <- no.shared(dune)
Shannon, Simpson, and Fisher diversity indices and species richness.
diversity(x, index = "shannon", groups, equalize.groups = FALSE, MARGIN = 1, base = exp(1)) simpson.unb(x, inverse = FALSE) fisher.alpha(x, MARGIN = 1, ...) specnumber(x, groups, MARGIN = 1)
diversity(x, index = "shannon", groups, equalize.groups = FALSE, MARGIN = 1, base = exp(1)) simpson.unb(x, inverse = FALSE) fisher.alpha(x, MARGIN = 1, ...) specnumber(x, groups, MARGIN = 1)
x |
Community data, a matrix-like object or a vector. |
index |
Diversity index, one of |
MARGIN |
Margin for which the index is computed. |
base |
The logarithm |
inverse |
Use inverse Simpson similarly as in
|
groups |
A grouping factor: if given, finds the diversity of communities pooled by the groups. |
equalize.groups |
Instead of observed abundances, standardize all communities to unit total. |
... |
Parameters passed to the function. |
Shannon or Shannon–Weaver (or Shannon–Wiener) index is defined as
, where
is the proportional abundance of species
and
is the base of the logarithm. It is most popular to use natural
logarithms, but some argue for base
(which makes sense,
but no real difference).
Both variants of Simpson's index are based on . Choice
simpson
returns and
invsimpson
returns .
simpson.unb
finds unbiased Simpson indices for discrete
samples (Hurlbert 1971, eq. 5). These are less sensitive to sample
size than the basic Simpson indices. The unbiased indices can be only
calculated for data of integer counts.
The diversity
function can find the total (or gamma) diversity
of pooled communities with argument groups
. The average alpha
diversity can be found as the mean of diversities by the same groups,
and their difference or ratio is an estimate of beta diversity (see
Examples). The pooling can be based either on the observed
abundancies, or all communities can be equalized to unit total before
pooling; see Jost (2007) for discussion. Functions
adipart
and multipart
provide canned
alternatives for estimating alpha, beta and gamma diversities in
hierarchical settings.
fisher.alpha
estimates the parameter of
Fisher's logarithmic series (see
fisherfit
).
The estimation is possible only for genuine
counts of individuals.
None of these diversity indices is usable for empty sampling units without any species, but some of the indices can give a numeric value. Filtering out these cases is left for the user.
Function specnumber
finds the number of species. With
MARGIN = 2
, it finds frequencies of species. If groups
is given, finds the total number of species in each group (see
example on finding one kind of beta diversity with this option).
Better stories can be told about Simpson's index than about
Shannon's index, and still grander narratives about
rarefaction (Hurlbert 1971). However, these indices are all very
closely related (Hill 1973), and there is no reason to despise one
more than others (but if you are a graduate student, don't drag me in,
but obey your Professor's orders). In particular, the exponent of the
Shannon index is linearly related to inverse Simpson (Hill 1973)
although the former may be more sensitive to rare species. Moreover,
inverse Simpson is asymptotically equal to rarefied species richness
in sample of two individuals, and Fisher's is very
similar to inverse Simpson.
A vector of diversity indices or numbers of species.
Jari Oksanen and Bob O'Hara (fisher.alpha
).
Fisher, R.A., Corbet, A.S. & Williams, C.B. (1943). The relation between the number of species and the number of individuals in a random sample of animal population. Journal of Animal Ecology 12, 42–58.
Hurlbert, S.H. (1971). The nonconcept of species diversity: a critique and alternative parameters. Ecology 52, 577–586.
Jost, L. (2007) Partitioning diversity into independent alpha and beta components. Ecology 88, 2427–2439.
These functions calculate only some basic indices, but many
others can be derived with them (see Examples). Facilities related to
diversity are discussed in a vegan vignette that can be read
with browseVignettes("vegan")
. Functions renyi
and tsallis
estimate a series of generalized diversity
indices. Function rarefy
finds estimated number of
species for given sample size. Beta diversity can be estimated with
betadiver
. Diversities can be partitioned with
adipart
and multipart
.
data(BCI, BCI.env) H <- diversity(BCI) simp <- diversity(BCI, "simpson") invsimp <- diversity(BCI, "inv") ## Unbiased Simpson unbias.simp <- simpson.unb(BCI) ## Fisher alpha alpha <- fisher.alpha(BCI) ## Plot all pairs(cbind(H, simp, invsimp, unbias.simp, alpha), pch="+", col="blue") ## Species richness (S) and Pielou's evenness (J): S <- specnumber(BCI) ## rowSums(BCI > 0) does the same... J <- H/log(S) ## beta diversity defined as gamma/alpha - 1: ## alpha is the average no. of species in a group, and gamma is the ## total number of species in the group (alpha <- with(BCI.env, tapply(specnumber(BCI), Habitat, mean))) (gamma <- with(BCI.env, specnumber(BCI, Habitat))) gamma/alpha - 1 ## similar calculations with Shannon diversity (alpha <- with(BCI.env, tapply(diversity(BCI), Habitat, mean))) # average (gamma <- with(BCI.env, diversity(BCI, groups=Habitat))) # pooled ## additive beta diversity based on Shannon index gamma-alpha
data(BCI, BCI.env) H <- diversity(BCI) simp <- diversity(BCI, "simpson") invsimp <- diversity(BCI, "inv") ## Unbiased Simpson unbias.simp <- simpson.unb(BCI) ## Fisher alpha alpha <- fisher.alpha(BCI) ## Plot all pairs(cbind(H, simp, invsimp, unbias.simp, alpha), pch="+", col="blue") ## Species richness (S) and Pielou's evenness (J): S <- specnumber(BCI) ## rowSums(BCI > 0) does the same... J <- H/log(S) ## beta diversity defined as gamma/alpha - 1: ## alpha is the average no. of species in a group, and gamma is the ## total number of species in the group (alpha <- with(BCI.env, tapply(specnumber(BCI), Habitat, mean))) (gamma <- with(BCI.env, specnumber(BCI, Habitat))) gamma/alpha - 1 ## similar calculations with Shannon diversity (alpha <- with(BCI.env, tapply(diversity(BCI), Habitat, mean))) # average (gamma <- with(BCI.env, diversity(BCI, groups=Habitat))) # pooled ## additive beta diversity based on Shannon index gamma-alpha
The dune meadow vegetation data, dune
, has cover class values
of 30 species on 20 sites. The corresponding environmental data frame
dune.env
has following entries:
data(dune) data(dune.env)
data(dune) data(dune.env)
dune
is a data frame of observations of 30 species at 20
sites. The species names are abbreviated to 4+4 letters (see
make.cepnames
). The following names are changed from
the original source (Jongman et al. 1987): Leontodon
autumnalis to Scorzoneroides, and Potentilla
palustris to Comarum.
dune.env
is a data frame of 20 observations on the following
5 variables:
a numeric vector of thickness of soil A1 horizon.
an ordered factor with levels: 1
< 2
<
4
< 5
.
a factor with levels: BF
(Biological
farming), HF
(Hobby farming), NM
(Nature
Conservation Management), and SF
(Standard Farming).
an ordered factor of land-use with levels: Hayfield
< Haypastu
< Pasture
.
an ordered factor with levels: 0
< 1
<
2
< 3
< 4
.
Jongman, R.H.G, ter Braak, C.J.F & van Tongeren, O.F.R. (1987). Data Analysis in Community and Landscape Ecology. Pudoc, Wageningen.
data(dune) data(dune.env)
data(dune) data(dune.env)
Classification table of the species in the dune
data
set.
data(dune.taxon) data(dune.phylodis)
data(dune.taxon) data(dune.phylodis)
dune.taxon
is data frame with 30 species (rows) classified into
five taxonomic levels (columns). dune.phylodis
is a
dist
object of estimated coalescence ages extracted from
doi:10.5061/dryad.63q27 (Zanne et al. 2014) using tools in packages
ape and phylobase.
The families and orders are based on APG IV (2016) in vascular plants and on Hill et al. (2006) in mosses. The higher levels (superorder and subclass) are based on Chase & Reveal (2009). Chase & Reveal (2009) treat Angiosperms and mosses as subclasses of class Equisetopsida (land plants), but brylogists have traditionally used much more inflated levels which are adjusted here to match Angiosperm classification.
APG IV [Angiosperm Phylogeny Group] (2016) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Bot. J. Linnean Soc. 181: 1–20.
Chase, M.W. & Reveal, J. L. (2009) A phylogenetic classification of the land plants to accompany APG III. Bot. J. Linnean Soc. 161: 122–127.
Hill, M.O et al. (2006) An annotated checklist of the mosses of Europe and Macaronesia. J. Bryology 28: 198–267.
Zanne A.E., Tank D.C., Cornwell, W.K., Eastman J.M., Smith, S.A., FitzJohn, R.G., McGlinn, D.J., O’Meara, B.C., Moles, A.T., Reich, P.B., Royer, D.L., Soltis, D.E., Stevens, P.F., Westoby, M., Wright, I.J., Aarssen, L., Bertin, R.I., Calaminus, A., Govaerts, R., Hemmings, F., Leishman, M.R., Oleksyn, J., Soltis, P.S., Swenson, N.G., Warman, L. & Beaulieu, J.M. (2014) Three keys to the radiation of angiosperms into freezing environments. Nature 506: 89–92.
Functions taxondive
, treedive
,
and treedist
use these data sets.
data(dune.taxon) data(dune.phylodis)
data(dune.taxon) data(dune.phylodis)
Function extracts eigenvalues from an object that has them. Many multivariate methods return such objects.
eigenvals(x, ...) ## S3 method for class 'cca' eigenvals(x, model = c("all", "unconstrained", "constrained"), constrained = NULL, ...) ## S3 method for class 'decorana' eigenvals(x, kind = c("additive", "axiswise", "decorana"), ...) ## S3 method for class 'eigenvals' summary(object, ...)
eigenvals(x, ...) ## S3 method for class 'cca' eigenvals(x, model = c("all", "unconstrained", "constrained"), constrained = NULL, ...) ## S3 method for class 'decorana' eigenvals(x, kind = c("additive", "axiswise", "decorana"), ...) ## S3 method for class 'eigenvals' summary(object, ...)
x |
An object from which to extract eigenvalues. |
object |
An |
model |
Which eigenvalues to return for objects that inherit from class
|
constrained |
Return only constrained eigenvalues. Deprecated as of vegan
2.5-0. Use |
kind |
Kind of eigenvalues returned for |
... |
Other arguments to the functions (usually ignored) |
This is a generic function that has methods for cca
,
wcmdscale
, pcnm
, prcomp
,
princomp
, dudi
(of ade4), and
pca
and pco
(of
labdsv) result objects. The default method also
extracts eigenvalues if the result looks like being from
eigen
or svd
. Functions
prcomp
and princomp
contain square roots
of eigenvalues that all called standard deviations, but
eigenvals
function returns their squares. Function
svd
contains singular values, but function
eigenvals
returns their squares. For constrained ordination
methods cca
, rda
and
capscale
the function returns the both constrained and
unconstrained eigenvalues concatenated in one vector, but the partial
component will be ignored. However, with argument
constrained = TRUE
only constrained eigenvalues are returned.
The summary
of eigenvals
result returns eigenvalues,
proportion explained and cumulative proportion explained. The result
object can have some negative eigenvalues (wcmdscale
,
dbrda
, pcnm
) which correspond to
imaginary axes of Euclidean mapping of non-Euclidean distances
(Gower 1985). In these case real axes (corresponding to positive
eigenvalues) will "explain" proportion >1 of total variation, and
negative eigenvalues bring the cumulative proportion to
1. capscale
will only find the positive eigenvalues
and only these are used in finding proportions. For
decorana
the importances and cumulative proportions
are only reported for kind = "additive"
, because other
alternatives do not add up to total inertia of the input data.
An object of class "eigenvals"
, which is a vector of
eigenvalues.
The summary
method returns an object of class
"summary.eigenvals"
, which is a matrix.
Jari Oksanen.
Gower, J. C. (1985). Properties of Euclidean and non-Euclidean distance matrices. Linear Algebra and its Applications 67, 81–97.
eigen
, svd
, prcomp
,
princomp
, cca
, rda
,
capscale
, wcmdscale
,
cca.object
.
data(varespec) data(varechem) mod <- cca(varespec ~ Al + P + K, varechem) ev <- eigenvals(mod) ev summary(ev) ## choose which eignevalues to return eigenvals(mod, model = "unconstrained")
data(varespec) data(varechem) mod <- cca(varespec ~ Al + P + K, varechem) ev <- eigenvals(mod) ev summary(ev) ## choose which eignevalues to return eigenvals(mod, model = "unconstrained")
The function fits environmental vectors or factors onto an
ordination. The projections of points onto vectors have maximum
correlation with corresponding environmental variables, and the
factors show the averages of factor levels. For continuous varaibles
this is equal to fitting a linear trend surface (plane in 2D) for a
variable (see ordisurf
); this trend surface can be
presented by showing its gradient (direction of steepest increase)
using an arrow. The environmental variables are the dependent
variables that are explained by the ordination scores, and each
dependent variable is analysed separately.
## Default S3 method: envfit(ord, env, permutations = 999, strata = NULL, choices=c(1,2), display = "sites", w, na.rm = FALSE, ...) ## S3 method for class 'formula' envfit(formula, data, ...) ## S3 method for class 'envfit' plot(x, choices = c(1,2), labels, arrow.mul, at = c(0,0), axis = FALSE, p.max = NULL, col = "blue", bg, add = TRUE, ...) ## S3 method for class 'envfit' scores(x, display, choices, arrow.mul=1, tidy = FALSE, ...) vectorfit(X, P, permutations = 0, strata = NULL, w, ...) factorfit(X, P, permutations = 0, strata = NULL, w, ...)
## Default S3 method: envfit(ord, env, permutations = 999, strata = NULL, choices=c(1,2), display = "sites", w, na.rm = FALSE, ...) ## S3 method for class 'formula' envfit(formula, data, ...) ## S3 method for class 'envfit' plot(x, choices = c(1,2), labels, arrow.mul, at = c(0,0), axis = FALSE, p.max = NULL, col = "blue", bg, add = TRUE, ...) ## S3 method for class 'envfit' scores(x, display, choices, arrow.mul=1, tidy = FALSE, ...) vectorfit(X, P, permutations = 0, strata = NULL, w, ...) factorfit(X, P, permutations = 0, strata = NULL, w, ...)
ord |
An ordination object or other structure from which the
ordination |
env |
Data frame, matrix or vector of environmental variables. The variables can be of mixed type (factors, continuous variables) in data frames. |
X |
Matrix or data frame of ordination scores. |
P |
Data frame, matrix or vector of environmental
variable(s). These must be continuous for |
permutations |
a list of control values for the permutations
as returned by the function |
formula , data
|
Model |
na.rm |
Remove points with missing values in ordination scores
or environmental variables. The operation is casewise: the whole
row of data is removed if there is a missing value and
|
x |
A result object from |
choices |
Axes to plotted. |
tidy |
Return scores that are compatible with ggplot2:
all scores are in a single |
labels |
Change plotting labels. The argument should be a list
with elements |
arrow.mul |
Multiplier for vector lengths. The arrows are
automatically scaled similarly as in |
at |
The origin of fitted arrows in the plot. If you plot arrows
in other places then origin, you probably have to specify
|
axis |
Plot axis showing the scaling of fitted arrows. |
p.max |
Maximum estimated |
col |
Colour in plotting. |
bg |
Background colour for labels. If |
add |
Results added to an existing ordination plot. |
strata |
An integer vector or factor specifying the strata for permutation. If supplied, observations are permuted only within the specified strata. |
display |
In fitting functions these are ordinary site scores or
linear combination scores
( |
w |
Weights used in fitting (concerns mainly |
... |
Parameters passed to |
Function envfit
finds vectors or factor averages of
environmental variables. Function plot.envfit
adds these in an
ordination diagram. If X
is a data.frame
,
envfit
uses factorfit
for factor
variables and
vectorfit
for other variables. If X
is a matrix or a
vector, envfit
uses only vectorfit
. Alternatively, the
model can be defined a simplified model formula
, where
the left hand side must be an ordination result object or a matrix of
ordination scores, and right hand
side lists the environmental variables. The formula interface can be
used for easier selection and/or transformation of environmental
variables. Only the main effects will be analysed even if interaction
terms were defined in the formula.
The ordination results are extracted with scores
and
all extra arguments are passed to the scores
. The fitted
models only apply to the results defined when extracting the scores
when using envfit
. For instance, scaling
in
constrained ordination (see scores.rda
,
scores.cca
) must be set in the same way in
envfit
and in the plot
or the ordination results (see
Examples).
The printed output of continuous variables (vectors) gives the
direction cosines which are the coordinates of the heads of unit
length vectors. In plot
these are scaled by their
correlation (square root of the column r2
) so that
“weak” predictors have shorter arrows than “strong”
predictors. You can see the scaled relative lengths using command
scores
. The plot
ted (and scaled) arrows are further
adjusted to the current graph using a constant multiplier: this will
keep the relative r2
-scaled lengths of the arrows but tries
to fill the current plot. You can see the multiplier using
ordiArrowMul(result_of_envfit)
, and set it with the
argument arrow.mul
.
Functions vectorfit
and factorfit
can be called directly.
Function vectorfit
finds directions in the ordination space
towards which the environmental vectors change most rapidly and to
which they have maximal correlations with the ordination
configuration. Function factorfit
finds averages of ordination
scores for factor levels. Function factorfit
treats ordered
and unordered factors similarly.
If permutations
, the significance of fitted vectors
or factors is assessed using permutation of environmental variables.
The goodness of fit statistic is squared correlation coefficient
(
).
For factors this is defined as
, where
and
are within-group and total sums of
squares. See
permutations
for additional details on
permutation tests in Vegan.
User can supply a vector of prior weights w
. If the ordination
object has weights, these will be used. In practise this means that
the row totals are used as weights with cca
or
decorana
results. If you do not like this, but want to
give equal weights to all sites, you should set w = NULL
. The
fitted vectors are similar to biplot arrows in constrained ordination
only when fitted to LC scores (display = "lc"
) and you set
scaling = "species"
(see scores.cca
). The
weighted fitting gives similar results to biplot arrows and class
centroids in cca
.
The lengths of arrows for fitted vectors are automatically adjusted
for the physical size of the plot, and the arrow lengths cannot be
compared across plots. For similar scaling of arrows, you must
explicitly set the arrow.mul
argument in the plot
command; see ordiArrowMul
and
ordiArrowTextXY
.
The results can be accessed with scores.envfit
function which
returns either the fitted vectors scaled by correlation coefficient or
the centroids of the fitted environmental variables, or a named list
of both.
Functions vectorfit
and factorfit
return lists of
classes vectorfit
and factorfit
which have a
print
method. The result object have the following items:
arrows |
Arrow endpoints from |
centroids |
Class centroids from |
r |
Goodness of fit statistic: Squared correlation coefficient |
permutations |
Number of permutations. |
control |
A list of control values for the permutations
as returned by the function |
pvals |
Empirical P-values for each variable. |
Function envfit
returns a list of class envfit
with
results of vectorfit
and envfit
as items.
Function plot.envfit
scales the vectors by correlation.
Fitted vectors have become the method of choice in displaying
environmental variables in ordination. Indeed, they are the optimal
way of presenting environmental variables in Constrained
Correspondence Analysis cca
, since there they are the
linear constraints.
In unconstrained ordination the relation between external variables
and ordination configuration may be less linear, and therefore other
methods than arrows may be more useful. The simplest is to adjust the
plotting symbol sizes (cex
, symbols
) by
environmental variables.
Fancier methods involve smoothing and regression methods that
abound in R, and ordisurf
provides a wrapper for some.
Jari Oksanen. The permutation test derives from the code suggested by Michael Scroggie.
A better alternative to vectors may be ordisurf
.
data(varespec, varechem) library(MASS) ord <- metaMDS(varespec) (fit <- envfit(ord, varechem, perm = 999)) scores(fit, "vectors") plot(ord) plot(fit) plot(fit, p.max = 0.05, col = "red") ## Adding fitted arrows to CCA. We use "lc" scores, and hope ## that arrows are scaled similarly in cca and envfit plots ord <- cca(varespec ~ Al + P + K, varechem) plot(ord, type="p") fit <- envfit(ord, varechem, perm = 999, display = "lc") plot(fit, p.max = 0.05, col = "red") ## 'scaling' must be set similarly in envfit and in ordination plot plot(ord, type = "p", scaling = "sites") fit <- envfit(ord, varechem, perm = 0, display = "lc", scaling = "sites") plot(fit, col = "red") ## Class variables, formula interface, and displaying the ## inter-class variability with ordispider, and semitransparent ## white background for labels (semitransparent colours are not ## supported by all graphics devices) data(dune) data(dune.env) ord <- cca(dune) fit <- envfit(ord ~ Moisture + A1, dune.env, perm = 0) plot(ord, type = "n") with(dune.env, ordispider(ord, Moisture, col="skyblue")) with(dune.env, points(ord, display = "sites", col = as.numeric(Moisture), pch=16)) plot(fit, cex=1.2, axis=TRUE, bg = rgb(1, 1, 1, 0.5)) ## Use shorter labels for factor centroids labels(fit) plot(ord) plot(fit, labels=list(factors = paste("M", c(1,2,4,5), sep = "")), bg = rgb(1,1,0,0.5))
data(varespec, varechem) library(MASS) ord <- metaMDS(varespec) (fit <- envfit(ord, varechem, perm = 999)) scores(fit, "vectors") plot(ord) plot(fit) plot(fit, p.max = 0.05, col = "red") ## Adding fitted arrows to CCA. We use "lc" scores, and hope ## that arrows are scaled similarly in cca and envfit plots ord <- cca(varespec ~ Al + P + K, varechem) plot(ord, type="p") fit <- envfit(ord, varechem, perm = 999, display = "lc") plot(fit, p.max = 0.05, col = "red") ## 'scaling' must be set similarly in envfit and in ordination plot plot(ord, type = "p", scaling = "sites") fit <- envfit(ord, varechem, perm = 0, display = "lc", scaling = "sites") plot(fit, col = "red") ## Class variables, formula interface, and displaying the ## inter-class variability with ordispider, and semitransparent ## white background for labels (semitransparent colours are not ## supported by all graphics devices) data(dune) data(dune.env) ord <- cca(dune) fit <- envfit(ord ~ Moisture + A1, dune.env, perm = 0) plot(ord, type = "n") with(dune.env, ordispider(ord, Moisture, col="skyblue")) with(dune.env, points(ord, display = "sites", col = as.numeric(Moisture), pch=16)) plot(fit, cex=1.2, axis=TRUE, bg = rgb(1, 1, 1, 0.5)) ## Use shorter labels for factor centroids labels(fit) plot(ord) plot(fit, labels=list(factors = paste("M", c(1,2,4,5), sep = "")), bg = rgb(1,1,0,0.5))
The function eventstar
finds the minimum () of the
evenness profile based on the Tsallis entropy. This scale factor
of the entropy represents a specific weighting of species
relative frequencies that leads to minimum evenness of the
community (Mendes et al. 2008).
eventstar(x, qmax = 5)
eventstar(x, qmax = 5)
x |
A community matrix or a numeric vector. |
qmax |
Maximum scale parameter of the Tsallis entropy to be used in
finding the minimum of Tsallis based evenness
in the range |
The function eventstar
finds a characteristic value of the scale
parameter of the Tsallis entropy corresponding to
minimum of the evenness (equitability) profile based on Tsallis entropy.
This value was proposed by Mendes et al. (2008) as
.
The index represents the scale parameter of
the one parameter Tsallis diversity family that leads to
the greatest deviation from the maximum equitability given the relative
abundance vector of a community.
The value of is found by identifying the minimum
of the evenness profile over scaling factor
by
one-dimensional minimization. Because evenness profile is
known to be a convex function, it is guaranteed that underlying
optimize
function will find a unique solution
if it is in the range c(0, qmax)
.
The scale parameter value is used to
find corresponding values of diversity (
),
evenness (
),
and numbers equivalent (
). For calculation
details, see
tsallis
and Examples below.
Mendes et al. (2008) advocated the use of
and corresponding diversity, evenness, and Hill numbers, because
it is a unique value representing the diversity profile, and is
is positively associated with rare species in the community,
thus it is a potentially useful indicator of certain
relative abundance distributions of the communities.
A data frame with columns:
qstar |
scale parameter value |
Estar |
Value of evenness based on normalized Tsallis
entropy at |
Hstar |
Value of Tsallis entropy at |
Dstar |
Value of Tsallis entropy at |
See tsallis
for calculation details.
Values for found by Mendes et al. (2008) ranged
from 0.56 and 1.12 presenting low variability, so an
interval between 0 and 5 should safely encompass
the possibly expected
values in practice,
but profiling the evenness and changing the value of
the
qmax
argument is advised if output values
near the range limits are found.
Eduardo Ribeiro Cunha [email protected] and Heloisa Beatriz Antoniazi Evangelista [email protected], with technical input of Péter Sólymos.
Mendes, R.S., Evangelista, L.R., Thomaz, S.M., Agostinho, A.A. and Gomes, L.C. (2008) A unified index to measure ecological diversity and species rarity. Ecography 31, 450–456.
Jost, L. (2007) Partitioning diversity into independent alpha and beta components. Ecology 88, 2427–2439.
Tsallis, C. (1988) Possible generalization of Boltzmann-Gibbs statistics. J. Stat. Phis. 52, 479–487.
Tsallis entropy: tsallis
data(BCI) (x <- eventstar(BCI[1:5,])) ## profiling y <- as.numeric(BCI[10,]) (z <- eventstar(y)) q <- seq(0, 2, 0.05) Eprof <- tsallis(y, scales=q, norm=TRUE) Hprof <- tsallis(y, scales=q) Dprof <- tsallis(y, scales=q, hill=TRUE) opar <- par(mfrow=c(3,1)) plot(q, Eprof, type="l", main="Evenness") abline(v=z$qstar, h=tsallis(y, scales=z$qstar, norm=TRUE), col=2) plot(q, Hprof, type="l", main="Diversity") abline(v=z$qstar, h=tsallis(y, scales=z$qstar), col=2) plot(q, Dprof, type="l", main="Effective number of species") abline(v=z$qstar, h=tsallis(y, scales=z$qstar, hill=TRUE), col=2) par(opar)
data(BCI) (x <- eventstar(BCI[1:5,])) ## profiling y <- as.numeric(BCI[10,]) (z <- eventstar(y)) q <- seq(0, 2, 0.05) Eprof <- tsallis(y, scales=q, norm=TRUE) Hprof <- tsallis(y, scales=q) Dprof <- tsallis(y, scales=q, hill=TRUE) opar <- par(mfrow=c(3,1)) plot(q, Eprof, type="l", main="Evenness") abline(v=z$qstar, h=tsallis(y, scales=z$qstar, norm=TRUE), col=2) plot(q, Hprof, type="l", main="Diversity") abline(v=z$qstar, h=tsallis(y, scales=z$qstar), col=2) plot(q, Dprof, type="l", main="Effective number of species") abline(v=z$qstar, h=tsallis(y, scales=z$qstar, hill=TRUE), col=2) par(opar)
Function fisherfit
fits Fisher's logseries to abundance
data. Function prestonfit
groups species frequencies into
doubling octave classes and fits Preston's lognormal model, and
function prestondistr
fits the truncated lognormal model
without pooling the data into octaves.
fisherfit(x, ...) prestonfit(x, tiesplit = TRUE, ...) prestondistr(x, truncate = -1, ...) ## S3 method for class 'prestonfit' plot(x, xlab = "Frequency", ylab = "Species", bar.col = "skyblue", line.col = "red", lwd = 2, ...) ## S3 method for class 'prestonfit' lines(x, line.col = "red", lwd = 2, ...) veiledspec(x, ...) as.fisher(x, ...) ## S3 method for class 'fisher' plot(x, xlab = "Frequency", ylab = "Species", bar.col = "skyblue", kind = c("bar", "hiplot", "points", "lines"), add = FALSE, ...) as.preston(x, tiesplit = TRUE, ...) ## S3 method for class 'preston' plot(x, xlab = "Frequency", ylab = "Species", bar.col = "skyblue", ...) ## S3 method for class 'preston' lines(x, xadjust = 0.5, ...)
fisherfit(x, ...) prestonfit(x, tiesplit = TRUE, ...) prestondistr(x, truncate = -1, ...) ## S3 method for class 'prestonfit' plot(x, xlab = "Frequency", ylab = "Species", bar.col = "skyblue", line.col = "red", lwd = 2, ...) ## S3 method for class 'prestonfit' lines(x, line.col = "red", lwd = 2, ...) veiledspec(x, ...) as.fisher(x, ...) ## S3 method for class 'fisher' plot(x, xlab = "Frequency", ylab = "Species", bar.col = "skyblue", kind = c("bar", "hiplot", "points", "lines"), add = FALSE, ...) as.preston(x, tiesplit = TRUE, ...) ## S3 method for class 'preston' plot(x, xlab = "Frequency", ylab = "Species", bar.col = "skyblue", ...) ## S3 method for class 'preston' lines(x, xadjust = 0.5, ...)
x |
Community data vector for fitting functions or their result
object for |
tiesplit |
Split frequencies |
truncate |
Truncation point for log-Normal model, in log2
units. Default value |
xlab , ylab
|
Labels for |
bar.col |
Colour of data bars. |
line.col |
Colour of fitted line. |
lwd |
Width of fitted line. |
kind |
Kind of plot to drawn: |
add |
Add to an existing plot. |
xadjust |
Adjustment of horizontal positions in octaves. |
... |
Other parameters passed to functions. Ignored in
|
In Fisher's logarithmic series the expected number of species
with
observed individuals is
(Fisher et al. 1943). The estimation is possible only for
genuine counts of individuals. The parameter
is used as
a diversity index which can be estimated with a separate function
fisher.alpha
. The parameter is taken as a
nuisance parameter which is not estimated separately but taken to be
. Helper function
as.fisher
transforms
abundance data into Fisher frequency table. Diversity will be given
as NA
for communities with one (or zero) species: there is no
reliable way of estimating their diversity, even if the equations
will return a bogus numeric value in some cases.
Preston (1948) was not satisfied with Fisher's model which seemed to
imply infinite species richness, and postulated that rare species is
a diminishing class and most species are in the middle of frequency
scale. This was achieved by collapsing higher frequency classes into
wider and wider “octaves” of doubling class limits: 1, 2, 3–4,
5–8, 9–16 etc. occurrences. It seems that Preston regarded
frequencies 1, 2, 4, etc.. as “tied” between octaves
(Williamson & Gaston 2005). This means that only half of the species
with frequency 1 are shown in the lowest octave, and the rest are
transferred to the second octave. Half of the species from the
second octave are transferred to the higher one as well, but this is
usually not as large a number of species. This practise makes data
look more lognormal by reducing the usually high lowest
octaves. This can be achieved by setting argument tiesplit = TRUE
.
With tiesplit = FALSE
the frequencies are not split,
but all ones are in the lowest octave, all twos in the second, etc.
Williamson & Gaston (2005) discuss alternative definitions in
detail, and they should be consulted for a critical review of
log-Normal model.
Any logseries data will look like lognormal when plotted in
Preston's way. The expected frequency at abundance octave
is defined by
, where
is the location of the mode and
the width,
both in
scale, and
is the expected
number of species at mode. The lognormal model is usually truncated
on the left so that some rare species are not observed. Function
prestonfit
fits the truncated lognormal model as a second
degree log-polynomial to the octave pooled data using Poisson (when
tiesplit = FALSE
) or quasi-Poisson (when tiesplit = TRUE
)
error. Function prestondistr
fits left-truncated
Normal distribution to transformed non-pooled
observations with direct maximization of log-likelihood. Function
prestondistr
is modelled after function
fitdistr
which can be used for alternative
distribution models.
The functions have common print
, plot
and lines
methods. The lines
function adds the fitted curve to the
octave range with line segments showing the location of the mode and
the width (sd) of the response. Function as.preston
transforms abundance data to octaves. Argument tiesplit
will
not influence the fit in prestondistr
, but it will influence
the barplot of the octaves.
The total extrapolated richness from a fitted Preston model can be
found with function veiledspec
. The function accepts results
both from prestonfit
and from prestondistr
. If
veiledspec
is called with a species count vector, it will
internally use prestonfit
. Function specpool
provides alternative ways of estimating the number of unseen
species. In fact, Preston's lognormal model seems to be truncated at
both ends, and this may be the main reason why its result differ
from lognormal models fitted in Rank–Abundance diagrams with
functions rad.lognormal
.
The function prestonfit
returns an object with fitted
coefficients
, and with observed (freq
) and fitted
(fitted
) frequencies, and a string describing the fitting
method
. Function prestondistr
omits the entry
fitted
. The function fisherfit
returns the result of
nlm
, where item estimate
is . The
result object is amended with the
nuisance
parameter and item
fisher
for the observed data from as.fisher
Bob O'Hara and Jari Oksanen.
Fisher, R.A., Corbet, A.S. & Williams, C.B. (1943). The relation between the number of species and the number of individuals in a random sample of animal population. Journal of Animal Ecology 12: 42–58.
Preston, F.W. (1948) The commonness and rarity of species. Ecology 29, 254–283.
Williamson, M. & Gaston, K.J. (2005). The lognormal distribution is not an appropriate null hypothesis for the species–abundance distribution. Journal of Animal Ecology 74, 409–422.
diversity
, fisher.alpha
,
radfit
, specpool
. Function
fitdistr
of MASS package was used as the
model for prestondistr
. Function density
can be used for
smoothed non-parametric estimation of responses, and
qqplot
is an alternative, traditional and more effective
way of studying concordance of observed abundances to any distribution model.
data(BCI) mod <- fisherfit(BCI[5,]) mod # prestonfit seems to need large samples mod.oct <- prestonfit(colSums(BCI)) mod.ll <- prestondistr(colSums(BCI)) mod.oct mod.ll plot(mod.oct) lines(mod.ll, line.col="blue3") # Different ## Smoothed density den <- density(log2(colSums(BCI))) lines(den$x, ncol(BCI)*den$y, lwd=2) # Fairly similar to mod.oct ## Extrapolated richness veiledspec(mod.oct) veiledspec(mod.ll)
data(BCI) mod <- fisherfit(BCI[5,]) mod # prestonfit seems to need large samples mod.oct <- prestonfit(colSums(BCI)) mod.ll <- prestondistr(colSums(BCI)) mod.oct mod.ll plot(mod.oct) lines(mod.ll, line.col="blue3") # Different ## Smoothed density den <- density(log2(colSums(BCI))) lines(den$x, ncol(BCI)*den$y, lwd=2) # Fairly similar to mod.oct ## Extrapolated richness veiledspec(mod.oct) veiledspec(mod.ll)
Functions goodness
and inertcomp
can
be used to assess the goodness of fit for individual sites or
species. Function vif.cca
and alias.cca
can be used to
analyse linear dependencies among constraints and conditions. In
addition, there are some other diagnostic tools (see 'Details').
## S3 method for class 'cca' goodness(object, choices, display = c("species", "sites"), model = c("CCA", "CA"), summarize = FALSE, addprevious = FALSE, ...) inertcomp(object, display = c("species", "sites"), unity = FALSE, proportional = FALSE) spenvcor(object) intersetcor(object) vif.cca(object) ## S3 method for class 'cca' alias(object, names.only = FALSE, ...)
## S3 method for class 'cca' goodness(object, choices, display = c("species", "sites"), model = c("CCA", "CA"), summarize = FALSE, addprevious = FALSE, ...) inertcomp(object, display = c("species", "sites"), unity = FALSE, proportional = FALSE) spenvcor(object) intersetcor(object) vif.cca(object) ## S3 method for class 'cca' alias(object, names.only = FALSE, ...)
object |
|
display |
Display |
choices |
Axes shown. Default is to show all axes of the
|
model |
Show constrained ( |
summarize |
Show only the accumulated total. |
addprevious |
Add the variation explained by previous components
when |
unity |
Scale inertia components to unit sum (sum of all items is 1). |
proportional |
Give the inertia components as proportional for
the corresponding total of the item (sum of each row is 1). This
option takes precedence over |
names.only |
Return only names of aliased variable(s) instead of defining equations. |
... |
Other parameters to the functions. |
Function goodness
gives cumulative proportion of inertia
accounted by species up to chosen axes. The proportions can be
assessed either by species or by sites depending on the argument
display
, but species are not available in distance-based
dbrda
. The function is not implemented for
capscale
.
Function inertcomp
decomposes the inertia into partial,
constrained and unconstrained components for each site or species.
Legendre & De Cáceres (2012) called these inertia
components as local contributions to beta-diversity (LCBD) and
species contributions to beta-diversity (SCBD), and they give these
as relative contributions summing up to unity (argument
unity = TRUE
). For this interpretation, appropriate dissimilarity
measures should be used in dbrda
or appropriate
standardization in rda
(Legendre & De
Cáceres 2012). The function is not implemented for
capscale
.
Function spenvcor
finds the so-called “species –
environment correlation” or (weighted) correlation of
weighted average scores and linear combination scores. This is a bad
measure of goodness of ordination, because it is sensitive to extreme
scores (like correlations are), and very sensitive to overfitting or
using too many constraints. Better models often have poorer
correlations. Function ordispider
can show the same
graphically.
Function intersetcor
finds the so-called “interset
correlation” or (weighted) correlation of weighted averages scores
and constraints. The defined contrasts are used for factor
variables. This is a bad measure since it is a correlation. Further,
it focuses on correlations between single contrasts and single axes
instead of looking at the multivariate relationship. Fitted vectors
(envfit
) provide a better alternative. Biplot scores
(see scores.cca
) are a multivariate alternative for
(weighted) correlation between linear combination scores and
constraints.
Function vif.cca
gives the variance inflation factors for each
constraint or contrast in factor constraints. In partial ordination,
conditioning variables are analysed together with constraints. Variance
inflation is a diagnostic tool to identify useless constraints. A
common rule is that values over 10 indicate redundant
constraints. If later constraints are complete linear combinations of
conditions or previous constraints, they will be completely removed
from the estimation, and no biplot scores or centroids are calculated
for these aliased constraints. A note will be printed with default
output if there are aliased constraints. Function alias
will
give the linear coefficients defining the aliased constraints, or
only their names with argument names.only = TRUE
.
The functions return matrices or vectors as is appropriate.
Jari Oksanen. The vif.cca
relies heavily on the code by
W. N. Venables. alias.cca
is a simplified version of
alias.lm
.
Greenacre, M. J. (1984). Theory and applications of correspondence analysis. Academic Press, London.
Gross, J. (2003). Variance inflation factors. R News 3(1), 13–15.
Legendre, P. & De Cáceres, M. (2012). Beta diversity as the variance of community data: dissimilarity coefficients and partitioning. Ecology Letters 16, 951–963. doi:10.1111/ele.12141
data(dune) data(dune.env) mod <- cca(dune ~ A1 + Management + Condition(Moisture), data=dune.env) goodness(mod, addprevious = TRUE) goodness(mod, addprevious = TRUE, summ = TRUE) # Inertia components inertcomp(mod, prop = TRUE) inertcomp(mod) # vif.cca vif.cca(mod) # Aliased constraints mod <- cca(dune ~ ., dune.env) mod vif.cca(mod) alias(mod) with(dune.env, table(Management, Manure)) # The standard correlations (not recommended) ## IGNORE_RDIFF_BEGIN spenvcor(mod) intersetcor(mod) ## IGNORE_RDIFF_END
data(dune) data(dune.env) mod <- cca(dune ~ A1 + Management + Condition(Moisture), data=dune.env) goodness(mod, addprevious = TRUE) goodness(mod, addprevious = TRUE, summ = TRUE) # Inertia components inertcomp(mod, prop = TRUE) inertcomp(mod) # vif.cca vif.cca(mod) # Aliased constraints mod <- cca(dune ~ ., dune.env) mod vif.cca(mod) alias(mod) with(dune.env, table(Management, Manure)) # The standard correlations (not recommended) ## IGNORE_RDIFF_BEGIN spenvcor(mod) intersetcor(mod) ## IGNORE_RDIFF_END
Function goodness.metaMDS
find goodness of fit measure for
points in nonmetric multidimensional scaling, and function
stressplot
makes a Shepard
diagram.
## S3 method for class 'metaMDS' goodness(object, dis, ...) ## Default S3 method: stressplot(object, dis, pch, p.col = "blue", l.col = "red", lwd = 2, ...)
## S3 method for class 'metaMDS' goodness(object, dis, ...) ## Default S3 method: stressplot(object, dis, pch, p.col = "blue", l.col = "red", lwd = 2, ...)
object |
|
dis |
Dissimilarities. This should not be used with
|
pch |
Plotting character for points. Default is dependent on the number of points. |
p.col , l.col
|
Point and line colours. |
lwd |
Line width. For |
... |
Other parameters to functions, e.g. graphical parameters. |
Function goodness.metaMDS
finds a goodness of fit statistic
for observations (points). This is defined so that sum of squared
values is equal to squared stress. Large values indicate poor fit.
The absolute values of the goodness statistic depend on the
definition of the stress: isoMDS
expresses
stress in percents, and therefore its goodness values are 100 times
higher than those of monoMDS
which expresses the
stress as a proportion.
Function stressplot
draws a Shepard diagram which is a plot
of ordination distances and monotone or linear fit line against
original dissimilarities. In addition, it displays two
correlation-like statistics on the goodness of fit in the graph.
The nonmetric fit is based on stress and defined as
. The “linear fit” is the squared
correlation between fitted values and ordination distances. For
monoMDS
, the “linear fit” and
from “stress type 2” are equal.
Both functions can be used with metaMDS
,
monoMDS
and isoMDS
. The original
dissimilarities should not be given for monoMDS
or
metaMDS
results (the latter tries to reconstruct the
dissimilarities using metaMDSredist
if
isoMDS
was used as its engine). With
isoMDS
the dissimilarities must be given. In
either case, the functions inspect that dissimilarities are
consistent with current ordination, and refuse to analyse
inconsistent dissimilarities. Function goodness.metaMDS
is
generic in vegan, but you must spell its name completely with
isoMDS
which has no class.
Function goodness
returns a vector of values. Function
stressplot
returns invisibly an object with items for
original dissimilarities, ordination distances and fitted values.
Jari Oksanen.
metaMDS
, monoMDS
,
isoMDS
, Shepard
. Similar
diagrams for eigenvector ordinations can be drawn with
stressplot.wcmdscale
, stressplot.cca
.
data(varespec) mod <- metaMDS(varespec) stressplot(mod) gof <- goodness(mod) gof plot(mod, display = "sites", type = "n") points(mod, display = "sites", cex = 2*gof/mean(gof))
data(varespec) mod <- metaMDS(varespec) stressplot(mod) gof <- goodness(mod) gof plot(mod, display = "sites", type = "n") points(mod, display = "sites", cex = 2*gof/mean(gof))
Indicator power calculation of Halme et al. (2009) or the congruence between indicator and target species.
indpower(x, type = 0)
indpower(x, type = 0)
x |
Community data frame or matrix. |
type |
The type of statistic to be returned. See Details for explanation. |
Halme et al. (2009) described an index of indicator power defined as
, where
and
.
is the number of sites,
is the number of shared occurrences of the indicator (
)
and the target (
) species.
and
are number
of occurrences of the indicator and target species. The
type
argument in the function call enables to choose which statistic to
return. type = 0
returns ,
type = 1
returns
,
type = 2
returns .
Total indicator power (TIP) of an indicator species is the column mean
(without its own value, see examples).
Halme et al. (2009) explain how to calculate confidence
intervals for these statistics, see Examples.
A matrix with indicator species as rows and target species as columns (this is indicated by the first letters of the row/column names).
Peter Solymos
Halme, P., Mönkkönen, M., Kotiaho, J. S, Ylisirniö, A-L. 2009. Quantifying the indicator power of an indicator species. Conservation Biology 23: 1008–1016.
data(dune) ## IP values ip <- indpower(dune) ## and TIP values diag(ip) <- NA (TIP <- rowMeans(ip, na.rm=TRUE)) ## p value calculation for a species ## from Halme et al. 2009 ## i is ID for the species i <- 1 fun <- function(x, i) indpower(x)[i,-i] ## 'c0' randomizes species occurrences os <- oecosimu(dune, fun, "c0", i=i, nsimul=99) ## get z values from oecosimu output z <- os$oecosimu$z ## p-value (p <- sum(z) / sqrt(length(z))) ## 'heterogeneity' measure (chi2 <- sum((z - mean(z))^2)) pchisq(chi2, df=length(z)-1) ## Halme et al.'s suggested output out <- c(TIP=TIP[i], significance=p, heterogeneity=chi2, minIP=min(fun(dune, i=i)), varIP=sd(fun(dune, i=i)^2)) out
data(dune) ## IP values ip <- indpower(dune) ## and TIP values diag(ip) <- NA (TIP <- rowMeans(ip, na.rm=TRUE)) ## p value calculation for a species ## from Halme et al. 2009 ## i is ID for the species i <- 1 fun <- function(x, i) indpower(x)[i,-i] ## 'c0' randomizes species occurrences os <- oecosimu(dune, fun, "c0", i=i, nsimul=99) ## get z values from oecosimu output z <- os$oecosimu$z ## p-value (p <- sum(z) / sqrt(length(z))) ## 'heterogeneity' measure (chi2 <- sum((z - mean(z))^2)) pchisq(chi2, df=length(z)-1) ## Halme et al.'s suggested output out <- c(TIP=TIP[i], significance=p, heterogeneity=chi2, minIP=min(fun(dune, i=i)), varIP=sd(fun(dune, i=i)^2)) out
This set of function extracts influence statistics and some other
linear model statistics directly from a constrained ordination result
object from cca
, rda
,
capscale
or dbrda
. The constraints are
linear model functions and these support functions return identical
results as the corresponding linear models (lm
), and you
can use their documentation. The main functions for normal usage are
leverage values (hatvalues
), standardized residuals
(rstandard
), studentized or leave-one-out residuals
(rstudent
), and Cook's distance
(cooks.distance
). In addition, vcov
returns the variance-covariance matrix of coefficients, and its
diagonal values the variances of coefficients. Other functions are
mainly support functions for these, but they can be used directly.
## S3 method for class 'cca' hatvalues(model, ...) ## S3 method for class 'cca' rstandard(model, type = c("response", "canoco"), ...) ## S3 method for class 'cca' rstudent(model, type = c("response", "canoco"), ...) ## S3 method for class 'cca' cooks.distance(model, type = c("response", "canoco"), ...) ## S3 method for class 'cca' sigma(object, type = c("response", "canoco"), ...) ## S3 method for class 'cca' vcov(object, type = "canoco", ...) ## S3 method for class 'cca' SSD(object, type = "canoco", ...) ## S3 method for class 'cca' qr(x, ...) ## S3 method for class 'cca' df.residual(object, ...)
## S3 method for class 'cca' hatvalues(model, ...) ## S3 method for class 'cca' rstandard(model, type = c("response", "canoco"), ...) ## S3 method for class 'cca' rstudent(model, type = c("response", "canoco"), ...) ## S3 method for class 'cca' cooks.distance(model, type = c("response", "canoco"), ...) ## S3 method for class 'cca' sigma(object, type = c("response", "canoco"), ...) ## S3 method for class 'cca' vcov(object, type = "canoco", ...) ## S3 method for class 'cca' SSD(object, type = "canoco", ...) ## S3 method for class 'cca' qr(x, ...) ## S3 method for class 'cca' df.residual(object, ...)
model , object , x
|
A constrained ordination result object. |
type |
Type of statistics used for extracting raw residuals and
residual standard deviation ( |
... |
Other arguments to functions (ignored). |
The vegan algorithm for constrained ordination uses linear model
(or weighted linear model in cca
) to find the fitted
values of dependent community data, and constrained ordination is
based on this fitted response (Legendre & Legendre 2012). The
hatvalues
give the leverage values of these constraints,
and the leverage is independent on the response data. Other influence
statistics (rstandard
, rstudent
,
cooks.distance
) are based on leverage, and on the raw
residuals and residual standard deviation (sigma
). With
type = "response"
the raw residuals are given by the
unconstrained component of the constrained ordination, and influence
statistics are a matrix with dimensions no. of observations times
no. of species. For cca
the statistics are the same as
obtained from the lm
model using Chi-square standardized
species data (see decostand
) as dependent variable, and
row sums of community data as weights, and for rda
the
lm
model uses non-modified community data and no
weights.
The algorithm in the CANOCO software constraints the results during
iteration by performing a linear regression of weighted averages (WA)
scores on constraints and taking the fitted values of this regression
as linear combination (LC) scores (ter Braak 1984). The WA scores are
directly found from species scores, but LC scores are linear
combinations of constraints in the regression. With type =
"canoco"
the raw residuals are the differences of WA and LC scores,
and the residual standard deviation (sigma
) is taken to
be the axis sum of squared WA scores minus one. These quantities have
no relationship to residual component of ordination, but they rather
are methodological artefacts of an algorithm that is not used in
vegan. The result is a matrix with dimensions no. of
observations times no. of constrained axes.
Function vcov
returns the matrix of variances and
covariances of regression coefficients. The diagonal values of this
matrix are the variances, and their square roots give the standard
errors of regression coefficients. The function is based on
SSD
that extracts the sum of squares and crossproducts
of residuals. The residuals are defined similarly as in influence
measures and with each type
they have similar properties and
limitations, and define the dimensions of the result matrix.
Function as.mlm
casts an ordination object to a multiple
linear model of class "mlm"
(see lm
), and similar
statistics can be derived from that modified object as with this set
of functions. However, there are some problems in the R
implementation of the further analysis of multiple linear model
objects. When the results differ, the current set of functions is more
probable to be correct. The use of as.mlm
objects should be
avoided.
Jari Oksanen
Legendre, P. and Legendre, L. (2012) Numerical Ecology. 3rd English ed. Elsevier.
ter Braak, C.J.F. (1984–): CANOCO – a FORTRAN program for canonical community ordination by [partial] [detrended] [canonical] correspondence analysis, principal components analysis and redundancy analysis. TNO Inst. of Applied Computer Sci., Stat. Dept. Wageningen, The Netherlands.
Corresponding lm
methods and
as.mlm.cca
. Function ordiresids
provides
lattice graphics for residuals.
data(varespec, varechem) mod <- cca(varespec ~ Al + P + K, varechem) ## leverage hatvalues(mod) plot(hatvalues(mod), type = "h") ## ordination plot with leverages: points with high leverage have ## similar LC and WA scores plot(mod, type = "n") ordispider(mod) # segment from LC to WA scores points(mod, dis="si", cex=5*hatvalues(mod), pch=21, bg=2) # WA scores text(mod, dis="bp", col=4) ## deviation and influence head(rstandard(mod)) head(cooks.distance(mod)) ## Influence measures from lm y <- decostand(varespec, "chi.square") # needed in cca y1 <- with(y, Cladstel) # take one species for lm lmod1 <- lm(y1 ~ Al + P + K, varechem, weights = rowSums(varespec)) ## numerically identical within 2e-15 all(abs(cooks.distance(lmod1) - cooks.distance(mod)[, "Cladstel"]) < 1e-8) ## t-values of regression coefficients based on type = "canoco" ## residuals coef(mod) coef(mod)/sqrt(diag(vcov(mod, type = "canoco")))
data(varespec, varechem) mod <- cca(varespec ~ Al + P + K, varechem) ## leverage hatvalues(mod) plot(hatvalues(mod), type = "h") ## ordination plot with leverages: points with high leverage have ## similar LC and WA scores plot(mod, type = "n") ordispider(mod) # segment from LC to WA scores points(mod, dis="si", cex=5*hatvalues(mod), pch=21, bg=2) # WA scores text(mod, dis="bp", col=4) ## deviation and influence head(rstandard(mod)) head(cooks.distance(mod)) ## Influence measures from lm y <- decostand(varespec, "chi.square") # needed in cca y1 <- with(y, Cladstel) # take one species for lm lmod1 <- lm(y1 ~ Al + P + K, varechem, weights = rowSums(varespec)) ## numerically identical within 2e-15 all(abs(cooks.distance(lmod1) - cooks.distance(mod)[, "Cladstel"]) < 1e-8) ## t-values of regression coefficients based on type = "canoco" ## residuals coef(mod) coef(mod)/sqrt(diag(vcov(mod, type = "canoco")))
The function performs isometric feature mapping which consists of three simple steps: (1) retain only some of the shortest dissimilarities among objects, (2) estimate all dissimilarities as shortest path distances, and (3) perform metric scaling (Tenenbaum et al. 2000).
isomap(dist, ndim=10, ...) isomapdist(dist, epsilon, k, path = "shortest", fragmentedOK =FALSE, ...) ## S3 method for class 'isomap' summary(object, ...) ## S3 method for class 'isomap' plot(x, net = TRUE, n.col = "gray", type = "points", ...)
isomap(dist, ndim=10, ...) isomapdist(dist, epsilon, k, path = "shortest", fragmentedOK =FALSE, ...) ## S3 method for class 'isomap' summary(object, ...) ## S3 method for class 'isomap' plot(x, net = TRUE, n.col = "gray", type = "points", ...)
dist |
Dissimilarities. |
ndim |
Number of axes in metric scaling (argument |
epsilon |
Shortest dissimilarity retained. |
k |
Number of shortest dissimilarities retained for a point. If
both |
path |
Method used in |
fragmentedOK |
What to do if dissimilarity matrix is
fragmented. If |
x , object
|
An |
net |
Draw the net of retained dissimilarities. |
n.col |
Colour of drawn net segments. This can also be a vector that is recycled for points, and the colour of the net segment is a mixture of joined points. |
type |
Plot observations either as |
... |
Other parameters passed to functions. |
The function isomap
first calls function isomapdist
for
dissimilarity transformation, and then performs metric scaling for the
result. All arguments to isomap
are passed to
isomapdist
. The functions are separate so that the
isompadist
transformation could be easily used with other
functions than simple linear mapping of cmdscale
.
Function isomapdist
retains either dissimilarities equal or shorter to
epsilon
, or if epsilon
is not given, at least k
shortest dissimilarities for a point. Then a complete dissimilarity
matrix is reconstructed using stepacross
using either
flexible shortest paths or extended dissimilarities (for details, see
stepacross
).
De'ath (1999) actually published essentially the same method before
Tenenbaum et al. (2000), and De'ath's function is available in function
xdiss
in non-CRAN package mvpart. The differences are that
isomap
introduced the k
criterion, whereas De'ath only
used epsilon
criterion. In practice, De'ath also retains
higher proportion of dissimilarities than typical isomap
.
The plot
function uses internally ordiplot
,
except that it adds text over net using ordilabel
. The
plot
function passes extra arguments to these functions. In
addition, vegan3d package has function
rgl.isomap
to make dynamic 3D plots that can
be rotated on the screen.
Function isomapdist
returns a dissimilarity object similar to
dist
. Function isomap
returns an object of class
isomap
with plot
and summary
methods. The
plot
function returns invisibly an object of class
ordiplot
. Function scores
can extract
the ordination scores.
Tenenbaum et al. (2000) justify isomap
as a tool of unfolding a
manifold (e.g. a 'Swiss Roll'). Even with a manifold structure, the
sampling must be even and dense so
that dissimilarities along a manifold are shorter than across the
folds. If data do not have such a manifold structure, the results are
very sensitive to parameter values.
Jari Oksanen
De'ath, G. (1999) Extended dissimilarity: a method of robust estimation of ecological distances from high beta diversity data. Plant Ecology 144, 191–199
Tenenbaum, J.B., de Silva, V. & Langford, J.C. (2000) A global network framework for nonlinear dimensionality reduction. Science 290, 2319–2323.
The underlying functions that do the proper work are
stepacross
, distconnected
and
cmdscale
. Function metaMDS
may trigger
stepacross
transformation, but usually only for
longest dissimilarities. The plot
method of vegan
minimum spanning tree function (spantree
) has even
more extreme way of isomapping things.
## The following examples also overlay minimum spanning tree to ## the graphics in red. op <- par(mar=c(4,4,1,1)+0.2, mfrow=c(2,2)) data(BCI) dis <- vegdist(BCI) tr <- spantree(dis) pl <- ordiplot(cmdscale(dis), main="cmdscale") lines(tr, pl, col="red") ord <- isomap(dis, k=3) ord pl <- plot(ord, main="isomap k=3") lines(tr, pl, col="red") pl <- plot(isomap(dis, k=5), main="isomap k=5") lines(tr, pl, col="red") pl <- plot(isomap(dis, epsilon=0.45), main="isomap epsilon=0.45") lines(tr, pl, col="red") par(op) ## colour points and web by the dominant species dom <- apply(BCI, 1, which.max) ## need nine colours, but default palette has only eight op <- palette(c(palette("default"), "sienna")) plot(ord, pch = 16, col = dom, n.col = dom) palette(op)
## The following examples also overlay minimum spanning tree to ## the graphics in red. op <- par(mar=c(4,4,1,1)+0.2, mfrow=c(2,2)) data(BCI) dis <- vegdist(BCI) tr <- spantree(dis) pl <- ordiplot(cmdscale(dis), main="cmdscale") lines(tr, pl, col="red") ord <- isomap(dis, k=3) ord pl <- plot(ord, main="isomap k=3") lines(tr, pl, col="red") pl <- plot(isomap(dis, k=5), main="isomap k=5") lines(tr, pl, col="red") pl <- plot(isomap(dis, epsilon=0.45), main="isomap epsilon=0.45") lines(tr, pl, col="red") par(op) ## colour points and web by the dominant species dom <- apply(BCI, 1, which.max) ## need nine colours, but default palette has only eight op <- palette(c(palette("default"), "sienna")) plot(ord, pch = 16, col = dom, n.col = dom) palette(op)
Function kendall.global
computes and tests the coefficient of
concordance among several judges (variables, species) through a
permutation test.
Function kendall.post
carries out a posteriori tests
of the contributions of individual judges (variables, species) to
the overall concordance of their group through permutation tests.
If several groups of judges are identified in the data table,
coefficients of concordance (kendall.global
) or a posteriori
tests (kendall.post
) will be computed for each group
separately. Use in ecology: to identify significant species
associations.
kendall.global(Y, group, nperm = 999, mult = "holm") kendall.post(Y, group, nperm = 999, mult = "holm")
kendall.global(Y, group, nperm = 999, mult = "holm") kendall.post(Y, group, nperm = 999, mult = "holm")
Y |
Data file (data frame or matrix) containing quantitative or semiquantitative data. Rows are objects and columns are judges (variables). In community ecology, that table is often a site-by-species table. |
group |
A vector defining how judges should be divided into groups. See example below. If groups are not explicitly defined, all judges in the data file will be considered as forming a single group. |
nperm |
Number of permutations to be performed. Default is 999. |
mult |
Correct P-values for multiple testing using the
alternatives described in |
Y
must contain quantitative data. They will be transformed to
ranks within each column before computation of the coefficient of
concordance.
The search for species associations described in Legendre (2005) proceeds in 3 steps:
(1) Correlation analysis of the species. A possible method is to
compute Ward's agglomerative clustering of a matrix of correlations
among the species. In detail: (1.1) compute a Pearson or Spearman
correlation matrix (correl.matrix
) among the species; (1.2)
turn it into a distance matrix: mat.D = as.dist(1-correl.matrix)
;
(1.3) carry out Ward's hierarchical
clustering of that matrix using hclust
:
clust.ward = hclust(mat.D, "ward")
; (1.4) plot the dendrogram:
plot(clust.ward, hang=-1)
; (1.5) cut the dendrogram in two
groups, retrieve the vector of species membership:
group.2 = cutree(clust.ward, k=2)
. (1.6) After steps 2 and 3 below,
you may
have to come back and try divisions of the species into k =
groups.
(2) Compute global tests of significance of the 2 (or more) groups
using the function kendall.global
and the vector defining the
groups. Groups that are not globally significant must be refined or
abandoned.
(3) Compute a posteriori tests of the contribution of individual
species to the concordance of their group using the function
kendall.post
and the vector defining the groups. If some
species have negative values for "Spearman.mean", this means that
these species clearly do not belong to the group, hence that group
is too inclusive. Go back to (1.5) and cut the dendrogram more
finely. The left and right groups can be cut separately,
independently of the levels along the dendrogram; write your own
vector of group membership if cutree
does not produce the
desired groups.
The corrections used for multiple testing are applied to the list of
P-values (P); they take into account the number of tests (k) carried
out simultaneously (number of groups in kendall.global
, or
number of species in kendall.post
). The corrections are
performed using function p.adjust
; see that function
for the description of the correction methods. In addition, there is
Šidák correction which defined as
.
A table containing the following information in rows. The columns
correspond to the groups of "judges" defined in vector "group". When
function Kendall.post
is used, there are as many tables as
the number of predefined groups.
W |
Kendall's coefficient of concordance, W. |
F |
F statistic. F = W*(m-1)/(1-W) where m is the number of judges. |
Prob.F |
Probability associated with the F statistic, computed from the F distribution with nu1 = n-1-(2/m) and nu2 = nu1*(m-1); n is the number of objects. |
Corrected prob.F |
Probabilities associated with F, corrected
using the method selected in parameter |
Chi2 |
Friedman's chi-square statistic (Friedman 1937) used in the permutation test of W. |
Prob.perm |
Permutational probabilities, uncorrected. |
Corrected prob.perm |
Permutational probabilities corrected
using the method selected in parameter |
Spearman.mean |
Mean of the Spearman correlations between the judge under test and all the other judges in the same group. |
W.per.species |
Contribution of the judge under test to the overall concordance statistic for that group. |
F. Guillaume Blanchet, University of Alberta, and Pierre Legendre, Université de Montréal
Friedman, M. 1937. The use of ranks to avoid the assumption of normality implicit in the analysis of variance. Journal of the American Statistical Association 32: 675-701.
Kendall, M. G. and B. Babington Smith. 1939. The problem of m rankings. Annals of Mathematical Statistics 10: 275-287.
Legendre, P. 2005. Species associations: the Kendall coefficient of concordance revisited. Journal of Agricultural, Biological, and Environmental Statistics 10: 226-245.
Legendre, P. 2009. Coefficient of concordance. In: Encyclopedia of Research Design. SAGE Publications (in press).
Siegel, S. and N. J. Castellan, Jr. 1988. Nonparametric statistics for the behavioral sciences. 2nd edition. McGraw-Hill, New York.
cor
, friedman.test
,
hclust
, cutree
, kmeans
,
cascadeKM
.
data(mite) mite.hel <- decostand(mite, "hel") # Reproduce the results shown in Table 2 of Legendre (2005), a single group mite.small <- mite.hel[c(4,9,14,22,31,34,45,53,61,69),c(13:15,23)] kendall.global(mite.small, nperm=49) kendall.post(mite.small, mult="holm", nperm=49) # Reproduce the results shown in Tables 3 and 4 of Legendre (2005), 2 groups group <-c(1,1,2,1,1,1,1,1,2,1,1,1,1,1,1,2,1,2,1,1,1,1,2,1,2,1,1,1,1,1,2,2,2,2,2) kendall.global(mite.hel, group=group, nperm=49) kendall.post(mite.hel, group=group, mult="holm", nperm=49) # NOTE: 'nperm' argument usually needs to be larger than 49. # It was set to this low value for demonstration purposes.
data(mite) mite.hel <- decostand(mite, "hel") # Reproduce the results shown in Table 2 of Legendre (2005), a single group mite.small <- mite.hel[c(4,9,14,22,31,34,45,53,61,69),c(13:15,23)] kendall.global(mite.small, nperm=49) kendall.post(mite.small, mult="holm", nperm=49) # Reproduce the results shown in Tables 3 and 4 of Legendre (2005), 2 groups group <-c(1,1,2,1,1,1,1,1,2,1,1,1,1,1,1,2,1,2,1,1,1,1,2,1,2,1,1,1,1,1,2,2,2,2,2) kendall.global(mite.hel, group=group, nperm=49) kendall.post(mite.hel, group=group, mult="holm", nperm=49) # NOTE: 'nperm' argument usually needs to be larger than 49. # It was set to this low value for demonstration purposes.
Function linestack
plots vertical one-dimensional plots for
numeric vectors. The plots are always labelled, but the labels
are moved vertically to avoid overwriting.
linestack(x, labels, cex = 0.8, side = "right", hoff = 2, air = 1.1, at = 0, add = FALSE, axis = FALSE, ...)
linestack(x, labels, cex = 0.8, side = "right", hoff = 2, air = 1.1, at = 0, add = FALSE, axis = FALSE, ...)
x |
Numeric vector to be plotted. |
labels |
Labels used instead of default (names of |
cex |
Size of the labels. |
side |
Put labels to the |
hoff |
Distance from the vertical axis to the label in units of the width of letter “m”. |
air |
Multiplier to string height to leave empty space between labels. |
at |
Position of plot in horizontal axis. |
add |
Add to an existing plot. |
axis |
Add axis to the plot. |
... |
Other graphical parameters to labels. |
The function returns invisibly the shifted positions of labels in user coordinates.
The function always draws labelled diagrams. If you want to have
unlabelled diagrams, you can use, e.g., plot
,
stripchart
or rug
.
Jari Oksanen with modifications by Gavin L. Simpson
## First DCA axis data(dune) ord <- decorana(dune) linestack(scores(ord, choices=1, display="sp")) linestack(scores(ord, choices=1, display="si"), side="left", add=TRUE) title(main="DCA axis 1") ## Expressions as labels N <- 10 # Number of sites df <- data.frame(Ca = rlnorm(N, 2), NO3 = rlnorm(N, 4), SO4 = rlnorm(N, 10), K = rlnorm(N, 3)) ord <- rda(df, scale = TRUE) ### vector of expressions for labels labs <- expression(Ca^{2+phantom()}, NO[3]^{-phantom()}, SO[4]^{2-phantom()}, K^{+phantom()}) scl <- "sites" linestack(scores(ord, choices = 1, display = "species", scaling = scl), labels = labs, air = 2) linestack(scores(ord, choices = 1, display = "site", scaling = scl), side = "left", add = TRUE) title(main = "PCA axis 1")
## First DCA axis data(dune) ord <- decorana(dune) linestack(scores(ord, choices=1, display="sp")) linestack(scores(ord, choices=1, display="si"), side="left", add=TRUE) title(main="DCA axis 1") ## Expressions as labels N <- 10 # Number of sites df <- data.frame(Ca = rlnorm(N, 2), NO3 = rlnorm(N, 4), SO4 = rlnorm(N, 10), K = rlnorm(N, 3)) ord <- rda(df, scale = TRUE) ### vector of expressions for labels labs <- expression(Ca^{2+phantom()}, NO[3]^{-phantom()}, SO[4]^{2-phantom()}, K^{+phantom()}) scl <- "sites" linestack(scores(ord, choices = 1, display = "species", scaling = scl), labels = labs, air = 2) linestack(scores(ord, choices = 1, display = "site", scaling = scl), side = "left", add = TRUE) title(main = "PCA axis 1")
Function is based on abbreviate
, and will
take given number of characters from the first (genus) and last
(epithet) component of botanical or zoological Latin name and combine
these into one shorter character string. The names will be unique and
more characters will be used if needed. The default usage makes names
with 4+4 characters popularized in Cornell Ecology Programs (CEP) and
often known as CEP names. Abbreviated names are useful in ordination
plots and other graphics to reduce clutter.
make.cepnames(names, minlengths = c(4,4), seconditem = FALSE, uniqgenera = FALSE, named = FALSE, method)
make.cepnames(names, minlengths = c(4,4), seconditem = FALSE, uniqgenera = FALSE, named = FALSE, method)
names |
The names to be abbreviated into a vector abbreviated names. |
minlengths |
The minimum lengths of first and second part of the abbreviation. If abbreviations are not unique, the parts can be longer. |
seconditem |
Take always the second part of the original name to the abbreviated name instead of the last part. |
uniqgenera |
Should the first part of the abbreviation (genus) also be unique. Unique genus can take space from the second part (epithet). |
method |
The |
named |
Should the result vector be named by original
|
Cornell Ecology Programs (CEP) used eight-letter abbreviations
for species and site names. In species, the names were formed by
taking four first letters of the generic name and four first letters
of the specific or subspecific epithet. The current function produces
CEP names as default, but it can also use other lengths. The function
is based on abbreviate
and can produce longer names if
basic names are not unique. If generic name is shorter than specified
minimun length, more characters can be used by the epithet. If
uniqgenera = TRUE
genus can use more characters, and these
reduce the number of characters available for the epithet. The
function drops characters from the end, but with method =
"both.sides"
the function tries to drop characters from other
positions, starting with lower-case wovels, in the final attempt to
abbreviate abbreviations.
Function returns a vector of abbreviated names.
The function does not handle Author names except strictly
two-part names with seconditem = TRUE
. It is often useful to
edit abbreviations manually.
Jari Oksanen
names <- c("Aa maderoi", "Capsella bursa-pastoris", "Taraxacum", "Cladina rangiferina", "Cladonia rangiformis", "Cladonia cornuta", "Cladonia cornuta var. groenlandica", "Rumex acetosa", "Rumex acetosella") make.cepnames(names) make.cepnames(names, uniqgenera = TRUE) make.cepnames(names, method = "both.sides")
names <- c("Aa maderoi", "Capsella bursa-pastoris", "Taraxacum", "Cladina rangiferina", "Cladonia rangiformis", "Cladonia cornuta", "Cladonia cornuta var. groenlandica", "Rumex acetosa", "Rumex acetosella") make.cepnames(names) make.cepnames(names, uniqgenera = TRUE) make.cepnames(names, method = "both.sides")
Function mantel
finds the Mantel statistic as a matrix
correlation between two dissimilarity matrices, and function
mantel.partial
finds the partial Mantel statistic as the
partial matrix correlation between three dissimilarity matrices. The
significance of the statistic is evaluated by permuting rows and
columns of the first dissimilarity matrix.
mantel(xdis, ydis, method="pearson", permutations=999, strata = NULL, na.rm = FALSE, parallel = getOption("mc.cores")) mantel.partial(xdis, ydis, zdis, method = "pearson", permutations = 999, strata = NULL, na.rm = FALSE, parallel = getOption("mc.cores"))
mantel(xdis, ydis, method="pearson", permutations=999, strata = NULL, na.rm = FALSE, parallel = getOption("mc.cores")) mantel.partial(xdis, ydis, zdis, method = "pearson", permutations = 999, strata = NULL, na.rm = FALSE, parallel = getOption("mc.cores"))
xdis , ydis , zdis
|
Dissimilarity matrices or |
method |
Correlation method, as accepted by |
permutations |
a list of control values for the permutations
as returned by the function |
strata |
An integer vector or factor specifying the strata for permutation. If supplied, observations are permuted only within the specified strata. |
na.rm |
Remove missing values in calculation of Mantel correlation. Use this option with care: Permutation tests can be biased, in particular if two matrices had missing values in matching positions. |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
Mantel statistic is simply a correlation between entries of two
dissimilarity matrices (some use cross products, but these are
linearly related). However, the significance cannot be directly
assessed, because there are entries for just
observations. Mantel developed asymptotic test, but here we use
permutations of
rows and columns of dissimilarity
matrix. Only the first matrix (
xdist
) will be permuted, and
the second is kept constant. See permutations
for
additional details on permutation tests in Vegan.
Partial Mantel statistic uses partial correlation
conditioned on the third matrix. Only the first matrix is permuted so
that the correlation structure between second and first matrices is
kept constant. Although mantel.partial
silently accepts other
methods than "pearson"
, partial correlations will probably be
wrong with other methods.
Borcard & Legendre (2012) warn against using partial Mantel test and
recommend instead Mantel correlogram
(mantel.correlog
).
The function uses cor
, which should accept
alternatives pearson
for product moment correlations and
spearman
or kendall
for rank correlations.
The function returns a list of class mantel
with following
components:
Call |
Function call. |
method |
Correlation method used, as returned by
|
statistic |
The Mantel statistic. |
signif |
Empirical significance level from permutations. |
perm |
A vector of permuted values. The distribution of
permuted values can be inspected with |
permutations |
Number of permutations. |
control |
A list of control values for the permutations
as returned by the function |
Jari Oksanen
Borcard, D. & Legendre, P. (2012) Is the Mantel correlogram powerful enough to be useful in ecological analysis? A simulation study. Ecology 93: 1473-1481.
Legendre, P. and Legendre, L. (2012) Numerical Ecology. 3rd English Edition. Elsevier.
## Is vegetation related to environment? data(varespec) data(varechem) veg.dist <- vegdist(varespec) # Bray-Curtis env.dist <- vegdist(scale(varechem), "euclid") mantel(veg.dist, env.dist) mantel(veg.dist, env.dist, method="spear")
## Is vegetation related to environment? data(varespec) data(varechem) veg.dist <- vegdist(varespec) # Bray-Curtis env.dist <- vegdist(scale(varechem), "euclid") mantel(veg.dist, env.dist) mantel(veg.dist, env.dist, method="spear")
Function mantel.correlog
computes a multivariate
Mantel correlogram. Proposed by Sokal (1986) and Oden and Sokal
(1986), the method is also described in Legendre and Legendre (2012,
pp. 819–821) and tested and compared in Borcard and Legendere (2012).
mantel.correlog(D.eco, D.geo=NULL, XY=NULL, n.class=0, break.pts=NULL, cutoff=TRUE, r.type="pearson", nperm=999, mult="holm", progressive=TRUE) ## S3 method for class 'mantel.correlog' plot(x, alpha=0.05, ...)
mantel.correlog(D.eco, D.geo=NULL, XY=NULL, n.class=0, break.pts=NULL, cutoff=TRUE, r.type="pearson", nperm=999, mult="holm", progressive=TRUE) ## S3 method for class 'mantel.correlog' plot(x, alpha=0.05, ...)
D.eco |
An ecological distance matrix, with class
either |
D.geo |
A geographic distance matrix, with class either
|
XY |
A file of Cartesian geographic coordinates of the
points. Default: |
n.class |
Number of classes. If |
break.pts |
Vector containing the break points of the distance
distribution. Provide (n.class+1) breakpoints, that is, a list with
a beginning and an ending point. Default: |
cutoff |
For the second half of the distance classes,
|
r.type |
Type of correlation in calculation of the Mantel
statistic. Default: |
nperm |
Number of permutations for the tests of
significance. Default: |
mult |
Correct P-values for multiple testing. The correction
methods are |
progressive |
Default: |
x |
Output of |
alpha |
Significance level for the points drawn with black
symbols in the correlogram. Default: |
... |
Other parameters passed from other functions. |
A correlogram is a graph in which spatial correlation values
are plotted, on the ordinate, as a function of the geographic distance
classes among the study sites along the abscissa. In a Mantel
correlogram, a Mantel correlation (Mantel 1967) is computed between a
multivariate (e.g. multi-species) distance matrix of the user's choice
and a design matrix representing each of the geographic distance
classes in turn. The Mantel statistic is tested through a
permutational Mantel test performed by vegan
's
mantel
function.
Borcard and Legendre (2012) show that the testing method in the
Mantel correlogram has correct type I error and power, contrary to
the simple and partial Mantel tests so often used by ecologists and
geneticists in spatial analysis (see mantel.partial
).
They also show that the test in Mantel correlograms is the same test
as used by Wagner (2004) in multiscale ordination
(mso
), and that it is closely related to the Geary’s
test in univariate correlograms.
When a correction for multiple testing is applied, more permutations
are necessary than in the no-correction case, to obtain significant
-values in the higher correlogram classes.
The print.mantel.correlog
function prints out the
correlogram. See examples.
mantel.res |
A table with the distance classes as rows and the
class indices, number of distances per class, Mantel statistics
(computed using Pearson's r, Spearman's r, or Kendall's tau), and
p-values as columns. A positive Mantel statistic indicates positive
spatial correlation. An additional column with p-values corrected for
multiple testing is added unless |
n.class |
The n umber of distance classes. |
break.pts |
The break points provided by the user or computed by the program. |
mult |
The name of the correction for multiple testing. No
correction: |
progressive |
A logical ( |
n.tests |
The number of distance classes for which Mantel tests have been computed and tested for significance. |
call |
The function call. |
Pierre Legendre, Université de Montréal
Borcard, D. & P. Legendre. 2012. Is the Mantel correlogram powerful enough to be useful in ecological analysis? A simulation study. Ecology 93: 1473-1481.
Legendre, P. and L. Legendre. 2012. Numerical ecology, 3rd English edition. Elsevier Science BV, Amsterdam.
Mantel, N. 1967. The detection of disease clustering and a generalized regression approach. Cancer Res. 27: 209-220.
Oden, N. L. and R. R. Sokal. 1986. Directional autocorrelation: an extension of spatial correlograms to two dimensions. Syst. Zool. 35: 608-617.
Sokal, R. R. 1986. Spatial data analysis and historical processes. 29-43 in: E. Diday et al. [eds.] Data analysis and informatics, IV. North-Holland, Amsterdam.
Sturges, H. A. 1926. The choice of a class interval. Journal of the American Statistical Association 21: 65–66.
Wagner, H.H. 2004. Direct multi-scale ordination with canonical correspondence analysis. Ecology 85: 342-351.
# Mite data available in "vegan" data(mite) data(mite.xy) mite.hel <- decostand(mite, "hellinger") # Detrend the species data by regression on the site coordinates mite.hel.resid <- resid(lm(as.matrix(mite.hel) ~ ., data=mite.xy)) # Compute the detrended species distance matrix mite.hel.D <- dist(mite.hel.resid) # Compute Mantel correlogram with cutoff, Pearson statistic mite.correlog <- mantel.correlog(mite.hel.D, XY=mite.xy, nperm=49) summary(mite.correlog) mite.correlog # or: print(mite.correlog) # or: print.mantel.correlog(mite.correlog) plot(mite.correlog) # Compute Mantel correlogram without cutoff, Spearman statistic mite.correlog2 <- mantel.correlog(mite.hel.D, XY=mite.xy, cutoff=FALSE, r.type="spearman", nperm=49) summary(mite.correlog2) mite.correlog2 plot(mite.correlog2) # NOTE: 'nperm' argument usually needs to be larger than 49. # It was set to this low value for demonstration purposes.
# Mite data available in "vegan" data(mite) data(mite.xy) mite.hel <- decostand(mite, "hellinger") # Detrend the species data by regression on the site coordinates mite.hel.resid <- resid(lm(as.matrix(mite.hel) ~ ., data=mite.xy)) # Compute the detrended species distance matrix mite.hel.D <- dist(mite.hel.resid) # Compute Mantel correlogram with cutoff, Pearson statistic mite.correlog <- mantel.correlog(mite.hel.D, XY=mite.xy, nperm=49) summary(mite.correlog) mite.correlog # or: print(mite.correlog) # or: print.mantel.correlog(mite.correlog) plot(mite.correlog) # Compute Mantel correlogram without cutoff, Spearman statistic mite.correlog2 <- mantel.correlog(mite.hel.D, XY=mite.xy, cutoff=FALSE, r.type="spearman", nperm=49) summary(mite.correlog2) mite.correlog2 plot(mite.correlog2) # NOTE: 'nperm' argument usually needs to be larger than 49. # It was set to this low value for demonstration purposes.
Add new points to an existing metaMDS
or
monoMDS
ordination.
MDSaddpoints(nmds, dis, neighbours = 5, maxit = 200) dist2xy(dist, pick, type = c("xy", "xx"), invert = FALSE)
MDSaddpoints(nmds, dis, neighbours = 5, maxit = 200) dist2xy(dist, pick, type = c("xy", "xx"), invert = FALSE)
nmds |
Result object from |
dis |
Rectangular non-symmetric dissimilarity matrix among new
points (rows) and old fixed points (columns). Such matrix can be
extracted from complete dissimilarities of both old and new points
with |
neighbours |
Number of nearest points used to get the starting locations for new points. |
maxit |
Maximum number of iterations. |
dist |
Input dissimilarities. |
pick |
Indices (integers) of selected observations or a logical
vector that is |
type |
|
invert |
Invert |
Function provides an interface to monoMDS
Fortran code to add new
points to an existing ordination that will be regarded as fixed. The
function has a similar role as predict
functions with
newdata
in Euclidean ordination (e.g. predict.cca
).
Input data must be a rectangular matrix of distances among new added
points (rows) and all fixed old points (columns). Such matrices can be
extracted from complete dissimilarities with helper function
dist2xy
. Function designdist2
can directly
calculate such rectangular dissimilarity matrices between sampling units
(rows) in two matries. In addition, analogue has distance
function that can calculate dissimilarities among two matrices,
including functions that cannot be specified in
designdist2
.
Great care is needed in preparing the dissimilarities for the input. The dissimilarity index must be exactly the same as in the fixed ordination, and columns must match old fixed points, and rows added new points.
Function return a list of class "nmds"
(there are no other
objects of that type in vegan) with following elements
points |
Coordinates of added new points |
seeds |
Starting coordinates for new points. |
deltastress |
Change of stress with added points. |
iters |
Number of iterations. |
cause |
Cause of termination of iterations. Integer for
convergence criteria in |
## Cross-validation: remove a point when performing NMDS and add as ## a new points data(dune) d <- vegdist(dune) ## remove point 3 from ordination mod3 <- metaMDS(dist2xy(d, 3, "xx", invert = TRUE), trace=0) ## add point 3 to the result MDSaddpoints(mod3, dist2xy(d, 3)) ## Use designdist2 d15 <- designdist(dune[1:15,]) m15 <- metaMDS(d15, trace=0) MDSaddpoints(m15, designdist2(dune[1:15,], dune[16:20,]))
## Cross-validation: remove a point when performing NMDS and add as ## a new points data(dune) d <- vegdist(dune) ## remove point 3 from ordination mod3 <- metaMDS(dist2xy(d, 3, "xx", invert = TRUE), trace=0) ## add point 3 to the result MDSaddpoints(mod3, dist2xy(d, 3)) ## Use designdist2 d15 <- designdist(dune[1:15,]) m15 <- metaMDS(d15, trace=0) MDSaddpoints(m15, designdist2(dune[1:15,], dune[16:20,]))
Function rotates a multidimensional scaling result so
that its first dimension is parallel to an external (environmental
variable). The function can handle the results from
metaMDS
or monoMDS
functions.
MDSrotate(object, vec, na.rm = FALSE, ...)
MDSrotate(object, vec, na.rm = FALSE, ...)
object |
|
vec |
An environmental variable or a matrix of such
variables. The number of variables must be lower than the number
of dimensions, and the solution is rotated to these variables in
the order they appear in the matrix. Alternatively |
na.rm |
Remove missing values from the continuous variable
|
... |
Other arguments (ignored). |
The orientation and rotation are undefined in multidimensional
scaling. Functions metaMDS
and metaMDS
can rotate their solutions to principal components so that the
dispersion of the points is highest on the first dimension. Sometimes
a different rotation is more intuitive, and MDSrotate
allows
rotation of the result so that the first axis is parallel to a given
external variable or two first variables are completely in a
two-dimensional plane etc. If several external variables are supplied,
they are applied in the order they are in the matrix. First axis is
rotated to the first supplied variable, and the second axis to the
second variable. Because variables are usually correlated, the second
variable is not usually aligned with the second axis, but it is
uncorrelated to later dimensions. There must be at least one free
dimension: the number of external variables must be lower than the
number of dimensions, and all used environmental variables are
uncorrelated with that free dimension.
Alternatively the method can rotate to discriminate the levels of a
factor using linear discriminant analysis
(lda
). This is hardly meaningful for
two-dimensional solutions, since all rotations in two dimensions
have the same separation of cluster levels. However, the function
can be useful in finding a two-dimensional projection of clusters
from more than two dimensions. The last dimension will always show
the residual variation, and for dimensions, only
discrimination vectors are used.
Function returns the original ordination result, but with
rotated scores (both site and species if available), and the
pc
attribute of scores set to FALSE
.
Rotation to a factor variable is an experimental feature and may
be removed. The discriminant analysis weights dimensions by their
discriminating power, but MDSrotate
performs a rigid
rotation. Therefore the solution may not be optimal.
Jari Oksanen
data(varespec) data(varechem) mod <- monoMDS(vegdist(varespec)) mod <- with(varechem, MDSrotate(mod, pH)) plot(mod) ef <- envfit(mod ~ pH, varechem, permutations = 0) plot(ef) ordisurf(mod ~ pH, varechem, knots = 1, add = TRUE)
data(varespec) data(varechem) mod <- monoMDS(vegdist(varespec)) mod <- with(varechem, MDSrotate(mod, pH)) plot(mod) ef <- envfit(mod ~ pH, varechem, permutations = 0) plot(ef) ordisurf(mod ~ pH, varechem, knots = 1, add = TRUE)
Function metaMDS
performs Nonmetric
Multidimensional Scaling (NMDS), and tries to find a stable solution
using several random starts. In addition, it standardizes the
scaling in the result, so that the configurations are easier to
interpret, and adds species scores to the site ordination. The
metaMDS
function does not provide actual NMDS, but it calls
another function for the purpose. Currently monoMDS
is
the default choice, and it is also possible to call the
isoMDS
(MASS package).
metaMDS(comm, distance = "bray", k = 2, try = 20, trymax = 20, engine = c("monoMDS", "isoMDS"), autotransform =TRUE, noshare = (engine == "isoMDS"), wascores = TRUE, expand = TRUE, trace = 1, plot = FALSE, previous.best, ...) ## S3 method for class 'metaMDS' plot(x, display = c("sites", "species"), choices = c(1, 2), type = "p", shrink = FALSE, cex = 0.7, ...) ## S3 method for class 'metaMDS' points(x, display = c("sites", "species"), choices = c(1,2), shrink = FALSE, select, cex = 0.7, ...) ## S3 method for class 'metaMDS' text(x, display = c("sites", "species"), labels, choices = c(1,2), shrink = FALSE, select, cex = 0.7, ...) ## S3 method for class 'metaMDS' scores(x, display = c("sites", "species"), shrink = FALSE, choices, tidy = FALSE, ...) metaMDSdist(comm, distance = "bray", autotransform = TRUE, noshare = TRUE, trace = 1, commname, zerodist = "ignore", distfun = vegdist, ...) metaMDSiter(dist, k = 2, try = 20, trymax = 20, trace = 1, plot = FALSE, previous.best, engine = "monoMDS", maxit = 200, parallel = getOption("mc.cores"), ...) initMDS(x, k=2) postMDS(X, dist, pc=TRUE, center=TRUE, halfchange, threshold=0.8, nthreshold=10, plot=FALSE, ...) metaMDSredist(object, ...)
metaMDS(comm, distance = "bray", k = 2, try = 20, trymax = 20, engine = c("monoMDS", "isoMDS"), autotransform =TRUE, noshare = (engine == "isoMDS"), wascores = TRUE, expand = TRUE, trace = 1, plot = FALSE, previous.best, ...) ## S3 method for class 'metaMDS' plot(x, display = c("sites", "species"), choices = c(1, 2), type = "p", shrink = FALSE, cex = 0.7, ...) ## S3 method for class 'metaMDS' points(x, display = c("sites", "species"), choices = c(1,2), shrink = FALSE, select, cex = 0.7, ...) ## S3 method for class 'metaMDS' text(x, display = c("sites", "species"), labels, choices = c(1,2), shrink = FALSE, select, cex = 0.7, ...) ## S3 method for class 'metaMDS' scores(x, display = c("sites", "species"), shrink = FALSE, choices, tidy = FALSE, ...) metaMDSdist(comm, distance = "bray", autotransform = TRUE, noshare = TRUE, trace = 1, commname, zerodist = "ignore", distfun = vegdist, ...) metaMDSiter(dist, k = 2, try = 20, trymax = 20, trace = 1, plot = FALSE, previous.best, engine = "monoMDS", maxit = 200, parallel = getOption("mc.cores"), ...) initMDS(x, k=2) postMDS(X, dist, pc=TRUE, center=TRUE, halfchange, threshold=0.8, nthreshold=10, plot=FALSE, ...) metaMDSredist(object, ...)
comm |
Community data. Alternatively, dissimilarities either as
a |
distance |
Dissimilarity index used in |
k |
Number of dimensions. NB., the number of points |
try , trymax
|
Minimum and maximum numbers of random starts in
search of stable solution. After |
engine |
The function used for MDS. The default is to use the
|
autotransform |
Use simple heuristics for possible data
transformation of typical community data (see below). If you do
not have community data, you should probably set
|
noshare |
Triggering of calculation step-across or extended
dissimilarities with function |
wascores |
Calculate species scores using function
|
expand |
Expand weighted averages of species in
|
trace |
Trace the function; |
plot |
Graphical tracing: plot interim results. You may want to set
|
previous.best |
Start searches from a previous solution. This can
also be a |
x |
|
choices |
Axes shown. |
type |
Plot type: |
display |
Display |
shrink |
Shrink back species scores if they were expanded originally. |
cex |
Character expansion for plotting symbols. |
tidy |
Return scores that are compatible with ggplot2:
all scores are in a single |
labels |
Optional test to be used instead of row names. |
select |
Items to be displayed. This can either be a logical
vector which is |
X |
Configuration from multidimensional scaling. |
commname |
The name of |
zerodist |
Handling of zero dissimilarities: either
|
distfun |
Dissimilarity function. Any function returning a
|
maxit |
Maximum number of iterations in the single NMDS run;
passed to the |
parallel |
Number of parallel processes or a predefined socket
cluster. If you use pre-defined socket clusters (say,
|
dist |
Dissimilarity matrix used in multidimensional scaling. |
pc |
Rotate to principal components. |
center |
Centre the configuration. |
halfchange |
Scale axes to half-change units. This defaults
|
threshold |
Largest dissimilarity used in half-change scaling. If
dissimilarities have a known (or inferred) ceiling, |
nthreshold |
Minimum number of points in half-change scaling. |
object |
A result object from |
... |
Other parameters passed to functions. Function
|
Non-metric Multidimensional Scaling (NMDS) is commonly
regarded as the most robust unconstrained ordination method in
community ecology (Minchin 1987). Function metaMDS
is a
wrapper function that calls several other functions to combine
Minchin's (1987) recommendations into one command. The complete
steps in metaMDS
are:
Transformation: If the data values are larger than common
abundance class scales, the function performs a Wisconsin double
standardization (wisconsin
). If the values look
very large, the function also performs sqrt
transformation. Both of these standardizations are generally found
to improve the results. However, the limits are completely
arbitrary (at present, data maximum 50 triggers sqrt
and triggers
wisconsin
). If you want to
have a full control of the analysis, you should set
autotransform = FALSE
and standardize and transform data
independently. The autotransform
is intended for community
data, and for other data types, you should set
autotransform = FALSE
. This step is perfomed using
metaMDSdist
, and the step is skipped if input were
dissimilarities.
Choice of dissimilarity: For a good result, you should use
dissimilarity indices that have a good rank order relation to
ordering sites along gradients (Faith et al. 1987). The default
is Bray-Curtis dissimilarity, because it often is the test
winner. However, any other dissimilarity index in
vegdist
can be used. Function
rankindex
can be used for finding the test winner
for you data and gradients. The default choice may be bad if you
analyse other than community data, and you should probably select
an appropriate index using argument distance
. This step is
performed using metaMDSdist
, and the step is skipped if
input were dissimilarities.
Step-across dissimilarities: Ordination may be very difficult
if a large proportion of sites have no shared species. In this
case, the results may be improved with stepacross
dissimilarities, or flexible shortest paths among all sites. The
default NMDS engine
is monoMDS
which is able
to break tied values at the maximum dissimilarity, and this often
is sufficient to handle cases with no shared species, and
therefore the default is not to use stepacross
with
monoMDS
. Function isoMDS
does
not handle tied values adequately, and therefore the default is to
use stepacross
always when there are sites with no
shared species with engine = "isoMDS"
. The
stepacross
is triggered by option noshare
. If
you do not like manipulation of original distances, you should set
noshare = FALSE
. This step is skipped if input data were
dissimilarities instead of community data. This step is performed
using metaMDSdist
, and the step is skipped always when
input were dissimilarities.
NMDS with random starts: NMDS easily gets trapped into local
optima, and you must start NMDS several times from random starts
to be confident that you have found the global solution. The
strategy in metaMDS
is to first run NMDS starting with the
metric scaling (cmdscale
which usually finds a good
solution but often close to a local optimum), or use the
previous.best
solution if supplied, and take its solution
as the standard (Run 0
). Then metaMDS
starts NMDS
from several random starts (minimum number is given by try
and maximum number by trymax
). These random starts are
generated by initMDS
. If a solution is better (has a lower
stress) than the previous standard, it is taken as the new
standard. If the solution is better or close to a standard,
metaMDS
compares two solutions using Procrustes analysis
(function procrustes
with option
symmetric = TRUE
). If the solutions are very similar in their
Procrustes rmse
and the largest residual is very small, the
solutions are regarded as repeated and the better one is taken
as the new standard. The conditions are stringent, and you may
have found good and relatively similar solutions although the
function is not yet satisfied. Setting trace = TRUE
will
monitor the final stresses, and plot = TRUE
will display
Procrustes overlay plots from each comparison. This step is
performed using metaMDSiter
. This is the first step
performed if input data (comm
) were dissimilarities. Random
starts can be run with parallel processing (argument
parallel
).
Scaling of the results: metaMDS
will run postMDS
for the final result. Function postMDS
provides the
following ways of “fixing” the indeterminacy of scaling and
orientation of axes in NMDS: Centring moves the origin to the
average of the axes; Principal components rotate the configuration
so that the variance of points is maximized on first dimension
(with function MDSrotate
you can alternatively
rotate the configuration so that the first axis is parallel to an
environmental variable); Half-change scaling scales the
configuration so that one unit means halving of community
similarity from replicate similarity. Half-change scaling is
based on closer dissimilarities where the relation between
ordination distance and community dissimilarity is rather linear
(the limit is set by argument threshold
). If there are
enough points below this threshold (controlled by the parameter
nthreshold
), dissimilarities are regressed on distances.
The intercept of this regression is taken as the replicate
dissimilarity, and half-change is the distance where similarity
halves according to linear regression. Obviously the method is
applicable only for dissimilarity indices scaled to , such as Kulczynski, Bray-Curtis and Canberra indices. If
half-change scaling is not used, the ordination is scaled to the
same range as the original dissimilarities. Half-change scaling is
skipped by default if input were dissimilarities, but can be
turned on with argument
halfchange = TRUE
. NB., The PC
rotation only changes the directions of reference axes, and it
does not influence the configuration or solution in general.
Species scores: Function adds the species scores to the final
solution as weighted averages using function
wascores
with given value of parameter
expand
. The expansion of weighted averages can be undone
with shrink = TRUE
in plot
or scores
functions, and the calculation of species scores can be suppressed
with wascores = FALSE
. This step is skipped if input were
dissimilarities and community data were unavailable. However, the
species scores can be added or replaced with
sppscores
.
Function metaMDS
returns an object of class
metaMDS
. The final site ordination is stored in the item
points
, and species ordination in the item species
,
and the stress in item stress
(NB, the scaling of the stress
depends on the engine
: isoMDS
uses
percents, and monoMDS
proportions in the range ). The other items store the information on the steps taken
and the items returned by the
engine
function. The object has
print
, plot
, points
and text
methods.
Functions metaMDSdist
and metaMDSredist
return
vegdist
objects. Function initMDS
returns a
random configuration which is intended to be used within
isoMDS
only. Functions metaMDSiter
and
postMDS
returns the result of NMDS with updated
configuration.
Non-linear optimization is a hard task, and the best possible solution
(“global optimum”) may not be found from a random starting
configuration. Most software solve this by starting from the result of
metric scaling (cmdscale
). This will probably give a
good result, but not necessarily the “global
optimum”. Vegan does the same, but metaMDS
tries to
verify or improve this first solution (“try 0”) using several
random starts and seeing if the result can be repeated or improved and
the improved solution repeated. If this does not succeed, you get a
message that the result could not be repeated. However, the result
will be at least as good as the usual standard strategy of starting
from metric scaling or it may be improved. You may not need to do
anything after such a message, but you can be satisfied with the
result. If you want to be sure that you probably have a “global
optimum” you may try the following instructions.
With default engine = "monoMDS"
the function will
tabulate the stopping criteria used, so that you can see which
criterion should be made more stringent. The criteria can be given
as arguments to metaMDS
and their current values are
described in monoMDS
. In particular, if you reach
the maximum number of iterations, you should increase the value of
maxit
. You may ask for a larger number of random starts
without losing the old ones giving the previous solution in
argument previous.best
.
In addition to slack convergence criteria and too low number
of random starts, wrong number of dimensions (argument k
)
is the most common reason for not being able to repeat similar
solutions. NMDS is usually run with a low number dimensions
(k=2
or k=3
), and for complex data increasing
k
by one may help. If you run NMDS with much higher number
of dimensions (say, k=10
or more), you should reconsider
what you are doing and drastically reduce k
. For very
heterogeneous data sets with partial disjunctions, it may help to
set stepacross
, but for most data sets the default
weakties = TRUE
is sufficient.
Please note that you can give all arguments of other
metaMDS*
functions and NMDS engine (default
monoMDS
) in your metaMDS
command,and you
should check documentation of these functions for details.
NMDS is often misunderstood and wrong claims of its properties are common on the Web and even in publications. It is often claimed that the NMDS configuration is non-metric which means that you cannot fit environmental variables or species onto that space. This is a false statement. In fact, the result configuration of NMDS is metric, and it can be used like any other ordination result. In NMDS the rank orders of Euclidean distances among points in ordination have a non-metric monotone relationship to any observed dissimilarities. The transfer function from observed dissimilarities to ordination distances is non-metric (Kruskal 1964a, 1964b), but the ordination result configuration is metric and observed dissimilarities can be of any kind (metric or non-metric).
The ordination configuration is usually rotated to principal
components in metaMDS
. The rotation is performed after
finding the result, and it only changes the direction of the
reference axes. The only important feature in the NMDS solution are
the ordination distances, and these do not change in
rotation. Similarly, the rank order of distances does not change in
uniform scaling or centring of configuration of points. You can also
rotate the NMDS solution to external environmental variables with
MDSrotate
. This rotation will also only change the
orientation of axes, but will not change the configuration of points
or distances between points in ordination space.
Function stressplot
displays the method graphically:
it plots the observed dissimilarities against distances in
ordination space, and also shows the non-metric monotone
regression.
metaMDS
uses monoMDS
as its
NMDS engine
from vegan version 2.0-0, when it replaced
the isoMDS
function. You can set argument
engine
to select the old engine.
Function metaMDS
is a simple wrapper for an NMDS engine
(either monoMDS
or isoMDS
) and
some support functions (metaMDSdist
,
stepacross
, metaMDSiter
, initMDS
,
postMDS
, wascores
). You can call these support
functions separately for better control of results. Data
transformation, dissimilarities and possible
stepacross
are made in function metaMDSdist
which returns a dissimilarity result. Iterative search (with
starting values from initMDS
with monoMDS
) is
made in metaMDSiter
. Processing of result configuration is
done in postMDS
, and species scores added by
wascores
. If you want to be more certain of reaching
a global solution, you can compare results from several independent
runs. You can also continue analysis from previous results or from
your own configuration. Function may not save the used
dissimilarity matrix (monoMDS
does), but
metaMDSredist
tries to reconstruct the used dissimilarities
with original data transformation and possible
stepacross
.
The metaMDS
function was designed to be used with community
data. If you have other type of data, you should probably set some
arguments to non-default values: probably at least wascores
,
autotransform
and noshare
should be FALSE
. If
you have negative data entries, metaMDS
will set the previous
to FALSE
with a warning.
Jari Oksanen
Faith, D. P, Minchin, P. R. and Belbin, L. (1987). Compositional dissimilarity as a robust measure of ecological distance. Vegetatio 69, 57–68.
Kruskal, J.B. (1964a). Multidimensional scaling by optimizing goodness-of-fit to a nonmetric hypothesis. Psychometrika 29, 1–28.
Kruskal, J.B. (1964b). Nonmetric multidimensional scaling: a numerical method. Psychometrika 29, 115–129.
Minchin, P.R. (1987). An evaluation of relative robustness of techniques for ecological ordinations. Vegetatio 69, 89–107.
monoMDS
(and isoMDS
),
decostand
, wisconsin
,
vegdist
, rankindex
, stepacross
,
procrustes
, wascores
, sppscores
,
MDSrotate
, ordiplot
, stressplot
.
## The recommended way of running NMDS (Minchin 1987) ## data(dune) ## IGNORE_RDIFF_BEGIN ## Global NMDS using monoMDS sol <- metaMDS(dune) sol plot(sol, type="t") ## Start from previous best solution sol <- metaMDS(dune, previous.best = sol) ## Local NMDS and stress 2 of monoMDS sol2 <- metaMDS(dune, model = "local", stress=2) sol2 ## Use Arrhenius exponent 'z' as a binary dissimilarity measure sol <- metaMDS(dune, distfun = betadiver, distance = "z") sol ## IGNORE_RDIFF_END
## The recommended way of running NMDS (Minchin 1987) ## data(dune) ## IGNORE_RDIFF_BEGIN ## Global NMDS using monoMDS sol <- metaMDS(dune) sol plot(sol, type="t") ## Start from previous best solution sol <- metaMDS(dune, previous.best = sol) ## Local NMDS and stress 2 of monoMDS sol2 <- metaMDS(dune, model = "local", stress=2) sol2 ## Use Arrhenius exponent 'z' as a binary dissimilarity measure sol <- metaMDS(dune, distfun = betadiver, distance = "z") sol ## IGNORE_RDIFF_END
Oribatid mite data. 70 soil cores collected by Daniel Borcard in 1989. See Borcard et al. (1992, 1994) for details.
data(mite) data(mite.env) data(mite.pcnm) data(mite.xy)
data(mite) data(mite.env) data(mite.pcnm) data(mite.xy)
There are three linked data sets: mite
that contains the data
on 35 species of Oribatid mites, mite.env
that contains
environmental data in the same sampling sites, mite.xy
that contains geographic coordinates, and mite.pcnm
that contains 22 PCNM base functions (columns) computed from the geographic
coordinates of the 70 sampling sites (Borcard & Legendre 2002).
The whole sampling area was 2.5 m x 10 m in size.
The fields in the environmental data are:
Substrate density (g/L)
Water content of the substrate (g/L)
Substrate type, factor with levels Sphagn1,
Sphagn2 Sphagn3 Sphagn Litter Barepeat Interface
Shrub density, an ordered factor with levels 1
<
2
< 3
Microtopography, a factor with levels Blanket
and Hummock
Pierre Legendre
Borcard, D., P. Legendre and P. Drapeau. 1992. Partialling out the spatial component of ecological variation. Ecology 73: 1045-1055.
Borcard, D. and P. Legendre. 1994. Environmental control and spatial structure in ecological communities: an example using Oribatid mites (Acari, Oribatei). Environmental and Ecological Statistics 1: 37-61.
Borcard, D. and P. Legendre. 2002. All-scale spatial analysis of ecological data by means of principal coordinates of neighbour matrices. Ecological Modelling 153: 51-68.
data(mite)
data(mite)
Function implements Kruskal's (1964a,b) non-metric multidimensional scaling (NMDS) using monotone regression and primary (“weak”) treatment of ties. In addition to traditional global NMDS, the function implements local NMDS, linear and hybrid multidimensional scaling.
monoMDS(dist, y, k = 2, model = c("global", "local", "linear", "hybrid"), threshold = 0.8, maxit = 200, weakties = TRUE, stress = 1, scaling = TRUE, pc = TRUE, smin = 1e-4, sfgrmin = 1e-7, sratmax=0.999999, ...) ## S3 method for class 'monoMDS' scores(x, display = "sites", shrink = FALSE, choices, tidy = FALSE, ...) ## S3 method for class 'monoMDS' plot(x, display = "sites", choices = c(1,2), type = "t", ...) ## S3 method for class 'monoMDS' points(x, choices = c(1,2), select, ...) ## S3 method for class 'monoMDS' text(x, labels, choices = c(1,2), select, ...)
monoMDS(dist, y, k = 2, model = c("global", "local", "linear", "hybrid"), threshold = 0.8, maxit = 200, weakties = TRUE, stress = 1, scaling = TRUE, pc = TRUE, smin = 1e-4, sfgrmin = 1e-7, sratmax=0.999999, ...) ## S3 method for class 'monoMDS' scores(x, display = "sites", shrink = FALSE, choices, tidy = FALSE, ...) ## S3 method for class 'monoMDS' plot(x, display = "sites", choices = c(1,2), type = "t", ...) ## S3 method for class 'monoMDS' points(x, choices = c(1,2), select, ...) ## S3 method for class 'monoMDS' text(x, labels, choices = c(1,2), select, ...)
dist |
Input dissimilarities. |
y |
Starting configuration. A random configuration will be generated if this is missing. |
k |
Number of dimensions. NB., the number of points |
model |
MDS model: |
threshold |
Dissimilarity below which linear regression is used alternately with monotone regression. |
maxit |
Maximum number of iterations. |
weakties |
Use primary or weak tie treatment, where equal
observed dissimilarities are allowed to have different fitted
values. if |
stress |
Use stress type 1 or 2 (see Details). |
scaling |
Scale final scores to unit root mean squares. |
pc |
Rotate final scores to principal components. |
smin , sfgrmin , sratmax
|
Convergence criteria: iterations stop
when stress drops below |
x |
A |
display |
Kind of scores. Normally there are only scores for
|
shrink |
Shrink back species scores if they were expanded in
|
tidy |
Return scores that are compatible with ggplot2:
all scores are in a single |
choices |
Dimensions returned or plotted. The default |
type |
The type of the plot: |
select |
Items to be displayed. This can either be a logical
vector which is |
labels |
Labels to be use used instead of row names. |
... |
Other parameters to the functions (ignored in
|
There are several versions of non-metric multidimensional
scaling in R, but monoMDS
offers the following unique
combination of features:
“Weak” treatment of ties (Kruskal 1964a,b), where tied dissimilarities can be broken in monotone regression. This is especially important for cases where compared sites share no species and dissimilarities are tied to their maximum value of one. Breaking ties allows these points to be at different distances and can help in recovering very long coenoclines (gradients). Functions in the smacof package also hav adequate tie treatment.
Handles missing values in a meaningful way.
Offers “local” and “hybrid” scaling in addition to usual “global” NMDS (see below).
Uses fast compiled code (isoMDS
of the
MASS package also uses compiled code).
Function monoMDS
uses Kruskal's (1964b) original monotone
regression to minimize the stress. There are two alternatives of
stress: Kruskal's (1964a,b) original or “stress 1” and an
alternative version or “stress 2” (Sibson 1972). Both of
these stresses can be expressed with a general formula
where are distances among points in ordination configuration,
are the fitted ordination distances, and
are the ordination distances under null model. For
“stress 1”
, and for “stress 2”
or mean distances. “Stress 2”
can be expressed as
,
where
is squared correlation between fitted values and
ordination distances, and so related to the “linear fit” of
stressplot
.
Function monoMDS
can fit several alternative NMDS variants that
can be selected with argument model
. The default model =
"global"
fits global NMDS, or Kruskal's (1964a,b) original NMDS
similar to isoMDS
(MASS). Alternative
model = "local"
fits local NMDS where independent monotone
regression is used for each point (Sibson 1972). Alternative
model = "linear"
fits a linear MDS. This fits a linear
regression instead of monotone, and is not identical to metric scaling
or principal coordinates analysis (cmdscale
) that
performs an eigenvector decomposition of dissimilarities (Gower
1966). Alternative model = "hybrid"
implements hybrid MDS that
uses monotone regression for all points and linear regression for
dissimilarities below or at a threshold
dissimilarity in
alternating steps (Faith et al. 1987). Function
stressplot
can be used to display the kind of regression
in each model
.
Scaling, orientation and direction of the axes is arbitrary.
However, the function always centres the axes, and the default
scaling
is to scale the configuration of unit root mean
square and to rotate the axes (argument pc
) to principal
components so that the first dimension shows the major variation.
It is possible to rotate the solution so that the first axis is
parallel to a given environmental variable using function
MDSrotate
.
Returns an object of class "monoMDS"
. The final scores
are returned in item points
(function scores
extracts
these results), and the stress in item stress
. In addition,
there is a large number of other items (but these may change without
notice in the future releases). There are no species scores, but these
can be added with sppscores
function.
NMDS is iterative, and the function stops when any of its
convergence criteria is met. There is actually no criterion of
assured convergence, and any solution can be a local optimum. You
should compare several random starts (or use monoMDS
via
metaMDS
) to assess if the solutions is likely a global
optimum.
The stopping criteria are:
maxit
: Maximum number of iterations. Reaching this
criterion means that solutions was almost certainly not found,
and maxit
should be increased.
smin
: Minimum stress. If stress is nearly zero,
the fit is almost perfect. Usually this means that data set is
too small for the requested analysis, and there may be several
different solutions that are almost as perfect. You should reduce
the number of dimensions (k
), get more data (more
observations) or use some other method, such as metric scaling
(cmdscale
, wcmdscale
).
sratmax
:Change in stress. Values close to one mean almost unchanged stress. This may mean a solution, but it can also signal stranding on suboptimal solution with flat stress surface.
sfgrmin
:Minimum scale factor. Values close to zero mean almost unchanged configuration. This may mean a solution, but will also happen in local optima.
This is the default NMDS function used in
metaMDS
. Function metaMDS
adds support
functions so that NMDS can be run like recommended by Minchin
(1987).
Peter R. Michin (Fortran core) and Jari Oksanen (R interface).
Faith, D.P., Minchin, P.R and Belbin, L. 1987. Compositional dissimilarity as a robust measure of ecological distance. Vegetatio 69, 57–68.
Gower, J.C. (1966). Some distance properties of latent root and vector methods used in multivariate analysis. Biometrika 53, 325–328.
Kruskal, J.B. 1964a. Multidimensional scaling by optimizing goodness-of-fit to a nonmetric hypothesis. Psychometrika 29, 1–28.
Kruskal, J.B. 1964b. Nonmetric multidimensional scaling: a numerical method. Psychometrika 29, 115–129.
Minchin, P.R. 1987. An evaluation of relative robustness of techniques for ecological ordinations. Vegetatio 69, 89–107.
Sibson, R. 1972. Order invariant methods for data analysis. Journal of the Royal Statistical Society B 34, 311–349.
metaMDS
for the vegan way of running NMDS,
and isoMDS
and smacof for some
alternative implementations of NMDS.
data(dune) dis <- vegdist(dune) m <- monoMDS(dis, model = "loc") m plot(m)
data(dune) dis <- vegdist(dune) m <- monoMDS(dis, model = "loc") m plot(m)
Mitchell-Olds & Shaw test concerns the location of the highest (hump)
or lowest (pit) value of a quadratic curve at given points. Typically,
it is used to study whether the quadratic hump or pit is located
within a studied interval. The current test is generalized so that it
applies generalized linear models (glm
) with link
function instead of simple quadratic curve. The test was popularized
in ecology for the analysis of humped species richness patterns
(Mittelbach et al. 2001), but it is more general. With logarithmic
link function, the quadratic response defines the Gaussian response
model of ecological gradients (ter Braak & Looman 1986), and the test
can be used for inspecting the location of Gaussian optimum within a
given range of the gradient. It can also be used to replace Tokeshi's
test of “bimodal” species frequency distribution.
MOStest(x, y, interval, ...) ## S3 method for class 'MOStest' plot(x, which = c(1,2,3,6), ...) fieller.MOStest(object, level = 0.95) ## S3 method for class 'MOStest' profile(fitted, alpha = 0.01, maxsteps = 10, del = zmax/5, ...) ## S3 method for class 'MOStest' confint(object, parm = 1, level = 0.95, ...)
MOStest(x, y, interval, ...) ## S3 method for class 'MOStest' plot(x, which = c(1,2,3,6), ...) fieller.MOStest(object, level = 0.95) ## S3 method for class 'MOStest' profile(fitted, alpha = 0.01, maxsteps = 10, del = zmax/5, ...) ## S3 method for class 'MOStest' confint(object, parm = 1, level = 0.95, ...)
x |
The independent variable or plotting object in |
y |
The dependent variable. |
interval |
The two points at which the test statistic is
evaluated. If missing, the extremes of |
which |
Subset of plots produced. Values |
object , fitted
|
A result object from |
level |
The confidence level required. |
alpha |
Maximum significance level allowed. |
maxsteps |
Maximum number of steps in the profile. |
del |
A step length parameter for the profile (see code). |
parm |
Ignored. |
... |
Other variables passed to functions. Function
|
The function fits a quadratic curve with given
family
and link function. If , this defines a unimodal curve with highest point at
(ter Braak & Looman 1986). If
, the
parabola has a minimum at
and the response is sometimes
called “bimodal”. The null hypothesis is that the extreme
point
is located within the interval given by points
and
. If the extreme point
is exactly at
, then
on shifted axis
. In the
test, origin of
x
is shifted to the values and
, and the test statistic is based on the differences of
deviances between the original model and model where the origin is
forced to the given location using the standard
anova.glm
function (Oksanen et al. 2001).
Mitchell-Olds & Shaw (1987) used the first degree coefficient with
its significance as estimated by the summary.glm
function. This give identical results with Normal error, but for
other error distributions it is preferable to use the test based on
differences in deviances in fitted models.
The test is often presented as a general test for the location of the hump, but it really is dependent on the quadratic fitted curve. If the hump is of different form than quadratic, the test may be insignificant.
Because of strong assumptions in the test, you should use the support
functions to inspect the fit. Function plot(..., which=1)
displays the data points, fitted quadratic model, and its approximate
95% confidence intervals (2 times SE). Function plot
with
which = 2
displays the approximate confidence interval of
the polynomial coefficients, together with two lines indicating the
combinations of the coefficients that produce the evaluated points of
x
. Moreover, the cross-hair shows the approximate confidence
intervals for the polynomial coefficients ignoring their
correlations. Higher values of which
produce corresponding
graphs from plot.lm
. That is, you must add 2 to the
value of which
in plot.lm
.
Function fieller.MOStest
approximates the confidence limits
of the location of the extreme point (hump or pit) using Fieller's
theorem following ter Braak & Looman (1986). The test is based on
quasideviance except if the family
is poisson
or binomial
. Function profile
evaluates the profile
deviance of the fitted model, and confint
finds the profile
based confidence limits following Oksanen et al. (2001).
The test is typically used in assessing the significance of diversity hump against productivity gradient (Mittelbach et al. 2001). It also can be used for the location of the pit (deepest points) instead of the Tokeshi test. Further, it can be used to test the location of the the Gaussian optimum in ecological gradient analysis (ter Braak & Looman 1986, Oksanen et al. 2001).
The function is based on glm
, and it returns the result
of object of glm
amended with the result of the test. The new
items in the MOStest
are:
isHump |
|
isBracketed |
|
hump |
Sorted vector of location of the hump or the pit and the points where the test was evaluated. |
coefficients |
Table of test statistics and their significances. |
Function fieller.MOStest
is based on package optgrad in
the Ecological Archives
(https://figshare.com/articles/dataset/Full_Archive/3521975)
accompanying Oksanen et al. (2001). The Ecological Archive package
optgrad also contains profile deviance method for the location
of the hump or pit, but the current implementation of profile
and confint
rather follow the example of
profile.glm
and confint.glm
in
the MASS package.
Jari Oksanen
Mitchell-Olds, T. & Shaw, R.G. 1987. Regression analysis of natural selection: statistical inference and biological interpretation. Evolution 41, 1149–1161.
Mittelbach, G.C. Steiner, C.F., Scheiner, S.M., Gross, K.L., Reynolds, H.L., Waide, R.B., Willig, R.M., Dodson, S.I. & Gough, L. 2001. What is the observed relationship between species richness and productivity? Ecology 82, 2381–2396.
Oksanen, J., Läärä, E., Tolonen, K. & Warner, B.G. 2001. Confidence intervals for the optimum in the Gaussian response function. Ecology 82, 1191–1197.
ter Braak, C.J.F & Looman, C.W.N 1986. Weighted averaging, logistic regression and the Gaussian response model. Vegetatio 65, 3–11.
The no-interaction model can be fitted with humpfit
.
## The Al-Mufti data analysed in humpfit(): mass <- c(140,230,310,310,400,510,610,670,860,900,1050,1160,1900,2480) spno <- c(1, 4, 3, 9, 18, 30, 20, 14, 3, 2, 3, 2, 5, 2) mod <- MOStest(mass, spno) ## Insignificant mod ## ... but inadequate shape of the curve op <- par(mfrow=c(2,2), mar=c(4,4,1,1)+.1) plot(mod) ## Looks rather like log-link with Poisson error and logarithmic biomass mod <- MOStest(log(mass), spno, family=quasipoisson) mod plot(mod) par(op) ## Confidence Limits fieller.MOStest(mod) confint(mod) plot(profile(mod))
## The Al-Mufti data analysed in humpfit(): mass <- c(140,230,310,310,400,510,610,670,860,900,1050,1160,1900,2480) spno <- c(1, 4, 3, 9, 18, 30, 20, 14, 3, 2, 3, 2, 5, 2) mod <- MOStest(mass, spno) ## Insignificant mod ## ... but inadequate shape of the curve op <- par(mfrow=c(2,2), mar=c(4,4,1,1)+.1) plot(mod) ## Looks rather like log-link with Poisson error and logarithmic biomass mod <- MOStest(log(mass), spno, family=quasipoisson) mod plot(mod) par(op) ## Confidence Limits fieller.MOStest(mod) confint(mod) plot(profile(mod))
Multiple Response Permutation Procedure (MRPP) provides a
test of whether there is a significant difference between two or more
groups of sampling units. Function meandist
finds the mean within
and between block dissimilarities.
mrpp(dat, grouping, permutations = 999, distance = "euclidean", weight.type = 1, strata = NULL, parallel = getOption("mc.cores")) meandist(dist, grouping, ...) ## S3 method for class 'meandist' summary(object, ...) ## S3 method for class 'meandist' plot(x, kind = c("dendrogram", "histogram"), cluster = "average", ylim, axes = TRUE, ...)
mrpp(dat, grouping, permutations = 999, distance = "euclidean", weight.type = 1, strata = NULL, parallel = getOption("mc.cores")) meandist(dist, grouping, ...) ## S3 method for class 'meandist' summary(object, ...) ## S3 method for class 'meandist' plot(x, kind = c("dendrogram", "histogram"), cluster = "average", ylim, axes = TRUE, ...)
dat |
data matrix or data frame in which rows are samples and columns are response variable(s), or a dissimilarity object or a symmetric square matrix of dissimilarities. |
grouping |
Factor or numeric index for grouping observations. |
permutations |
a list of control values for the permutations
as returned by the function |
distance |
Choice of distance metric that measures the
dissimilarity between two observations . See |
weight.type |
choice of group weights. See Details below for options. |
strata |
An integer vector or factor specifying the strata for permutation. If supplied, observations are permuted only within the specified strata. |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
dist |
A |
.
object , x
|
A |
kind |
Draw a dendrogram or a histogram; see Details. |
cluster |
A clustering method for the |
ylim |
Limits for vertical axes (optional). |
axes |
Draw scale for the vertical axis. |
... |
Further arguments passed to functions. |
Multiple Response Permutation Procedure (MRPP) provides a test of
whether there is a significant difference between two or more groups
of sampling units. This difference may be one of location (differences
in mean) or one of spread (differences in within-group distance;
cf. Warton et al. 2012). Function mrpp
operates on a
data.frame
matrix where rows are observations and responses
data matrix. The response(s) may be uni- or multivariate. The method
is philosophically and mathematically allied with analysis of
variance, in that it compares dissimilarities within and among
groups. If two groups of sampling units are really different (e.g. in
their species composition), then average of the within-group
compositional dissimilarities ought to be less than the average of the
dissimilarities between two random collection of sampling units drawn
from the entire population.
The mrpp statistic is the overall weighted mean of
within-group means of the pairwise dissimilarities among sampling
units. The choice of group weights is currently not clear. The
mrpp
function offers three choices: (1) group size (),
(2) a degrees-of-freedom analogue (
), and (3) a weight that
is the number of unique distances calculated among
sampling
units (
).
The mrpp
algorithm first calculates all pairwise distances in
the entire dataset, then calculates . It then permutes the
sampling units and their associated pairwise distances, and
recalculates
based on the permuted data. It repeats the
permutation step
permutations
times. The significance test is
the fraction of permuted deltas that are less than the observed delta,
with a small sample correction. The function also calculates the
change-corrected within-group agreement ,
where
is the expected
assessed as the
average of dissimilarities.
If the first argument dat
can be interpreted as
dissimilarities, they will be used directly. In other cases the
function treats dat
as observations, and uses
vegdist
to find the dissimilarities. The default
distance
is Euclidean as in the traditional use of the method,
but other dissimilarities in vegdist
also are available.
Function meandist
calculates a matrix of mean within-cluster
dissimilarities (diagonal) and between-cluster dissimilarities
(off-diagonal elements), and an attribute n
of grouping
counts. Function summary
finds the within-class, between-class
and overall means of these dissimilarities, and the MRPP statistics
with all weight.type
options and the Classification Strength,
CS (Van Sickle and Hughes, 2000). CS is defined for dissimilarities as
, where
is the
mean between cluster dissimilarity and
is the mean
within cluster dissimilarity with
weight.type = 1
. The function
does not perform significance tests for these statistics, but you must
use mrpp
with appropriate weight.type
. There is
currently no significance test for CS, but mrpp
with
weight.type = 1
gives the correct test for
and a good approximation for CS. Function
plot
draws a
dendrogram or a histogram of the result matrix based on the
within-group and between group dissimilarities. The dendrogram is
found with the method given in the cluster
argument using
function hclust
. The terminal segments hang to
within-cluster dissimilarity. If some of the clusters are more
heterogeneous than the combined class, the leaf segment are reversed.
The histograms are based on dissimilarities, but ore otherwise similar
to those of Van Sickle and Hughes (2000): horizontal line is drawn at
the level of mean between-cluster dissimilarity and vertical lines
connect within-cluster dissimilarities to this line.
The function returns a list of class mrpp with following items:
call |
Function call. |
delta |
The overall weighted mean of group mean distances. |
E.delta |
expected delta, under the null hypothesis of no group structure. This is the mean of original dissimilarities. |
CS |
Classification strength (Van Sickle and Hughes,
2000). Currently not implemented and always |
n |
Number of observations in each class. |
classdelta |
Mean dissimilarities within classes. The overall
|
.
Pvalue |
Significance of the test. |
A |
A chance-corrected estimate of the proportion of the distances explained by group identity; a value analogous to a coefficient of determination in a linear model. |
distance |
Choice of distance metric used; the "method" entry of the dist object. |
weight.type |
The choice of group weights used. |
boot.deltas |
The vector of "permuted deltas," the deltas
calculated from each of the permuted datasets. The distribution of
this item can be inspected with |
permutations |
The number of permutations used. |
control |
A list of control values for the permutations
as returned by the function |
This difference may be one of location (differences in mean) or one of
spread (differences in within-group distance). That is, it may find a
significant difference between two groups simply because one of those
groups has a greater dissimilarities among its sampling units. Most
mrpp
models can be analysed with adonis2
which seems
not suffer from the same problems as mrpp
and is a more robust
alternative.
M. Henry H. Stevens [email protected] and Jari Oksanen.
B. McCune and J. B. Grace. 2002. Analysis of Ecological Communities. MjM Software Design, Gleneden Beach, Oregon, USA.
P. W. Mielke and K. J. Berry. 2001. Permutation Methods: A Distance Function Approach. Springer Series in Statistics. Springer.
J. Van Sickle and R. M. Hughes 2000. Classification strengths of ecoregions, catchments, and geographic clusters of aquatic vertebrates in Oregon. J. N. Am. Benthol. Soc. 19:370–384.
Warton, D.I., Wright, T.W., Wang, Y. 2012. Distance-based multivariate analyses confound location and dispersion effects. Methods in Ecology and Evolution, 3, 89–101
anosim
for a similar test based on ranks, and
mantel
for comparing dissimilarities against continuous
variables, and
vegdist
for obtaining dissimilarities,
adonis2
is a more robust alternative in most cases.
data(dune) data(dune.env) dune.mrpp <- with(dune.env, mrpp(dune, Management)) dune.mrpp # Save and change plotting parameters def.par <- par(no.readonly = TRUE) layout(matrix(1:2,nr=1)) plot(dune.ord <- metaMDS(dune, trace=0), type="text", display="sites" ) with(dune.env, ordihull(dune.ord, Management)) with(dune.mrpp, { fig.dist <- hist(boot.deltas, xlim=range(c(delta,boot.deltas)), main="Test of Differences Among Groups") abline(v=delta); text(delta, 2*mean(fig.dist$counts), adj = -0.5, expression(bold(delta)), cex=1.5 ) } ) par(def.par) ## meandist dune.md <- with(dune.env, meandist(vegdist(dune), Management)) dune.md summary(dune.md) plot(dune.md) plot(dune.md, kind="histogram")
data(dune) data(dune.env) dune.mrpp <- with(dune.env, mrpp(dune, Management)) dune.mrpp # Save and change plotting parameters def.par <- par(no.readonly = TRUE) layout(matrix(1:2,nr=1)) plot(dune.ord <- metaMDS(dune, trace=0), type="text", display="sites" ) with(dune.env, ordihull(dune.ord, Management)) with(dune.mrpp, { fig.dist <- hist(boot.deltas, xlim=range(c(delta,boot.deltas)), main="Test of Differences Among Groups") abline(v=delta); text(delta, 2*mean(fig.dist$counts), adj = -0.5, expression(bold(delta)), cex=1.5 ) } ) par(def.par) ## meandist dune.md <- with(dune.env, meandist(vegdist(dune), Management)) dune.md summary(dune.md) plot(dune.md) plot(dune.md, kind="histogram")
The function mso
adds an attribute vario
to
an object of class "cca"
that describes the spatial
partitioning of the cca
object and performs an optional
permutation test for the spatial independence of residuals. The
function plot.mso
creates a diagnostic plot of the spatial
partitioning of the "cca"
object.
mso(object.cca, object.xy, grain = 1, round.up = FALSE, permutations = 0) msoplot(x, alpha = 0.05, explained = FALSE, ylim = NULL, legend = "topleft", ...)
mso(object.cca, object.xy, grain = 1, round.up = FALSE, permutations = 0) msoplot(x, alpha = 0.05, explained = FALSE, ylim = NULL, legend = "topleft", ...)
object.cca |
|
object.xy |
A vector, matrix or data frame with the spatial
coordinates of the data represented by |
grain |
Interval size for distance classes. |
round.up |
Determines the choice of breaks. If false, distances are rounded to the nearest multiple of grain. If true, distances are rounded to the upper multiple of grain. |
permutations |
a list of control values for the permutations
as returned by the function |
x |
A result object of |
alpha |
Significance level for the two-sided permutation test of the Mantel statistic for spatial independence of residual inertia and for the point-wise envelope of the variogram of the total variance. A Bonferroni-type correction can be achieved by dividing the overall significance value (e.g. 0.05) by the number of distance classes. |
explained |
If false, suppresses the plotting of the variogram of explained variance. |
ylim |
Limits for y-axis. |
legend |
The x and y co-ordinates to be used to position the legend.
They can be specified by keyword or in any way which is accepted
by |
... |
Other arguments passed to functions. |
The Mantel test is an adaptation of the function
mantel
to the parallel testing of several distance
classes and similar to multivariate mantel.correlog
.
It compares the mean inertia in each distance class to the pooled
mean inertia of all other distance classes.
If there are explanatory variables (RDA, CCA, pRDA, pCCA) and a
significance test for residual autocorrelation was performed when
running the function mso
, the function plot.mso
will
print an estimate of how much the autocorrelation (based on
significant distance classes) causes the global error variance of the
regression analysis to be underestimated
The function mso
returns an amended cca
or rda
object with the additional attributes grain
, H
,
H.test
and vario
.
grain |
The grain attribute defines the interval size of the distance classes . |
H |
H is an object of class 'dist' and contains the geographic distances between observations. |
H.test |
H.test contains a set of dummy variables that describe
which pairs of observations (rows = elements of |
vario |
The vario attribute is a data frame that contains some or all of the following components for the rda case (cca case in brackets):
|
The function is based on the code published in the Ecological Archives E085-006 (doi:10.1890/02-0738).
The responsible author was Helene Wagner.
Wagner, H.H. 2004. Direct multi-scale ordination with canonical correspondence analysis. Ecology 85: 342–351.
## Reconstruct worked example of Wagner (submitted): X <- matrix(c(1, 2, 3, 2, 1, 0), 3, 2) Y <- c(3, -1, -2) tmat <- c(1:3) ## Canonical correspondence analysis (cca): Example.cca <- cca(X, Y) Example.cca <- mso(Example.cca, tmat) msoplot(Example.cca) Example.cca$vario ## Correspondence analysis (ca): Example.ca <- mso(cca(X), tmat) msoplot(Example.ca) ## Unconstrained ordination with test for autocorrelation ## using oribatid mite data set as in Wagner (2004) data(mite) data(mite.env) data(mite.xy) mite.cca <- cca(log(mite + 1)) mite.cca <- mso(mite.cca, mite.xy, grain = 1, permutations = 99) msoplot(mite.cca) mite.cca ## Constrained ordination with test for residual autocorrelation ## and scale-invariance of species-environment relationships mite.cca <- cca(log(mite + 1) ~ SubsDens + WatrCont + Substrate + Shrub + Topo, mite.env) mite.cca <- mso(mite.cca, mite.xy, permutations = 99) msoplot(mite.cca) mite.cca
## Reconstruct worked example of Wagner (submitted): X <- matrix(c(1, 2, 3, 2, 1, 0), 3, 2) Y <- c(3, -1, -2) tmat <- c(1:3) ## Canonical correspondence analysis (cca): Example.cca <- cca(X, Y) Example.cca <- mso(Example.cca, tmat) msoplot(Example.cca) Example.cca$vario ## Correspondence analysis (ca): Example.ca <- mso(cca(X), tmat) msoplot(Example.ca) ## Unconstrained ordination with test for autocorrelation ## using oribatid mite data set as in Wagner (2004) data(mite) data(mite.env) data(mite.xy) mite.cca <- cca(log(mite + 1)) mite.cca <- mso(mite.cca, mite.xy, grain = 1, permutations = 99) msoplot(mite.cca) mite.cca ## Constrained ordination with test for residual autocorrelation ## and scale-invariance of species-environment relationships mite.cca <- cca(log(mite + 1) ~ SubsDens + WatrCont + Substrate + Shrub + Topo, mite.env) mite.cca <- mso(mite.cca, mite.xy, permutations = 99) msoplot(mite.cca) mite.cca
In multiplicative diversity partitioning, mean values of alpha diversity at lower levels of a sampling hierarchy are compared to the total diversity in the entire data set or the pooled samples (gamma diversity).
multipart(...) ## Default S3 method: multipart(y, x, index=c("renyi", "tsallis"), scales = 1, global = FALSE, relative = FALSE, nsimul=99, method = "r2dtable", ...) ## S3 method for class 'formula' multipart(formula, data, index=c("renyi", "tsallis"), scales = 1, global = FALSE, relative = FALSE, nsimul=99, method = "r2dtable", ...)
multipart(...) ## Default S3 method: multipart(y, x, index=c("renyi", "tsallis"), scales = 1, global = FALSE, relative = FALSE, nsimul=99, method = "r2dtable", ...) ## S3 method for class 'formula' multipart(formula, data, index=c("renyi", "tsallis"), scales = 1, global = FALSE, relative = FALSE, nsimul=99, method = "r2dtable", ...)
y |
A community matrix. |
x |
A matrix with same number of rows as in |
formula |
A two sided model formula in the form |
data |
A data frame where to look for variables defined in the
right hand side of |
index |
Character, the entropy index to be calculated (see Details). |
relative |
Logical, if |
scales |
Numeric, of length 1, the order of the generalized diversity index to be used. |
global |
Logical, indicates the calculation of beta diversity values, see Details. |
nsimul |
Number of permutations to use. If |
method |
Null model method: either a name (character string) of
a method defined in |
... |
Other arguments passed to |
Multiplicative diversity partitioning is based on Whittaker's (1972) ideas, that has recently been generalised to one parametric diversity families (i.e. Rényi and Tsallis) by Jost (2006, 2007). Jost recommends to use the numbers equivalents (Hill numbers), instead of pure diversities, and proofs, that this satisfies the multiplicative partitioning requirements.
The current implementation of multipart
calculates Hill numbers
based on the functions renyi
and tsallis
(provided as index
argument).
If values for more than one scales
are desired,
it should be done in separate runs, because it adds extra dimensionality
to the implementation, which has not been resolved efficiently.
Alpha diversities are then the averages of these Hill numbers for
each hierarchy levels, the global gamma diversity is the alpha value
calculated for the highest hierarchy level.
When global = TRUE
, beta is calculated relative to the global gamma value:
when global = FALSE
, beta is calculated relative to local
gamma values (local gamma means the diversity calculated for a particular
cluster based on the pooled abundance vector):
where is a particular cluster at hierarchy level
.
Then beta diversity value for level
is the mean of the beta
values of the clusters at that level,
.
If relative = TRUE
, the respective beta diversity values are
standardized by their maximum possible values ()
given as
(the number of lower level units
in a given cluster
).
The expected diversity components are calculated nsimul
times by individual based randomization of the community data matrix.
This is done by the "r2dtable"
method in oecosimu
by default.
An object of class "multipart"
with same structure as
"oecosimu"
objects.
Péter Sólymos, [email protected]
Jost, L. (2006). Entropy and diversity. Oikos, 113, 363–375.
Jost, L. (2007). Partitioning diversity into independent alpha and beta components. Ecology, 88, 2427–2439.
Whittaker, R. (1972). Evolution and measurement of species diversity. Taxon, 21, 213–251.
See adipart
for additive diversity partitioning,
hiersimu
for hierarchical null model testing
and oecosimu
for permutation settings and calculating -values.
## NOTE: 'nsimul' argument usually needs to be >= 99 ## here much lower value is used for demonstration data(mite) data(mite.xy) data(mite.env) ## Function to get equal area partitions of the mite data cutter <- function (x, cut = seq(0, 10, by = 2.5)) { out <- rep(1, length(x)) for (i in 2:(length(cut) - 1)) out[which(x > cut[i] & x <= cut[(i + 1)])] <- i return(out)} ## The hierarchy of sample aggregation levsm <- with(mite.xy, data.frame( l2=cutter(y, cut = seq(0, 10, by = 2.5)), l3=cutter(y, cut = seq(0, 10, by = 5)))) ## Multiplicative diversity partitioning multipart(mite, levsm, index="renyi", scales=1, nsimul=19) multipart(mite ~ l2 + l3, levsm, index="renyi", scales=1, nsimul=19) multipart(mite ~ ., levsm, index="renyi", scales=1, nsimul=19, relative=TRUE) multipart(mite ~ ., levsm, index="renyi", scales=1, nsimul=19, global=TRUE)
## NOTE: 'nsimul' argument usually needs to be >= 99 ## here much lower value is used for demonstration data(mite) data(mite.xy) data(mite.env) ## Function to get equal area partitions of the mite data cutter <- function (x, cut = seq(0, 10, by = 2.5)) { out <- rep(1, length(x)) for (i in 2:(length(cut) - 1)) out[which(x > cut[i] & x <= cut[(i + 1)])] <- i return(out)} ## The hierarchy of sample aggregation levsm <- with(mite.xy, data.frame( l2=cutter(y, cut = seq(0, 10, by = 2.5)), l3=cutter(y, cut = seq(0, 10, by = 5)))) ## Multiplicative diversity partitioning multipart(mite, levsm, index="renyi", scales=1, nsimul=19) multipart(mite ~ l2 + l3, levsm, index="renyi", scales=1, nsimul=19) multipart(mite ~ ., levsm, index="renyi", scales=1, nsimul=19, relative=TRUE) multipart(mite ~ ., levsm, index="renyi", scales=1, nsimul=19, global=TRUE)
Patches or local communities are regarded as nested if they all could be subsets of the same community. In general, species poor communities should be subsets of species rich communities, and rare species should only occur in species rich communities.
nestedchecker(comm) nestedn0(comm) nesteddisc(comm, niter = 200) nestedtemp(comm, ...) nestednodf(comm, order = TRUE, weighted = FALSE, wbinary = FALSE) nestedbetasor(comm) nestedbetajac(comm) ## S3 method for class 'nestedtemp' plot(x, kind = c("temperature", "incidence"), col=rev(heat.colors(100)), names = FALSE, ...) ## S3 method for class 'nestednodf' plot(x, col = "red", names = FALSE, ...)
nestedchecker(comm) nestedn0(comm) nesteddisc(comm, niter = 200) nestedtemp(comm, ...) nestednodf(comm, order = TRUE, weighted = FALSE, wbinary = FALSE) nestedbetasor(comm) nestedbetajac(comm) ## S3 method for class 'nestedtemp' plot(x, kind = c("temperature", "incidence"), col=rev(heat.colors(100)), names = FALSE, ...) ## S3 method for class 'nestednodf' plot(x, col = "red", names = FALSE, ...)
comm |
Community data. |
niter |
Number of iterations to reorder tied columns. |
x |
Result object for a |
col |
Colour scheme for matrix temperatures. |
kind |
The kind of plot produced. |
names |
Label columns and rows in the plot using names in |
order |
Order rows and columns by frequencies. |
weighted |
Use species abundances as weights of interactions. |
wbinary |
Modify original method so that binary data give the same result in weighted and and unweighted analysis. |
... |
Other arguments to functions. |
The nestedness functions evaluate alternative indices of nestedness.
The functions are intended to be used together with Null model
communities and used as an argument in oecosimu
to analyse
the non-randomness of results.
Function nestedchecker
gives the number of checkerboard units,
or 2x2 submatrices where both species occur once but on different
sites (Stone & Roberts 1990).
Function nestedn0
implements
nestedness measure N0 which is the number of absences from the sites
which are richer than the most pauperate site species occurs
(Patterson & Atmar 1986).
Function nesteddisc
implements discrepancy index which is the
number of ones that should be shifted to fill a row with ones in a
table arranged by species frequencies (Brualdi & Sanderson
1999). The original definition arranges species (columns) by their
frequencies, but did not have any method of handling tied
frequencies. The nesteddisc
function tries to order tied
columns to minimize the discrepancy statistic but this is rather
slow, and with a large number of tied columns there is no guarantee
that the best ordering was found (argument niter
gives the
maximum number of tried orders). In that case a warning of tied
columns will be issued.
Function nestedtemp
finds the matrix temperature which is
defined as the sum of “surprises” in arranged matrix. In
arranged unsurprising matrix all species within proportion given by
matrix fill are in the upper left corner of the matrix, and the
surprise of the absence or presences is the diagonal distance from the
fill line (Atmar & Patterson 1993). Function tries to pack species and
sites to a low temperature (Rodríguez-Gironés
& Santamaria 2006), but this is an iterative procedure, and the
temperatures usually vary among runs. Function nestedtemp
also
has a plot
method which can display either incidences or
temperatures of the surprises. Matrix temperature was rather vaguely
described (Atmar & Patterson 1993), but
Rodríguez-Gironés & Santamaria (2006) are
more explicit and their description is used here. However, the results
probably differ from other implementations, and users should be
cautious in interpreting the results. The details of calculations are
explained in the vignette
Design decisions and
implementation that you can read using functions
browseVignettes
. Function
nestedness
in the bipartite package is
a direct port of the BINMATNEST programme of
Rodríguez-Gironés & Santamaria (2006).
Function nestednodf
implements a nestedness metric based on
overlap and decreasing fill (Almeida-Neto et al., 2008). Two basic
properties are required for a matrix to have the maximum degree of
nestedness according to this metric: (1) complete overlap of 1's
from right to left columns and from down to up rows, and (2)
decreasing marginal totals between all pairs of columns and all
pairs of rows. The nestedness statistic is evaluated separately for
columns (N columns
) for rows (N rows
) and combined for
the whole matrix (NODF
). If you set order = FALSE
,
the statistic is evaluated with the current matrix ordering allowing
tests of other meaningful hypothesis of matrix structure than
default ordering by row and column totals (breaking ties by total
abundances when weighted = TRUE
) (see Almeida-Neto et
al. 2008). With weighted = TRUE
, the function finds the
weighted version of the index (Almeida-Neto & Ulrich,
2011). However, this requires quantitative null models for adequate
testing. Almeida-Neto & Ulrich (2011) say that you have positive
nestedness if values in the first row/column are higher than in the
second. With this condition, weighted analysis of binary data will
always give zero nestedness. With argument wbinary = TRUE
,
equality of rows/columns also indicates nestedness, and binary data
will give identical results in weighted and unweighted analysis.
However, this can also influence the results of weighted analysis so
that the results may differ from Almeida-Neto & Ulrich (2011).
Functions nestedbetasor
and nestedbetajac
find
multiple-site dissimilarities and decompose these into components of
turnover and nestedness following Baselga (2012); the pairwise
dissimilarities can be found with designdist
. This can
be seen as a decomposition of beta diversity (see
betadiver
). Function nestedbetasor
uses
Sørensen dissimilarity and the turnover component is
Simpson dissimilarity (Baselga 2012), and nestedbetajac
uses
analogous methods with the Jaccard index. The functions return a
vector of three items: turnover, nestedness and their sum which is
the multiple Sørensen or Jaccard dissimilarity. The
last one is the total beta diversity (Baselga 2012). The functions
will treat data as presence/absence (binary) and they can be used
with binary nullmodel
. The overall dissimilarity is
constant in all nullmodel
s that fix species (column)
frequencies ("c0"
), and all components are constant if row
columns are also fixed (e.g., model "quasiswap"
), and the
functions are not meaningful with these null models.
The result returned by a nestedness function contains an item called
statistic
, but the other components differ among functions. The
functions are constructed so that they can be handled by
oecosimu
.
Jari Oksanen and Gustavo Carvalho (nestednodf
).
Almeida-Neto, M., Guimarães, P., Guimarães, P.R., Loyola, R.D. & Ulrich, W. (2008). A consistent metric for nestedness analysis in ecological systems: reconciling concept and measurement. Oikos 117, 1227–1239.
Almeida-Neto, M. & Ulrich, W. (2011). A straightforward computational approach for measuring nestedness using quantitative matrices. Env. Mod. Software 26, 173–178.
Atmar, W. & Patterson, B.D. (1993). The measurement of order and disorder in the distribution of species in fragmented habitat. Oecologia 96, 373–382.
Baselga, A. (2012). The relationship between species replacement, dissimilarity derived from nestedness, and nestedness. Global Ecol. Biogeogr. 21, 1223–1232.
Brualdi, R.A. & Sanderson, J.G. (1999). Nested species subsets, gaps, and discrepancy. Oecologia 119, 256–264.
Patterson, B.D. & Atmar, W. (1986). Nested subsets and the structure of insular mammalian faunas and archipelagos. Biol. J. Linnean Soc. 28, 65–82.
Rodríguez-Gironés, M.A. & Santamaria, L. (2006). A new algorithm to calculate the nestedness temperature of presence-absence matrices. J. Biogeogr. 33, 924–935.
Stone, L. & Roberts, A. (1990). The checkerboard score and species distributions. Oecologia 85, 74–79.
Wright, D.H., Patterson, B.D., Mikkelson, G.M., Cutler, A. & Atmar, W. (1998). A comparative analysis of nested subset patterns of species composition. Oecologia 113, 1–20.
In general, the functions should be used with oecosimu
which generates Null model communities to assess the non-randomness of
nestedness patterns.
data(sipoo) ## Matrix temperature out <- nestedtemp(sipoo) out plot(out) plot(out, kind="incid") ## Use oecosimu to assess the non-randomness of checker board units nestedchecker(sipoo) oecosimu(sipoo, nestedchecker, "quasiswap") ## Another Null model and standardized checkerboard score oecosimu(sipoo, nestedchecker, "r00", statistic = "C.score")
data(sipoo) ## Matrix temperature out <- nestedtemp(sipoo) out plot(out) plot(out, kind="incid") ## Use oecosimu to assess the non-randomness of checker board units nestedchecker(sipoo) oecosimu(sipoo, nestedchecker, "quasiswap") ## Another Null model and standardized checkerboard score oecosimu(sipoo, nestedchecker, "r00", statistic = "C.score")
Extract the number of ‘observations’ from a vegan model fit.
## S3 method for class 'cca' nobs(object, ...)
## S3 method for class 'cca' nobs(object, ...)
object |
A fitted model object. |
... |
Further arguments to be passed to methods. |
Function nobs
is generic in R, and
vegan provides methods for objects from
betadisper
, cca
and other related
methods, CCorA
, decorana
,
isomap
, metaMDS
, pcnm
,
procrustes
, radfit
,
varpart
and wcmdscale
.
A single number, normally an integer, giving the number of observations.
Jari Oksanen
The nullmodel
function creates an object,
which can serve as a basis for Null Model simulation
via the simulate
method.
The update
method updates the nullmodel
object without sampling (effective for sequential algorithms).
smbind
binds together multiple simmat
objects.
nullmodel(x, method) ## S3 method for class 'nullmodel' print(x, ...) ## S3 method for class 'nullmodel' simulate(object, nsim = 1, seed = NULL, burnin = 0, thin = 1, ...) ## S3 method for class 'nullmodel' update(object, nsim = 1, seed = NULL, ...) ## S3 method for class 'simmat' print(x, ...) smbind(object, ..., MARGIN, strict = TRUE)
nullmodel(x, method) ## S3 method for class 'nullmodel' print(x, ...) ## S3 method for class 'nullmodel' simulate(object, nsim = 1, seed = NULL, burnin = 0, thin = 1, ...) ## S3 method for class 'nullmodel' update(object, nsim = 1, seed = NULL, ...) ## S3 method for class 'simmat' print(x, ...) smbind(object, ..., MARGIN, strict = TRUE)
x |
A community matrix.
For the |
method |
Character, specifying one of the null model algorithms
listed on the help page of |
object |
An object of class |
nsim |
Positive integer, the number of simulated matrices to return.
For the |
seed |
An object specifying if and how the random number
generator should be initialized ("seeded").
Either |
burnin |
Nonnegative integer, specifying the number of steps discarded before starting simulation. Active only for sequential null model algorithms. Ignored for non-sequential null model algorithms. |
thin |
Positive integer, number of simulation steps made between each returned matrix. Active only for sequential null model algorithms. Ignored for non-sequential null model algorithms. |
MARGIN |
Integer, indicating the dimension over which multiple
|
strict |
Logical, if consistency of the time series attributes
( |
... |
Additional arguments supplied to algorithms.
In case of |
The purpose of the nullmodel
function is to
create an object, where all necessary statistics of the
input matrix are calculated only once.
This information is reused, but not recalculated
in each step of the simulation process done by
the simulate
method.
The simulate
method carries out the simulation,
the simulated matrices are stored in an array.
For sequential algorithms, the method updates the state
of the input nullmodel
object.
Therefore, it is possible to do diagnostic
tests on the returned simmat
object,
and make further simulations, or use
increased thinning value if desired.
The update
method makes burnin steps in case
of sequential algorithms to update the status of the
input model without any attempt to return matrices.
For non-sequential algorithms the method does nothing.
update
is the preferred way of making burnin iterations
without sampling. Alternatively, burnin can be done
via the simulate
method. For convergence
diagnostics, it is recommended to use the
simulate
method without burnin.
The input nullmodel object is updated, so further
samples can be simulated if desired without having
to start the process all over again. See Examples.
The smbind
function can be used to combine multiple
simmat
objects. This comes handy when null model
simulations are stratified by sites (MARGIN = 1
)
or by species (MARGIN = 2
), or in the case when
multiple objects are returned by identical/consistent settings
e.g. during parallel computations (MARGIN = 3
).
Sanity checks are made to ensure that combining multiple
objects is sensible, but it is the user's responsibility
to check independence of the simulated matrices
and the null distribution has converged
in case of sequential null model algorithms.
The strict = FALSE
setting can relax
checks regarding start, end, and thinning values
for sequential null models.
The function nullmodel
returns an object of class nullmodel
.
It is a set of objects sharing the same environment:
data: |
original matrix in integer mode. |
nrow: |
number of rows. |
ncol: |
number of columns. |
rowSums: |
row sums. |
colSums: |
column sums. |
rowFreq: |
row frequencies (number of nonzero cells). |
colFreq: |
column frequencies (number of nonzero cells). |
totalSum: |
total sum. |
fill: |
number of nonzero cells in the matrix. |
commsim: |
the |
state: |
current state of the permutations,
a matrix similar to the original.
It is |
iter: |
current number of iterations
for sequential algorithms.
It is |
The simulate
method returns an object of class simmat
.
It is an array of simulated matrices (third dimension
corresponding to nsim
argument).
The update
method returns the current state (last updated matrix)
invisibly, and update the input object for sequential algorithms.
For non sequential algorithms, it returns NULL
.
The smbind
function returns an object of class simmat
.
Care must be taken when the input matrix only contains a single
row or column. Such input is invalid for swapping and hypergeometric
distribution (calling r2dtable
) based algorithms.
This also applies to cases when the input is stratified into subsets.
Jari Oksanen and Peter Solymos
commsim
, make.commsim
,
permatfull
, permatswap
data(mite) x <- as.matrix(mite)[1:12, 21:30] ## non-sequential nullmodel (nm <- nullmodel(x, "r00")) (sm <- simulate(nm, nsim=10)) ## sequential nullmodel (nm <- nullmodel(x, "swap")) (sm1 <- simulate(nm, nsim=10, thin=5)) (sm2 <- simulate(nm, nsim=10, thin=5)) ## sequential nullmodel with burnin and extra updating (nm <- nullmodel(x, "swap")) (sm1 <- simulate(nm, burnin=10, nsim=10, thin=5)) (sm2 <- simulate(nm, nsim=10, thin=5)) ## sequential nullmodel with separate initial burnin (nm <- nullmodel(x, "swap")) nm <- update(nm, nsim=10) (sm2 <- simulate(nm, nsim=10, thin=5)) ## combining multiple simmat objects ## stratification nm1 <- nullmodel(x[1:6,], "r00") sm1 <- simulate(nm1, nsim=10) nm2 <- nullmodel(x[7:12,], "r00") sm2 <- simulate(nm2, nsim=10) smbind(sm1, sm2, MARGIN=1) ## binding subsequent samples from sequential algorithms ## start, end, thin retained nm <- nullmodel(x, "swap") nm <- update(nm, nsim=10) sm1 <- simulate(nm, nsim=10, thin=5) sm2 <- simulate(nm, nsim=20, thin=5) sm3 <- simulate(nm, nsim=10, thin=5) smbind(sm3, sm2, sm1, MARGIN=3) ## 'replicate' based usage which is similar to the output ## of 'parLapply' or 'mclapply' in the 'parallel' package ## start, end, thin are set, also noting number of chains smfun <- function(x, burnin, nsim, thin) { nm <- nullmodel(x, "swap") nm <- update(nm, nsim=burnin) simulate(nm, nsim=nsim, thin=thin) } smlist <- replicate(3, smfun(x, burnin=50, nsim=10, thin=5), simplify=FALSE) smbind(smlist, MARGIN=3) # Number of permuted matrices = 30 ## Not run: ## parallel null model calculations library(parallel) if (.Platform$OS.type == "unix") { ## forking on Unix systems smlist <- mclapply(1:3, function(i) smfun(x, burnin=50, nsim=10, thin=5)) smbind(smlist, MARGIN=3) } ## socket type cluster, works on all platforms cl <- makeCluster(3) clusterEvalQ(cl, library(vegan)) clusterExport(cl, c("smfun", "x")) smlist <- parLapply(cl, 1:3, function(i) smfun(x, burnin=50, nsim=10, thin=5)) stopCluster(cl) smbind(smlist, MARGIN=3) ## End(Not run)
data(mite) x <- as.matrix(mite)[1:12, 21:30] ## non-sequential nullmodel (nm <- nullmodel(x, "r00")) (sm <- simulate(nm, nsim=10)) ## sequential nullmodel (nm <- nullmodel(x, "swap")) (sm1 <- simulate(nm, nsim=10, thin=5)) (sm2 <- simulate(nm, nsim=10, thin=5)) ## sequential nullmodel with burnin and extra updating (nm <- nullmodel(x, "swap")) (sm1 <- simulate(nm, burnin=10, nsim=10, thin=5)) (sm2 <- simulate(nm, nsim=10, thin=5)) ## sequential nullmodel with separate initial burnin (nm <- nullmodel(x, "swap")) nm <- update(nm, nsim=10) (sm2 <- simulate(nm, nsim=10, thin=5)) ## combining multiple simmat objects ## stratification nm1 <- nullmodel(x[1:6,], "r00") sm1 <- simulate(nm1, nsim=10) nm2 <- nullmodel(x[7:12,], "r00") sm2 <- simulate(nm2, nsim=10) smbind(sm1, sm2, MARGIN=1) ## binding subsequent samples from sequential algorithms ## start, end, thin retained nm <- nullmodel(x, "swap") nm <- update(nm, nsim=10) sm1 <- simulate(nm, nsim=10, thin=5) sm2 <- simulate(nm, nsim=20, thin=5) sm3 <- simulate(nm, nsim=10, thin=5) smbind(sm3, sm2, sm1, MARGIN=3) ## 'replicate' based usage which is similar to the output ## of 'parLapply' or 'mclapply' in the 'parallel' package ## start, end, thin are set, also noting number of chains smfun <- function(x, burnin, nsim, thin) { nm <- nullmodel(x, "swap") nm <- update(nm, nsim=burnin) simulate(nm, nsim=nsim, thin=thin) } smlist <- replicate(3, smfun(x, burnin=50, nsim=10, thin=5), simplify=FALSE) smbind(smlist, MARGIN=3) # Number of permuted matrices = 30 ## Not run: ## parallel null model calculations library(parallel) if (.Platform$OS.type == "unix") { ## forking on Unix systems smlist <- mclapply(1:3, function(i) smfun(x, burnin=50, nsim=10, thin=5)) smbind(smlist, MARGIN=3) } ## socket type cluster, works on all platforms cl <- makeCluster(3) clusterEvalQ(cl, library(vegan)) clusterExport(cl, c("smfun", "x")) smlist <- parLapply(cl, 1:3, function(i) smfun(x, burnin=50, nsim=10, thin=5)) stopCluster(cl) smbind(smlist, MARGIN=3) ## End(Not run)
Function evaluates a statistic or a vector of statistics in
community and evaluates its significance in a series of simulated
random communities. The approach has been used traditionally for
the analysis of nestedness, but the function is more general and can
be used with any statistics evaluated with simulated
communities. Function oecosimu
collects and evaluates the
statistics. The Null model communities are described in
make.commsim
and permatfull
/
permatswap
, the definition of Null models in
nullmodel
, and nestedness statistics in
nestednodf
(which describes several alternative
statistics, including nestedness temperature, , checker
board units, nestedness discrepancy and NODF).
oecosimu(comm, nestfun, method, nsimul = 99, burnin = 0, thin = 1, statistic = "statistic", alternative = c("two.sided", "less", "greater"), batchsize = NA, parallel = getOption("mc.cores"), ...) ## S3 method for class 'oecosimu' as.ts(x, ...) ## S3 method for class 'oecosimu' toCoda(x)
oecosimu(comm, nestfun, method, nsimul = 99, burnin = 0, thin = 1, statistic = "statistic", alternative = c("two.sided", "less", "greater"), batchsize = NA, parallel = getOption("mc.cores"), ...) ## S3 method for class 'oecosimu' as.ts(x, ...) ## S3 method for class 'oecosimu' toCoda(x)
comm |
Community data, or a Null model object generated by
|
nestfun |
Function analysed. Some nestedness functions are
provided in vegan (see |
method |
Null model method: either a name (character string) of
a method defined in |
nsimul |
Number of simulated null communities (ignored if
|
burnin |
Number of null communities discarded before proper
analysis in sequential methods (such as |
thin |
Number of discarded null communities between two
evaluations of nestedness statistic in sequential methods (ignored
with non-sequential methods or when |
statistic |
The name of the statistic returned by
|
alternative |
a character string specifying the alternative
hypothesis, must be one of |
batchsize |
Size in Megabytes of largest simulation object. If
a larger structure would be produced, the analysis is broken
internally into batches. With default |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
x |
An |
... |
Other arguments to functions. |
Function oecosimu
is a wrapper that evaluates a statistic
using function given by nestfun
, and then simulates a series
of null models based on nullmodel
, and evaluates the
statistic on these null models. The vegan packages contains
some nestedness functions that are described separately
(nestedchecker
, nesteddisc
,
nestedn0
, nestedtemp
,
nestednodf
), but many other functions can be used as
long as they are meaningful with simulated communities. An
applicable function must return either the statistic as a plain
number or a vector, or as a list element "statistic"
(like
chisq.test
), or in an item whose name is given in the
argument statistic
. The statistic can be a single number
(like typical for a nestedness index), or it can be a vector. The
vector indices can be used to analyse site (row) or species (column)
properties, see treedive
for an example. Raup-Crick
index (raupcrick
) gives an example of using a
dissimilarities.
The Null model type can be given as a name (quoted character string)
that is used to define a Null model in make.commsim
.
These include all binary models described by Wright et al. (1998),
Jonsson (2001), Gotelli & Entsminger (2003), Miklós &
Podani (2004), and some others. There are several quantitative Null
models, such those discussed by Hardy (2008), and several that are
unpublished (see make.commsim
,
permatfull
, permatswap
for
discussion). The user can also define her own commsim
function (see Examples).
Function works by first defining a nullmodel
with
given commsim
, and then generating a series of
simulated communities with simulate.nullmodel
. A
shortcut can be used for any of these stages and the input can be
Community data (comm
), Null model function
(nestfun
) and the number of simulations (nsimul
).
A nullmodel
object and the number of
simulations, and argument method
is ignored.
A three-dimensional array of simulated communities generated
with simulate.nullmodel
, and arguments
method
and nsimul
are ignored.
The last case allows analysing several statistics with the same simulations.
The function first generates simulations with given
nullmodel
and then analyses these using the
nestfun
. With large data sets and/or large number of
simulations, the generated objects can be very large, and if the
memory is exhausted, the analysis can become very slow and the
system can become unresponsive. The simulation will be broken into
several smaller batches if the simulated nullmodel
objective will be above the set batchsize
to avoid memory
problems (see object.size
for estimating the size of
the current data set). The parallel processing still increases the
memory needs. The parallel processing is only used for evaluating
nestfun
. The main load may be in simulation of the
nullmodel
, and parallel
argument does not help
there.
Function as.ts
transforms the simulated results of sequential
methods into a time series or a ts
object. This allows
using analytic tools for time series in studying the sequences (see
examples). Function toCoda
transforms the simulated results
of sequential methods into an "mcmc"
object of the
coda package. The coda package provides functions for
the analysis of stationarity, adequacy of sample size,
autocorrelation, need of burn-in and much more for sequential
methods, and summary of the results. Please consult the
documentation of the coda package.
Function permustats
provides support to the standard
density
, densityplot
,
qqnorm
and qqmath
functions for
the simulated values.
Function oecosimu
returns an object of class
"oecosimu"
. The result object has items statistic
and
oecosimu
. The statistic
contains the complete object
returned by nestfun
for the original data. The
oecosimu
component contains the following items:
statistic |
Observed values of the statistic. |
simulated |
Simulated values of the statistic. |
means |
Mean values of the statistic from simulations. |
z |
Standardized effect sizes (SES, a.k.a. the |
pval |
The |
alternative |
The type of testing as given in argument |
method |
The |
isSeq |
|
If you wonder about the name of oecosimu
, look at journal
names in the References (and more in nestedtemp
).
The internal structure of the function was radically changed in
vegan 2.2-0 with introduction of commsim
and
nullmodel
and deprecation of
commsimulator
.
Jari Oksanen and Peter Solymos
Hardy, O. J. (2008) Testing the spatial phylogenetic structure of local communities: statistical performances of different null models and test statistics on a locally neutral community. Journal of Ecology 96, 914–926.
Gotelli, N.J. & Entsminger, N.J. (2003). Swap algorithms in null model analysis. Ecology 84, 532–535.
Jonsson, B.G. (2001) A null model for randomization tests of nestedness in species assemblages. Oecologia 127, 309–313.
Miklós, I. & Podani, J. (2004). Randomization of presence-absence matrices: comments and new algorithms. Ecology 85, 86–92.
Wright, D.H., Patterson, B.D., Mikkelson, G.M., Cutler, A. & Atmar, W. (1998). A comparative analysis of nested subset patterns of species composition. Oecologia 113, 1–20.
Function oecosimu
currently defines null models with
commsim
and generates the simulated null model
communities with nullmodel
and
simulate.nullmodel
. For other applications of
oecosimu
, see treedive
and
raupcrick
.
See also nestedtemp
(that also discusses other
nestedness functions) and treedive
for another
application.
## Use the first eigenvalue of correspondence analysis as an index ## of structure: a model for making your own functions. data(sipoo) ## Traditional nestedness statistics (number of checkerboard units) oecosimu(sipoo, nestedchecker, "r0") ## sequential model, one-sided test, a vector statistic out <- oecosimu(sipoo, decorana, "swap", burnin=100, thin=10, statistic="evals", alt = "greater") out ## Inspect the swap sequence as a time series object plot(as.ts(out)) lag.plot(as.ts(out)) acf(as.ts(out)) ## Density plot densityplot(permustats(out), as.table = TRUE, layout = c(1,4)) ## Use quantitative null models to compare ## mean Bray-Curtis dissimilarities data(dune) meandist <- function(x) mean(vegdist(x, "bray")) mbc1 <- oecosimu(dune, meandist, "r2dtable") mbc1 ## Define your own null model as a 'commsim' function: shuffle cells ## in each row foo <- function(x, n, nr, nc, ...) { out <- array(0, c(nr, nc, n)) for (k in seq_len(n)) out[,,k] <- apply(x, 2, function(z) sample(z, length(z))) out } cf <- commsim("myshuffle", foo, isSeq = FALSE, binary = FALSE, mode = "double") oecosimu(dune, meandist, cf) ## Use pre-built null model nm <- simulate(nullmodel(sipoo, "curveball"), 99) oecosimu(nm, nestedchecker) ## Several chains of a sequential model -- this can be generalized ## for parallel processing (see ?smbind) nm <- replicate(5, simulate(nullmodel(sipoo, "swap"), 99, thin=10, burnin=100), simplify = FALSE) ## nm is now a list of nullmodels: use smbind to combine these into one ## nullmodel with several chains ## IGNORE_RDIFF_BEGIN nm <- smbind(nm, MARGIN = 3) nm oecosimu(nm, nestedchecker) ## IGNORE_RDIFF_END ## After this you can use toCoda() and tools in the coda package to ## analyse the chains (these will show that thin, burnin and nsimul are ## all too low for real analysis).
## Use the first eigenvalue of correspondence analysis as an index ## of structure: a model for making your own functions. data(sipoo) ## Traditional nestedness statistics (number of checkerboard units) oecosimu(sipoo, nestedchecker, "r0") ## sequential model, one-sided test, a vector statistic out <- oecosimu(sipoo, decorana, "swap", burnin=100, thin=10, statistic="evals", alt = "greater") out ## Inspect the swap sequence as a time series object plot(as.ts(out)) lag.plot(as.ts(out)) acf(as.ts(out)) ## Density plot densityplot(permustats(out), as.table = TRUE, layout = c(1,4)) ## Use quantitative null models to compare ## mean Bray-Curtis dissimilarities data(dune) meandist <- function(x) mean(vegdist(x, "bray")) mbc1 <- oecosimu(dune, meandist, "r2dtable") mbc1 ## Define your own null model as a 'commsim' function: shuffle cells ## in each row foo <- function(x, n, nr, nc, ...) { out <- array(0, c(nr, nc, n)) for (k in seq_len(n)) out[,,k] <- apply(x, 2, function(z) sample(z, length(z))) out } cf <- commsim("myshuffle", foo, isSeq = FALSE, binary = FALSE, mode = "double") oecosimu(dune, meandist, cf) ## Use pre-built null model nm <- simulate(nullmodel(sipoo, "curveball"), 99) oecosimu(nm, nestedchecker) ## Several chains of a sequential model -- this can be generalized ## for parallel processing (see ?smbind) nm <- replicate(5, simulate(nullmodel(sipoo, "swap"), 99, thin=10, burnin=100), simplify = FALSE) ## nm is now a list of nullmodels: use smbind to combine these into one ## nullmodel with several chains ## IGNORE_RDIFF_BEGIN nm <- smbind(nm, MARGIN = 3) nm oecosimu(nm, nestedchecker) ## IGNORE_RDIFF_END ## After this you can use toCoda() and tools in the coda package to ## analyse the chains (these will show that thin, burnin and nsimul are ## all too low for real analysis).
Functions to add arrows, line segments, regular grids of
points. The ordination diagrams can be produced by vegan
plot.cca
, plot.decorana
or
ordiplot
.
ordiarrows(ord, groups, levels, replicates, order.by, display = "sites", col = 1, show.groups, startmark, label = FALSE, length = 0.1, ...) ordisegments(ord, groups, levels, replicates, order.by, display = "sites", col = 1, show.groups, label = FALSE, ...) ordigrid(ord, levels, replicates, display = "sites", lty = c(1,1), col = c(1,1), lwd = c(1,1), ...)
ordiarrows(ord, groups, levels, replicates, order.by, display = "sites", col = 1, show.groups, startmark, label = FALSE, length = 0.1, ...) ordisegments(ord, groups, levels, replicates, order.by, display = "sites", col = 1, show.groups, label = FALSE, ...) ordigrid(ord, levels, replicates, display = "sites", lty = c(1,1), col = c(1,1), lwd = c(1,1), ...)
ord |
An ordination object or an |
groups |
Factor giving the groups for which the graphical item is drawn. |
levels , replicates
|
Alternatively, regular
groups can be defined with arguments |
order.by |
Order points by increasing order of this variable
within |
display |
Item to displayed. |
show.groups |
Show only given groups. This can be a vector, or
|
label |
Label the |
startmark |
plotting character used to mark the first item. The
default is to use no mark, and for instance, |
col |
Colour of lines, |
length |
Length of edges of the arrow head (in inches). |
lty , lwd
|
Line type, line width used for
|
... |
Parameters passed to graphical functions such as
|
Function ordiarrows
draws arrows
and
ordisegments
draws line segments
between
successive items in the groups. Function ordigrid
draws line
segments
both within the groups and for the
corresponding items among the groups.
These functions add graphical items to ordination graph: You must draw a graph first.
Jari Oksanen
The functions pass parameters to basic graphical functions, and
you may wish to change the default values in arrows
,
lines
and segments
. You can pass
parameters to scores
as well.
example(pyrifos) mod <- rda(pyrifos) plot(mod, type = "n") ## Annual succession by ditches, colour by dose ordiarrows(mod, ditch, label = TRUE, col = as.numeric(dose)) legend("topright", levels(dose), lty=1, col=1:5, title="Dose") ## Show only control and highest Pyrifos treatment plot(mod, type = "n") ordiarrows(mod, ditch, label = TRUE, show.groups = c("2", "3", "5", "11")) ordiarrows(mod, ditch, label = TRUE, show = c("6", "9"), col = 2) legend("topright", c("Control", "Pyrifos 44"), lty = 1, col = c(1,2))
example(pyrifos) mod <- rda(pyrifos) plot(mod, type = "n") ## Annual succession by ditches, colour by dose ordiarrows(mod, ditch, label = TRUE, col = as.numeric(dose)) legend("topright", levels(dose), lty=1, col=1:5, title="Dose") ## Show only control and highest Pyrifos treatment plot(mod, type = "n") ordiarrows(mod, ditch, label = TRUE, show.groups = c("2", "3", "5", "11")) ordiarrows(mod, ditch, label = TRUE, show = c("6", "9"), col = 2) legend("topright", c("Control", "Pyrifos 44"), lty = 1, col = c(1,2))
Support functions to assist with drawing of vectors (arrows) on
ordination plots. ordiArrowMul
finds the multiplier for the
coordinates of the head of the vector such that they occupy
fill
proportion of the plot region. ordiArrowTextXY
finds coordinates for the locations of labels
to be drawn just
beyond the head of the vector.
ordiArrowTextXY(x, labels, display, choices = c(1,2), rescale = TRUE, fill = 0.75, at = c(0,0), cex = NULL, ...) ordiArrowMul(x, at = c(0,0), fill = 0.75, display, choices = c(1,2), ...)
ordiArrowTextXY(x, labels, display, choices = c(1,2), rescale = TRUE, fill = 0.75, at = c(0,0), cex = NULL, ...) ordiArrowMul(x, at = c(0,0), fill = 0.75, display, choices = c(1,2), ...)
x |
An R object, from which |
labels |
Change plotting labels. A character vector of labels for
which label coordinates are sought. If not supplied, these will be
determined from the row names of |
display |
a character string known to |
choices |
Axes to be plotted. |
rescale |
logical; should the coordinates in or extracted from
|
fill |
numeric; the proportion of the plot to fill by the span of the arrows. |
at |
The origin of fitted arrows in the plot. If you plot arrows
in other places than origin, you probably have to specify
|
cex |
Character expansion for text. |
... |
ordiArrowMul
finds a multiplier to scale a bunch of
arrows to fill an ordination plot, and ordiArrowTextXY
finds
the coordinates for labels of these arrows. NB.,
ordiArrowTextXY
does not draw labels; it simply returns
coordinates at which the labels should be drawn for use with another
function, such as text
.
For ordiArrowTextXY
, a 2-column matrix of coordinates for the
label centres in the coordinate system of the currently active
plotting device.
For ordiArrowMul
, a length-1 vector containing the scaling
factor.
Jari Oksanen, with modifications by Gavin L. Simpson
## Scale arrows by hand to fill 80% of the plot ## Biplot arrows by hand data(varespec, varechem) ord <- cca(varespec ~ Al + P + K, varechem) plot(ord, display = c("species","sites")) ## biplot scores bip <- scores(ord, choices = 1:2, display = "bp") ## scaling factor for arrows to fill 80% of plot (mul <- ordiArrowMul(bip, fill = 0.8)) bip.scl <- bip * mul # Scale the biplot scores labs <- rownames(bip) # Arrow labels ## calculate coordinate of labels for arrows (bip.lab <- ordiArrowTextXY(bip.scl, rescale = FALSE, labels = labs)) ## arrows will touch the bounding box of the text arrows(0, 0, bip.scl[,1], bip.scl[,2], length = 0.1) ordilabel(bip.lab, labels = labs) ## Handling of ordination objects directly mul2 <- ordiArrowMul(ord, display = "bp", fill = 0.8) stopifnot(all.equal(mul, mul2))
## Scale arrows by hand to fill 80% of the plot ## Biplot arrows by hand data(varespec, varechem) ord <- cca(varespec ~ Al + P + K, varechem) plot(ord, display = c("species","sites")) ## biplot scores bip <- scores(ord, choices = 1:2, display = "bp") ## scaling factor for arrows to fill 80% of plot (mul <- ordiArrowMul(bip, fill = 0.8)) bip.scl <- bip * mul # Scale the biplot scores labs <- rownames(bip) # Arrow labels ## calculate coordinate of labels for arrows (bip.lab <- ordiArrowTextXY(bip.scl, rescale = FALSE, labels = labs)) ## arrows will touch the bounding box of the text arrows(0, 0, bip.scl[,1], bip.scl[,2], length = 0.1) ordilabel(bip.lab, labels = labs) ## Handling of ordination objects directly mul2 <- ordiArrowMul(ord, display = "bp", fill = 0.8) stopifnot(all.equal(mul, mul2))
Functions to add convex hulls, “spider” graphs, ellipses
or cluster dendrogram to ordination diagrams. The ordination
diagrams can be produced by vegan
plot.cca
,
plot.decorana
or ordiplot
.
ordihull(ord, groups, display = "sites", draw = c("lines","polygon", "none"), col = NULL, alpha = 127, show.groups, label = FALSE, border = NULL, lty = NULL, lwd = NULL, ...) ordiellipse(ord, groups, display="sites", kind = c("sd","se", "ehull"), conf, draw = c("lines","polygon", "none"), w, col = NULL, alpha = 127, show.groups, label = FALSE, border = NULL, lty = NULL, lwd=NULL, ...) ordibar(ord, groups, display = "sites", kind = c("sd", "se"), conf, w, col = 1, show.groups, label = FALSE, lwd = NULL, length = 0, ...) ordispider(ord, groups, display="sites", w, spiders = c("centroid", "median"), show.groups, label = FALSE, col = NULL, lty = NULL, lwd = NULL, ...) ordicluster(ord, cluster, prune = 0, display = "sites", w, col = 1, draw = c("segments", "none"), ...) ## S3 method for class 'ordihull' summary(object, ...) ## S3 method for class 'ordiellipse' summary(object, ...) ordiareatest(ord, groups, area = c("hull", "ellipse"), kind = "sd", permutations = 999, parallel = getOption("mc.cores"), ...)
ordihull(ord, groups, display = "sites", draw = c("lines","polygon", "none"), col = NULL, alpha = 127, show.groups, label = FALSE, border = NULL, lty = NULL, lwd = NULL, ...) ordiellipse(ord, groups, display="sites", kind = c("sd","se", "ehull"), conf, draw = c("lines","polygon", "none"), w, col = NULL, alpha = 127, show.groups, label = FALSE, border = NULL, lty = NULL, lwd=NULL, ...) ordibar(ord, groups, display = "sites", kind = c("sd", "se"), conf, w, col = 1, show.groups, label = FALSE, lwd = NULL, length = 0, ...) ordispider(ord, groups, display="sites", w, spiders = c("centroid", "median"), show.groups, label = FALSE, col = NULL, lty = NULL, lwd = NULL, ...) ordicluster(ord, cluster, prune = 0, display = "sites", w, col = 1, draw = c("segments", "none"), ...) ## S3 method for class 'ordihull' summary(object, ...) ## S3 method for class 'ordiellipse' summary(object, ...) ordiareatest(ord, groups, area = c("hull", "ellipse"), kind = "sd", permutations = 999, parallel = getOption("mc.cores"), ...)
ord |
An ordination object or an |
groups |
Factor giving the groups for which the graphical item is drawn. |
display |
Item to displayed. |
draw |
character; how should objects be represented on the plot?
For |
col |
Colour of hull or ellipse lines (if |
alpha |
Transparency of the fill |
show.groups |
Show only given groups. This can be a vector, or
|
label |
Label the |
w |
Weights used to find the average within group. Weights are
used automatically for |
kind |
Draw standard deviations of points ( |
conf |
Confidence limit for ellipses, e.g. 0.95. If given, the
corresponding |
spiders |
Are centres or spider bodies calculated either as centroids (averages) or spatial medians. |
cluster |
Result of hierarchic cluster analysis, such as
|
prune |
Number of upper level hierarchies removed from the
dendrogram. If |
object |
A result object from |
area |
Evaluate the area of convex hulls of |
permutations |
a list of control values for the permutations
as returned by the function |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
lty , lwd , border
|
Vectors of these parameters can be supplied
and will be applied (if appropriate) for each element of
|
length |
Width (in inches) of the small (“caps”) at the
ends of the bar segment (passed to |
... |
Parameters passed to graphical functions or to
|
Function ordihull
draws lines
or
polygon
s for the convex
hulls found by function chull
encircling
the items in the groups.
Function ordiellipse
draws lines
or
polygon
s for ellipses by groups
. The function
can either draw standard deviation of points (kind="sd"
) or
standard error of the (weighted) centroids (kind="se"
), and
the (weighted) correlation defines the direction of the principal
axis of the ellipse. When kind = "se"
is used together with
argument conf
, the ellipses will show the confidence regions
for the locations of group centroids. With kind="ehull"
the
function draws an ellipse that encloses all points of a group using
ellipsoidhull
(cluster package).
Function ordibar
draws crossed “error bars” using
either either standard deviation of point scores or standard error
of the (weighted) average of scores. These are the principal axes of
the corresponding ordiellipse
, and are found by principal
component analysis of the (weighted) covariance matrix.
Functions ordihull
and ordiellipse
return invisibly an
object that has a summary
method that returns the coordinates
of centroids and areas of the hulls or ellipses. Function
ordiareatest
studies the one-sided hypothesis that these
areas are smaller than with randomized groups
. Argument
kind
can be used to select the kind of ellipse, and has no
effect with convex hulls.
Function ordispider
draws a ‘spider’ diagram where
each point is connected to the group centroid with
segments
. Weighted centroids are used in the
correspondence analysis methods cca
and
decorana
or if the user gives the weights in the
call. If ordispider
is called with cca
or
rda
result without groups
argument, the
function connects each ‘WA’ scores to the corresponding
‘LC’ score. If the argument is a (invisible
)
ordihull
object, the function will connect the points of the
hull to their centroid.
Function ordicluster
overlays a cluster dendrogram onto
ordination. It needs the result from a hierarchic clustering such as
hclust
or agnes
, or other with
a similar structure. Function ordicluster
connects cluster
centroids to each other with line segments
. Function
uses centroids of all points in the clusters, and is therefore
similar to average linkage methods.
Functions ordihull
, ordiellipse
and ordispider
return the invisible
plotting structure.
Function ordispider
return the coordinates to which each
point is connected (centroids or ‘LC’ scores).
Function ordihull
and ordiellipse
return invisibly an
object that has a summary
method that returns the coordinates
of centroids and areas of the hulls or ellipses. Function
ordiareatest
studies the one-sided hypothesis that these
areas are smaller than with randomized groups
.
These functions add graphical items to ordination graph: You
must draw a graph first. To draw line segments, grids or arrows, see
ordisegments
, ordigrid
andordiarrows
.
Jari Oksanen
The functions pass parameters to basic graphical functions,
and you may wish to change the default values in
lines
, segments
and
polygon
. You can pass parameters to
scores
as well. Underlying functions for
ordihull
is chull
. The underlying function for
ellipsoid hulls in ordiellipse
is
ellipsoidhull
.
data(dune) data(dune.env) mod <- cca(dune ~ Management, dune.env) plot(mod, type="n", scaling = "symmetric") ## Catch the invisible result of ordihull... pl <- with(dune.env, ordihull(mod, Management, scaling = "symmetric", label = TRUE)) ## ... and find centres and areas of the hulls summary(pl) ## use more colours and add ellipsoid hulls plot(mod, type = "n") pl <- with(dune.env, ordihull(mod, Management, scaling = "symmetric", col = 1:4, draw="polygon", label =TRUE)) with(dune.env, ordiellipse(mod, Management, scaling = "symmetric", kind = "ehull", col = 1:4, lwd=3)) ## ordispider to connect WA and LC scores plot(mod, dis=c("wa","lc"), type="p") ordispider(mod) ## Other types of plots plot(mod, type = "p", display="sites") cl <- hclust(vegdist(dune)) ordicluster(mod, cl, prune=3, col = cutree(cl, 4)) ## confidence ellipse: location of the class centroids plot(mod, type="n", display = "sites") with(dune.env, text(mod, display="sites", labels = as.character(Management), col=as.numeric(Management))) pl <- with(dune.env, ordiellipse(mod, Management, kind="se", conf=0.95, lwd=2, draw = "polygon", col=1:4, border=1:4, alpha=63)) summary(pl) ## add confidence bars with(dune.env, ordibar(mod, Management, kind="se", conf=0.95, lwd=2, col=1:4, label=TRUE))
data(dune) data(dune.env) mod <- cca(dune ~ Management, dune.env) plot(mod, type="n", scaling = "symmetric") ## Catch the invisible result of ordihull... pl <- with(dune.env, ordihull(mod, Management, scaling = "symmetric", label = TRUE)) ## ... and find centres and areas of the hulls summary(pl) ## use more colours and add ellipsoid hulls plot(mod, type = "n") pl <- with(dune.env, ordihull(mod, Management, scaling = "symmetric", col = 1:4, draw="polygon", label =TRUE)) with(dune.env, ordiellipse(mod, Management, scaling = "symmetric", kind = "ehull", col = 1:4, lwd=3)) ## ordispider to connect WA and LC scores plot(mod, dis=c("wa","lc"), type="p") ordispider(mod) ## Other types of plots plot(mod, type = "p", display="sites") cl <- hclust(vegdist(dune)) ordicluster(mod, cl, prune=3, col = cutree(cl, 4)) ## confidence ellipse: location of the class centroids plot(mod, type="n", display = "sites") with(dune.env, text(mod, display="sites", labels = as.character(Management), col=as.numeric(Management))) pl <- with(dune.env, ordiellipse(mod, Management, kind="se", conf=0.95, lwd=2, draw = "polygon", col=1:4, border=1:4, alpha=63)) summary(pl) ## add confidence bars with(dune.env, ordibar(mod, Management, kind="se", conf=0.95, lwd=2, col=1:4, label=TRUE))
Function ordilabel
is similar to
text
, but the text is on an opaque label. This can help
in crowded ordination plots: you still cannot see all text labels, but
at least the uppermost ones are readable. Argument priority
helps to
make the most important labels visible. Function can be used in pipe
after ordination plot
or ordiplot
command.
ordilabel(x, display, labels, choices = c(1, 2), priority, select, cex = 0.8, fill = "white", border = NULL, col = NULL, xpd = TRUE, ...)
ordilabel(x, display, labels, choices = c(1, 2), priority, select, cex = 0.8, fill = "white", border = NULL, col = NULL, xpd = TRUE, ...)
x |
An ordination object an any object known to
|
display |
Kind of scores displayed (passed to
|
labels |
Optional text used in plots. If this is not given, the text is found from the ordination object. |
choices |
Axes shown (passed to |
priority |
Vector of the same length as the number of labels. The items with high priority will be plotted uppermost. |
select |
Items to be displayed. This can either be a logical
vector which is |
cex |
Character expansion for the text (passed to
|
fill |
Background colour of the labels (the |
border |
The colour and visibility of the border of the label as
defined in |
col |
Text colour. |
xpd |
Draw labels also outside the plot region. |
... |
Other arguments (passed to |
The function may be useful with crowded ordination plots, in
particular together with argument priority
. You will not see
all text labels, but at least some are readable. Function can be used
as a part of a pipe (|>
) in place of text
after an
ordination plot
command (see Examples).
Other alternatives for cluttered plots are
identify.ordiplot
, orditorp
,
ordipointlabel
and orditkplot
(in vegan3d package).
Jari Oksanen
plot.cca
and text.ordiplot
that
can use the function with argument bg
.
data(dune) ord <- cca(dune) plot(ord, type = "n") ## add text ordilabel(ord, dis="sites", cex=1.2, font=3, fill="hotpink", col="blue") ## You may prefer separate plots, but here species as well ordilabel(ord, dis="sp", font=2, priority=colSums(dune)) ## use in a pipe plot(ord, type = "n") |> ordilabel("spec", font = 3, priority = colSums(dune)) |> points("sites", pch=21, bg = "yellow", col = "blue")
data(dune) ord <- cca(dune) plot(ord, type = "n") ## add text ordilabel(ord, dis="sites", cex=1.2, font=3, fill="hotpink", col="blue") ## You may prefer separate plots, but here species as well ordilabel(ord, dis="sp", font=2, priority=colSums(dune)) ## use in a pipe plot(ord, type = "n") |> ordilabel("spec", font = 3, priority = colSums(dune)) |> points("sites", pch=21, bg = "yellow", col = "blue")
Function ordiplot
is an alternative plotting
function which works with any vegan ordination object and many
non-vegan objects. In addition, plot
functions for
vegan ordinations return invisibly an "ordiplot"
object,
and this allows using ordiplot
support functions with this
result: identify
can be used to add labels to selected site,
species or constraint points, and points
and text
can
add elements to the plot, and used in a pipe to add scores into plot
by layers.
ordiplot(ord, choices = c(1, 2), type="points", display, optimize = FALSE, arrows = FALSE, length = 0.05, arr.mul, xlim, ylim, ...) ## S3 method for class 'ordiplot' points(x, what, select, arrows = FALSE, length = 0.05, arr.mul, ...) ## S3 method for class 'ordiplot' text(x, what, labels, select, optimize = FALSE, arrows = FALSE, length = 0.05, arr.mul, bg, ...) ## S3 method for class 'ordiplot' identify(x, what, labels, ...)
ordiplot(ord, choices = c(1, 2), type="points", display, optimize = FALSE, arrows = FALSE, length = 0.05, arr.mul, xlim, ylim, ...) ## S3 method for class 'ordiplot' points(x, what, select, arrows = FALSE, length = 0.05, arr.mul, ...) ## S3 method for class 'ordiplot' text(x, what, labels, select, optimize = FALSE, arrows = FALSE, length = 0.05, arr.mul, bg, ...) ## S3 method for class 'ordiplot' identify(x, what, labels, ...)
ord |
A result from an ordination. |
choices |
Axes shown. |
type |
The type of graph which may be |
display |
Display only "sites" or "species". The default for most
methods is to display both, but for |
xlim , ylim
|
the x and y limits (min,max) of the plot. |
... |
Other graphical parameters. |
x |
A result object from |
what |
Items identified in the ordination plot. The types depend
on the kind of plot used. Most methods know |
labels |
Optional text used for labels. Row names of scores will be used if this is missing. |
optimize |
Optimize locations of text to reduce overlap and plot
point in the actual locations of the scores. Uses
|
arrows |
Draw arrows from the origin. This will always be
|
length |
Length of arrow heads (see |
arr.mul |
Numeric multiplier to arrow lenghts; this will also set
|
bg |
Background colour for labels. If |
select |
Items to be displayed. This can either be a logical
vector which is |
Function ordiplot
draws an ordination diagram with default of
black circles for sites and red crosses for species. It returns
invisibly an object of class ordiplot
.
The function can handle output from several alternative ordination
methods. For cca
, rda
and
decorana
it uses their plot
method with option
type = "points"
. In addition, the plot
functions of
these methods return invisibly an ordiplot
object which can
be used by identify.ordiplot
to label points. For other
ordinations it relies on scores
to extract the scores.
For full user control of plots, it is best to call ordiplot
with type = "none"
and save the result, and then add sites and
species using points.ordiplot
or text.ordiplot
which
both pass all their arguments to the corresponding default graphical
functions. Alternatively, points
and text
can be used in
pipe which allows an intuitive way of building up plots by layers. In
addition, function ordilabel
and
ordipointlabel
can be used in pipe after ordiplot
or other vegan ordination plot
commands. See Examples.
Function ordiplot
returns invisibly an object of class
ordiplot
with used scores. In general, vegan plot
functions for ordination results will also return an invisible
ordiplot
object. If the plot(..., type = "n")
was used
originally, the plot is empty, and items can be added with the
invisible object. Functions points
and text
return
their input object without modification, which allows chaining these
commands with pipes. Function identify.ordiplot
uses this
object to label the point.
Jari Oksanen
With argument bg
function calls ordilabel
to draw text on non-transparent label, and with argument
optimize = TRUE
function calls ordipointlabel
to
optimize the locations of text labels to minimize
over-plotting. Functions ordilabel
and
ordipointlabel
can be used in a pipe together with
ordiplot
methods text
and points
. Function
plot.cca
uses ordiplot
methods text
and
points
in configurable plots, and these accept the
arguments of the ordiplot
methods described here.
## Draw a plot for a non-vegan ordination (cmdscale). data(dune) dune.dis <- vegdist(wisconsin(dune)) dune.mds <- cmdscale(dune.dis, eig = TRUE) dune.mds$species <- wascores(dune.mds$points, dune, expand = TRUE) pl <- ordiplot(dune.mds, type = "none") points(pl, "sites", pch=21, col="red", bg="yellow") text(pl, "species", col="blue", cex=0.9) ## same plot using pipes (|>) ordiplot(dune.mds, type="n") |> points("sites", pch=21, col="red", bg="yellow") |> text("species", col="blue", cex=0.9) ## Some people think that species should be shown with arrows in PCA. ## Other ordination methods also return an invisible ordiplot object and ## we can use pipes to draw those arrows. mod <- rda(dune) plot(mod, type="n") |> points("sites", pch=16, col="red") |> text("species", arrows = TRUE, length=0.05, col="blue") ## Default plot of the previous using identify to label selected points ## Not run: pl <- ordiplot(dune.mds) identify(pl, "spec") ## End(Not run)
## Draw a plot for a non-vegan ordination (cmdscale). data(dune) dune.dis <- vegdist(wisconsin(dune)) dune.mds <- cmdscale(dune.dis, eig = TRUE) dune.mds$species <- wascores(dune.mds$points, dune, expand = TRUE) pl <- ordiplot(dune.mds, type = "none") points(pl, "sites", pch=21, col="red", bg="yellow") text(pl, "species", col="blue", cex=0.9) ## same plot using pipes (|>) ordiplot(dune.mds, type="n") |> points("sites", pch=21, col="red", bg="yellow") |> text("species", col="blue", cex=0.9) ## Some people think that species should be shown with arrows in PCA. ## Other ordination methods also return an invisible ordiplot object and ## we can use pipes to draw those arrows. mod <- rda(dune) plot(mod, type="n") |> points("sites", pch=16, col="red") |> text("species", arrows = TRUE, length=0.05, col="blue") ## Default plot of the previous using identify to label selected points ## Not run: pl <- ordiplot(dune.mds) identify(pl, "spec") ## End(Not run)
Function produces ordination plots with points and text labels to the points. The points are in the fixed locations given by the ordination, but the locations of the text labels are optimized to minimize overplotting. The function is useful with moderately crowded ordination plots.
ordipointlabel(x, display = c("sites", "species"), choices = c(1, 2), col = c(1, 2), pch = c("o", "+"), font = c(1, 1), cex = c(0.7, 0.7), add = inherits(x, "ordiplot"), labels, bg, select, ...) ## S3 method for class 'ordipointlabel' plot(x, ...)
ordipointlabel(x, display = c("sites", "species"), choices = c(1, 2), col = c(1, 2), pch = c("o", "+"), font = c(1, 1), cex = c(0.7, 0.7), add = inherits(x, "ordiplot"), labels, bg, select, ...) ## S3 method for class 'ordipointlabel' plot(x, ...)
x |
For |
display |
Scores displayed in the plot. The default is to show
|
choices |
Axes shown. |
col , pch , font , cex
|
Colours, point types, font style and
character expansion for each kind of scores displayed in the
plot. These should be vectors of the same length as the number of
items in |
add |
Add to an existing plot. Default is |
labels |
Labels used in graph. Species (variable) and SU (row)
names are used if this is missing. Labels must be given in one
vector for all scores of |
bg |
Background colour for labels. If this is given, texts is
drawn over non-transparent background. Either a single colour or
vector of colours for each |
select |
Items to be displayed. This can either be a logical
vector which is |
... |
The function uses simulated annealing (optim
,
method = "SANN"
) to optimize the locations of the text labels
to the points. There are eight possible locations: up, down, two sides
and four corners. There is a weak preference to text away from zero,
and a weak avoidance of corners. The locations and goodness of
solution varies between runs, and there is no guarantee of finding the
global optimum, or the same text locations twice. The optimization can
take a long time in difficult cases with a high number of potential
overlaps. Several sets of scores can be displayed in one plot.
The function can be used in a pipe where the first command is an
ordination plot
command with type = "n"
or to add
points and lablels to save vegan ordination plot object. See
examples.
The function returns invisibly an object of class
ordipointlabel
with items xy
for coordinates of
points, labels
for coordinates of labels, items pch
,
cex
and font
for graphical parameters of each point or
label. In addition, it returns the result of optim
as
an attribute "optim"
. The unit of overlap is the area
of character "m"
, and with varying graphical parameters the
smallest alternative.
There is a plot
method based on orditkplot
but it
does not alter or reset the graphical parameters via par
.
The result object from ordipointlabel
inherits from
orditkplot
of vegan3d package, and it may
be possible to further edit the result object with
orditkplot
, but for good results it is
necessary that the points span the whole horizontal axis without empty
margins.
Jari Oksanen
The function is invoked for one set of scores (one
display
) from text.ordiplot
and
plot.cca
with argument optimize = TRUE
.
data(dune, dune.env) ord <- cca(dune) ordipointlabel(ord) ## Use in a pipe: optimize species, sites & centroids together ord <- cca(dune ~ Management + Moisture, dune.env) plot(ord, scaling = "symmetric", type = "n") |> ordipointlabel(c("sites","species","centroids"), cex=c(0.7,0.7,1), col = c("black","red","blue"), font = c(1,3,1), pch=c(1,3,4), xpd=TRUE) |> text("biplot", col = "blue", bg = "white", cex=1)
data(dune, dune.env) ord <- cca(dune) ordipointlabel(ord) ## Use in a pipe: optimize species, sites & centroids together ord <- cca(dune ~ Management + Moisture, dune.env) plot(ord, scaling = "symmetric", type = "n") |> ordipointlabel(c("sites","species","centroids"), cex=c(0.7,0.7,1), col = c("black","red","blue"), font = c(1,3,1), pch=c(1,3,4), xpd=TRUE) |> text("biplot", col = "blue", bg = "white", cex=1)
The function provides plot.lm
style diagnostic plots
for the results of constrained ordination from cca
,
rda
, dbrda
and
capscale
. Normally you do not need these plots,
because ordination is descriptive and does not make assumptions on
the distribution of the residuals. However, if you permute residuals
in significance tests (anova.cca
), you may be
interested in inspecting that the residuals really are exchangeable
and independent of fitted values.
ordiresids(x, kind = c("residuals", "scale", "qqmath"), residuals = "working", type = c("p", "smooth", "g"), formula, ...)
ordiresids(x, kind = c("residuals", "scale", "qqmath"), residuals = "working", type = c("p", "smooth", "g"), formula, ...)
x |
|
kind |
The type of plot: |
residuals |
The kind of residuals and fitted values, with alternatives
|
type |
The type of plot. The argument is passed on to lattice functions. |
formula |
Formula to override the default plot. The formula can
contain items |
... |
Other arguments passed to lattice functions. |
The default plots are similar as in plot.lm
, but they
use Lattice
functions
xyplot
and qqmath
. The
alternatives have default formulae but these can be replaced by the
user. The elements available in formula or in the groups
argument
are Fitted
, Residuals
, Species
and Sites
.
With residuals = "response"
and residuals = "working"
the fitted values and residuals are found with functions
fitted.cca
and residuals.cca
. With
residuals = "standardized"
the residuals are found with
rstandard.cca
, and with residuals = "studentized"
they are found with rstudent.cca
, and in both cases the
fitted values are standardized with sigma.cca
.
The function returns a Lattice
object that can
displayed as plot.
Jari Oksanen
plot.lm
, fitted.cca
,
residuals.cca
, rstandard.cca
,
rstudent.cca
, sigma.cca
,
Lattice
, xyplot
,
qqmath
.
data(varespec) data(varechem) mod <- cca(varespec ~ Al + P + K, varechem) ordiresids(mod) ordiresids(mod, formula = Residuals ~ Fitted | Species, residuals="standard", cex = 0.5)
data(varespec) data(varechem) mod <- cca(varespec ~ Al + P + K, varechem) ordiresids(mod) ordiresids(mod, formula = Residuals ~ Fitted | Species, residuals="standard", cex = 0.5)
Automatic stepwise model building for constrained ordination methods
(cca
, rda
, dbrda
,
capscale
). The function ordistep
is modelled
after step
and can do forward, backward and stepwise
model selection using permutation tests. Function ordiR2step
performs forward model choice solely on adjusted and
-value.
ordistep(object, scope, direction = c("both", "backward", "forward"), Pin = 0.05, Pout = 0.1, permutations = how(nperm = 199), steps = 50, trace = TRUE, ...) ordiR2step(object, scope, Pin = 0.05, R2scope = TRUE, permutations = how(nperm = 499), trace = TRUE, R2permutations = 1000, ...)
ordistep(object, scope, direction = c("both", "backward", "forward"), Pin = 0.05, Pout = 0.1, permutations = how(nperm = 199), steps = 50, trace = TRUE, ...) ordiR2step(object, scope, Pin = 0.05, R2scope = TRUE, permutations = how(nperm = 499), trace = TRUE, R2permutations = 1000, ...)
object |
In |
scope |
Defines the range of models examined in the stepwise
search. This can be a list containing components |
direction |
The mode of stepwise search, can be one of |
Pin , Pout
|
Limits of permutation |
R2scope |
Use adjusted |
permutations |
a list of control values for the permutations as
returned by the function |
steps |
Maximum number of iteration steps of dropping and adding terms. |
trace |
If positive, information is printed during the model building. Larger values may give more information. |
R2permutations |
Number of permutations used in the estimation of
adjusted |
... |
The basic functions for model choice in constrained ordination are
add1.cca
and drop1.cca
. With these functions,
ordination models can be chosen with standard R function
step
which bases the term choice on AIC. AIC-like
statistics for ordination are provided by functions
deviance.cca
and extractAIC.cca
(with
similar functions for rda
). Actually, constrained
ordination methods do not have AIC, and therefore the step
may not be trusted. This function provides an alternative using
permutation -values.
Function ordistep
defines the model, scope
of models
considered, and direction
of the procedure similarly as
step
. The function alternates with drop
and
add
steps and stops when the model was not changed during one
step. The -
and +
signs in the summary table indicate
which stage is performed. It is often sensible to have Pout
Pin
in stepwise models to avoid cyclic adds and drops
of single terms.
Function ordiR2step
builds model forward so that it maximizes
adjusted (function
RsquareAdj
) at every
step, and stopping when the adjusted starts to decrease,
or the adjusted
of the
scope
is exceeded, or the
selected permutation -value is exceeded (Blanchet et
al. 2008). The second criterion is ignored with option
R2scope =
FALSE
, and the third criterion can be ignored setting Pin = 1
(or higher). The function cannot be used if adjusted
cannot be calculated. If the number of predictors is higher than the
number of observations, adjusted
is also unavailable.
Such models can be analysed with
R2scope = FALSE
, but the
variable selection will stop if models become overfitted and adjusted
cannot be calculated, and the adjusted
will be reported as zero. The
of
cca
is
based on simulations (see RsquareAdj
) and different runs
of ordiR2step
can give different results.
Functions ordistep
(based on values) and
ordiR2step
(based on adjusted and hence on eigenvalues) can select
variables in different order.
Functions return the selected model with one additional
component, anova
, which contains brief information of steps
taken. You can suppress voluminous output during model building by
setting trace = FALSE
, and find the summary of model history
in the anova
item.
Jari Oksanen
Blanchet, F. G., Legendre, P. & Borcard, D. (2008) Forward selection of explanatory variables. Ecology 89, 2623–2632.
The function handles constrained ordination methods
cca
, rda
, dbrda
and
capscale
. The underlying functions are
add1.cca
and drop1.cca
, and the function
is modelled after standard step
(which also can be
used directly but uses AIC for model choice, see
extractAIC.cca
). Function ordiR2step
builds
upon RsquareAdj
.
## See add1.cca for another example ### Dune data data(dune) data(dune.env) mod0 <- rda(dune ~ 1, dune.env) # Model with intercept only mod1 <- rda(dune ~ ., dune.env) # Model with all explanatory variables ## With scope present, the default direction is "both" mod <- ordistep(mod0, scope = formula(mod1)) mod ## summary table of steps mod$anova ## Example of ordistep, forward ordistep(mod0, scope = formula(mod1), direction="forward") ## Example of ordiR2step (always forward) ## stops because R2 of 'mod1' exceeded ordiR2step(mod0, mod1)
## See add1.cca for another example ### Dune data data(dune) data(dune.env) mod0 <- rda(dune ~ 1, dune.env) # Model with intercept only mod1 <- rda(dune ~ ., dune.env) # Model with all explanatory variables ## With scope present, the default direction is "both" mod <- ordistep(mod0, scope = formula(mod1)) mod ## summary table of steps mod$anova ## Example of ordistep, forward ordistep(mod0, scope = formula(mod1), direction="forward") ## Example of ordiR2step (always forward) ## stops because R2 of 'mod1' exceeded ordiR2step(mod0, mod1)
Function ordisurf
fits a smooth surface for given variable and
plots the result on ordination diagram.
## Default S3 method: ordisurf(x, y, choices = c(1, 2), knots = 10, family = "gaussian", col = "red", isotropic = TRUE, thinplate = TRUE, bs = "tp", fx = FALSE, add = FALSE, display = "sites", w, main, nlevels = 10, levels, npoints = 31, labcex = 0.6, bubble = FALSE, cex = 1, select = TRUE, method = "REML", gamma = 1, plot = TRUE, lwd.cl = par("lwd"), ...) ## S3 method for class 'formula' ordisurf(formula, data, ...) ## S3 method for class 'ordisurf' calibrate(object, newdata, ...) ## S3 method for class 'ordisurf' plot(x, what = c("contour","persp","gam"), add = FALSE, bubble = FALSE, col = "red", cex = 1, nlevels = 10, levels, labcex = 0.6, lwd.cl = par("lwd"), ...)
## Default S3 method: ordisurf(x, y, choices = c(1, 2), knots = 10, family = "gaussian", col = "red", isotropic = TRUE, thinplate = TRUE, bs = "tp", fx = FALSE, add = FALSE, display = "sites", w, main, nlevels = 10, levels, npoints = 31, labcex = 0.6, bubble = FALSE, cex = 1, select = TRUE, method = "REML", gamma = 1, plot = TRUE, lwd.cl = par("lwd"), ...) ## S3 method for class 'formula' ordisurf(formula, data, ...) ## S3 method for class 'ordisurf' calibrate(object, newdata, ...) ## S3 method for class 'ordisurf' plot(x, what = c("contour","persp","gam"), add = FALSE, bubble = FALSE, col = "red", cex = 1, nlevels = 10, levels, labcex = 0.6, lwd.cl = par("lwd"), ...)
x |
For |
y |
Variable to be plotted / modelled as a function of the ordination scores. |
choices |
Ordination axes. |
knots |
Number of initial knots in |
family |
Error distribution in |
col |
Colour of contours. |
isotropic , thinplate
|
Fit an isotropic smooth surface (i.e. same
smoothness in both ordination dimensions) via
|
bs |
a two letter character string indicating the smoothing basis
to use. (e.g. |
fx |
indicates whether the smoothers are fixed degree of freedom
regression splines ( |
add |
Add contours to an existing diagram or draw a new plot? |
display |
Type of scores known by |
w |
Prior weights on the data. Weights of the ordination object
will be used if the object has attribute |
main |
The main title for the plot, or as default the name of plotted variable in a new plot. |
nlevels , levels
|
Either a vector of |
npoints |
numeric; the number of locations at which to evaluate the fitted surface. This represents the number of locations in each dimension. |
labcex |
Label size in contours. Setting this zero will suppress labels. |
bubble |
Use a “bubble plot” for points, or vary the point
diameter by the value of the plotted variable. If |
cex |
Character expansion of plotting symbols. |
select |
Logical; specify |
method |
character; the smoothing parameter estimation
method. Options allowed are: |
gamma |
Multiplier to inflate model degrees of freedom in GCV or
UBRE/AIC score by. This effectively places an extra penalty on
complex models. An oft-used value is |
plot |
logical; should any plotting be done by
|
lwd.cl |
numeric; the |
formula , data
|
Alternative definition of the fitted model as
|
object |
An |
newdata |
Coordinates in two-dimensional ordination for new points. |
what |
character; what type of plot to produce. |
... |
Other parameters passed to |
Function ordisurf
fits a smooth surface using penalised
splines (Wood 2003) in gam
, and uses
predict.gam
to find fitted values in a regular
grid. The smooth surface can be fitted with an extra penalty that
allows the entire smoother to be penalized back to 0 degrees of
freedom, effectively removing the term from the model (see Marra &
Wood, 2011). The addition of this extra penalty is invoked by
setting argument select
to TRUE
. An alternative is to
use a spline basis that includes shrinkage (bs = "ts"
or
bs = "cs"
).
ordisurf()
exposes a large number of options from
gam
for specifying the basis functions used for
the surface. If you stray from the defaults, do read the
Notes section below and relevant documentation in
s
and smooth.terms
.
The function plots the fitted contours with convex hull of data points
either over an existing ordination diagram or draws a new plot. If
select = TRUE
and the smooth is effectively penalised out of
the model, no contours will be plotted.
gam
determines the degree of smoothness for the
fitted response surface during model fitting, unless fx =
TRUE
. Argument method
controls how gam
performs this smoothness selection. See gam
for
details of the available options. Using "REML"
or "ML"
yields p-values for smooths with the best coverage properties if such
things matter to you.
The function uses scores
to extract ordination scores,
and x
can be any result object known by that function.
The user can supply a vector of prior weights w
. If the
ordination object has weights, these will be used. In practise this
means that the row totals are used as weights with cca
or decorana
results. If you do not like this, but want
to give equal weights to all sites, you should set w =
NULL
. The behaviour is consistent with envfit
. For
complete accordance with constrained cca
, you should set
display = "lc"
.
Function calibrate
returns the fitted values of the response
variable. The newdata
must be coordinates of points for which
the fitted values are desired. The function is based on
predict.gam
and will pass extra arguments to
that function.
ordisurf
is usually called for its side effect of drawing the
contour plot. The function returns a result object of class
"ordisurf"
that inherits from gam
used
internally to fit the surface, but adds an item grid
that
contains the data for the grid surface. The item grid
has
elements x
and y
which are vectors of axis coordinates,
and element z
that is a matrix of fitted values for
contour
. The values outside the convex hull of observed
points are indicated as NA
in z
. The
gam
component of the result can be used for
further analysis like predicting new values (see
predict.gam
).
The fitted GAM is a regression model and has the usual assumptions of such models. Of particular note is the assumption of independence of residuals. If the observations are not independent (e.g. they are repeat measures on a set of objects, or from an experimental design, inter alia) do not trust the p-values from the GAM output.
If you need further control (i.e. to add additional fixed effects to
the model, or use more complex smoothers), extract the ordination
scores using the scores
function and then generate your own
gam
call.
The default is to use an isotropic smoother via
s
employing thin plate regression splines
(bs = "tp"
). These make sense in ordination as they have
equal smoothing in all directions and are rotation invariant. However,
if different degrees of smoothness along dimensions are required, an
anisotropic smooth surface may be more applicable. This can be
achieved through the use of isotropic = FALSE
, wherein the
surface is fitted via a tensor product smoother via
te
(unless bs = "ad"
, in which case
separate splines for each dimension are fitted using
s
).
Cubic regression splines and P splines can only be used with
isotropic = FALSE
.
Adaptive smooths (bs = "ad"
), especially in two dimensions,
require a large number of observations; without many hundreds of
observations, the default complexities for the smoother will exceed
the number of observations and fitting will fail.
To get the old behaviour of ordisurf
use select = FALSE
,
method = "GCV.Cp"
, fx = FALSE
, and bs = "tp"
. The
latter two options are the current defaults.
Graphical arguments supplied to plot.ordisurf
are passed on to
the underlying plotting functions, contour
, persp
, and
plot.gam
. The exception to this is that arguments
col
and cex
can not currently be passed to
plot.gam
because of a bug in the way that function
evaluates arguments when arranging the plot.
A work-around is to call plot.gam
directly on the
result of a call to ordisurf
. See the Examples for an
illustration of this.
Dave Roberts, Jari Oksanen and Gavin L. Simpson
Marra, G.P & Wood, S.N. (2011) Practical variable selection for generalized additive models. Comput. Stat. Data Analysis 55, 2372–2387.
Wood, S.N. (2003) Thin plate regression splines. J. R. Statist. Soc. B 65, 95–114.
For basic routines gam
,
and scores
. Function
envfit
provides a more traditional and compact
alternative.
data(varespec) data(varechem) vare.dist <- vegdist(varespec) vare.mds <- monoMDS(vare.dist) ## IGNORE_RDIFF_BEGIN ordisurf(vare.mds ~ Baresoil, varechem, bubble = 5) ## as above but without the extra penalties on smooth terms, ## and using GCV smoothness selection (old behaviour of `ordisurf()`): ordisurf(vare.mds ~ Baresoil, varechem, col = "blue", add = TRUE, select = FALSE, method = "GCV.Cp") ## Cover of Cladina arbuscula fit <- ordisurf(vare.mds ~ Cladarbu, varespec, family=quasipoisson) ## Get fitted values calibrate(fit) ## Variable selection via additional shrinkage penalties ## This allows non-significant smooths to be selected out ## of the model not just to a linear surface. There are 2 ## options available: ## - option 1: `select = TRUE` --- the *default* ordisurf(vare.mds ~ Baresoil, varechem, method = "REML", select = TRUE) ## - option 2: use a basis with shrinkage ordisurf(vare.mds ~ Baresoil, varechem, method = "REML", bs = "ts") ## or bs = "cs" with `isotropic = FALSE` ## IGNORE_RDIFF_END ## Plot method plot(fit, what = "contour") ## Plotting the "gam" object plot(fit, what = "gam") ## 'col' and 'cex' not passed on ## or via plot.gam directly library(mgcv) plot.gam(fit, cex = 2, pch = 1, col = "blue") ## 'col' effects all objects drawn... ### controlling the basis functions used ## Use Duchon splines ordisurf(vare.mds ~ Baresoil, varechem, bs = "ds") ## A fixed degrees of freedom smooth, must use 'select = FALSE' ordisurf(vare.mds ~ Baresoil, varechem, knots = 4, fx = TRUE, select = FALSE) ## An anisotropic smoother with cubic regression spline bases ordisurf(vare.mds ~ Baresoil, varechem, isotropic = FALSE, bs = "cr", knots = 4) ## An anisotropic smoother with cubic regression spline with ## shrinkage bases & different degrees of freedom in each dimension ordisurf(vare.mds ~ Baresoil, varechem, isotropic = FALSE, bs = "cs", knots = c(3,4), fx = TRUE, select = FALSE)
data(varespec) data(varechem) vare.dist <- vegdist(varespec) vare.mds <- monoMDS(vare.dist) ## IGNORE_RDIFF_BEGIN ordisurf(vare.mds ~ Baresoil, varechem, bubble = 5) ## as above but without the extra penalties on smooth terms, ## and using GCV smoothness selection (old behaviour of `ordisurf()`): ordisurf(vare.mds ~ Baresoil, varechem, col = "blue", add = TRUE, select = FALSE, method = "GCV.Cp") ## Cover of Cladina arbuscula fit <- ordisurf(vare.mds ~ Cladarbu, varespec, family=quasipoisson) ## Get fitted values calibrate(fit) ## Variable selection via additional shrinkage penalties ## This allows non-significant smooths to be selected out ## of the model not just to a linear surface. There are 2 ## options available: ## - option 1: `select = TRUE` --- the *default* ordisurf(vare.mds ~ Baresoil, varechem, method = "REML", select = TRUE) ## - option 2: use a basis with shrinkage ordisurf(vare.mds ~ Baresoil, varechem, method = "REML", bs = "ts") ## or bs = "cs" with `isotropic = FALSE` ## IGNORE_RDIFF_END ## Plot method plot(fit, what = "contour") ## Plotting the "gam" object plot(fit, what = "gam") ## 'col' and 'cex' not passed on ## or via plot.gam directly library(mgcv) plot.gam(fit, cex = 2, pch = 1, col = "blue") ## 'col' effects all objects drawn... ### controlling the basis functions used ## Use Duchon splines ordisurf(vare.mds ~ Baresoil, varechem, bs = "ds") ## A fixed degrees of freedom smooth, must use 'select = FALSE' ordisurf(vare.mds ~ Baresoil, varechem, knots = 4, fx = TRUE, select = FALSE) ## An anisotropic smoother with cubic regression spline bases ordisurf(vare.mds ~ Baresoil, varechem, isotropic = FALSE, bs = "cr", knots = 4) ## An anisotropic smoother with cubic regression spline with ## shrinkage bases & different degrees of freedom in each dimension ordisurf(vare.mds ~ Baresoil, varechem, isotropic = FALSE, bs = "cs", knots = c(3,4), fx = TRUE, select = FALSE)
The function adds text
or points
to
ordination plots. Text will be used if this can be done without
overwriting other text labels, and points will be used otherwise. The
function can help in reducing clutter in ordination graphics, but
manual editing may still be necessary.
orditorp(x, display, labels, choices = c(1, 2), priority, select, cex = 0.7, pcex, col = par("col"), pcol, pch = par("pch"), air = 1, ...)
orditorp(x, display, labels, choices = c(1, 2), priority, select, cex = 0.7, pcex, col = par("col"), pcol, pch = par("pch"), air = 1, ...)
x |
A result object from ordination or an |
display |
Items to be displayed in the plot. Only one
alternative is allowed. Typically this is |
labels |
Optional text used for labels. Row names of scores will be used if this is missing. |
choices |
Axes shown. |
priority |
Text will be used for items with higher priority if labels overlap. This should be vector of the same length as the number of items plotted. |
select |
Items to be displayed. This can either be a logical
vector which is |
cex , pcex
|
Text and point sizes, see |
col , pcol
|
Text and point colours, see |
pch |
Plotting character, see |
air |
Amount of empty space between text labels. Values <1 allow overlapping text. |
... |
Other arguments to |
Function orditorp
will add either text or points to an existing
plot. The items with high priority
will be added first
and text
will be used if this can be done without
overwriting previous labels,and points
will be used
otherwise. If priority
is missing, labels will be added from the
outskirts to the centre. Function orditorp
can be used
with most ordination results, or plotting results from
ordiplot
or ordination plot functions
(plot.cca
, plot.decorana
,
plot.metaMDS
). Function can also be used in a pipe
(|>
) where the first command is a vegan ordination
plot
command or ordiplot
.
Arguments can be passed to the relevant scores
method
for the ordination object (x
) being drawn. See the relevant
scores
help page for arguments that can be used.
The function returns invisibly the The function returns invisibly a
logical vector where TRUE
means that item was labelled with
text and FALSE
means that it was marked with a point. If
function is used in an ordiplot
pipe, it will return the
input ordiplot
object, but amend the plotted scores with this
vector as attribute "orditorp"
. The returned vector can be used
as the select
argument in ordination text
and
points
functions.
Jari Oksanen
## A cluttered ordination plot : data(BCI) mod <- cca(BCI) plot(mod, dis="sp", type="t") # Now with orditorp and abbreviated species names cnam <- make.cepnames(names(BCI)) plot(mod, dis="sp", type="n") stems <- colSums(BCI) orditorp(mod, "sp", label = cnam, priority=stems, pch="+", pcol="grey") ## show select in action set.seed(1) take <- sample(ncol(BCI), 50) plot(mod, dis="sp", type="n") stems <- colSums(BCI) orditorp(mod, "sp", label = cnam, priority=stems, select = take, pch="+", pcol="grey")
## A cluttered ordination plot : data(BCI) mod <- cca(BCI) plot(mod, dis="sp", type="t") # Now with orditorp and abbreviated species names cnam <- make.cepnames(names(BCI)) plot(mod, dis="sp", type="n") stems <- colSums(BCI) orditorp(mod, "sp", label = cnam, priority=stems, pch="+", pcol="grey") ## show select in action set.seed(1) take <- sample(ncol(BCI), 50) plot(mod, dis="sp", type="n") stems <- colSums(BCI) orditorp(mod, "sp", label = cnam, priority=stems, select = take, pch="+", pcol="grey")
Functions ordicloud
, ordisplom
and ordixyplot
provide an interface to plot ordination results using Trellis
functions cloud
, splom
and xyplot
in package lattice.
ordixyplot(x, data = NULL, formula, display = "sites", choices = 1:3, panel = "panel.ordi", aspect = "iso", envfit, type = c("p", "biplot"), ...) ordisplom(x, data=NULL, formula = NULL, display = "sites", choices = 1:3, panel = "panel.ordi", type = "p", ...) ordicloud(x, data = NULL, formula, display = "sites", choices = 1:3, panel = "panel.ordi3d", prepanel = "prepanel.ordi3d", ...)
ordixyplot(x, data = NULL, formula, display = "sites", choices = 1:3, panel = "panel.ordi", aspect = "iso", envfit, type = c("p", "biplot"), ...) ordisplom(x, data=NULL, formula = NULL, display = "sites", choices = 1:3, panel = "panel.ordi", type = "p", ...) ordicloud(x, data = NULL, formula, display = "sites", choices = 1:3, panel = "panel.ordi3d", prepanel = "prepanel.ordi3d", ...)
x |
An ordination result that |
data |
Optional data to amend ordination results. The ordination
results are found from |
formula |
Formula to define the plots. A default formula will be
used if this is omitted. The
ordination axes must be called by the same names as in the
ordination results (and these names vary among methods). In
|
display |
The kind of scores: an argument passed to
|
choices |
The axes selected: an argument passed to
|
panel , prepanel
|
The names of the panel and prepanel functions. |
aspect |
The aspect of the plot (passed to the lattice function). |
envfit |
Result of |
type |
The type of plot. This knows the same alternatives as
|
... |
Arguments passed to |
The functions provide an interface to the corresponding lattice
functions. All graphical parameters are passed to the lattice
function so that these graphs are extremely configurable. See
Lattice
and xyplot
,
splom
and cloud
for
details, usage and possibilities.
The argument x
must always be an ordination result. The scores
are extracted with vegan function scores
so that
these functions work with all vegan ordinations and many others.
The formula
is used to define the models. All functions have
simple default formulae which are used if formula
is missing.
If formula is omitted in ordisplom
it
produces a pairs plot of ordination axes and variables in
data
. If formula
is given, ordination results must be
referred to as .
and other variables by their names. In other
functions, the formula must use the names of ordination scores and names
of data
.
The ordination scores are found from x
, and data
is
optional. The data
should contain other variables than
ordination scores to be used in plots. Typically, they are
environmental variables (typically factors) to define panels or plot
symbols.
The proper work is done by the panel function. The layout can be
changed by defining own panel functions. See
panel.xyplot
,
panel.splom
and
panel.cloud
for details and survey of
possibilities.
Ordination graphics should always be isometric: same scale should be
used in all axes. This is controlled (and can be changed) with
argument aspect
in ordixyplot
. In ordicloud
the
isometric scaling is defined in panel
and prepanel
functions. You must replace these functions if you want to have
non-isometric scaling of graphs. You cannot select isometric scaling
in ordisplom
.
The function return Lattice
objects of class
"trellis"
.
Jari Oksanen
Lattice
,
xyplot
,
splom
,
cloud
,
panel.splom
,
panel.cloud
data(dune, dune.env) ord <- cca(dune) ## Pairs plots ordisplom(ord) ordisplom(ord, data=dune.env, choices=1:2) ordisplom(ord, data=dune.env, form = ~ . | Management, groups=Manure) ## Scatter plot with polygons ordixyplot(ord, data=dune.env, form = CA1 ~ CA2 | Management, groups=Manure, type = c("p","polygon")) ## Choose a different scaling ordixyplot(ord, scaling = "symmetric") ## ... Slices of third axis ordixyplot(ord, form = CA1 ~ CA2 | equal.count(CA3, 4), type = c("g","p", "polygon")) ## Display environmental variables ordixyplot(ord, envfit = envfit(ord ~ Management + A1, dune.env, choices=1:3)) ## 3D Scatter plots ordicloud(ord, form = CA2 ~ CA3*CA1, groups = Manure, data = dune.env) ordicloud(ord, form = CA2 ~ CA3*CA1 | Management, groups = Manure, data = dune.env, auto.key = TRUE, type = c("p","h"))
data(dune, dune.env) ord <- cca(dune) ## Pairs plots ordisplom(ord) ordisplom(ord, data=dune.env, choices=1:2) ordisplom(ord, data=dune.env, form = ~ . | Management, groups=Manure) ## Scatter plot with polygons ordixyplot(ord, data=dune.env, form = CA1 ~ CA2 | Management, groups=Manure, type = c("p","polygon")) ## Choose a different scaling ordixyplot(ord, scaling = "symmetric") ## ... Slices of third axis ordixyplot(ord, form = CA1 ~ CA2 | equal.count(CA3, 4), type = c("g","p", "polygon")) ## Display environmental variables ordixyplot(ord, envfit = envfit(ord ~ Management + A1, dune.env, choices=1:3)) ## 3D Scatter plots ordicloud(ord, form = CA2 ~ CA3*CA1, groups = Manure, data = dune.env) ordicloud(ord, form = CA2 ~ CA3*CA1 | Management, groups = Manure, data = dune.env, auto.key = TRUE, type = c("p","h"))
This function computed classical PCNM by the principal coordinate analysis of a truncated distance matrix. These are commonly used to transform (spatial) distances to rectangular data that suitable for constrained ordination or regression.
pcnm(dis, threshold, w, dist.ret = FALSE)
pcnm(dis, threshold, w, dist.ret = FALSE)
dis |
A distance matrix. |
threshold |
A threshold value or truncation distance. If
missing, minimum distance giving connected network will be
used. This is found as the longest distance in the minimum spanning
tree of |
w |
Prior weights for rows. |
dist.ret |
Return the distances used to calculate the PCNMs. |
Principal Coordinates of Neighbourhood Matrix (PCNM) map distances between rows onto rectangular matrix on rows using a truncation threshold for long distances (Borcard & Legendre 2002). If original distances were Euclidean distances in two dimensions (like normal spatial distances), they could be mapped onto two dimensions if there is no truncation of distances. Because of truncation, there will be a higher number of principal coordinates. The selection of truncation distance has a huge influence on the PCNM vectors. The default is to use the longest distance to keep data connected. The distances above truncation threshold are given an arbitrary value of 4 times threshold. For regular data, the first PCNM vectors show a wide scale variation and later PCNM vectors show smaller scale variation (Borcard & Legendre 2002), but for irregular data the interpretation is not as clear.
The PCNM functions are used to express distances in rectangular form
that is similar to normal explanatory variables used in, e.g.,
constrained ordination (rda
, cca
and
dbrda
) or univariate regression (lm
)
together with environmental variables (row weights should be supplied
with cca
; see Examples). This is regarded as a more
powerful method than forcing rectangular environmental data into
distances and using them in partial mantel analysis
(mantel.partial
) together with geographic distances
(Legendre et al. 2008, but see Tuomisto & Ruokolainen 2008).
The function is based on pcnm
function in Dray's unreleased
spacemakeR package. The differences are that the current
function uses spantree
as an internal support
function. The current function also can use prior weights for rows by
using weighted metric scaling of wcmdscale
. The use of
row weights allows finding orthonormal PCNMs also for correspondence
analysis (e.g., cca
).
A list of the following elements:
values |
Eigenvalues obtained by the principal coordinates analysis. |
vectors |
Eigenvectors obtained by the principal coordinates
analysis. They are scaled to unit norm. The vectors can be extracted
with |
threshold |
Truncation distance. |
dist |
The distance matrix where values above |
Jari Oksanen, based on the code of Stephane Dray.
Borcard D. and Legendre P. (2002) All-scale spatial analysis of ecological data by means of principal coordinates of neighbour matrices. Ecological Modelling 153, 51–68.
Legendre, P., Borcard, D and Peres-Neto, P. (2008) Analyzing or explaining beta diversity? Comment. Ecology 89, 3238–3244.
Tuomisto, H. & Ruokolainen, K. (2008) Analyzing or explaining beta diversity? A reply. Ecology 89, 3244–3256.
## Example from Borcard & Legendre (2002) data(mite.xy) pcnm1 <- pcnm(dist(mite.xy)) op <- par(mfrow=c(1,3)) ## Map of PCNMs in the sample plot ordisurf(mite.xy, scores(pcnm1, choi=1), bubble = 4, main = "PCNM 1") ordisurf(mite.xy, scores(pcnm1, choi=2), bubble = 4, main = "PCNM 2") ordisurf(mite.xy, scores(pcnm1, choi=3), bubble = 4, main = "PCNM 3") par(op) ## Plot first PCNMs against each other ordisplom(pcnm1, choices=1:4) ## Weighted PCNM for CCA data(mite) rs <- rowSums(mite)/sum(mite) pcnmw <- pcnm(dist(mite.xy), w = rs) ord <- cca(mite ~ scores(pcnmw)) ## Multiscale ordination: residual variance should have no distance ## trend msoplot(mso(ord, mite.xy))
## Example from Borcard & Legendre (2002) data(mite.xy) pcnm1 <- pcnm(dist(mite.xy)) op <- par(mfrow=c(1,3)) ## Map of PCNMs in the sample plot ordisurf(mite.xy, scores(pcnm1, choi=1), bubble = 4, main = "PCNM 1") ordisurf(mite.xy, scores(pcnm1, choi=2), bubble = 4, main = "PCNM 2") ordisurf(mite.xy, scores(pcnm1, choi=3), bubble = 4, main = "PCNM 3") par(op) ## Plot first PCNMs against each other ordisplom(pcnm1, choices=1:4) ## Weighted PCNM for CCA data(mite) rs <- rowSums(mite)/sum(mite) pcnmw <- pcnm(dist(mite.xy), w = rs) ord <- cca(mite ~ scores(pcnmw)) ## Multiscale ordination: residual variance should have no distance ## trend msoplot(mso(ord, mite.xy))
Individual (for count data) or incidence (for presence-absence data) based null models can be generated for community level simulations. Options for preserving characteristics of the original matrix (rows/columns sums, matrix fill) and restricted permutations (based on strata) are discussed in the Details section.
permatfull(m, fixedmar = "both", shuffle = "both", strata = NULL, mtype = "count", times = 99, ...) permatswap(m, method = "quasiswap", fixedmar="both", shuffle = "both", strata = NULL, mtype = "count", times = 99, burnin = 0, thin = 1, ...) ## S3 method for class 'permat' print(x, digits = 3, ...) ## S3 method for class 'permat' summary(object, ...) ## S3 method for class 'summary.permat' print(x, digits = 2, ...) ## S3 method for class 'permat' plot(x, type = "bray", ylab, xlab, col, lty, lowess = TRUE, plot = TRUE, text = TRUE, ...) ## S3 method for class 'permat' lines(x, type = "bray", ...) ## S3 method for class 'permat' as.ts(x, type = "bray", ...) ## S3 method for class 'permat' toCoda(x)
permatfull(m, fixedmar = "both", shuffle = "both", strata = NULL, mtype = "count", times = 99, ...) permatswap(m, method = "quasiswap", fixedmar="both", shuffle = "both", strata = NULL, mtype = "count", times = 99, burnin = 0, thin = 1, ...) ## S3 method for class 'permat' print(x, digits = 3, ...) ## S3 method for class 'permat' summary(object, ...) ## S3 method for class 'summary.permat' print(x, digits = 2, ...) ## S3 method for class 'permat' plot(x, type = "bray", ylab, xlab, col, lty, lowess = TRUE, plot = TRUE, text = TRUE, ...) ## S3 method for class 'permat' lines(x, type = "bray", ...) ## S3 method for class 'permat' as.ts(x, type = "bray", ...) ## S3 method for class 'permat' toCoda(x)
m |
A community data matrix with plots (samples) as rows and species (taxa) as columns. |
fixedmar |
character, stating which of the row/column sums should
be preserved ( |
strata |
Numeric vector or factor with length same as
|
mtype |
Matrix data type, either |
times |
Number of permuted matrices. |
method |
Character for method used for the swap algorithm
( |
shuffle |
Character, indicating whether individuals
( |
burnin |
Number of null communities discarded before proper
analysis in sequential ( |
thin |
Number of discarded permuted matrices between two
evaluations in sequential ( |
x , object
|
Object of class |
digits |
Number of digits used for rounding. |
ylab , xlab , col , lty
|
graphical parameters for the |
type |
Character, type of plot to be displayed: |
lowess , plot , text
|
Logical arguments for the |
... |
Other arguments passed to |
The function permatfull
is useful when matrix fill is
allowed to vary, and matrix type is count
. The fixedmar
argument is used to set constraints for permutation. If none
of the margins are fixed, cells are randomised within the matrix. If
rows
or columns
are fixed, cells within rows or columns
are randomised, respectively. If both
margins are fixed, the
r2dtable
function is used that is based on Patefield's
(1981) algorithm. For presence absence data, matrix fill should be
necessarily fixed, and permatfull
is a wrapper for the function
make.commsim
. The r00, r0, c0, quasiswap
algorithms of make.commsim
are used for "none",
"rows", "columns", "both"
values of the fixedmar
argument,
respectively
The shuffle
argument only have effect if the mtype =
"count"
and permatfull
function is used with "none",
"rows", "columns"
values of fixedmar
. All other cases for
count data are individual based randomisations. The "samp"
and
"both"
options result fixed matrix fill. The "both"
option means that individuals are shuffled among non zero cells
ensuring that there are no cell with zeros as a result, then cell
(zero and new valued cells) are shuffled.
The function permatswap
is useful when with matrix fill
(i.e. the proportion of empty cells) and row/columns sums should be
kept constant. permatswap
uses different kinds of swap
algorithms, and row and columns sums are fixed in all cases. For
presence-absence data, the swap
and tswap
methods of
make.commsim
can be used. For count data, a special
swap algorithm ('swapcount') is implemented that results in permuted
matrices with fixed marginals and matrix fill at the same time.
The 'quasiswapcount' algorithm (method="quasiswap"
and
mtype="count"
) uses the same trick as Carsten Dormann's
swap.web
function in the package
bipartite. First, a random matrix is generated by the
r2dtable
function retaining row and column sums. Then
the original matrix fill is reconstructed by sequential steps to
increase or decrease matrix fill in the random matrix. These steps are
based on swapping 2x2 submatrices (see 'swapcount' algorithm for
details) to maintain row and column totals. This algorithm generates
independent matrices in each step, so burnin
and thin
arguments are not considered. This is the default method, because this
is not sequential (as swapcount
is) so independence of subsequent
matrices does not have to be checked.
The swapcount
algorithm (method="swap"
and
mtype="count"
) tries to find 2x2 submatrices (identified by 2
random row and 2 random column indices), that can be swapped in order
to leave column and row totals and fill unchanged. First, the
algorithm finds the largest value in the submatrix that can be swapped
() and whether in diagonal or antidiagonal way. Submatrices
that contain values larger than zero in either diagonal or
antidiagonal position can be swapped. Swap means that the values in
diagonal or antidiagonal positions are decreased by
, while
remaining cells are increased by
. A swap is made only if fill
doesn't change. This algorithm is sequential, subsequent matrices are
not independent, because swaps modify little if the matrix is
large. In these cases many burnin steps and thinning is needed to get
independent random matrices. Although this algorithm is implemented in
C, large burnin and thin values can slow it down
considerably. WARNING: according to simulations, this algorithm seems
to be biased and non random, thus its use should be avoided!
The algorithm "swsh"
in the function permatswap
is a
hybrid algorithm. First, it makes binary quasiswaps to keep row and
column incidences constant, then non-zero values are modified
according to the shuffle
argument (only "samp"
and
"both"
are available in this case, because it is applied only
on non-zero values). It also recognizes the fixedmar
argument which cannot be "both"
(vegan versions <= 2.0
had this algorithm with fixedmar = "none"
).
The algorithm "abuswap"
produces two kinds of null models
(based on fixedmar="columns"
or fixedmar="rows"
) as
described in Hardy (2008; randomization scheme 2x and 3x,
respectively). These preserve column and row occurrences, and column
or row sums at the same time. (Note that similar constraints
can be achieved by the non sequential "swsh"
algorithm
with fixedmar
argument set to "columns"
or
"rows"
, respectively.)
Constraints on row/column sums, matrix fill, total sum and sums within
strata can be checked by the summary
method. plot
method
is for visually testing the randomness of the permuted matrices,
especially for the sequential swap algorithms. If there are any
tendency in the graph, higher burnin
and thin
values can
help for sequential methods. New lines can be added to existing plot
with the lines
method.
Unrestricted and restricted permutations: if strata
is
NULL
, functions perform unrestricted permutations. Otherwise,
it is used for restricted permutations. Each strata should contain at
least 2 rows in order to perform randomization (in case of low row
numbers, swap algorithms can be rather slow). If the design is not
well balanced (i.e. same number of observations within each stratum),
permuted matrices may be biased because same constraints are forced on
submatrices of different dimensions. This often means, that the number
of potential permutations will decrease with their dimensions. So the
more constraints we put, the less randomness can be expected.
The plot
method is useful for graphically testing for trend and
independence of permuted matrices. This is especially important when
using sequential algorithms ("swap", "tswap", "abuswap"
).
The as.ts
method can be used to extract Bray-Curtis
dissimilarities or Chi-squared values as time series. This can further
used in testing independence (see Examples). The method toCoda
is useful for accessing diagnostic tools available in the coda
package.
Functions permatfull
and permatswap
return an
object of class "permat"
containing the the function call
(call
), the original data matrix used for permutations
(orig
) and a list of permuted matrices with length times
(perm
).
The summary
method returns various statistics as a list
(including mean Bray-Curtis dissimilarities calculated pairwise among
original and permuted matrices, Chi-square statistics, and check
results of the constraints; see Examples). Note that when
strata
is used in the original call, summary calculation may
take longer.
The plot
creates a plot as a side effect.
The as.ts
method returns an object of class "ts"
.
Péter Sólymos, [email protected] and Jari Oksanen
Original references for presence-absence algorithms are
given on help page of make.commsim
.
Hardy, O. J. (2008) Testing the spatial phylogenetic structure of local communities: statistical performances of different null models and test statistics on a locally neutral community. Journal of Ecology 96, 914–926.
Patefield, W. M. (1981) Algorithm AS159. An efficient method of generating r x c tables with given row and column totals. Applied Statistics 30, 91–97.
For other functions to permute matrices:
make.commsim
, r2dtable
,
sample
.
For the use of these permutation algorithms: oecosimu
,
adipart
, hiersimu
.
For time-series diagnostics: Box.test
,
lag.plot
, tsdiag
, ar
,
arima
For underlying low level implementation:
commsim
and nullmodel
.
## A simple artificial community data matrix. m <- matrix(c( 1,3,2,0,3,1, 0,2,1,0,2,1, 0,0,1,2,0,3, 0,0,0,1,4,3 ), 4, 6, byrow=TRUE) ## Using the quasiswap algorithm to create a ## list of permuted matrices, where ## row/columns sums and matrix fill are preserved: x1 <- permatswap(m, "quasiswap") summary(x1) ## Unrestricted permutation retaining ## row/columns sums but not matrix fill: x2 <- permatfull(m) summary(x2) ## Unrestricted permutation of presence-absence type ## not retaining row/columns sums: x3 <- permatfull(m, "none", mtype="prab") x3$orig ## note: original matrix is binarized! summary(x3) ## Restricted permutation, ## check sums within strata: x4 <- permatfull(m, strata=c(1,1,2,2)) summary(x4) ## NOTE: 'times' argument usually needs to be >= 99 ## here much lower value is used for demonstration ## Not sequential algorithm data(BCI) a <- permatswap(BCI, "quasiswap", times=19) ## Sequential algorithm b <- permatswap(BCI, "abuswap", fixedmar="col", burnin=0, thin=100, times=19) opar <- par(mfrow=c(2,2)) plot(a, main="Not sequential") plot(b, main="Sequential") plot(a, "chisq") plot(b, "chisq") par(opar) ## Extract Bray-Curtis dissimilarities ## as time series bc <- as.ts(b) ## Lag plot lag.plot(bc) ## First order autoregressive model mar <- arima(bc, c(1,0,0)) mar ## Ljung-Box test of residuals Box.test(residuals(mar)) ## Graphical diagnostics tsdiag(mar)
## A simple artificial community data matrix. m <- matrix(c( 1,3,2,0,3,1, 0,2,1,0,2,1, 0,0,1,2,0,3, 0,0,0,1,4,3 ), 4, 6, byrow=TRUE) ## Using the quasiswap algorithm to create a ## list of permuted matrices, where ## row/columns sums and matrix fill are preserved: x1 <- permatswap(m, "quasiswap") summary(x1) ## Unrestricted permutation retaining ## row/columns sums but not matrix fill: x2 <- permatfull(m) summary(x2) ## Unrestricted permutation of presence-absence type ## not retaining row/columns sums: x3 <- permatfull(m, "none", mtype="prab") x3$orig ## note: original matrix is binarized! summary(x3) ## Restricted permutation, ## check sums within strata: x4 <- permatfull(m, strata=c(1,1,2,2)) summary(x4) ## NOTE: 'times' argument usually needs to be >= 99 ## here much lower value is used for demonstration ## Not sequential algorithm data(BCI) a <- permatswap(BCI, "quasiswap", times=19) ## Sequential algorithm b <- permatswap(BCI, "abuswap", fixedmar="col", burnin=0, thin=100, times=19) opar <- par(mfrow=c(2,2)) plot(a, main="Not sequential") plot(b, main="Sequential") plot(a, "chisq") plot(b, "chisq") par(opar) ## Extract Bray-Curtis dissimilarities ## as time series bc <- as.ts(b) ## Lag plot lag.plot(bc) ## First order autoregressive model mar <- arima(bc, c(1,0,0)) mar ## Ljung-Box test of residuals Box.test(residuals(mar)) ## Graphical diagnostics tsdiag(mar)
The permustats
function extracts permutation results of
vegan functions. Its support functions can find quantiles and
standardized effect sizes, plot densities and Q-Q plots.
permustats(x, ...) ## S3 method for class 'permustats' summary(object, interval = 0.95, alternative, ...) ## S3 method for class 'permustats' densityplot(x, data, xlab = "Permutations", ...) ## S3 method for class 'permustats' density(x, observed = TRUE, ...) ## S3 method for class 'permustats' qqnorm(y, observed = TRUE, ...) ## S3 method for class 'permustats' qqmath(x, data, observed = TRUE, sd.scale = FALSE, ylab = "Permutations", ...) ## S3 method for class 'permustats' boxplot(x, scale = FALSE, names, ...) ## S3 method for class 'permustats' pairs(x, ...)
permustats(x, ...) ## S3 method for class 'permustats' summary(object, interval = 0.95, alternative, ...) ## S3 method for class 'permustats' densityplot(x, data, xlab = "Permutations", ...) ## S3 method for class 'permustats' density(x, observed = TRUE, ...) ## S3 method for class 'permustats' qqnorm(y, observed = TRUE, ...) ## S3 method for class 'permustats' qqmath(x, data, observed = TRUE, sd.scale = FALSE, ylab = "Permutations", ...) ## S3 method for class 'permustats' boxplot(x, scale = FALSE, names, ...) ## S3 method for class 'permustats' pairs(x, ...)
object , x , y
|
The object to be handled. |
interval |
numeric; the coverage interval reported. |
alternative |
A character string specifying the limits used for
the |
xlab , ylab
|
Arguments of
|
observed |
Add observed statistic among permutations. |
sd.scale |
Scale permutations to unit standard deviation and observed statistic to standardized effect size. |
data |
Ignored. |
scale |
Use standardized effect size (SES). |
names |
Names of boxes (default: names of statistics). |
... |
Other arguments passed to the function. In
|
The permustats
function extracts permutation results and
observed statistics from several vegan functions that perform
permutations or simulations.
The summary
method of permustats
estimates the
standardized effect sizes (SES) as the difference of observed
statistic and mean of permutations divided by the standard deviation
of permutations (also known as -values). It also prints the
the mean, median, and limits which contain
interval
percent
of permuted values. With the default (interval = 0.95
), for
two-sided test these are (2.5%, 97.5%) and for one-sided tests
either 5% or 95% quantile and the -value depending on the
test direction. The mean, quantiles and
values are evaluated
from permuted values without observed statistic, but the
-value is evaluated with the observed statistic. The
intervals and the
-value are evaluated with the same test
direction as in the original test, but this can be changed with
argument
alternative
. Several permustats
objects can
be combined with c
function. The c
function checks
that statistics are equal, but performs no other sanity tests.
The density
and densityplot
methods display the
kernel density estimates of permuted values. When observed value of
the statistic is included in the permuted values, the
densityplot
method marks the observed statistic as a vertical
line. However the density
method uses its standard plot
method and cannot mark the observed value.
The qqnorm
and qqmath
display Q-Q plots of
permutations, optionally together with the observed value (default)
which is shown as horizontal line in plots. qqnorm
plots
permutation values against standard Normal variate. qqmath
defaults to the standard Normal as well, but can accept other
alternatives (see standard qqmath
). The
qqmath
function can also plot observed statistic as
standardized effect size (SES) with standandized permutations
(argument sd.scale
). The permutations are standardized
without the observed statistic, similarly as in summary
.
Functions density
and qqnorm
are based
on standard R methods and accept their arguments. They only handle
one statistic, and cannot be used when several test statistic were
evaluated. The densityplot
and
qqmath
are lattice graphics, and can be
used either for one or for several statistics. All these functions
pass arguments to their underlying functions; see their
documentation. Functions qqmath
and
densityplot
default to use same axis scaling
in all subplots of the lattice. You can use argument scales
to
set independent scaling for subplots when this is appropriate (see
xyplot
for an exhaustive list of arguments).
Function boxplot
draws the box-and-whiskers plots of effect
size, or the difference of permutations and observed statistic. If
scale = TRUE
, permutations are standardized to unit standard
deviation, and the plot will show the standardized effect sizes.
Function pairs
plots permutation values of statistics against
each other. The function passes extra arguments to
pairs
.
The permustats
can extract permutation statistics from the
results of adonis2
,
anosim
, anova.cca
, mantel
,
mantel.partial
, mrpp
,
oecosimu
, ordiareatest
,
permutest.cca
, protest
, and
permutest.betadisper
.
The permustats
function returns an object of class
"permustats"
. This is a list of items "statistic"
for
observed statistics, permutations
which contains permuted
values, and alternative
which contains text defining the
character of the test ("two.sided"
, "less"
or
"greater"
). The qqnorm
and
density
methods return their standard result objects.
Jari Oksanen with contributions from Gavin L. Simpson
(permustats.permutest.betadisper
method and related
modifications to summary.permustats
and the print
method) and Eduard Szöcs (permustats.anova.cca).
density
, densityplot
,
qqnorm
, qqmath
.
data(dune, dune.env) mod <- adonis2(dune ~ Management + A1, data = dune.env) ## use permustats perm <- permustats(mod) summary(perm) densityplot(perm) qqmath(perm) boxplot(perm, scale=TRUE, lty=1, pch=16, cex=0.6, col="hotpink", ylab="SES") abline(h=0, col="skyblue") ## example of multiple types of statistic mod <- with(dune.env, betadisper(vegdist(dune), Management)) pmod <- permutest(mod, nperm = 99, pairwise = TRUE) perm <- permustats(pmod) summary(perm, interval = 0.90)
data(dune, dune.env) mod <- adonis2(dune ~ Management + A1, data = dune.env) ## use permustats perm <- permustats(mod) summary(perm) densityplot(perm) qqmath(perm) boxplot(perm, scale=TRUE, lty=1, pch=16, cex=0.6, col="hotpink", ylab="SES") abline(h=0, col="skyblue") ## example of multiple types of statistic mod <- with(dune.env, betadisper(vegdist(dune), Management)) pmod <- permutest(mod, nperm = 99, pairwise = TRUE) perm <- permustats(pmod) summary(perm, interval = 0.90)
From version 2.2-0, vegan has significantly improved access to restricted permutations which brings it into line with those offered by Canoco. The permutation designs are modelled after the permutation schemes of Canoco 3.1 (ter Braak, 1990).
vegan currently provides for the following features within permutation tests:
Free permutation of DATA, also known as randomisation,
Free permutation of DATA within the levels of a grouping variable,
Restricted permutations for line transects or time series,
Permutation of groups of samples whilst retaining the within-group ordering,
Restricted permutations for spatial grids,
Blocking, samples are never permuted between blocks, and
Split-plot designs, with permutation of whole plots, split plots, or both.
Above, we use DATA to mean either the observed data themselves or some function of the data, for example the residuals of an ordination model in the presence of covariables.
These capabilities are provided by functions from the permute
package. The user can request a particular type of permutation by
supplying the permutations
argument of a function with an
object returned by how
, which defines how
samples should be permuted. Alternatively, the user can simply
specify the required number of permutations and a simple
randomisation procedure will be performed. Finally, the user can
supply a matrix of permutations (with number of rows equal to the
number of permutations and number of columns equal to the number of
observations in the data) and vegan will use these
permutations instead of generating new permutations.
The majority of functions in vegan allow for the full range of
possibilities outlined above. Exceptions include
kendall.post
and kendall.global
.
The Null hypothesis for the first two types of permutation test listed above assumes free exchangeability of DATA (within the levels of the grouping variable, if specified). Dependence between observations, such as that which arises due to spatial or temporal autocorrelation, or more-complicated experimental designs, such as split-plot designs, violates this fundamental assumption of the test and requires more complex restricted permutation test designs. It is these designs that are available via the permute package and to which vegan provides access from version 2.2-0 onwards.
Unless otherwise stated in the help pages for specific functions, permutation tests in vegan all follow the same format/structure:
An appropriate test statistic is chosen. Which statistic is chosen should be described on the help pages for individual functions.
The value of the test statistic is evaluate for the observed
data and analysis/model and recorded. Denote this value
.
The DATA are randomly permuted according to one of the above schemes, and the value of the test statistic for this permutation is evaluated and recorded.
Step 3 is repeated a total of times, where
is
the number of permutations requested. Denote these values as
, where
Count the number of values of the test statistic,
, in the Null distribution that are as extreme as
test statistic for the observed data
. Denote this
count as
.
We use the phrase as extreme to include cases where a two-sided test is performed and large negative values of the test statistic should be considered.
The permutation p-value is computed as
The above description illustrates why the default number of
permutations specified in vegan functions takes values of 199 or
999 for example. Pretty p values are achieved because the
in the denominator results in division by 200 or 1000, for
the 199 or 999 random permutations used in the test.
The simple intuition behind the presence of in the numerator
and denominator is that these represent the inclusion of the observed
value of the statistic in the Null distribution (e.g. Manly 2006).
Phipson & Smyth (2010) present a more compelling explanation for the
inclusion of
in the numerator and denominator of the
p value calculation.
Fisher (1935) had in mind that a permutation test would involve enumeration of all possible permutations of the data yielding an exact test. However, doing this complete enumeration may not be feasible in practice owing to the potentially vast number of arrangements of the data, even in modestly-sized data sets with free permutation of samples. As a result we evaluate the p value as the tail probability of the Null distribution of the test statistic directly from the random sample of possible permutations. Phipson & Smyth (2010) show that the naive calculation of the permutation p value is
which leads to an invalid test with incorrect type I error rate. They go on to show that by replacing the unknown tail probability (the p value) of the Null distribution with the biased estimator
that the positive bias induced is of just the right size to account for the uncertainty in the estimation of the tail probability from the set of randomly sampled permutations to yield a test with the correct type I error rate.
The estimator described above is correct for the situation where permutations of the data are samples randomly without replacement. This is not strictly what happens in vegan because permutations are drawn pseudo-randomly independent of one another. Note that the actual chance of this happening is practice is small but the functions in permute do not guarantee to generate a unique set of permutations unless complete enumeration of permutations is requested. This is not feasible for all but the smallest of data sets or restrictive of permutation designs, but in such cases the chance of drawing a set of permutations with repeats is lessened as the sample size, and thence the size of set of all possible permutations, increases.
Under the situation of sampling permutations with replacement then,
the tail probability calculated from the biased estimator
described above is somewhat conservative, being too large by
an amount that depends on the number of possible values that the test
statistic can take under permutation of the data (Phipson & Smyth,
2010). This represents a slight loss of statistical power for the
conservative p value calculation used here. However, unless
sample sizes are small and the the permutation design such that the
set of values that the test statistic can take is also small, this
loss of power is unlikely to be critical.
The minimum achievable p-value is
and hence depends on the number of permutations evaluated. However,
one cannot simply increase the number of permutations () to
achieve a potentially lower p-value unless the number of observations
available permits such a number of permutations. This is unlikely to
be a problem for all but the smallest data sets when free permutation
(randomisation) is valid, but in restricted permutation designs with a
low number of observations, there may not be as many unique
permutations of the data as you might desire to reach the required
level of significance.
It is currently the responsibility of the user to determine the total
number of possible permutations for their DATA. The number of
possible permutations allowed under the specified design can be
calculated using numPerms
from the
permute package. Heuristics employed within the
shuffleSet
function used by vegan can be
triggered to generate the entire set of permutations instead of a
random set. The settings controlling the triggering of the complete
enumeration step are contained within a permutation design created
using link[permute]{how}
and can be set by the user. See
how
for details.
Limits on the total number of permutations of DATA are more
severe in temporally or spatially ordered data or experimental designs
with low replication. For example, a time series of
observations has just 100 possible permutations including the
observed ordering.
In situations where only a low number of permutations is possible due to the nature of DATA or the experimental design, enumeration of all permutations becomes important and achievable computationally.
Above, we have provided only a brief overview of the capabilities of
vegan and permute. To get the best out of the new
functionality and for details on how to set up permutation designs
using how
, consult the vignette
Restricted permutations; using the permute package supplied
with permute and accessible via vignette("permutations",
package = "permute").
The permutations are based on the random number generator provided
by R. This may change in R releases and change the permutations
and vegan test results. One such change was in R release
3.6.0. The new version is clearly better for permutation tests and
you should use it. However, if you need to reproduce old results,
you can set the R random number generator to a previous version
with RNGversion
.
Gavin L. Simpson
Manly, B. F. J. (2006). Randomization, Bootstrap and Monte Carlo Methods in Biology, Third Edition. Chapman and Hall/CRC.
Phipson, B., & Smyth, G. K. (2010). Permutation P-values should never be zero: calculating exact P-values when permutations are randomly drawn. Statistical Applications in Genetics and Molecular Biology, 9, Article 39. DOI: 10.2202/1544-6115.1585
ter Braak, C. J. F. (1990). Update notes: CANOCO version 3.1. Wageningen: Agricultural Mathematics Group. (UR).
See also:
Davison, A. C., & Hinkley, D. V. (1997). Bootstrap Methods and their Application. Cambridge University Press.
permutest
for the main interface in vegan. See
also how
for details on permutation design
specification, shuffleSet
for the code used to
generate a set of permutations, numPerms
for
a function to return the size of the set of possible permutations
under the current design.
Implements a permutation-based test of multivariate homogeneity of
group dispersions (variances) for the results of a call to
betadisper
.
## S3 method for class 'betadisper' permutest(x, pairwise = FALSE, permutations = 999, parallel = getOption("mc.cores"), ...)
## S3 method for class 'betadisper' permutest(x, pairwise = FALSE, permutations = 999, parallel = getOption("mc.cores"), ...)
x |
an object of class |
pairwise |
logical; perform pairwise comparisons of group means? |
permutations |
a list of control values for the permutations
as returned by the function |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
... |
Arguments passed to other methods. |
To test if one or more groups is more variable than the others, ANOVA
of the distances to group centroids can be performed and parametric
theory used to interpret the significance of F. An alternative is to
use a permutation test. permutest.betadisper
permutes model
residuals to generate a permutation distribution of F under the Null
hypothesis of no difference in dispersion between groups.
Pairwise comparisons of group mean dispersions can be performed by
setting argument pairwise
to TRUE
. A classical t test
is performed on the pairwise group dispersions. This is combined with a
permutation test based on the t statistic calculated on pairwise group
dispersions. An alternative to the classical comparison of group
dispersions, is to calculate Tukey's Honest Significant Differences
between groups, via TukeyHSD.betadisper
.
permutest.betadisper
returns a list of class
"permutest.betadisper"
with the following components:
tab |
the ANOVA table which is an object inheriting from class
|
pairwise |
a list with components |
groups |
character; the levels of the grouping factor. |
control |
a list, the result of a call to
|
Gavin L. Simpson
Anderson, M.J. (2006) Distance-based tests for homogeneity of multivariate dispersions. Biometrics 62(1), 245–253.
Anderson, M.J., Ellingsen, K.E. & McArdle, B.H. (2006) Multivariate dispersion as a measure of beta diversity. Ecology Letters 9(6), 683–693.
For the main fitting function see betadisper
. For
an alternative approach to determining which groups are more variable,
see TukeyHSD.betadisper
.
data(varespec) ## Bray-Curtis distances between samples dis <- vegdist(varespec) ## First 16 sites grazed, remaining 8 sites ungrazed groups <- factor(c(rep(1,16), rep(2,8)), labels = c("grazed","ungrazed")) ## Calculate multivariate dispersions mod <- betadisper(dis, groups) mod ## Perform test anova(mod) ## Permutation test for F pmod <- permutest(mod, permutations = 99, pairwise = TRUE) ## Tukey's Honest Significant Differences (mod.HSD <- TukeyHSD(mod)) plot(mod.HSD) ## Has permustats() method pstat <- permustats(pmod) densityplot(pstat, scales = list(x = list(relation = "free"))) qqmath(pstat, scales = list(relation = "free"))
data(varespec) ## Bray-Curtis distances between samples dis <- vegdist(varespec) ## First 16 sites grazed, remaining 8 sites ungrazed groups <- factor(c(rep(1,16), rep(2,8)), labels = c("grazed","ungrazed")) ## Calculate multivariate dispersions mod <- betadisper(dis, groups) mod ## Perform test anova(mod) ## Permutation test for F pmod <- permutest(mod, permutations = 99, pairwise = TRUE) ## Tukey's Honest Significant Differences (mod.HSD <- TukeyHSD(mod)) plot(mod.HSD) ## Has permustats() method pstat <- permustats(pmod) densityplot(pstat, scales = list(x = list(relation = "free"))) qqmath(pstat, scales = list(relation = "free"))
Functions to plot or extract results of constrained correspondence analysis
(cca
), redundancy analysis (rda
), distance-based
redundancy analysis (dbrda
) or
constrained analysis of principal coordinates (capscale
).
## S3 method for class 'cca' plot(x, choices = c(1, 2), display = c("sp", "wa", "cn"), scaling = "species", type, xlim, ylim, const, correlation = FALSE, hill = FALSE, optimize = FALSE, arrows = FALSE, spe.par = list(), sit.par = list(), con.par = list(), bip.par = list(), cen.par = list(), reg.par = list(), ...) ## S3 method for class 'cca' text(x, display = "sites", labels, choices = c(1, 2), scaling = "species", arrow.mul, head.arrow = 0.05, select, const, axis.bp = FALSE, correlation = FALSE, hill = FALSE, ...) ## S3 method for class 'cca' points(x, display = "sites", choices = c(1, 2), scaling = "species", arrow.mul, head.arrow = 0.05, select, const, axis.bp = FALSE, correlation = FALSE, hill = FALSE, ...) ## S3 method for class 'cca' scores(x, choices = c(1,2), display = "all", scaling = "species", hill = FALSE, tidy = FALSE, droplist = TRUE, ...) ## S3 method for class 'rda' scores(x, choices = c(1,2), display = "all", scaling = "species", const, correlation = FALSE, tidy = FALSE, droplist = TRUE, ...) ## S3 method for class 'cca' summary(object, digits = max(3, getOption("digits") - 3), ...) ## S3 method for class 'cca' labels(object, display, ...)
## S3 method for class 'cca' plot(x, choices = c(1, 2), display = c("sp", "wa", "cn"), scaling = "species", type, xlim, ylim, const, correlation = FALSE, hill = FALSE, optimize = FALSE, arrows = FALSE, spe.par = list(), sit.par = list(), con.par = list(), bip.par = list(), cen.par = list(), reg.par = list(), ...) ## S3 method for class 'cca' text(x, display = "sites", labels, choices = c(1, 2), scaling = "species", arrow.mul, head.arrow = 0.05, select, const, axis.bp = FALSE, correlation = FALSE, hill = FALSE, ...) ## S3 method for class 'cca' points(x, display = "sites", choices = c(1, 2), scaling = "species", arrow.mul, head.arrow = 0.05, select, const, axis.bp = FALSE, correlation = FALSE, hill = FALSE, ...) ## S3 method for class 'cca' scores(x, choices = c(1,2), display = "all", scaling = "species", hill = FALSE, tidy = FALSE, droplist = TRUE, ...) ## S3 method for class 'rda' scores(x, choices = c(1,2), display = "all", scaling = "species", const, correlation = FALSE, tidy = FALSE, droplist = TRUE, ...) ## S3 method for class 'cca' summary(object, digits = max(3, getOption("digits") - 3), ...) ## S3 method for class 'cca' labels(object, display, ...)
x , object
|
A |
choices |
Axes shown. |
display |
Scores shown. These must include some of the
alternatives |
scaling |
Scaling for species and site scores. Either species
( The type of scores can also be specified as one of |
correlation , hill
|
logical; if |
optimize |
Optimize locations of text to reduce overlap and plot
point in the actual locations of the scores. Uses
|
arrows |
Draw arrows from the origin. This will always be
|
spe.par , sit.par , con.par , bip.par , cen.par , reg.par
|
Lists of graphical parameters for species, sites, constraints (lc scores), biplot and text, centroids and regression. These take precedence over globally set parameters and defaults. |
tidy |
Return scores that are compatible with
ggplot2: all scores are in a single |
type |
Type of plot: partial match to |
xlim , ylim
|
the x and y limits (min,max) of the plot. |
labels |
Optional text to be used instead of row names. If you
use this, it is good to check the default labels and their order
using |
arrow.mul |
Factor to expand arrows in the graph. Arrows will be scaled automatically to fit the graph if this is missing. |
head.arrow |
Default length of arrow heads. |
select |
Items to be displayed. This can either be a logical
vector which is |
const |
General scaling constant to |
droplist |
Return a matrix instead of a named list when only one kind of scores were requested. |
axis.bp |
Draw |
digits |
Number of digits in output. |
... |
Parameters passed to graphical functions. These will be
applied to all score types, but will be superseded by score type
parameters list (except |
Same plot
function will be used for cca
,
rda
, dbrda
and
capscale
. This produces a quick, standard plot with
current scaling
.
The plot
function sets colours (col
), plotting
characters (pch
) and character sizes (cex
) to default
values for each score type. The defaults can be changed with global
parameters (“dot arguments”) applied to all score types, or a
list of parameters for a specified score type (spe.par
,
sit.par
etc.) which take precedence over global parameters and
defaults. This allows full control of graphics. The scores are plotted
with text.ordiplot
and points.ordiplot
and
accept paremeters of these functions. In addition to standard
graphical parameters, text can be plotted over non-transparent label
with arbument bg = <colour>
, and location of text can be
optimized to avoid over-writing with argument optimize = TRUE
,
and argument arrows = TRUE
to draw arrows pointing to the
ordination scores.
the plot
function returns (invisible) ordiplot
object. You can save this object and use it to construct your plot
with ordiplot
functions points
and text
. These
functions can be used in pipe (|>
) which allows incremental
building of plots with full control of graphical parameters for each
score type. With pipe it is best to first create an empty plot with
plot(<cca-result>, type = "n")
and then add elements with
points
, text
of ordiplot
or
ordilabel
. Within pipe, the first argument should be a
quoted score type, and then the grapcical parameters. The full
object may contain scores with names
‘species’, ‘sites’, ‘constraints’, ‘biplot’, ‘regression’, ‘centroids’
(some of these may be missing depending on your model and are only
available if given in display
). The first
plot
will set the dimensions of graph, and if you do not use
some score type there may be empty white space. In addition to
ordiplot
text
and points
, you can also use
ordilabel
and ordipointlabel
in a
pipe. Unlike in basic plot
, there are no defaults for score
types, but all graphical parameters must be set in the command in
pipe. On the other hand, there may be more flexibility in these
settings than in plot
arguments, in particular in
ordilabel
and ordipointlabel
.
Environmental variables receive a special treatment. With
display="bp"
, arrows will be drawn. These are labelled with
text
and unlabelled with points
. The arrows have
basically unit scaling, but if sites were scaled (scaling
"sites"
or "symmetric"
), the scores of requested axes
are adjusted to the plotting area. With
scaling = "species"
or scaling = "none"
, the arrows will
be consistent with vectors fitted to linear combination scores
(display = "lc"
in function envfit
), but with
other scaling alternatives they will differ. The basic plot
function uses a simple heuristics for adjusting the unit-length arrows
to the current plot area, but the user can give the expansion factor
in arrow.mul
. With display="cn"
the centroids of levels
of factor
variables are displayed. With this option continuous
variables still are presented as arrows and ordered factors as arrows
and centroids. With display = "reg"
arrows will be drawn for
regression coefficients (a.k.a. canonical coefficients) of constraints
and conditions. Biplot arrows can be interpreted individually, but
regression coefficients must be interpreted all together: the LC score
for each site is the sum of regressions displayed by arrows. The
partialled out conditions are zero and not shown in biplot arrows, but
they are shown for regressions, and show the effect that must be
partialled out to get the LC scores. The biplot arrows are more
standard and more easily interpreted, and regression arrows should be
used only if you know that you need them.
The ordination object has text
and points
methods that
can be used to add items to an existing plot from the ordination
result directly. These should be used with extreme care, because you
must set scaling and other graphical parameters exactly similarly as
in the original plot
command. It is best to avoid using these
historic functions and instead configure plot
command or use
pipe.
Palmer (1993) suggested using linear constraints (“LC scores”)
in ordination diagrams, because these gave better results in
simulations and site scores (“WA scores”) are a step from
constrained to unconstrained analysis. However, McCune (1997) showed
that noisy environmental variables (and all environmental measurements
are noisy) destroy “LC scores” whereas “WA scores” were
little affected. Therefore the plot
function uses site scores
(“WA scores”) as the default. This is consistent with the usage
in statistics and other functions in R (lda
,
cancor
).
The plot
function returns
invisibly a plotting structure which can be used by function
identify.ordiplot
to identify the points or other
functions in the ordiplot
family or in a pipe to add new
graphicael elements with ordiplot
text
and
points
or with ordilabel
and
ordipointlabel
.
Jari Oksanen
The function builds upon ordiplot
and its
text
and points
functions. See these to find new
graphical parameters such as arrows
(for drawing arrows),
bg
(for writing text on non-transparent label) and
optimize
(to move text labels of points to avoid overwriting).
data(dune, dune.env) mod <- cca(dune ~ Moisture + Management, dune.env) ## default and modified plot plot(mod, scaling="sites") plot(mod, scaling="sites", type = "text", sit.par = list(type = "points", pch=21, col="red", bg="yellow", cex=1.2), spe.par = list(col="blue", cex=0.8), cen.par = list(bg="white")) ## same with pipe plot(mod, type="n", scaling="sites") |> points("sites", pch=21, col="red", bg = "yellow", cex=1.2) |> text("species", col="blue", cex=0.8) |> text("biplot") |> text("centroids", bg="white") ## LC scores & factors mean much overplotting: try optimize=TRUE plot(mod, display = c("lc","sp","cn"), optimize = TRUE, bip.par = list(optimize = FALSE)) # arrows and optimize mix poorly ## catch the invisible result and use ordiplot support - the example ## will make a biplot with arrows for species and correlation scaling pca <- rda(dune) pl <- plot(pca, type="n", scaling="sites", correlation=TRUE) with(dune.env, points(pl, "site", pch=21, col=1, bg=Management)) text(pl, "sp", arrow=TRUE, length=0.05, col=4, cex=0.6, xpd=TRUE) with(dune.env, legend("bottomleft", levels(Management), pch=21, pt.bg=1:4, bty="n")) ## Pipe plot(pca, type="n", scaling="sites", correlation=TRUE) |> points("sites", pch=21, col = 1, cex=1.5, bg = dune.env$Management) |> text("species", col = "blue", arrows = TRUE, xpd = TRUE, font = 3) ## Scaling can be numeric or more user-friendly names ## e.g. Hill's scaling for (C)CA scrs <- scores(mod, scaling = "sites", hill = TRUE) ## or correlation-based scores in PCA/RDA scrs <- scores(rda(dune ~ A1 + Moisture + Management, dune.env), scaling = "sites", correlation = TRUE)
data(dune, dune.env) mod <- cca(dune ~ Moisture + Management, dune.env) ## default and modified plot plot(mod, scaling="sites") plot(mod, scaling="sites", type = "text", sit.par = list(type = "points", pch=21, col="red", bg="yellow", cex=1.2), spe.par = list(col="blue", cex=0.8), cen.par = list(bg="white")) ## same with pipe plot(mod, type="n", scaling="sites") |> points("sites", pch=21, col="red", bg = "yellow", cex=1.2) |> text("species", col="blue", cex=0.8) |> text("biplot") |> text("centroids", bg="white") ## LC scores & factors mean much overplotting: try optimize=TRUE plot(mod, display = c("lc","sp","cn"), optimize = TRUE, bip.par = list(optimize = FALSE)) # arrows and optimize mix poorly ## catch the invisible result and use ordiplot support - the example ## will make a biplot with arrows for species and correlation scaling pca <- rda(dune) pl <- plot(pca, type="n", scaling="sites", correlation=TRUE) with(dune.env, points(pl, "site", pch=21, col=1, bg=Management)) text(pl, "sp", arrow=TRUE, length=0.05, col=4, cex=0.6, xpd=TRUE) with(dune.env, legend("bottomleft", levels(Management), pch=21, pt.bg=1:4, bty="n")) ## Pipe plot(pca, type="n", scaling="sites", correlation=TRUE) |> points("sites", pch=21, col = 1, cex=1.5, bg = dune.env$Management) |> text("species", col = "blue", arrows = TRUE, xpd = TRUE, font = 3) ## Scaling can be numeric or more user-friendly names ## e.g. Hill's scaling for (C)CA scrs <- scores(mod, scaling = "sites", hill = TRUE) ## or correlation-based scores in PCA/RDA scrs <- scores(rda(dune ~ A1 + Moisture + Management, dune.env), scaling = "sites", correlation = TRUE)
Principal Response Curves (PRC) are a special case of
Redundancy Analysis (rda
) for multivariate responses in
repeated observation design. They were originally suggested for
ecological communities. They should be easier to interpret than
traditional constrained ordination. They can also be used to study how
the effects of a factor A
depend on the levels of a factor
B
, that is A + A:B
, in a multivariate response
experiment.
prc(response, treatment, time, ...) ## S3 method for class 'prc' summary(object, axis = 1, scaling = "sites", const, digits = 4, correlation = FALSE, ...) ## S3 method for class 'prc' plot(x, species = TRUE, select, scaling = "symmetric", axis = 1, correlation = FALSE, const, type = "l", xlab, ylab, ylim, lty = 1:5, col = 1:6, pch, legpos, cex = 0.8, ...)
prc(response, treatment, time, ...) ## S3 method for class 'prc' summary(object, axis = 1, scaling = "sites", const, digits = 4, correlation = FALSE, ...) ## S3 method for class 'prc' plot(x, species = TRUE, select, scaling = "symmetric", axis = 1, correlation = FALSE, const, type = "l", xlab, ylab, ylim, lty = 1:5, col = 1:6, pch, legpos, cex = 0.8, ...)
response |
Multivariate response data. Typically these are community (species) data. If the data are counts, they probably should be log transformed prior to the analysis. |
treatment |
A factor for treatments. |
time |
An unordered factor defining the observations times in the repeated design. |
object , x
|
An |
axis |
Axis shown (only one axis can be selected). |
scaling |
Scaling of species scores, identical to the
The type of scores can also be specified as one of |
const |
General scaling constant for species scores (see
|
digits |
Number of significant digits displayed. |
correlation |
logical; if |
species |
Display species scores. |
select |
Vector to select displayed species. This can be a vector
of indices or a logical vector which is |
type |
Type of plot: |
xlab , ylab
|
Text to replace default axis labels. |
ylim |
Limits for the vertical axis. |
lty , col , pch
|
Line type, colour and plotting characters (defaults supplied). |
legpos |
The position of the |
cex |
Character expansion for symbols and species labels. |
... |
Other parameters passed to functions. |
PRC is a special case of rda
with a single
factor for treatment
and a single factor for time
points
in repeated observations. In vegan, the corresponding
rda
model is defined as rda(response ~ treatment *
time + Condition(time))
. Since the time
appears twice in the
model formula, its main effects will be aliased, and only the main
effect of treatment and interaction terms are available, and will be
used in PRC. Instead of usual multivariate ordination diagrams, PRC
uses canonical (regression) coefficients and species scores for a
single axis. All that the current functions do is to provide a special
summary
and plot
methods that display the
rda
results in the PRC fashion. The current version only
works with default contrasts (contr.treatment
) in which
the coefficients are contrasts against the first level, and the levels
must be arranged so that the first level is the control (or a
baseline). If necessary, you must change the baseline level with
function relevel
.
Function summary
prints the species scores and the
coefficients. Function plot
plots coefficients against
time
using matplot
, and has similar defaults.
The graph (and PRC) is meaningful only if the first treatment
level is the control, as the results are contrasts to the first level
when unordered factors are used. The plot also displays species scores
on the right vertical axis using function
linestack
. Typically the number of species is so high
that not all can be displayed with the default settings, but users can
reduce character size or padding (air
) in
linestack
, or select
only a subset of the
species. A legend will be displayed unless suppressed with
legpos = NA
, and the functions tries to guess where to put the
legend if legpos
is not supplied.
The function is a special case of rda
and returns its
result object (see cca.object
). However, a special
summary
and plot
methods display returns differently
than in rda
.
The first level of treatment
must be the
control: use function relevel
to guarantee the correct
reference level. The current version will ignore user setting of
contrasts
and always use treatment contrasts
(contr.treatment
). The time
must be an unordered
factor.
Jari Oksanen and Cajo ter Braak
van den Brink, P.J. & ter Braak, C.J.F. (1999). Principal response curves: Analysis of time-dependent multivariate responses of biological community to stress. Environmental Toxicology and Chemistry, 18, 138–148.
## Chlorpyrifos experiment and experimental design: Pesticide ## treatment in ditches (replicated) and followed over from 4 weeks ## before to 24 weeks after exposure data(pyrifos) week <- gl(11, 12, labels=c(-4, -1, 0.1, 1, 2, 4, 8, 12, 15, 19, 24)) dose <- factor(rep(c(0.1, 0, 0, 0.9, 0, 44, 6, 0.1, 44, 0.9, 0, 6), 11)) ditch <- gl(12, 1, length=132) ## IGNORE_RDIFF_BEGIN ## PRC mod <- prc(pyrifos, dose, week) mod # RDA summary(mod) # PRC logabu <- colSums(pyrifos) plot(mod, select = logabu > 100) ## IGNORE_RDIFF_END ## Ditches are randomized, we have a time series, and are only ## interested in the first axis ctrl <- how(plots = Plots(strata = ditch,type = "free"), within = Within(type = "series"), nperm = 99) anova(mod, permutations = ctrl, first=TRUE)
## Chlorpyrifos experiment and experimental design: Pesticide ## treatment in ditches (replicated) and followed over from 4 weeks ## before to 24 weeks after exposure data(pyrifos) week <- gl(11, 12, labels=c(-4, -1, 0.1, 1, 2, 4, 8, 12, 15, 19, 24)) dose <- factor(rep(c(0.1, 0, 0, 0.9, 0, 44, 6, 0.1, 44, 0.9, 0, 6), 11)) ditch <- gl(12, 1, length=132) ## IGNORE_RDIFF_BEGIN ## PRC mod <- prc(pyrifos, dose, week) mod # RDA summary(mod) # PRC logabu <- colSums(pyrifos) plot(mod, select = logabu > 100) ## IGNORE_RDIFF_END ## Ditches are randomized, we have a time series, and are only ## interested in the first axis ctrl <- how(plots = Plots(strata = ditch,type = "free"), within = Within(type = "series"), nperm = 99) anova(mod, permutations = ctrl, first=TRUE)
Function predict
can be used to find site and species scores or
estimates of the response data with new data sets, Function
calibrate
estimates values of constraints with new data set.
Functions fitted
and residuals
return estimates of
response data.
## S3 method for class 'cca' fitted(object, model = c("CCA", "CA", "pCCA"), type = c("response", "working"), ...) ## S3 method for class 'capscale' fitted(object, model = c("CCA", "CA", "pCCA", "Imaginary"), type = c("response", "working"), ...) ## S3 method for class 'cca' residuals(object, ...) ## S3 method for class 'cca' predict(object, newdata, type = c("response", "wa", "sp", "lc", "working"), rank = "full", model = c("CCA", "CA"), scaling = "none", hill = FALSE, ...) ## S3 method for class 'rda' predict(object, newdata, type = c("response", "wa", "sp", "lc", "working"), rank = "full", model = c("CCA", "CA"), scaling = "none", correlation = FALSE, const, ...) ## S3 method for class 'dbrda' predict(object, newdata, type = c("response", "lc", "wa", "working"), rank = "full", model = c("CCA", "CA"), scaling = "none", const, ...) ## S3 method for class 'cca' calibrate(object, newdata, rank = "full", ...) ## S3 method for class 'cca' coef(object, norm = FALSE, ...) ## S3 method for class 'decorana' predict(object, newdata, type = c("response", "sites", "species"), rank = 4, ...)
## S3 method for class 'cca' fitted(object, model = c("CCA", "CA", "pCCA"), type = c("response", "working"), ...) ## S3 method for class 'capscale' fitted(object, model = c("CCA", "CA", "pCCA", "Imaginary"), type = c("response", "working"), ...) ## S3 method for class 'cca' residuals(object, ...) ## S3 method for class 'cca' predict(object, newdata, type = c("response", "wa", "sp", "lc", "working"), rank = "full", model = c("CCA", "CA"), scaling = "none", hill = FALSE, ...) ## S3 method for class 'rda' predict(object, newdata, type = c("response", "wa", "sp", "lc", "working"), rank = "full", model = c("CCA", "CA"), scaling = "none", correlation = FALSE, const, ...) ## S3 method for class 'dbrda' predict(object, newdata, type = c("response", "lc", "wa", "working"), rank = "full", model = c("CCA", "CA"), scaling = "none", const, ...) ## S3 method for class 'cca' calibrate(object, newdata, rank = "full", ...) ## S3 method for class 'cca' coef(object, norm = FALSE, ...) ## S3 method for class 'decorana' predict(object, newdata, type = c("response", "sites", "species"), rank = 4, ...)
object |
|
model |
Show constrained ( |
newdata |
New data frame to be used in prediction or in
calibration. Usually this a new community data frame, but with
|
type |
The type of prediction, fitted values or residuals:
|
rank |
The rank or the number of axes used in the approximation.
The default is to use all axes (full rank) of the |
scaling |
logical, character, or numeric; Scaling or predicted
scores with the same meaning as in |
correlation , hill
|
logical; correlation-like scores or Hill's
scaling as appropriate for RDA and CCA respectively. See
|
const |
Constant multiplier for RDA scores. This will be used
only when |
norm |
Coefficients for variables that are centred and scaled to unit norm. |
... |
Other parameters to the functions. |
Function fitted
gives the approximation of the original data
matrix or dissimilarities from the ordination result either in the
scale of the response or as scaled internally by the function.
Function residuals
gives the approximation of the original data
from the unconstrained ordination. With argument type =
"response"
the fitted.cca
and residuals.cca
function
both give the same marginal totals as the original data matrix, and
fitted and residuals do not add up to the original data. Functions
fitted
and residuals
for dbrda
and
capscale
give the dissimilarities with type =
"response"
, but these are not additive. However, the
"working"
scores are additive for capscale
(but
not for dbrda
). The fitted
and residuals
for capscale
and dbrda
will include the
additive constant if that was requested in the function call. All
variants of fitted
and residuals
are defined so that for
model mod <- cca(y ~ x)
, cca(fitted(mod))
is equal to
constrained ordination, and cca(residuals(mod))
is equal to
unconstrained part of the ordination.
Function predict
can find the estimate of the original data
matrix or dissimilarities (type = "response"
) with any rank.
With rank = "full"
it is identical to fitted
. In
addition, the function can find the species scores or site scores from
the community data matrix for cca
or rda
.
The function can be used with new data, and it can be used to add new
species or site scores to existing ordinations. The function returns
(weighted) orthonormal scores by default, and you must specify
explicit scaling
to add those scores to ordination
diagrams. With type = "wa"
the function finds the site scores
from species scores. In that case, the new data can contain new sites,
but species must match in the original and new data. With type="sp"
the function finds species scores from site constraints
(linear combination scores). In that case the new data can contain new
species, but sites must match in the original and new data. With
type = "lc"
the function finds the linear combination scores
for sites from environmental data. In that case the new data frame
must contain all constraining and conditioning environmental variables
of the model formula. With type = "response"
or
type = "working"
the new data must contain environmental variables
if constrained component is desired, and community data matrix if
residual or unconstrained component is desired. With these types, the
function uses newdata
to find new "lc"
(constrained) or
"wa"
scores (unconstrained) and then finds the response or
working data from these new row scores and species scores. The
original site (row) and species (column) weights are used for
type = "response"
and type = "working"
in correspondence
analysis (cca
) and therefore the number of rows must
match in the original data and newdata
.
If a completely new data frame is created, extreme care is needed
defining variables similarly as in the original model, in particular
with (ordered) factors. If ordination was performed with the formula
interface, the newdata
can be a data frame or matrix, but
extreme care is needed that the columns match in the original and
newdata
.
Function calibrate.cca
finds estimates of constraints from
community ordination or "wa"
scores from cca
,
rda
and capscale
. This is often known as
calibration, bioindication or environmental reconstruction, and it
is equivalent to performing Weighted Averaging (see
wascores
). As a Weighted Averaging method it uses
deshrinking where the sum of weighted prediction errors is
zero. Basically, the method is similar to projecting site scores
onto biplot arrows, but it uses regression coefficients. The
function can be called with newdata
so that cross-validation
is possible. The newdata
may contain new sites, but species
must match in the original and new data. The function does not work
with ‘partial’ models with Condition
term, and it
cannot be used with newdata
for capscale
or
dbrda
results. The results may only be interpretable
for continuous variables.
Function coef
will give the regression coefficients from centred
environmental variables (constraints and conditions) to linear
combination scores. The coefficients are for unstandardized environmental
variables. The coefficients will be NA
for aliased effects.
Function predict.decorana
is similar to predict.cca
.
However, type = "species"
is not available in detrended
correspondence analysis (DCA), because detrending destroys the mutual
reciprocal averaging (except for the first axis when rescaling is not
used). Detrended CA does not attempt to approximate the original data
matrix, so type = "response"
has no meaning in detrended
analysis (except with rank = 1
).
The functions return matrices, vectors or dissimilarities as is appropriate.
Jari Oksanen.
Greenacre, M. J. (1984). Theory and applications of correspondence analysis. Academic Press, London.
cca
, rda
, dbrda
,
capscale
, decorana
,
goodness.cca
.
data(dune, dune.env) mod <- cca(dune ~ A1 + Management + Condition(Moisture), data=dune.env) # Definition of the concepts 'fitted' and 'residuals' mod cca(fitted(mod)) cca(residuals(mod)) # Remove rare species (freq==1) from 'cca' and find their scores # 'passively'. freq <- specnumber(dune, MARGIN=2) freq mod <- cca(dune[, freq>1] ~ A1 + Management + Condition(Moisture), dune.env) ## IGNORE_RDIFF_BEGIN predict(mod, type="sp", newdata=dune[, freq==1], scaling="species") # New sites predict(mod, type="lc", new=data.frame(A1 = 3, Management="NM", Moisture="2"), scal=2) # Calibration and residual plot mod <- cca(dune ~ A1, dune.env) head(pred <- calibrate(mod)) ## For single variable similar to weighted averaging calibration, but ## different deshrinking head(wascores(wascores(dune.env$A1, dune, expand=TRUE), t(dune), expand=TRUE)) ## IGNORE_RDIFF_END with(dune.env, plot(A1, pred - A1, ylab="Prediction Error")) abline(h=0)
data(dune, dune.env) mod <- cca(dune ~ A1 + Management + Condition(Moisture), data=dune.env) # Definition of the concepts 'fitted' and 'residuals' mod cca(fitted(mod)) cca(residuals(mod)) # Remove rare species (freq==1) from 'cca' and find their scores # 'passively'. freq <- specnumber(dune, MARGIN=2) freq mod <- cca(dune[, freq>1] ~ A1 + Management + Condition(Moisture), dune.env) ## IGNORE_RDIFF_BEGIN predict(mod, type="sp", newdata=dune[, freq==1], scaling="species") # New sites predict(mod, type="lc", new=data.frame(A1 = 3, Management="NM", Moisture="2"), scal=2) # Calibration and residual plot mod <- cca(dune ~ A1, dune.env) head(pred <- calibrate(mod)) ## For single variable similar to weighted averaging calibration, but ## different deshrinking head(wascores(wascores(dune.env$A1, dune, expand=TRUE), t(dune), expand=TRUE)) ## IGNORE_RDIFF_END with(dune.env, plot(A1, pred - A1, ylab="Prediction Error")) abline(h=0)
Function procrustes
rotates a configuration to maximum similarity
with another configuration. Function protest
tests the
non-randomness (significance) between two configurations.
procrustes(X, Y, scale = TRUE, symmetric = FALSE, scores = "sites", ...) ## S3 method for class 'procrustes' summary(object, digits = getOption("digits"), ...) ## S3 method for class 'procrustes' plot(x, kind=1, choices=c(1,2), to.target = TRUE, type = "p", xlab, ylab, main, ar.col = "blue", length=0.05, cex = 0.7, ...) ## S3 method for class 'procrustes' points(x, display = c("target", "rotated"), choices = c(1,2), truemean = FALSE, ...) ## S3 method for class 'procrustes' text(x, display = c("target", "rotated"), choices = c(1,2), labels, truemean = FALSE, ...) ## S3 method for class 'procrustes' lines(x, type = c("segments", "arrows"), choices = c(1, 2), truemean = FALSE, ...) ## S3 method for class 'procrustes' residuals(object, ...) ## S3 method for class 'procrustes' fitted(object, truemean = TRUE, ...) ## S3 method for class 'procrustes' predict(object, newdata, truemean = TRUE, ...) protest(X, Y, scores = "sites", permutations = how(nperm = 999), ...)
procrustes(X, Y, scale = TRUE, symmetric = FALSE, scores = "sites", ...) ## S3 method for class 'procrustes' summary(object, digits = getOption("digits"), ...) ## S3 method for class 'procrustes' plot(x, kind=1, choices=c(1,2), to.target = TRUE, type = "p", xlab, ylab, main, ar.col = "blue", length=0.05, cex = 0.7, ...) ## S3 method for class 'procrustes' points(x, display = c("target", "rotated"), choices = c(1,2), truemean = FALSE, ...) ## S3 method for class 'procrustes' text(x, display = c("target", "rotated"), choices = c(1,2), labels, truemean = FALSE, ...) ## S3 method for class 'procrustes' lines(x, type = c("segments", "arrows"), choices = c(1, 2), truemean = FALSE, ...) ## S3 method for class 'procrustes' residuals(object, ...) ## S3 method for class 'procrustes' fitted(object, truemean = TRUE, ...) ## S3 method for class 'procrustes' predict(object, newdata, truemean = TRUE, ...) protest(X, Y, scores = "sites", permutations = how(nperm = 999), ...)
X |
Target matrix |
Y |
Matrix to be rotated. |
scale |
Allow scaling of axes of |
symmetric |
Use symmetric Procrustes statistic (the rotation will still be non-symmetric). |
scores |
Kind of scores used. This is the |
x , object
|
An object of class |
digits |
Number of digits in the output. |
kind |
For |
choices |
Axes (dimensions) plotted. |
xlab , ylab
|
Axis labels, if defaults unacceptable. |
main |
Plot title, if default unacceptable. |
display |
Show only the |
to.target |
Draw arrows to point to target. |
type |
The type of plot drawn. In |
truemean |
Use the original range of target matrix instead of
centring the fitted values. Function |
newdata |
Matrix of coordinates to be rotated and translated to the target. |
permutations |
a list of control values for the permutations
as returned by the function |
ar.col |
Arrow colour. |
length |
Width of the arrow head. |
labels |
Character vector of text labels. Rownames of the result object are used as default. |
cex |
Character expansion for points or text. |
... |
Other parameters passed to functions. In |
Procrustes rotation rotates a matrix to maximum similarity with a
target matrix minimizing sum of squared differences. Procrustes
rotation is typically used in comparison of ordination results. It is
particularly useful in comparing alternative solutions in
multidimensional scaling. If scale=FALSE
, the function only
rotates matrix Y
. If scale=TRUE
, it scales linearly
configuration Y
for maximum similarity. Since Y
is scaled
to fit X
, the scaling is non-symmetric. However, with
symmetric=TRUE
, the configurations are scaled to equal
dispersions and a symmetric version of the Procrustes statistic
is computed.
Instead of matrix, X
and Y
can be results from an
ordination from which scores
can extract results.
Function procrustes
passes extra arguments to
scores
, scores.cca
etc. so that you can
specify arguments such as scaling
.
Function plot
plots a procrustes
object and returns
invisibly an ordiplot
object so that function
identify.ordiplot
can be used for identifying
points. The items in the ordiplot
object are called
heads
and points
with kind=1
(ordination
diagram) and sites
with kind=2
(residuals). In
ordination diagrams, the arrow heads point to the target
configuration if to.target = TRUE
, and to rotated
configuration if to.target = FALSE
. Target and original
rotated axes are shown as cross hairs in two-dimensional Procrustes
analysis, and with a higher number of dimensions, the rotated axes
are projected onto plot with their scaled and centred
range. Function plot
passes parameters to underlying plotting
functions. For full control of plots, you can draw the axes using
plot
with kind = 0
, and then add items with
points
or lines
. These functions pass all parameters
to the underlying functions so that you can select the plotting
characters, their size, colours etc., or you can select the width,
colour and type of line segments
or arrows, or you can
select the orientation and head width of arrows
.
Function residuals
returns the pointwise
residuals, and fitted
the fitted values, either centred to zero
mean (if truemean=FALSE
) or with the original scale (these
hardly make sense if symmetric = TRUE
). In
addition, there are summary
and print
methods.
If matrix X
has a lower number of columns than matrix
Y
, then matrix X
will be filled with zero columns to
match dimensions. This means that the function can be used to rotate
an ordination configuration to an environmental variable (most
practically extracting the result with the fitted
function). Function predict
can be used to add new rotated
coordinates to the target. The predict
function will always
translate coordinates to the original non-centred matrix. The
function cannot be used with newdata
for symmetric
analysis.
Function protest
performs symmetric Procrustes analysis
repeatedly to estimate the significance of the Procrustes
statistic. Function protest
uses a correlation-like statistic
derived from the symmetric Procrustes sum of squares as
, and also prints the sum of
squares of the symmetric analysis, sometimes called
. Function
protest
has own
print
method, but otherwise uses procrustes
methods. Thus plot
with a protest
object yields a
Procrustean superimposition plot.
Function procrustes
returns an object of class
procrustes
with items. Function protest
inherits from
procrustes
, but amends that with some new items:
Yrot |
Rotated matrix |
X |
Target matrix. |
ss |
Sum of squared differences between |
rotation |
Orthogonal rotation matrix. |
translation |
Translation of the origin. |
scale |
Scaling factor. |
xmean |
The centroid of the target. |
symmetric |
Type of |
call |
Function call. |
t0 |
This and the following items are only in class
|
t |
Procrustes correlations from permutations. The distribution
of these correlations can be inspected with |
signif |
Significance of |
permutations |
Number of permutations. |
control |
A list of control values for the permutations
as returned by the function |
control |
the list passed to argument |
The function protest
follows Peres-Neto & Jackson (2001),
but the implementation is still after Mardia et al.
(1979).
Jari Oksanen
Mardia, K.V., Kent, J.T. and Bibby, J.M. (1979). Multivariate Analysis. Academic Press.
Peres-Neto, P.R. and Jackson, D.A. (2001). How well do multivariate data sets match? The advantages of a Procrustean superimposition approach over the Mantel test. Oecologia 129: 169-178.
monoMDS
, for obtaining
objects for procrustes
, and mantel
for an
alternative to protest
without need of dimension reduction. See
how
for details on specifying the type of
permutation required.
## IGNORE_RDIFF_BEGIN data(varespec) vare.dist <- vegdist(wisconsin(varespec)) mds.null <- monoMDS(vare.dist, y = cmdscale(vare.dist)) mds.alt <- monoMDS(vare.dist) vare.proc <- procrustes(mds.alt, mds.null) vare.proc summary(vare.proc) plot(vare.proc) plot(vare.proc, kind=2) residuals(vare.proc) ## IGNORE_RDIFF_END
## IGNORE_RDIFF_BEGIN data(varespec) vare.dist <- vegdist(wisconsin(varespec)) mds.null <- monoMDS(vare.dist, y = cmdscale(vare.dist)) mds.alt <- monoMDS(vare.dist) vare.proc <- procrustes(mds.alt, mds.null) vare.proc summary(vare.proc) plot(vare.proc) plot(vare.proc, kind=2) residuals(vare.proc) ## IGNORE_RDIFF_END
The data are log transformed abundances of aquatic invertebrate in twelve ditches studied in eleven times before and after an insecticide treatment.
data(pyrifos)
data(pyrifos)
A data frame with 132 observations on the log-transformed (log(10*x + 1)
) abundances
of 178 species. There are only twelve sites (ditches, mesocosms), but
these were studied repeatedly in eleven occasions. The treatment
levels, treatment times, or ditch ID's are not in the data frame, but
the data are very regular, and the example below shows how to obtain
these external variables.
This data set was obtained from an experiment in outdoor
experimental ditches. Twelve mesocosms were allocated at random to
treatments; four served as controls, and the remaining eight were
treated once with the insecticide chlorpyrifos, with nominal dose
levels of 0.1, 0.9, 6, and 44 g/ L in two mesocosms
each. The example data set invertebrates.
Sampling was done 11 times, from week -4 pre-treatment through
week 24 post-treatment, giving a total of 132 samples (12 mesocosms
times 11 sampling dates), see van den Brink & ter Braak (1999) for
details. The data set contains only the species data,
but the example below shows how to obtain the treatment, time and
ditch ID variables.
CANOCO 4 example data, with the permission of Cajo J. F. ter Braak.
van den Brink, P.J. & ter Braak, C.J.F. (1999). Principal response curves: Analysis of time-dependent multivariate responses of biological community to stress. Environmental Toxicology and Chemistry, 18, 138–148.
data(pyrifos) ditch <- gl(12, 1, length=132) week <- gl(11, 12, labels=c(-4, -1, 0.1, 1, 2, 4, 8, 12, 15, 19, 24)) dose <- factor(rep(c(0.1, 0, 0, 0.9, 0, 44, 6, 0.1, 44, 0.9, 0, 6), 11))
data(pyrifos) ditch <- gl(12, 1, length=132) week <- gl(11, 12, labels=c(-4, -1, 0.1, 1, 2, 4, 8, 12, 15, 19, 24)) dose <- factor(rep(c(0.1, 0, 0, 0.9, 0, 44, 6, 0.1, 44, 0.9, 0, 6), 11))
Functions construct rank – abundance or dominance / diversity or Whittaker plots and fit brokenstick, preemption, log-Normal, Zipf and Zipf-Mandelbrot models of species abundance.
## Default S3 method: radfit(x, ...) rad.null(x, family=poisson, ...) rad.preempt(x, family = poisson, ...) rad.lognormal(x, family = poisson, ...) rad.zipf(x, family = poisson, ...) rad.zipfbrot(x, family = poisson, ...) ## S3 method for class 'radline' predict(object, newdata, total, ...) ## S3 method for class 'radfit' plot(x, BIC = FALSE, legend = TRUE, ...) ## S3 method for class 'radfit.frame' plot(x, order.by, BIC = FALSE, model, legend = TRUE, as.table = TRUE, ...) ## S3 method for class 'radline' plot(x, xlab = "Rank", ylab = "Abundance", type = "b", ...) radlattice(x, BIC = FALSE, ...) ## S3 method for class 'radfit' lines(x, ...) ## S3 method for class 'radfit' points(x, ...) as.rad(x) ## S3 method for class 'rad' plot(x, xlab = "Rank", ylab = "Abundance", log = "y", ...)
## Default S3 method: radfit(x, ...) rad.null(x, family=poisson, ...) rad.preempt(x, family = poisson, ...) rad.lognormal(x, family = poisson, ...) rad.zipf(x, family = poisson, ...) rad.zipfbrot(x, family = poisson, ...) ## S3 method for class 'radline' predict(object, newdata, total, ...) ## S3 method for class 'radfit' plot(x, BIC = FALSE, legend = TRUE, ...) ## S3 method for class 'radfit.frame' plot(x, order.by, BIC = FALSE, model, legend = TRUE, as.table = TRUE, ...) ## S3 method for class 'radline' plot(x, xlab = "Rank", ylab = "Abundance", type = "b", ...) radlattice(x, BIC = FALSE, ...) ## S3 method for class 'radfit' lines(x, ...) ## S3 method for class 'radfit' points(x, ...) as.rad(x) ## S3 method for class 'rad' plot(x, xlab = "Rank", ylab = "Abundance", log = "y", ...)
x |
Data frame, matrix or a vector giving species abundances, or an object to be plotted. |
family |
Error distribution (passed to |
object |
A fitted result object. |
newdata |
Ranks used for ordinations. All models can interpolate to non-integer “ranks” (although this may be approximate), but extrapolation may fail |
total |
The new total used for predicting abundance. Observed total count is used if this is omitted. |
order.by |
A vector used for ordering sites in plots. |
BIC |
Use Bayesian Information Criterion, BIC, instead of
Akaike's AIC. The penalty in BIC is |
model |
Show only the specified model. If missing, AIC is used
to select the model. The model names (which can be abbreviated)
are |
legend |
Add legend of line colours. |
as.table |
Arrange panels starting from upper left corner (passed
to |
xlab , ylab
|
Labels for |
type |
Type of the plot, |
log |
Use logarithmic scale for given axis. The default
|
... |
Other parameters to functions. |
Rank–Abundance Dominance (RAD) or Dominance/Diversity plots (Whittaker 1965) display logarithmic species abundances against species rank order. These plots are supposed to be effective in analysing types of abundance distributions in communities. These functions fit some of the most popular models mainly following Wilson (1991).
Functions rad.null
, rad.preempt
, rad.lognormal
,
rad.zipf
and zipfbrot
fit the individual models
(described below) for a single vector (row of data frame), and
function radfit
fits all models. The argument of the function
radfit
can be either a vector for a single community or a data
frame where each row represents a distinct community.
Function rad.null
fits a brokenstick model where the expected
abundance of species at rank is
(Pielou
1975), where
is the total number of individuals (site total)
and
is the total number of species in the community. This
gives a Null model where the individuals are randomly distributed
among observed species, and there are no fitted parameters.
Function
rad.preempt
fits the niche preemption model,
a.k.a. geometric series or Motomura model, where the expected
abundance of species at rank
is
. The only
estimated parameter is the preemption coefficient
which
gives the decay rate of abundance per rank. The niche preemption
model is a straight line in a RAD plot. Function
rad.lognormal
fits a log-Normal model which assumes that the
logarithmic abundances are distributed Normally, or ,
where
is a Normal deviate. Function
rad.zipf
fits
the Zipf model where
is the fitted proportion of the most abundant species,
and
is a decay coefficient. The Zipf–Mandelbrot model
(
rad.zipfbrot
) adds one parameter: after which
of the Zipf model changes into a meaningless scaling constant
.
Log-Normal and Zipf models are generalized linear models
(glm
) with logarithmic link function. Zipf–Mandelbrot
adds one nonlinear parameter to the Zipf model, and is fitted using
nlm
for the nonlinear parameter and estimating other
parameters and log-Likelihood with glm
. Preemption
model is fitted as a purely nonlinear model. There are no estimated
parameters in the Null model.
The default family
is poisson
which is
appropriate only for genuine counts (integers), but other families
that accept link = "log"
can be used. Families
Gamma
or gaussian
may be appropriate for
abundance data, such as cover. The best model is selected by
AIC
. Therefore ‘quasi’ families such as
quasipoisson
cannot be used: they do not have
AIC
nor log-Likelihood needed in non-linear models.
All these functions have their own plot
functions. When
radfit
was applied for a data frame, plot
uses
Lattice
graphics, and other plot
functions use ordinary graphics. The ordinary graphics functions
return invisibly an ordiplot
object for observed points,
and function identify.ordiplot
can be used to label
selected species. Alternatively, radlattice
uses
Lattice
graphics to display each radfit
model of a single site in a separate panel together with their AIC or
BIC values.
Function as.rad
is a base function to construct ordered RAD
data. Its plot
is used by other RAD plot
functions
which pass extra arguments (such as xlab
and log
) to
this function. The function returns an ordered vector of taxa
occurring in a site, and a corresponding attribute "index"
of
included taxa.
Functions rad.null
, rad.preempt
, rad.lognormal
,
zipf
and zipfbrot
fit each a single RAD model to a
single site. The result object has class "radline"
and
inherits from glm
, and can be handled by some (but not
all) glm
methods.
Function radfit
fits all models either to a single site or to
all rows of a data frame or a matrix. When fitted to a single site,
the function returns an object of class "radfit"
with items
y
(observed values), family
, and models
which is a list of fitted "radline"
models. When applied for a
data frame or matrix, radfit
function returns an object of
class "radfit.frame"
which is a list of "radfit"
objects, each item names by the corresponding row name.
All result objects ("radline"
, "radfit"
,
"radfit.frame"
) can be accessed with same method functions.
The following methods are available: AIC
,
coef
, deviance
, logLik
. In
addition the fit results can be accessed with fitted
,
predict
and residuals
(inheriting from
residuals.glm
). The graphical functions were discussed
above in Details.
The RAD models are usually fitted for proportions instead of original
abundances. However, nothing in these models seems to require division
of abundances by site totals, and original observations are used in
these functions. If you wish to use proportions, you must standardize
your data by site totals, e.g. with decostand
and use
appropriate family
such as Gamma
.
The lognormal model is fitted in a standard way, but I do think this is not quite correct – at least it is not equivalent to fitting Normal density to log abundances like originally suggested (Preston 1948).
Some models may fail. In particular, estimation of the Zipf-Mandelbrot
model is difficult. If the fitting fails, NA
is returned.
Wilson (1991) defined preemption model as , where
is the fitted proportion of the first species. However, parameter
is completely defined by
since the fitted
proportions must add to one, and therefore I handle preemption as a
one-parameter model.
Veiled log-Normal model was included in earlier releases of this
function, but it was removed because it was flawed: an implicit veil
line also appears in the ordinary log-Normal. The latest release version
with rad.veil
was 1.6-10
.
Jari Oksanen
Pielou, E.C. (1975) Ecological Diversity. Wiley & Sons.
Preston, F.W. (1948) The commonness and rarity of species. Ecology 29, 254–283.
Whittaker, R. H. (1965) Dominance and diversity in plant communities. Science 147, 250–260.
Wilson, J. B. (1991) Methods for fitting dominance/diversity curves. Journal of Vegetation Science 2, 35–46.
fisherfit
and prestonfit
.
An alternative approach is to use
qqnorm
or qqplot
with any distribution.
For controlling graphics: Lattice
,
xyplot
, lset
.
data(BCI) mod <- rad.lognormal(BCI[5,]) mod plot(mod) mod <- radfit(BCI[1,]) ## Standard plot overlaid for all models ## Preemption model is a line plot(mod) ## log for both axes: Zipf model is a line plot(mod, log = "xy") ## Lattice graphics separately for each model radlattice(mod) # Take a subset of BCI to save time and nerves mod <- radfit(BCI[3:5,]) mod plot(mod, pch=".")
data(BCI) mod <- rad.lognormal(BCI[5,]) mod plot(mod) mod <- radfit(BCI[1,]) ## Standard plot overlaid for all models ## Preemption model is a line plot(mod) ## log for both axes: Zipf model is a line plot(mod, log = "xy") ## Lattice graphics separately for each model radlattice(mod) # Take a subset of BCI to save time and nerves mod <- radfit(BCI[3:5,]) mod plot(mod, pch=".")
Rank correlations between dissimilarity indices and gradient separation.
rankindex(grad, veg, indices = c("euc", "man", "gow", "bra", "kul"), stepacross = FALSE, method = "spearman", metric = c("euclidean", "mahalanobis", "manhattan", "gower"), ...)
rankindex(grad, veg, indices = c("euc", "man", "gow", "bra", "kul"), stepacross = FALSE, method = "spearman", metric = c("euclidean", "mahalanobis", "manhattan", "gower"), ...)
grad |
The gradient variable or matrix. |
veg |
The community data matrix. |
indices |
Dissimilarity indices compared, partial matches to
alternatives in |
stepacross |
Use |
method |
Correlation method used. |
metric |
Metric to evaluate the gradient separation. See Details. |
... |
Other parameters to |
A good dissimilarity index for multidimensional scaling should have
a high rank-order similarity with gradient separation. The function
compares most indices in vegdist
against gradient
separation using rank correlation coefficients in
cor
. The gradient separation between each point is
assessed using given metric
. The default is to use Euclidean
distance of continuous variables scaled to unit variance, or to use
Gower metric for mixed data using function
daisy
when grad
has factors. The other
alternatives are Mahalanabis distances which are based on
grad
matrix scaled so that columns are orthogonal
(uncorrelated) and have unit variance, or Manhattan distances of
grad
variables scaled to unit range.
The indices
argument can accept any dissimilarity
indices besides the ones calculated by the
vegdist
function. For this, the argument value
should be a (possibly named) list of functions.
Each function must return a valid 'dist' object with dissimilarities,
similarities are not accepted and should be converted into dissimilarities
beforehand.
Returns a named vector of rank correlations.
There are several problems in using rank correlation coefficients.
Typically there are very many ties when gradient
separation values are derived from just
observations.
Due to floating point arithmetics, many tied values differ by
machine epsilon and are arbitrarily ranked differently by
rank
used in cor.test
. Two indices
which are identical with certain
transformation or standardization may differ slightly
(magnitude ) and this may lead into third or fourth decimal
instability in rank correlations. Small differences in rank
correlations should not be taken too seriously. Probably this method
should be replaced with a sounder method, but I do not yet know
which... You may experiment with
mantel
,
anosim
or even protest
.
Earlier version of this function used method = "kendall"
, but
that is far too slow in large data sets.
The functions returning dissimilarity objects should be self contained,
because the ...
argument passes additional parameters
to stepacross
and not to the functions supplied
via the indices
argument.
Jari Oksanen, with additions from Peter Solymos
Faith, F.P., Minchin, P.R. and Belbin, L. (1987). Compositional dissimilarity as a robust measure of ecological distance. Vegetatio 69, 57-68.
vegdist
, stepacross
,
no.shared
, monoMDS
,
cor
, Machine
, and for
alternatives anosim
, mantel
and
protest
.
data(varespec) data(varechem) ## The variables are automatically scaled rankindex(varechem, varespec) rankindex(varechem, wisconsin(varespec)) ## Using non vegdist indices as functions funs <- list(Manhattan=function(x) dist(x, "manhattan"), Gower=function(x) cluster:::daisy(x, "gower"), Ochiai=function(x) designdist(x, "1-J/sqrt(A*B)")) rankindex(scale(varechem), varespec, funs)
data(varespec) data(varechem) ## The variables are automatically scaled rankindex(varechem, varespec) rankindex(varechem, wisconsin(varespec)) ## Using non vegdist indices as functions funs <- list(Manhattan=function(x) dist(x, "manhattan"), Gower=function(x) cluster:::daisy(x, "gower"), Ochiai=function(x) designdist(x, "1-J/sqrt(A*B)")) rankindex(scale(varechem), varespec, funs)
Rarefied species richness for community ecologists.
rarefy(x, sample, se = FALSE, MARGIN = 1) rrarefy(x, sample) drarefy(x, sample) rarecurve(x, step = 1, sample, xlab = "Sample Size", ylab = "Species", label = TRUE, col, lty, tidy = FALSE, ...) rareslope(x, sample)
rarefy(x, sample, se = FALSE, MARGIN = 1) rrarefy(x, sample) drarefy(x, sample) rarecurve(x, step = 1, sample, xlab = "Sample Size", ylab = "Species", label = TRUE, col, lty, tidy = FALSE, ...) rareslope(x, sample)
x |
Community data, a matrix-like object or a vector. |
MARGIN |
Margin for which the index is computed. |
sample |
Subsample size for rarefying community, either a single value or a vector. |
se |
Estimate standard errors. |
step |
Step size for sample sizes in rarefaction curves. |
xlab , ylab
|
Axis labels in plots of rarefaction curves. |
label |
Label rarefaction curves by rownames of |
col , lty
|
plotting colour and line type, see
|
tidy |
Instead of drawing a |
... |
Parameters passed to |
Function rarefy
gives the expected species richness in random
subsamples of size sample
from the community. The size of
sample
should be smaller than total community size, but the
function will work for larger sample
as well (with a warning)
and return non-rarefied species richness (and standard error =
0). If sample
is a vector, rarefaction of all observations is
performed for each sample size separately. Rarefaction can be
performed only with genuine counts of individuals. The function
rarefy
is based on Hurlbert's (1971) formulation, and the
standard errors on Heck et al. (1975).
Function rrarefy
generates one randomly rarefied community
data frame or vector of given sample
size. The sample
can be a vector giving the sample sizes for each row. If the
sample
size is equal to or larger than the observed number
of individuals, the non-rarefied community will be returned. The
random rarefaction is made without replacement so that the variance
of rarefied communities is rather related to rarefaction proportion
than to the size of the sample
. Random rarefaction is
sometimes used to remove the effects of different sample
sizes. This is usually a bad idea: random rarefaction discards valid
data, introduces random error and reduces the quality of the data
(McMurdie & Holmes 2014). It is better to use normalizing
transformations (decostand
in vegan) possible
with variance stabilization (decostand
and
dispweight
in vegan) and methods that are not
sensitive to sample sizes.
Function drarefy
returns probabilities that species occur in
a rarefied community of size sample
. The sample
can be
a vector giving the sample sizes for each row. If the sample
is equal to or larger than the observed number of individuals, all
observed species will have sampling probability 1.
Function rarecurve
draws a rarefaction curve for each row of
the input data. The rarefaction curves are evaluated using the
interval of step
sample sizes, always including 1 and total
sample size. If sample
is specified, a vertical line is
drawn at sample
with horizontal lines for the rarefied
species richnesses.
Function rareslope
calculates the slope of rarecurve
(derivative of rarefy
) at given sample
size; the
sample
need not be an integer.
Rarefaction functions should be used for observed counts. If you think it is necessary to use a multiplier to data, rarefy first and then multiply. Removing rare species before rarefaction can also give biased results. Observed count data normally include singletons (species with count 1), and if these are missing, functions issue warnings. These may be false positives, but it is recommended to check that the observed counts are not multiplied or rare taxa are not removed.
A vector of rarefied species richness values. With a single
sample
and se = TRUE
, function rarefy
returns a
2-row matrix with rarefied richness (S
) and its standard error
(se
). If sample
is a vector in rarefy
, the
function returns a matrix with a column for each sample
size,
and if se = TRUE
, rarefied richness and its standard error are
on consecutive lines.
Function rarecurve
returns invisible
list of
rarefy
results corresponding each drawn curve. Alternatively,
with tidy = TRUE
it returns a data frame that can be used in
ggplot2 graphics.
Jari Oksanen
Heck, K.L., van Belle, G. & Simberloff, D. (1975). Explicit calculation of the rarefaction diversity measurement and the determination of sufficient sample size. Ecology 56, 1459–1461.
Hurlbert, S.H. (1971). The nonconcept of species diversity: a critique and alternative parameters. Ecology 52, 577–586.
McMurdie, P.J. & Holmes, S. (2014). Waste not, want not: Why rarefying microbiome data is inadmissible. PLoS Comput Biol 10(4): e1003531. doi:10.1371/journal.pcbi.1003531
Use specaccum
for species accumulation curves
where sites are sampled instead of individuals. specpool
extrapolates richness to an unknown sample size.
data(BCI) S <- specnumber(BCI) # observed number of species (raremax <- min(rowSums(BCI))) Srare <- rarefy(BCI, raremax) plot(S, Srare, xlab = "Observed No. of Species", ylab = "Rarefied No. of Species") abline(0, 1) rarecurve(BCI, step = 20, sample = raremax, col = "blue", cex = 0.6)
data(BCI) S <- specnumber(BCI) # observed number of species (raremax <- min(rowSums(BCI))) Srare <- rarefy(BCI, raremax) plot(S, Srare, xlab = "Observed No. of Species", ylab = "Rarefied No. of Species") abline(0, 1) rarecurve(BCI, step = 20, sample = raremax, col = "blue", cex = 0.6)
Function finds the Raup-Crick dissimilarity which is a probability of number of co-occurring species with species occurrence probabilities proportional to species frequencies.
raupcrick(comm, null = "r1", nsimul = 999, chase = FALSE, ...)
raupcrick(comm, null = "r1", nsimul = 999, chase = FALSE, ...)
comm |
Community data which will be treated as presence/absence data. |
null |
Null model used as the |
nsimul |
Number of null communities for assessing the dissimilarity index. |
chase |
Use the Chase et al. (2011) method of tie handling (not recommended except for comparing the results against the Chase script). |
... |
Other parameters passed to |
Raup-Crick index is the probability that compared sampling
units have non-identical species composition. This probability can
be regarded as a dissimilarity, although it is not metric: identical
sampling units can have dissimilarity slightly above , the
dissimilarity can be nearly zero over a range of shared species, and
sampling units with no shared species can have dissimilarity
slightly below
. Moreover, communities sharing rare species
appear as more similar (lower probability of finding rare species
together), than communities sharing the same number of common
species.
The function will always treat the data as binary (presence/ absence).
The probability is assessed using simulation with
oecosimu
where the test statistic is the observed
number of shared species between sampling units evaluated against a
community null model (see Examples). The default null model is
"r1"
where the probability of selecting species is
proportional to the species frequencies.
The vegdist
function implements a variant of the
Raup-Crick index with equal sampling probabilities for species using
exact analytic equations without simulation. This corresponds to
null
model "r0"
which also can be used with the
current function. All other null model methods of
oecosimu
can be used with the current function, but
they are new unpublished methods.
The function returns an object inheriting from
dist
which can be interpreted as a dissimilarity
matrix.
The test statistic is the number of shared species, and this is
typically tied with a large number of simulation results. The tied
values are handled differently in the current function and in the
function published with Chase et al. (2011). In vegan, the
index is the number of simulated values that are smaller or
equal than the observed value, but smaller than observed value is
used by Chase et al. (2011) with option split = FALSE
in
their script; this can be achieved with chase = TRUE
in
vegan. Chase et al. (2011) script with split = TRUE
uses half of tied simulation values to calculate a distance measure,
and that choice cannot be directly reproduced in vegan (it is the
average of vegan raupcrick
results with
chase = TRUE
and chase = FALSE
).
The function was developed after Brian Inouye contacted us and informed us about the method in Chase et al. (2011), and the function takes its idea from the code that was published with their paper. The current function was written by Jari Oksanen.
Chase, J.M., Kraft, N.J.B., Smith, K.G., Vellend, M. and Inouye,
B.D. (2011). Using null models to disentangle variation in community
dissimilarity from variation in -diversity.
Ecosphere 2:art24 doi:10.1890/ES10-00117.1
The function is based on oecosimu
. Function
vegdist
with method = "raup"
implements a related
index but with equal sampling densities of species, and
designdist
demonstrates its calculation.
## data set with variable species richness data(sipoo) ## default raupcrick dr1 <- raupcrick(sipoo) ## use null model "r0" of oecosimu dr0 <- raupcrick(sipoo, null = "r0") ## vegdist(..., method = "raup") corresponds to 'null = "r0"' d <- vegdist(sipoo, "raup") op <- par(mfrow=c(2,1), mar=c(4,4,1,1)+.1) plot(dr1 ~ d, xlab = "Raup-Crick with Null R1", ylab="vegdist") plot(dr0 ~ d, xlab = "Raup-Crick with Null R0", ylab="vegdist") par(op) ## The calculation is essentially as in the following oecosimu() call, ## except that designdist() is replaced with faster code ## Not run: oecosimu(sipoo, function(x) designdist(x, "J", "binary"), method = "r1") ## End(Not run)
## data set with variable species richness data(sipoo) ## default raupcrick dr1 <- raupcrick(sipoo) ## use null model "r0" of oecosimu dr0 <- raupcrick(sipoo, null = "r0") ## vegdist(..., method = "raup") corresponds to 'null = "r0"' d <- vegdist(sipoo, "raup") op <- par(mfrow=c(2,1), mar=c(4,4,1,1)+.1) plot(dr1 ~ d, xlab = "Raup-Crick with Null R1", ylab="vegdist") plot(dr0 ~ d, xlab = "Raup-Crick with Null R0", ylab="vegdist") par(op) ## The calculation is essentially as in the following oecosimu() call, ## except that designdist() is replaced with faster code ## Not run: oecosimu(sipoo, function(x) designdist(x, "J", "binary"), method = "r1") ## End(Not run)
read.cep
reads a file formatted with relaxed strict CEP format
used in Canoco software, among others.
read.cep(file, positive=TRUE)
read.cep(file, positive=TRUE)
file |
File name (character variable). |
positive |
Only positive entries, like in community data. |
Cornell Ecology Programs (CEP) introduced several data formats
designed for punched cards. One of these was the ‘condensed
strict’ format which was adopted by popular software DECORANA and
TWINSPAN. A relaxed variant of this format was later adopted in
Canoco software (ter Braak 1984). Function read.cep
reads
legacy files written in this format.
The condensed CEP and CANOCO formats have:
Two or three title cards, most importantly specifying the format and the number of items per record.
Data in condensed format: First number on the line is the site identifier (an integer), and it is followed by pairs (‘couplets’) of numbers identifying the species and its abundance (an integer and a floating point number).
Species and site names, given in Fortran format (10A8)
:
Ten names per line, eight columns for each.
With option positive = TRUE
the function removes all rows and
columns with zero or negative marginal sums. In community data
with only positive entries, this removes empty sites and species.
If data entries can be negative, this ruins data, and such data sets
should be read in with option positive = FALSE
.
Returns a data frame, where columns are species and rows are
sites. Column and row names are taken from the CEP file, and changed
into unique R names by make.names
after stripping the blanks.
Function read.cep
used Fortran to read data in vegan
2.4-5 and earlier, but Fortran I/O is no longer allowed in CRAN
packages, and the function was re-written in R. The original
Fortran code was more robust, and there are several legacy data sets
that may fail with the current version, but could be read with the
previous Fortran version. CRAN package cepreader makes
available the original Fortran-based code run in a separate
subprocess. The cepreader package can also read ‘free’
and ‘open’ Canoco formats that are not handled in this
function.
The function is based on read.fortran
. If the
REAL
format defines a decimal part for species abundances
(such as F5.1
), read.fortran
divides the
input with the corresponding power of 10 even when the input data
had explicit decimal separator. With F5.1
, 100 would become
10, and 0.1 become 0.01. Function read.cep
tries to undo this
division, but you should check the scaling of results after reading
the data, and if necessary, multiply results to the original scale.
Jari Oksanen
ter Braak, C.J.F. (1984–): CANOCO – a FORTRAN program for canonical community ordination by [partial] [detrended] [canonical] correspondence analysis, principal components analysis and redundancy analysis. TNO Inst. of Applied Computer Sci., Stat. Dept. Wageningen, The Netherlands.
## Provided that you have the file "dune.spe" ## Not run: theclassic <- read.cep("dune.spe") ## End(Not run)
## Provided that you have the file "dune.spe" ## Not run: theclassic <- read.cep("dune.spe") ## End(Not run)
Function renyi
find Rényi diversities with any
scale or the corresponding Hill number (Hill 1973). Function
renyiaccum
finds these statistics with accumulating sites.
renyi(x, scales = c(0, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64, Inf), hill = FALSE) ## S3 method for class 'renyi' plot(x, ...) renyiaccum(x, scales = c(0, 0.5, 1, 2, 4, Inf), permutations = 100, raw = FALSE, collector = FALSE, subset, ...) ## S3 method for class 'renyiaccum' plot(x, what = c("Collector", "mean", "Qnt 0.025", "Qnt 0.975"), type = "l", ...) ## S3 method for class 'renyiaccum' persp(x, theta = 220, col = heat.colors(100), zlim, ...)
renyi(x, scales = c(0, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64, Inf), hill = FALSE) ## S3 method for class 'renyi' plot(x, ...) renyiaccum(x, scales = c(0, 0.5, 1, 2, 4, Inf), permutations = 100, raw = FALSE, collector = FALSE, subset, ...) ## S3 method for class 'renyiaccum' plot(x, what = c("Collector", "mean", "Qnt 0.025", "Qnt 0.975"), type = "l", ...) ## S3 method for class 'renyiaccum' persp(x, theta = 220, col = heat.colors(100), zlim, ...)
x |
Community data matrix or plotting object. |
scales |
Scales of Rényi diversity. |
hill |
Calculate Hill numbers. |
permutations |
Usually an integer giving the number
permutations, but can also be a list of control values for the
permutations as returned by the function |
raw |
if |
collector |
Accumulate the diversities in the order the sites are
in the data set, and the collector curve can be plotted against
summary of permutations. The argument is ignored if |
subset |
logical expression indicating sites (rows) to keep: missing
values are taken as |
what |
Items to be plotted. |
type |
Type of plot, where |
theta |
Angle defining the viewing direction (azimuthal) in
|
col |
Colours used for surface. Single colour will be passed on,
and vector colours will be
selected by the midpoint of a rectangle in |
zlim |
Limits of vertical axis. |
... |
Other arguments which are passed to |
Common diversity
indices are special cases of
Rényi diversity
where is a scale parameter, and Hill (1975) suggested to
use so-called ‘Hill numbers’ defined as
. Some Hill numbers are the number of species with
,
or the exponent of Shannon
diversity with
, inverse Simpson with
and
with
. According
to the theory of diversity ordering, one community can be regarded as
more diverse than another only if its Rényi diversities are all higher
(Tóthmérész 1995).
The plot
method for renyi
uses lattice graphics,
and displays the diversity values against each scale in separate panel
for each site together with minimum, maximum and median values in the
complete data.
Function renyiaccum
is similar to specaccum
but
finds Rényi or Hill diversities at given scales
for random permutations of accumulated sites. Its plot
function uses lattice function xyplot
to display the accumulation curves for each value of scales
in a separate panel. In addition, it has a persp
method to
plot the diversity surface against scale and number and
sites. Similar dynamic graphics can be made with
rgl.renyiaccum
in vegan3d package.
Function renyi
returns a data frame of selected
indices. Function renyiaccum
with argument raw = FALSE
returns a three-dimensional array, where the first dimension are the
accumulated sites, second dimension are the diversity scales, and
third dimension are the summary statistics mean
, stdev
,
min
, max
, Qnt 0.025
and Qnt 0.975
. With
argument raw = TRUE
the statistics on the third dimension are
replaced with individual permutation results.
Roeland Kindt and Jari Oksanen
Hill, M.O. (1973). Diversity and evenness: a unifying notation and its consequences. Ecology 54, 427–473.
Kindt, R., Van Damme, P., Simons, A.J. (2006). Tree diversity in western Kenya: using profiles to characterise richness and evenness. Biodiversity and Conservation 15, 1253–1270.
Tóthmérész, B. (1995). Comparison of different methods for diversity ordering. Journal of Vegetation Science 6, 283–290.
diversity
for diversity indices, and
specaccum
for ordinary species accumulation curves, and
xyplot
, persp
.
data(BCI) i <- sample(nrow(BCI), 12) mod <- renyi(BCI[i,]) plot(mod) mod <- renyiaccum(BCI[i,]) plot(mod, as.table=TRUE, col = c(1, 2, 2)) persp(mod)
data(BCI) i <- sample(nrow(BCI), 12) mod <- renyi(BCI[i,]) plot(mod) mod <- renyiaccum(BCI[i,]) plot(mod, as.table=TRUE, col = c(1, 2, 2)) persp(mod)
Function takes a hierarchical clustering tree from
hclust
and a vector of values and reorders the
clustering tree in the order of the supplied vector, maintaining the
constraints on the tree. This is a method of generic function
reorder
and an alternative to reordering a
"dendrogram"
object with reorder.dendrogram
## S3 method for class 'hclust' reorder(x, wts, agglo.FUN = c("mean", "min", "max", "sum", "uwmean"), ...) ## S3 method for class 'hclust' rev(x) ## S3 method for class 'hclust' scores(x, display = "internal", ...) cutreeord(tree, k = NULL, h = NULL)
## S3 method for class 'hclust' reorder(x, wts, agglo.FUN = c("mean", "min", "max", "sum", "uwmean"), ...) ## S3 method for class 'hclust' rev(x) ## S3 method for class 'hclust' scores(x, display = "internal", ...) cutreeord(tree, k = NULL, h = NULL)
x , tree
|
hierarchical clustering from |
wts |
numeric vector for reordering. |
agglo.FUN |
a function for weights agglomeration, see below. |
display |
return |
k , h
|
scalars or vectors giving the numbers of desired groups or the heights
where the tree should be cut (passed to function
|
... |
additional arguments (ignored). |
Dendrograms can be ordered in many ways. The reorder
function
reorders an hclust
tree and provides an alternative to
reorder.dendrogram
which can reorder a
dendrogram
. The current function will also work
differently when the agglo.FUN
is "mean"
: the
reorder.dendrogram
will always take the direct mean of
member groups ignoring their sizes, but this function will used
weighted.mean
weighted by group sizes, so that the
group mean is always the mean of member leaves (terminal nodes). If
you want to ignore group sizes, you can use unweighted mean with
"uwmean"
.
The function accepts only a limited list of agglo.FUN
functions for assessing the value of wts
for groups. The
ordering is always ascending, but the order of leaves can be
reversed with rev
.
Function scores
finds the coordinates of nodes as a two-column
matrix. For terminal nodes (leaves) this the value at which the item
is merged to the tree, and the labels can still hang
below this
level (see plot.hclust
).
Function cutreeord
cuts a tree to groups numbered from left to
right in the tree. It is based on the standard function
cutree
which numbers the groups in the order they appear
in the input data instead of the order in the tree.
Reordered hclust
result object with added item
value
that gives the value of the statistic at each merge
level.
These functions should really be in base R.
Jari Oksanen
hclust
for getting clustering trees,
as.hclust.spantree
to change a vegan minimum
spanning tree to an hclust
object, and
dendrogram
and reorder.dendrogram
for an
alternative implementation.
## reorder by water content of soil data(mite, mite.env) hc <- hclust(vegdist(wisconsin(sqrt(mite)))) ohc <- with(mite.env, reorder(hc, WatrCont)) plot(hc) plot(ohc) ## label leaves by the observed value, and each branching point ## (internal node) by the cluster mean with(mite.env, plot(ohc, labels=round(WatrCont), cex=0.7)) ordilabel(scores(ohc), label=round(ohc$value), cex=0.7) ## Slightly different from reordered 'dendrogram' which ignores group ## sizes in assessing means. den <- as.dendrogram(hc) den <- with(mite.env, reorder(den, WatrCont, agglo.FUN = mean)) plot(den)
## reorder by water content of soil data(mite, mite.env) hc <- hclust(vegdist(wisconsin(sqrt(mite)))) ohc <- with(mite.env, reorder(hc, WatrCont)) plot(hc) plot(ohc) ## label leaves by the observed value, and each branching point ## (internal node) by the cluster mean with(mite.env, plot(ohc, labels=round(WatrCont), cex=0.7)) ordilabel(scores(ohc), label=round(ohc$value), cex=0.7) ## Slightly different from reordered 'dendrogram' which ignores group ## sizes in assessing means. den <- as.dendrogram(hc) den <- with(mite.env, reorder(den, WatrCont, agglo.FUN = mean)) plot(den)
The functions finds the adjusted R-square.
## Default S3 method: RsquareAdj(x, n, m, ...) ## S3 method for class 'rda' RsquareAdj(x, ...) ## S3 method for class 'cca' RsquareAdj(x, permutations = 1000, ...)
## Default S3 method: RsquareAdj(x, n, m, ...) ## S3 method for class 'rda' RsquareAdj(x, ...) ## S3 method for class 'cca' RsquareAdj(x, permutations = 1000, ...)
x |
Unadjusted R-squared or an object from which the terms for evaluation or adjusted R-squared can be found. |
n , m
|
Number of observations and number of degrees of freedom in the fitted model. |
permutations |
Number of permutations to use when computing the adjusted
R-squared for a cca. The permutations can be calculated in parallel by
specifying the number of cores which is passed to |
... |
Other arguments (ignored) except in the case of cca in
which these arguments are passed to |
The default method finds the adjusted from the
unadjusted
, number of observations, and number
of degrees of freedom in the fitted model. The specific methods find
this information from the fitted result object. There are specific
methods for
rda
(also used for distance-based RDA),
cca
, lm
and glm
. Adjusted,
or even unadjusted, may not be available in
some cases, and then the functions will return
NA
.
values are available only for
gaussian
models in glm
.
The adjusted, of
cca
is computed using a
permutation approach developed by Peres-Neto et al. (2006). By
default 1000 permutations are used.
The functions return a list of items r.squared
and
adj.r.squared
.
Legendre, P., Oksanen, J. and ter Braak, C.J.F. (2011). Testing the significance of canonical axes in redundancy analysis. Methods in Ecology and Evolution 2, 269–277.
Peres-Neto, P., P. Legendre, S. Dray and D. Borcard. 2006. Variation partitioning of species data matrices: estimation and comparison of fractions. Ecology 87, 2614–2625.
varpart
uses RsquareAdj
.
data(mite) data(mite.env) ## rda m <- rda(decostand(mite, "hell") ~ ., mite.env) RsquareAdj(m) ## cca m <- cca(decostand(mite, "hell") ~ ., mite.env) RsquareAdj(m) ## default method RsquareAdj(0.8, 20, 5)
data(mite) data(mite.env) ## rda m <- rda(decostand(mite, "hell") ~ ., mite.env) RsquareAdj(m) ## cca m <- cca(decostand(mite, "hell") ~ ., mite.env) RsquareAdj(m) ## default method RsquareAdj(0.8, 20, 5)
Function to access either species or site scores for specified axes
in some ordination methods. The scores
function is generic in
vegan, and vegan ordination functions have their own
scores
functions that are documented separately with the
method (see e.g. scores.cca
,
scores.metaMDS
, scores.decorana
). This
help file documents the default scores
method that is only
used for non-vegan ordination objects.
## Default S3 method: scores(x, choices, display=c("sites", "species", "both"), tidy = FALSE, ...)
## Default S3 method: scores(x, choices, display=c("sites", "species", "both"), tidy = FALSE, ...)
x |
An ordination result. |
choices |
Ordination axes. If missing, default method returns all axes. |
display |
Partial match to access scores for |
tidy |
Return |
... |
Other parameters (unused). |
Function scores
is a generic method in vegan. Several
vegan functions have their own scores
methods with their
own defaults and with some new arguments. This help page describes
only the default method. For other methods, see, e.g.,
scores.cca
, scores.rda
,
scores.decorana
.
All vegan ordination functions should have a scores
method which should be used to extract the scores instead of
directly accessing them. Scaling and transformation of scores should
also happen in the scores
function. If the scores
function is available, the results can be plotted using
ordiplot
, ordixyplot
etc., and the
ordination results can be compared in procrustes
analysis.
The scores.default
function is used to extract scores from
non-vegan ordination results. Many standard ordination
methods of libraries do not have a specific class
, and no
specific method can be written for them. However,
scores.default
guesses where some commonly used functions
keep their site scores and possible species scores.
If x
is a matrix, scores.default
returns the chosen
columns of that matrix, ignoring whether species or sites were
requested (do not regard this as a bug but as a feature, please).
Currently the function seems to work at least for isoMDS
,
prcomp
, princomp
and some ade4 objects.
It may work in other cases or fail mysteriously.
The function returns a matrix of scores if one type is requested, or a
named list of matrices if display = "both"
, or a
ggplot2 compatible data frame if tidy = TRUE
.
Jari Oksanen
Specific scores
functions include (but are not limited to)
scores.cca
, scores.rda
,
scores.decorana
, scores.envfit
,
scores.metaMDS
, scores.monoMDS
and
scores.pcnm
. These have somewhat different interface
– scores.cca
in particular – but all work with
keywords display="sites"
and return a matrix. However, they
may also return a list of matrices, and some other scores
methods will have quite different arguments.
data(varespec) vare.pca <- prcomp(varespec) scores(vare.pca, choices=c(1,2))
data(varespec) vare.pca <- prcomp(varespec) scores(vare.pca, choices=c(1,2))
Screeplot methods for plotting variances of ordination axes/components
and overlaying broken stick distributions. Also, provides alternative
screeplot methods for princomp
and prcomp
.
## S3 method for class 'cca' screeplot(x, bstick = FALSE, type = c("barplot", "lines"), npcs = min(10, if (is.null(x$CCA) || x$CCA$rank == 0) x$CA$rank else x$CCA$rank), ptype = "o", bst.col = "red", bst.lty = "solid", xlab = "Component", ylab = "Inertia", main = deparse(substitute(x)), legend = bstick, ...) ## S3 method for class 'decorana' screeplot(x, bstick = FALSE, type = c("barplot", "lines"), npcs = 4, ptype = "o", bst.col = "red", bst.lty = "solid", xlab = "Component", ylab = "Inertia", main = deparse(substitute(x)), legend = bstick, ...) ## S3 method for class 'prcomp' screeplot(x, bstick = FALSE, type = c("barplot", "lines"), npcs = min(10, length(x$sdev)), ptype = "o", bst.col = "red", bst.lty = "solid", xlab = "Component", ylab = "Inertia", main = deparse(substitute(x)), legend = bstick, ...) ## S3 method for class 'princomp' screeplot(x, bstick = FALSE, type = c("barplot", "lines"), npcs = min(10, length(x$sdev)), ptype = "o", bst.col = "red", bst.lty = "solid", xlab = "Component", ylab = "Inertia", main = deparse(substitute(x)), legend = bstick, ...) bstick(n, ...) ## Default S3 method: bstick(n, tot.var = 1, ...) ## S3 method for class 'cca' bstick(n, ...) ## S3 method for class 'prcomp' bstick(n, ...) ## S3 method for class 'princomp' bstick(n, ...) ## S3 method for class 'decorana' bstick(n, ...)
## S3 method for class 'cca' screeplot(x, bstick = FALSE, type = c("barplot", "lines"), npcs = min(10, if (is.null(x$CCA) || x$CCA$rank == 0) x$CA$rank else x$CCA$rank), ptype = "o", bst.col = "red", bst.lty = "solid", xlab = "Component", ylab = "Inertia", main = deparse(substitute(x)), legend = bstick, ...) ## S3 method for class 'decorana' screeplot(x, bstick = FALSE, type = c("barplot", "lines"), npcs = 4, ptype = "o", bst.col = "red", bst.lty = "solid", xlab = "Component", ylab = "Inertia", main = deparse(substitute(x)), legend = bstick, ...) ## S3 method for class 'prcomp' screeplot(x, bstick = FALSE, type = c("barplot", "lines"), npcs = min(10, length(x$sdev)), ptype = "o", bst.col = "red", bst.lty = "solid", xlab = "Component", ylab = "Inertia", main = deparse(substitute(x)), legend = bstick, ...) ## S3 method for class 'princomp' screeplot(x, bstick = FALSE, type = c("barplot", "lines"), npcs = min(10, length(x$sdev)), ptype = "o", bst.col = "red", bst.lty = "solid", xlab = "Component", ylab = "Inertia", main = deparse(substitute(x)), legend = bstick, ...) bstick(n, ...) ## Default S3 method: bstick(n, tot.var = 1, ...) ## S3 method for class 'cca' bstick(n, ...) ## S3 method for class 'prcomp' bstick(n, ...) ## S3 method for class 'princomp' bstick(n, ...) ## S3 method for class 'decorana' bstick(n, ...)
x |
an object from which the component variances can be determined. |
bstick |
logical; should the broken stick distribution be drawn? |
npcs |
the number of components to be plotted. |
type |
the type of plot. |
ptype |
if |
bst.col , bst.lty
|
the colour and line type used to draw the broken stick distribution. |
xlab , ylab , main
|
graphics parameters. |
legend |
logical; draw a legend? |
n |
an object from which the variances can be extracted or the
number of variances (components) in the case of
|
tot.var |
the total variance to be split. |
... |
arguments passed to other methods. |
The functions provide screeplots for most ordination methods in
vegan and enhanced versions with broken stick for
prcomp
and princomp
.
Function bstick
gives the brokenstick values which are ordered
random proportions, defined as (Legendre & Legendre 2012), where
is the total and
is the number of brokenstick
components (cf.
radfit
). Broken stick has
been recommended as a stopping rule in principal component analysis
(Jackson 1993): principal components should be retained as long as
observed eigenvalues are higher than corresponding random broken stick
components.
The bstick
function is generic. The default needs the number of
components and the total, and specific methods extract this
information from ordination results. There also is a bstick
method for cca
. However, the broken stick model is not
strictly valid for correspondence analysis (CA), because eigenvalues
of CA are defined to be , whereas brokenstick
components have no such restrictions. The brokenstick components in
detrended correspondence analysis (DCA) assume that input data are of
full rank, and additive eigenvalues are used in
screeplot
(see
decorana
).
Function screeplot
draws a plot on the currently active device,
and returns invisibly the xy.coords
of the points or
bars for the eigenvalues.
Function bstick
returns a numeric vector of broken stick
components.
Gavin L. Simpson
Jackson, D. A. (1993). Stopping rules in principal components analysis: a comparison of heuristical and statistical approaches. Ecology 74, 2204–2214.
Legendre, P. and Legendre, L. (2012) Numerical Ecology. 3rd English ed. Elsevier.
cca
, decorana
, princomp
and
prcomp
for the ordination functions, and
screeplot
for the stock version.
data(varespec) vare.pca <- rda(varespec, scale = TRUE) bstick(vare.pca) screeplot(vare.pca, bstick = TRUE, type = "lines")
data(varespec) vare.pca <- rda(varespec, scale = TRUE) bstick(vare.pca) screeplot(vare.pca, bstick = TRUE, type = "lines")
Discriminating species between two groups using Bray-Curtis dissimilarities
simper(comm, group, permutations = 999, parallel = 1, ...) ## S3 method for class 'simper' summary(object, ordered = TRUE, digits = max(3,getOption("digits") - 3), ...)
simper(comm, group, permutations = 999, parallel = 1, ...) ## S3 method for class 'simper' summary(object, ordered = TRUE, digits = max(3,getOption("digits") - 3), ...)
comm |
Community data. |
group |
Factor describing the group structure. If this is missing or has only one level, contributions are estimated for non-grouped data and dissimilarities only show the overall heterogeneity in species abundances. |
permutations |
a list of control values for the permutations
as returned by the function |
object |
an object returned by |
ordered |
Logical; Should the species be ordered by their average contribution? |
digits |
Number of digits in output. |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
... |
Parameters passed to other functions. In |
Similarity percentage, simper
(Clarke 1993) is based
on the decomposition of Bray-Curtis dissimilarity index (see
vegdist
, designdist
). The contribution
of individual species to the overall Bray-Curtis dissimilarity
is given by
where is the abundance of species
in sampling units
and
. The overall index is the sum of the individual
contributions over all
species
.
The simper
functions performs pairwise comparisons of groups
of sampling units and finds the contribution of each species to the
average between-group Bray-Curtis dissimilarity. Although the method
is called “Similarity Percentages”, it really studied
dissimilarities instead of similarities (Clarke 1993).
The function displays most important species for each pair of
groups
. These species contribute at least to 70 % of the
differences between groups. The function returns much more
extensive results (including all species) which can be accessed
directly from the result object (see section Value). Function
summary
transforms the result to a list of data frames. With
argument ordered = TRUE
the data frames also include the
cumulative contributions and are ordered by species contribution.
The results of simper
can be very difficult to interpret and
they are often misunderstood even in publications. The method gives
the contribution of each species to overall dissimilarities, but
these are caused by variation in species abundances, and only partly
by differences among groups. Even if you make groups that are
copies of each other, the method will single out species with high
contribution, but these are not contributions to non-existing
between-group differences but to random noise variation in species
abundances. The most abundant species usually have highest
variances, and they have high contributions even when they do not
differ among groups. Permutation tests study the differences among
groups, and they can be used to find out the species for which the
differences among groups is an important component of their
contribution to dissimilarities. Analysis without group
argument will find species contributions to the average overall
dissimilarity among sampling units. These non-grouped contributions
can be compared to grouped contributions to see how much added value
the grouping has for each species.
A list of class "simper"
with following items:
species |
The species names. |
average |
Species contribution to average between-group dissimilarity. |
overall |
The average between-group dissimilarity. This is the sum of
the item |
sd |
Standard deviation of contribution. |
ratio |
Average to sd ratio. |
ava , avb
|
Average abundances per group. |
ord |
An index vector to order vectors by their contribution or
order |
cusum |
Ordered cumulative contribution. These are based on item
|
p |
Permutation |
Eduard Szöcs and Jari Oksanen.
Clarke, K.R. 1993. Non-parametric multivariate analyses of changes in community structure. Australian Journal of Ecology, 18, 117–143.
Function meandist
shows the average between-group
dissimilarities (as well as the within-group dissimilarities).
data(dune) data(dune.env) (sim <- with(dune.env, simper(dune, Management, permutations = 99))) ## IGNORE_RDIFF_BEGIN summary(sim) ## IGNORE_RDIFF_END
data(dune) data(dune.env) (sim <- with(dune.env, simper(dune, Management, permutations = 99))) ## IGNORE_RDIFF_BEGIN summary(sim) ## IGNORE_RDIFF_END
Function simulates a response data frame so that it adds
Gaussian error to the fitted responses of Redundancy Analysis
(rda
), Constrained Correspondence Analysis
(cca
) or distance-based RDA (capscale
).
The function is a special case of generic simulate
, and
works similarly as simulate.lm
.
## S3 method for class 'rda' simulate(object, nsim = 1, seed = NULL, indx = NULL, rank = "full", correlated = FALSE, ...)
## S3 method for class 'rda' simulate(object, nsim = 1, seed = NULL, indx = NULL, rank = "full", correlated = FALSE, ...)
object |
|
nsim |
number of response matrices to be simulated. Only one
dissimilarity matrix is returned for |
seed |
an object specifying if and how the random number
generator should be initialized (‘seeded’). See
|
indx |
Index of residuals added to the fitted values, such as
produced by |
rank |
The rank of the constrained component: passed to
|
correlated |
Are species regarded as correlated in parametric
simulation or when |
... |
additional optional arguments (ignored). |
The implementation follows "lm"
method of
simulate
, and adds Gaussian (Normal) error to the fitted
values (fitted.rda
) using function rnorm
if correlated = FALSE
or mvrnorm
if
correlated = TRUE
. The standard deviations (rnorm
)
or covariance matrices for species (mvrnorm
) are
estimated from the residuals after fitting the constraints.
Alternatively, the function can take a permutation index that is used
to add permuted residuals (unconstrained component) to the fitted
values. Raw data are used in rda
. Internal Chi-square
transformed data are used in cca
within the function,
but the returned matrix is similar to the original input data. The
simulation is performed on internal metric scaling data in
capscale
, but the function returns the Euclidean
distances calculated from the simulated data. The simulation uses
only the real components, and the imaginary dimensions are ignored.
If nsim = 1
, returns a matrix or dissimilarities (in
capscale
) with similar additional arguments on random
number seed as simulate
. If nsim > 1
, returns a
similar array as returned by simulate.nullmodel
with
similar attributes.
Jari Oksanen
simulate
for the generic case and for
lm
objects, and simulate.nullmodel
for
community null model simulation. Functions fitted.rda
and fitted.cca
return fitted values without the error
component. See rnorm
and mvrnorm
(MASS package) for simulating Gaussian random error.
data(dune) data(dune.env) mod <- rda(dune ~ Moisture + Management, dune.env) ## One simulation update(mod, simulate(mod) ~ .) ## An impression of confidence regions of site scores plot(mod, display="sites") for (i in 1:5) lines(procrustes(mod, update(mod, simulate(mod) ~ .)), col="blue") ## Simulate a set of null communities with permutation of residuals simulate(mod, indx = shuffleSet(nrow(dune), 99))
data(dune) data(dune.env) mod <- rda(dune ~ Moisture + Management, dune.env) ## One simulation update(mod, simulate(mod) ~ .) ## An impression of confidence regions of site scores plot(mod, display="sites") for (i in 1:5) lines(procrustes(mod, update(mod, simulate(mod) ~ .)), col="blue") ## Simulate a set of null communities with permutation of residuals simulate(mod, indx = shuffleSet(nrow(dune), 99))
Land birds on islands covered by coniferous forest in the Sipoo Archipelago, southern Finland.
data(sipoo) data(sipoo.map)
data(sipoo) data(sipoo.map)
The sipoo
data frame contains data of occurrences of 50 land
bird species on 18 islands in the Sipoo Archipelago (Simberloff &
Martin, 1991, Appendix 3). The species are referred by 4+4 letter
abbreviation of their Latin names (but using five letters in two
species names to make these unique).
The sipoo.map
data contains the geographic coordinates of the
islands in the ETRS89-TM35FIN coordinate system (EPSG:3067) and the
areas of islands in hectares.
Simberloff, D. & Martin, J.-L. (1991). Nestedness of insular avifaunas: simple summary statistics masking complex species patterns. Ornis Fennica 68:178–192.
data(sipoo) data(sipoo.map) plot(N ~ E, data=sipoo.map, asp = 1)
data(sipoo) data(sipoo.map) plot(N ~ E, data=sipoo.map, asp = 1)
Function spantree
finds a minimum spanning tree
connecting all points, but disregarding dissimilarities that are at or
above the threshold or NA
.
spantree(d, toolong = 0) ## S3 method for class 'spantree' as.hclust(x, ...) ## S3 method for class 'spantree' cophenetic(x) spandepth(x) ## S3 method for class 'spantree' plot(x, ord, cex = 0.7, type = "p", labels, dlim, FUN = sammon, ...) ## S3 method for class 'spantree' lines(x, ord, display="sites", col = 1, ...)
spantree(d, toolong = 0) ## S3 method for class 'spantree' as.hclust(x, ...) ## S3 method for class 'spantree' cophenetic(x) spandepth(x) ## S3 method for class 'spantree' plot(x, ord, cex = 0.7, type = "p", labels, dlim, FUN = sammon, ...) ## S3 method for class 'spantree' lines(x, ord, display="sites", col = 1, ...)
d |
Dissimilarity data inheriting from class |
toolong |
Shortest dissimilarity regarded as |
x |
A |
ord |
An ordination configuration, or an ordination result known
by |
cex |
Character expansion factor. |
type |
Observations are plotted as points with
|
labels |
Text used with |
dlim |
A ceiling value used to highest |
FUN |
Ordination function to find the configuration from
cophenetic dissimilarities. If the supplied |
display |
Type of |
col |
Colour of line segments. This can be a vector which is recycled for points, and the line colour will be a mixture of two joined points. |
... |
Other parameters passed to functions. |
Function spantree
finds a minimum spanning tree for
dissimilarities (there may be several minimum spanning trees, but the
function finds only one). Dissimilarities at or above the threshold
toolong
and NA
s are disregarded, and the spanning tree
is found through other dissimilarities. If the data are disconnected,
the function will return a disconnected tree (or a forest), and the
corresponding link is NA
. Connected subtrees can be identified
using distconnected
.
Minimum spanning tree is closely related to single linkage
clustering, a.k.a. nearest neighbour clustering, and in genetics as
neighbour joining tree available in hclust
and
agnes
functions. The most important practical
difference is that minimum spanning tree has no concept of cluster
membership, but always joins individual points to each other. Function
as.hclust
can change the spantree
result into a
corresponding hclust
object.
Function cophenetic
finds distances between all points along
the tree segments. Function spandepth
returns the depth of
each node. The nodes of a tree are either leaves (with one link) or
internal nodes (more than one link). The leaves are recursively
removed from the tree, and the depth is the layer at with the leaf
was removed. In disconnected spantree
object (in a forest)
each tree is analysed separately and disconnected nodes not in any
tree have depth zero.
Function plot
displays the tree over a
supplied ordination configuration, and lines
adds a spanning
tree to an ordination graph. If configuration is not supplied for plot
,
the function ordinates the cophenetic dissimilarities of the
spanning tree and overlays the tree on this result. The default
ordination function is sammon
(package MASS),
because Sammon scaling emphasizes structure in the neighbourhood of
nodes and may be able to beautifully represent the tree (you may need
to set dlim
, and sometimes the results will remain
twisted). These ordination methods do not work with disconnected
trees, but you must supply the ordination configuration. Function
lines
will overlay the tree in an existing plot.
Function spantree
uses Prim's method
implemented as priority-first search for dense graphs (Sedgewick
1990). Function cophenetic
uses function
stepacross
with option path = "extended"
. The
spantree
is very fast, but cophenetic
is slow in very
large data sets.
Function spantree
returns an object of class spantree
which is a
list with two vectors, each of length . The
number of links in a tree is one less the number of observations, and
the first item is omitted. The items are
kid |
The child node of the parent, starting from parent number
two. If there is no link from the parent, value will be |
dist |
Corresponding distance. If |
labels |
Names of nodes as found from the input dissimilarities. |
call |
The function call. |
In principle, minimum spanning tree is equivalent to single linkage
clustering that can be performed using hclust
or
agnes
. However, these functions combine
clusters to each other and the information of the actually connected points
(the “single link”) cannot be recovered from the result. The
graphical output of a single linkage clustering plotted with
ordicluster
will look very different from an equivalent
spanning tree plotted with lines.spantree
.
Jari Oksanen
Sedgewick, R. (1990). Algorithms in C. Addison Wesley.
vegdist
or dist
for getting
dissimilarities, and hclust
or
agnes
for single linkage clustering.
data(dune) dis <- vegdist(dune) tr <- spantree(dis) ## Add tree to a metric scaling plot(tr, cmdscale(dis), type = "t") ## Find a configuration to display the tree neatly plot(tr, type = "t") ## Depths of nodes depths <- spandepth(tr) plot(tr, type = "t", label = depths) ## Plot as a dendrogram cl <- as.hclust(tr) plot(cl) ## cut hclust tree to classes and show in colours in spantree plot(tr, col = cutree(cl, 5), pch=16)
data(dune) dis <- vegdist(dune) tr <- spantree(dis) ## Add tree to a metric scaling plot(tr, cmdscale(dis), type = "t") ## Find a configuration to display the tree neatly plot(tr, type = "t") ## Depths of nodes depths <- spandepth(tr) plot(tr, type = "t", label = depths) ## Plot as a dendrogram cl <- as.hclust(tr) plot(cl) ## cut hclust tree to classes and show in colours in spantree plot(tr, col = cutree(cl, 5), pch=16)
Function specaccum
finds species accumulation curves or the
number of species for a certain number of sampled sites or
individuals.
specaccum(comm, method = "exact", permutations = 100, conditioned =TRUE, gamma = "jack1", w = NULL, subset, ...) ## S3 method for class 'specaccum' plot(x, add = FALSE, random = FALSE, ci = 2, ci.type = c("bar", "line", "polygon"), col = par("fg"), lty = 1, ci.col = col, ci.lty = 1, ci.length = 0, xlab, ylab = x$method, ylim, xvar = c("sites", "individuals", "effort"), ...) ## S3 method for class 'specaccum' boxplot(x, add = FALSE, ...) fitspecaccum(object, model, method = "random", ...) ## S3 method for class 'fitspecaccum' plot(x, col = par("fg"), lty = 1, xlab = "Sites", ylab = x$method, ...) ## S3 method for class 'specaccum' predict(object, newdata, interpolation = c("linear", "spline"), ...) ## S3 method for class 'fitspecaccum' predict(object, newdata, ...) specslope(object, at)
specaccum(comm, method = "exact", permutations = 100, conditioned =TRUE, gamma = "jack1", w = NULL, subset, ...) ## S3 method for class 'specaccum' plot(x, add = FALSE, random = FALSE, ci = 2, ci.type = c("bar", "line", "polygon"), col = par("fg"), lty = 1, ci.col = col, ci.lty = 1, ci.length = 0, xlab, ylab = x$method, ylim, xvar = c("sites", "individuals", "effort"), ...) ## S3 method for class 'specaccum' boxplot(x, add = FALSE, ...) fitspecaccum(object, model, method = "random", ...) ## S3 method for class 'fitspecaccum' plot(x, col = par("fg"), lty = 1, xlab = "Sites", ylab = x$method, ...) ## S3 method for class 'specaccum' predict(object, newdata, interpolation = c("linear", "spline"), ...) ## S3 method for class 'fitspecaccum' predict(object, newdata, ...) specslope(object, at)
comm |
Community data set. |
method |
Species accumulation method (partial match). Method
|
permutations |
Number of permutations with |
conditioned |
Estimation of standard deviation is conditional on the empirical dataset for the exact SAC |
gamma |
Method for estimating the total extrapolated number of species in the
survey area by function |
w |
Weights giving the sampling effort. |
subset |
logical expression indicating sites (rows) to keep: missing
values are taken as |
x |
A |
add |
Add to an existing graph. |
random |
Draw each random simulation separately instead of drawing their average and confidence intervals. |
ci |
Multiplier used to get confidence intervals from standard
deviation (standard error of the estimate). Value |
ci.type |
Type of confidence intervals in the graph: |
col |
Colour for drawing lines. |
lty |
line type (see |
ci.col |
Colour for drawing lines or filling the
|
ci.lty |
Line type for confidence intervals or border of the
|
ci.length |
Length of horizontal bars (in inches) at the end of
vertical bars with |
xlab , ylab
|
Labels for |
ylim |
the y limits of the plot. |
xvar |
Variable used for the horizontal axis:
|
object |
Either a community data set or fitted |
model |
Nonlinear regression model ( |
newdata |
Optional data used in prediction interpreted as number of sampling units (sites). If missing, fitted values are returned. |
interpolation |
Interpolation method used with |
at |
Number of plots where the slope is evaluated. Can be a real number. |
... |
Other parameters to functions. |
Species accumulation curves (SAC) are used to compare diversity
properties of community data sets using different accumulator
functions. The classic method is "random"
which finds the mean
SAC and its standard deviation from random permutations of the data,
or subsampling without replacement (Gotelli & Colwell 2001). The
"exact"
method finds the expected SAC using sample-based
rarefaction method that has been independently developed numerous
times (Chiarucci et al. 2008) and it is often known as Mao Tau
estimate (Colwell et al. 2012). The unconditional standard deviation
for the exact SAC represents a moment-based estimation that is not
conditioned on the empirical data set (sd for all samples > 0). The
unconditional standard deviation is based on an estimation of the
extrapolated number of species in the survey area (a.k.a. gamma
diversity), as estimated by function specpool
. The
conditional standard deviation that was developed by Jari Oksanen (not
published, sd=0 for all samples). Method "coleman"
finds the
expected SAC and its standard deviation following Coleman et
al. (1982). All these methods are based on sampling sites without
replacement. In contrast, the method = "rarefaction"
finds the
expected species richness and its standard deviation by sampling
individuals instead of sites. It achieves this by applying function
rarefy
with number of individuals corresponding to
average number of individuals per site.
Methods "random"
and "collector"
can take weights
(w
) that give the sampling effort for each site. The weights
w
do not influence the order the sites are accumulated, but
only the value of the sampling effort so that not all sites are
equal. The summary results are expressed against sites even when the
accumulation uses weights (methods "random"
,
"collector"
), or is based on individuals
("rarefaction"
). The actual sampling effort is given as item
Effort
or Individuals
in the printed result. For
weighted "random"
method the effort refers to the average
effort per site, or sum of weights per number of sites. With
weighted method = "random"
, the averaged species richness is
found from linear interpolation of single random permutations.
Therefore at least the first value (and often several first) have
NA
richness, because these values cannot be interpolated in
all cases but should be extrapolated. The plot
function
defaults to display the results as scaled to sites, but this can be
changed selecting xvar = "effort"
(weighted methods) or
xvar = "individuals"
(with method = "rarefaction"
).
The summary
and boxplot
methods are available for
method = "random"
.
Function predict
for specaccum
can return the values
corresponding to newdata
. With method
"exact"
,
"rarefaction"
and "coleman"
the function uses analytic
equations for interpolated non-integer values, and for other methods
linear (approx
) or spline (spline
)
interpolation. If newdata
is not given, the function returns
the values corresponding to the data. NB., the fitted values with
method="rarefaction"
are based on rounded integer counts, but
predict
can use fractional non-integer counts with
newdata
and give slightly different results.
Function fitspecaccum
fits a nonlinear (nls
)
self-starting species accumulation model. The input object
can be a result of specaccum
or a community in data frame. In
the latter case the function first fits a specaccum
model and
then proceeds with fitting the nonlinear model. The function can
apply a limited set of nonlinear regression models suggested for
species-area relationship (Dengler 2009). All these are
selfStart
models. The permissible alternatives are
"arrhenius"
(SSarrhenius
), "gleason"
(SSgleason
), "gitay"
(SSgitay
),
"lomolino"
(SSlomolino
) of vegan
package. In addition the following standard R models are available:
"asymp"
(SSasymp
), "gompertz"
(SSgompertz
), "michaelis-menten"
(SSmicmen
), "logis"
(SSlogis
),
"weibull"
(SSweibull
). See these functions for
model specification and details.
When weights w
were used the fit is based on accumulated
effort and in model = "rarefaction"
on accumulated number of
individuals. The plot
is still based on sites, unless other
alternative is selected with xvar
.
Function predict
for fitspecaccum
uses
predict.nls
, and you can pass all arguments to that
function. In addition, fitted
, residuals
, nobs
,
coef
, AIC
, logLik
and deviance
work on
the result object.
Function specslope
evaluates the derivative of the species
accumulation curve at given number of sample plots, and gives the
rate of increase in the number of species. The function works with
specaccum
result object when this is based on analytic models
"exact"
, "rarefaction"
or "coleman"
, and with
non-linear regression results of fitspecaccum
.
Nonlinear regression may fail for any reason, and some of the
fitspecaccum
models are fragile and may not succeed.
Function specaccum
returns an object of class
"specaccum"
, and fitspecaccum
a model of class
"fitspecaccum"
that adds a few items to the
"specaccum"
(see the end of the list below):
call |
Function call. |
method |
Accumulator method. |
sites |
Number of sites. For |
effort |
Average sum of weights corresponding to the number of
sites when model was fitted with argument |
richness |
The number of species corresponding to number of
sites. With |
sd |
The standard deviation of SAC (or its standard error). This
is |
perm |
Permutation results with |
weights |
Matrix of accumulated weights corresponding to the
columns of the |
fitted , residuals , coefficients
|
Only in |
models |
Only in |
The SAC with method = "exact"
was
developed by Roeland Kindt, and its standard deviation by Jari
Oksanen (both are unpublished). The method = "coleman"
underestimates the SAC because it does not handle properly sampling
without replacement. Further, its standard deviation does not take
into account species correlations, and is generally too low.
Roeland Kindt [email protected] and Jari Oksanen.
Chiarucci, A., Bacaro, G., Rocchini, D. & Fattorini, L. (2008). Discovering and rediscovering the sample-based rarefaction formula in the ecological literature. Commun. Ecol. 9: 121–123.
Coleman, B.D, Mares, M.A., Willis, M.R. & Hsieh, Y. (1982). Randomness, area and species richness. Ecology 63: 1121–1133.
Colwell, R.K., Chao, A., Gotelli, N.J., Lin, S.Y., Mao, C.X., Chazdon, R.L. & Longino, J.T. (2012). Models and estimators linking individual-based and sample-based rarefaction, extrapolation and comparison of assemblages. J. Plant Ecol. 5: 3–21.
Dengler, J. (2009). Which function describes the species-area relationship best? A review and empirical evaluation. Journal of Biogeography 36, 728–744.
Gotelli, N.J. & Colwell, R.K. (2001). Quantifying biodiversity: procedures and pitfalls in measurement and comparison of species richness. Ecol. Lett. 4, 379–391.
rarefy
and rrarefy
are related
individual based models. Other accumulation models are
poolaccum
for extrapolated richness, and
renyiaccum
and tsallisaccum
for
diversity indices. Underlying graphical functions are
boxplot
, matlines
,
segments
and polygon
.
data(BCI) sp1 <- specaccum(BCI) sp2 <- specaccum(BCI, "random") sp2 summary(sp2) plot(sp1, ci.type="poly", col="blue", lwd=2, ci.lty=0, ci.col="lightblue") boxplot(sp2, col="yellow", add=TRUE, pch="+") ## Fit Lomolino model to the exact accumulation mod1 <- fitspecaccum(sp1, "lomolino") coef(mod1) fitted(mod1) plot(sp1) ## Add Lomolino model using argument 'add' plot(mod1, add = TRUE, col=2, lwd=2) ## Fit Arrhenius models to all random accumulations mods <- fitspecaccum(sp2, "arrh") plot(mods, col="hotpink") boxplot(sp2, col = "yellow", border = "blue", lty=1, cex=0.3, add= TRUE) ## Use nls() methods to the list of models sapply(mods$models, AIC)
data(BCI) sp1 <- specaccum(BCI) sp2 <- specaccum(BCI, "random") sp2 summary(sp2) plot(sp1, ci.type="poly", col="blue", lwd=2, ci.lty=0, ci.col="lightblue") boxplot(sp2, col="yellow", add=TRUE, pch="+") ## Fit Lomolino model to the exact accumulation mod1 <- fitspecaccum(sp1, "lomolino") coef(mod1) fitted(mod1) plot(sp1) ## Add Lomolino model using argument 'add' plot(mod1, add = TRUE, col=2, lwd=2) ## Fit Arrhenius models to all random accumulations mods <- fitspecaccum(sp2, "arrh") plot(mods, col="hotpink") boxplot(sp2, col = "yellow", border = "blue", lty=1, cex=0.3, add= TRUE) ## Use nls() methods to the list of models sapply(mods$models, AIC)
The functions estimate the extrapolated species richness in a species
pool, or the number of unobserved species. Function specpool
is based on incidences in sample sites, and gives a single estimate
for a collection of sample sites (matrix). Function estimateR
is based on abundances (counts) on single sample site.
specpool(x, pool, smallsample = TRUE) estimateR(x, ...) specpool2vect(X, index = c("jack1","jack2", "chao", "boot","Species")) poolaccum(x, permutations = 100, minsize = 3) estaccumR(x, permutations = 100, parallel = getOption("mc.cores")) ## S3 method for class 'poolaccum' summary(object, display, alpha = 0.05, ...) ## S3 method for class 'poolaccum' plot(x, alpha = 0.05, type = c("l","g"), ...)
specpool(x, pool, smallsample = TRUE) estimateR(x, ...) specpool2vect(X, index = c("jack1","jack2", "chao", "boot","Species")) poolaccum(x, permutations = 100, minsize = 3) estaccumR(x, permutations = 100, parallel = getOption("mc.cores")) ## S3 method for class 'poolaccum' summary(object, display, alpha = 0.05, ...) ## S3 method for class 'poolaccum' plot(x, alpha = 0.05, type = c("l","g"), ...)
x |
Data frame or matrix with species data or the analysis result
for |
pool |
A vector giving a classification for pooling the sites in the species data. If missing, all sites are pooled together. |
smallsample |
Use small sample correction |
X , object
|
A |
index |
The selected index of extrapolated richness. |
permutations |
Usually an integer giving the number
permutations, but can also be a list of control values for the
permutations as returned by the function |
minsize |
Smallest number of sampling units reported. |
parallel |
Number of parallel processes or a predefined socket
cluster. With |
display |
Indices to be displayed. |
alpha |
Level of quantiles shown. This proportion will be left outside symmetric limits. |
type |
Type of graph produced in |
... |
Other parameters (not used). |
Many species will always remain unseen or undetected in a collection of sample plots. The function uses some popular ways of estimating the number of these unseen species and adding them to the observed species richness (Palmer 1990, Colwell & Coddington 1994).
The incidence-based estimates in specpool
use the frequencies
of species in a collection of sites.
In the following, is the extrapolated richness in a pool,
is the observed number of species in the
collection,
and
are the number of species
occurring only in one or only in two sites in the collection,
is the frequency of species
, and
is the number of
sites in the collection. The variants of extrapolated richness in
specpool
are:
Chao |
|
Chao bias-corrected |
|
First order jackknife |
|
Second order jackknife |
|
Bootstrap |
|
specpool
normally uses basic Chao equation, but when there
are no doubletons () it switches to bias-corrected
version. In that case the Chao equation simplifies to
.
The abundance-based estimates in estimateR
use counts
(numbers of individuals) of species in a single site. If called for
a matrix or data frame, the function will give separate estimates
for each site. The two variants of extrapolated richness in
estimateR
are bias-corrected Chao and ACE (O'Hara 2005, Chiu
et al. 2014). The Chao estimate is similar as the bias corrected
one above, but refers to the number of species with
abundance
instead of number of sites, and the small-sample
correction is not used. The ACE estimate is defined as:
ACE |
|
where |
|
|
Here refers to number of species with abundance
and
is the number of rare
species,
is the number of abundant species, with an
arbitrary
threshold of abundance 10 for rare species, and
is
the number
of individuals in rare species.
Functions estimate the standard errors of the estimates. These only
concern the number of added species, and assume that there is no
variance in the observed richness. The equations of standard errors
are too complicated to be reproduced in this help page, but they can
be studied in the R source code of the function and are discussed
in the vignette
that can be read with the
browseVignettes("vegan")
. The standard error are based on the
following sources: Chiu et al. (2014) for the Chao estimates and
Smith and van Belle (1984) for the first-order Jackknife and the
bootstrap (second-order jackknife is still missing). For the
variance estimator of see O'Hara (2005).
Functions poolaccum
and estaccumR
are similar to
specaccum
, but estimate extrapolated richness indices
of specpool
or estimateR
in addition to number of
species for random ordering of sampling units. Function
specpool
uses presence data and estaccumR
count
data. The functions share summary
and plot
methods. The summary
returns quantile envelopes of
permutations corresponding the given level of alpha
and
standard deviation of permutations for each sample size. NB., these
are not based on standard deviations estimated within specpool
or estimateR
, but they are based on permutations. The
plot
function shows the mean and envelope of permutations
with given alpha
for models. The selection of models can be
restricted and order changes using the display
argument in
summary
or plot
. For configuration of plot
command, see xyplot
.
Function specpool
returns a data frame with entries for
observed richness and each of the indices for each class in
pool
vector. The utility function specpool2vect
maps
the pooled values into a vector giving the value of selected
index
for each original site. Function estimateR
returns the estimates and their standard errors for each
site. Functions poolaccum
and estimateR
return
matrices of permutation results for each richness estimator, the
vector of sample sizes and a table of means
of permutations
for each estimator.
The functions are based on assumption that there is a species
pool: The community is closed so that there is a fixed pool size
. In general, the functions give only the lower limit of
species richness: the real richness is
, and there is
a consistent bias in the estimates. Even the bias-correction in Chao
only reduces the bias, but does not remove it completely (Chiu et
al. 2014).
Optional small sample correction was added to specpool
in
vegan 2.2-0. It was not used in the older literature (Chao
1987), but it is recommended recently (Chiu et al. 2014).
Bob O'Hara (estimateR
) and Jari Oksanen.
Chao, A. (1987). Estimating the population size for capture-recapture data with unequal catchability. Biometrics 43, 783–791.
Chiu, C.H., Wang, Y.T., Walther, B.A. & Chao, A. (2014). Improved nonparametric lower bound of species richness via a modified Good-Turing frequency formula. Biometrics 70, 671–682.
Colwell, R.K. & Coddington, J.A. (1994). Estimating terrestrial biodiversity through extrapolation. Phil. Trans. Roy. Soc. London B 345, 101–118.
O'Hara, R.B. (2005). Species richness estimators: how many species can dance on the head of a pin? J. Anim. Ecol. 74, 375–386.
Palmer, M.W. (1990). The estimation of species richness by extrapolation. Ecology 71, 1195–1198.
Smith, E.P & van Belle, G. (1984). Nonparametric estimation of species richness. Biometrics 40, 119–129.
veiledspec
, diversity
, beals
,
specaccum
.
data(dune) data(dune.env) pool <- with(dune.env, specpool(dune, Management)) pool op <- par(mfrow=c(1,2)) boxplot(specnumber(dune) ~ Management, data = dune.env, col = "hotpink", border = "cyan3") boxplot(specnumber(dune)/specpool2vect(pool) ~ Management, data = dune.env, col = "hotpink", border = "cyan3") par(op) data(BCI) ## Accumulation model pool <- poolaccum(BCI) summary(pool, display = "chao") plot(pool) ## Quantitative model estimateR(BCI[1:5,])
data(dune) data(dune.env) pool <- with(dune.env, specpool(dune, Management)) pool op <- par(mfrow=c(1,2)) boxplot(specnumber(dune) ~ Management, data = dune.env, col = "hotpink", border = "cyan3") boxplot(specnumber(dune)/specpool2vect(pool) ~ Management, data = dune.env, col = "hotpink", border = "cyan3") par(op) data(BCI) ## Accumulation model pool <- poolaccum(BCI) summary(pool, display = "chao") plot(pool) ## Quantitative model estimateR(BCI[1:5,])
Distance-based ordination (dbrda
,
capscale
, metaMDS
, monoMDS
,
wcmdscale
) has no information on species, but some
methods may add species scores if community data were
available. However, the species scores may be missing (and they always
are in dbrda
and wcmdscale
), or they may
not have a close relation to used dissimilarity index. This function
will add the species scores or replace the existing species scores in
distance-based methods.
sppscores(object) <- value
sppscores(object) <- value
object |
Ordination result from |
value |
Community data to find the species scores. |
Distances have no information on species (columns, variables), and
hence distance-based ordination has no information on species
scores. However, the species scores can be added as supplementary
information after the analysis to help the interpretation of
results. Some ordination methods (capscale
,
metaMDS
) can supplement the species scores during the
analysis if community data were available in the analysis.
In capscale
the species scores are found by projecting
the community data to site ordination (linear combination scores),
and the scores are accurate if the analysis used Euclidean
distances. If the dissimilarity index can be expressed as Euclidean
distances of transformed data (for instance, Chord and Hellinger
Distances), the species scores based on transformed data will be
accurate, but the function still finds the dissimilarities with
untransformed data. Usually community dissimilarities differ in two
significant ways from Euclidean distances: They are bound to maximum
1, and they use absolute differences instead of squared
differences. In such cases, it may be better to use species scores
that are transformed so that their Euclidean distances have a good
linear relation to used dissimilarities. It is often useful to
standardize data so that each row has unit total, and perform
squareroot transformation to damp down the effect of squared
differences (see Examples).
Functions dbrda
and wcmdscale
never find
the species scores, but they mathematically similar to
capscale
, and similar rules should be followed when
supplementing the species scores.
Functions for species scores in metaMDS
and
monoMDS
use weighted averages (wascores
)
to find the species scores. These have better relationship with most
dissimilarities than the projection scores used in metric ordination,
but similar transformation of the community data should be used both
in dissimilarities and in species scores.
Replacement function adds the species scores or replaces the old scores in the ordination object.
Jari Oksanen
Function envfit
finds similar scores, but based on
correlations. The species scores for non-metric ordination use
wascores
which can also used directly on any
ordination result.
data(BCI, BCI.env) mod <- dbrda(vegdist(BCI) ~ Habitat, BCI.env) ## add species scores sppscores(mod) <- BCI ## Euclidean distances of BCI differ from used dissimilarity plot(vegdist(BCI), dist(BCI)) ## more linear relationship plot(vegdist(BCI), dist(sqrt(decostand(BCI, "total")))) ## better species scores sppscores(mod) <- sqrt(decostand(BCI, "total"))
data(BCI, BCI.env) mod <- dbrda(vegdist(BCI) ~ Habitat, BCI.env) ## add species scores sppscores(mod) <- BCI ## Euclidean distances of BCI differ from used dissimilarity plot(vegdist(BCI), dist(BCI)) ## more linear relationship plot(vegdist(BCI), dist(sqrt(decostand(BCI, "total")))) ## better species scores sppscores(mod) <- sqrt(decostand(BCI, "total"))
These functions provide self-starting species-area models for
non-linear regression (nls
). They can also be used for
fitting species accumulation models in
fitspecaccum
. These models (and many more) are reviewed
by Dengler (2009).
SSarrhenius(area, k, z) SSgleason(area, k, slope) SSgitay(area, k, slope) SSlomolino(area, Asym, xmid, slope)
SSarrhenius(area, k, z) SSgleason(area, k, slope) SSgitay(area, k, slope) SSlomolino(area, Asym, xmid, slope)
area |
Area or size of the sample: the independent variable. |
k , z , slope , Asym , xmid
|
Estimated model parameters: see Details. |
All these functions are assumed to be used for species richness (number of species) as the independent variable, and area or sample size as the independent variable. Basically, these define least squares models of untransformed data, and will differ from models for transformed species richness or models with non-Gaussian error.
The Arrhenius model (SSarrhenius
) is the expression
k*area^z
. This is the most classical model that can be found in
any textbook of ecology (and also in Dengler 2009). Parameter z
is the steepness of the species-area curve, and k
is the
expected number of species in a unit area.
The Gleason model (SSgleason
) is a linear expression
k + slope*log(area)
(Dengler 200). This is a linear model,
and starting values give the final estimates; it is provided to
ease comparison with other models.
The Gitay model (SSgitay
) is a quadratic logarithmic expression
(k + slope*log(area))^2
(Gitay et al. 1991, Dengler
2009). Parameter slope
is the steepness of the species-area
curve, and k
is the square root of expected richness in a unit
area.
The Lomolino model (SSlomolino
) is
Asym/(1 + slope^log(xmid/area))
(Lomolino 2000, Dengler 2009).
Parameter Asym
is the asymptotic maximum number of species,
slope
is the maximum slope of increase of richness, and
xmid
is the area where half of the maximum richness is
achieved.
In addition to these models, several other models studied by Dengler
(2009) are available in standard R self-starting models:
Michaelis-Menten (SSmicmen
), Gompertz
(SSgompertz
), logistic (SSlogis
), Weibull
(SSweibull
), and some others that may be useful.
Numeric vector of the same length as area
. It is the value of
the expression of each model. If all arguments are names of objects
the gradient matrix with respect to these names is attached as an
attribute named gradient
.
Jari Oksanen.
Dengler, J. (2009) Which function describes the species-area relationship best? A review and empirical evaluation. Journal of Biogeography 36, 728–744.
Gitay, H., Roxburgh, S.H. & Wilson, J.B. (1991) Species-area relationship in a New Zealand tussock grassland, with implications for nature reserve design and for community structure. Journal of Vegetation Science 2, 113–118.
Lomolino, M. V. (2000) Ecology's most general, yet protean pattern: the species-area relationship. Journal of Biogeography 27, 17–26.
## Get species area data: sipoo.map gives the areas of islands data(sipoo, sipoo.map) S <- specnumber(sipoo) plot(S ~ area, sipoo.map, xlab = "Island Area (ha)", ylab = "Number of Species", ylim = c(1, max(S))) ## The Arrhenius model marr <- nls(S ~ SSarrhenius(area, k, z), data=sipoo.map) marr ## confidence limits from profile likelihood confint(marr) ## draw a line xtmp <- with(sipoo.map, seq(min(area), max(area), len=51)) lines(xtmp, predict(marr, newdata=data.frame(area = xtmp)), lwd=2) ## The normal way is to use linear regression on log-log data, ## but this will be different from the previous: mloglog <- lm(log(S) ~ log(area), data=sipoo.map) mloglog lines(xtmp, exp(predict(mloglog, newdata=data.frame(area=xtmp))), lty=2) ## Gleason: log-linear mgle <- nls(S ~ SSgleason(area, k, slope), sipoo.map) lines(xtmp, predict(mgle, newdata=data.frame(area=xtmp)), lwd=2, col=2) ## Gitay: quadratic of log-linear mgit <- nls(S ~ SSgitay(area, k, slope), sipoo.map) lines(xtmp, predict(mgit, newdata=data.frame(area=xtmp)), lwd=2, col = 3) ## Lomolino: using original names of the parameters (Lomolino 2000): mlom <- nls(S ~ SSlomolino(area, Smax, A50, Hill), sipoo.map) mlom lines(xtmp, predict(mlom, newdata=data.frame(area=xtmp)), lwd=2, col = 4) ## One canned model of standard R: mmic <- nls(S ~ SSmicmen(area, Asym, slope), sipoo.map) lines(xtmp, predict(mmic, newdata = data.frame(area=xtmp)), lwd =2, col = 5) legend("bottomright", c("Arrhenius", "log-log linear", "Gleason", "Gitay", "Lomolino", "Michaelis-Menten"), col=c(1,1,2,3,4,5), lwd=c(2,1,2,2,2,2), lty=c(1,2,1,1,1,1)) ## compare models (AIC) allmods <- list(Arrhenius = marr, Gleason = mgle, Gitay = mgit, Lomolino = mlom, MicMen= mmic) sapply(allmods, AIC)
## Get species area data: sipoo.map gives the areas of islands data(sipoo, sipoo.map) S <- specnumber(sipoo) plot(S ~ area, sipoo.map, xlab = "Island Area (ha)", ylab = "Number of Species", ylim = c(1, max(S))) ## The Arrhenius model marr <- nls(S ~ SSarrhenius(area, k, z), data=sipoo.map) marr ## confidence limits from profile likelihood confint(marr) ## draw a line xtmp <- with(sipoo.map, seq(min(area), max(area), len=51)) lines(xtmp, predict(marr, newdata=data.frame(area = xtmp)), lwd=2) ## The normal way is to use linear regression on log-log data, ## but this will be different from the previous: mloglog <- lm(log(S) ~ log(area), data=sipoo.map) mloglog lines(xtmp, exp(predict(mloglog, newdata=data.frame(area=xtmp))), lty=2) ## Gleason: log-linear mgle <- nls(S ~ SSgleason(area, k, slope), sipoo.map) lines(xtmp, predict(mgle, newdata=data.frame(area=xtmp)), lwd=2, col=2) ## Gitay: quadratic of log-linear mgit <- nls(S ~ SSgitay(area, k, slope), sipoo.map) lines(xtmp, predict(mgit, newdata=data.frame(area=xtmp)), lwd=2, col = 3) ## Lomolino: using original names of the parameters (Lomolino 2000): mlom <- nls(S ~ SSlomolino(area, Smax, A50, Hill), sipoo.map) mlom lines(xtmp, predict(mlom, newdata=data.frame(area=xtmp)), lwd=2, col = 4) ## One canned model of standard R: mmic <- nls(S ~ SSmicmen(area, Asym, slope), sipoo.map) lines(xtmp, predict(mmic, newdata = data.frame(area=xtmp)), lwd =2, col = 5) legend("bottomright", c("Arrhenius", "log-log linear", "Gleason", "Gitay", "Lomolino", "Michaelis-Menten"), col=c(1,1,2,3,4,5), lwd=c(2,1,2,2,2,2), lty=c(1,2,1,1,1,1)) ## compare models (AIC) allmods <- list(Arrhenius = marr, Gleason = mgle, Gitay = mgit, Lomolino = mlom, MicMen= mmic) sapply(allmods, AIC)
Function stepacross
tries to replace dissimilarities with
shortest paths stepping across intermediate
sites while regarding dissimilarities above a threshold as missing
data (NA
). With path = "shortest"
this is the flexible shortest
path (Williamson 1978, Bradfield & Kenkel 1987),
and with path = "extended"
an
approximation known as extended dissimilarities (De'ath 1999).
The use of stepacross
should improve the ordination with high
beta diversity, when there are many sites with no species in common.
stepacross(dis, path = "shortest", toolong = 1, trace = TRUE, ...)
stepacross(dis, path = "shortest", toolong = 1, trace = TRUE, ...)
dis |
Dissimilarity data inheriting from class |
path |
The method of stepping across (partial match)
Alternative |
toolong |
Shortest dissimilarity regarded as |
trace |
Trace the calculations. |
... |
Other parameters (ignored). |
Williamson (1978) suggested using flexible shortest paths to estimate
dissimilarities between sites which have nothing in common, or no shared
species. With path = "shortest"
function stepacross
replaces dissimilarities that are
toolong
or longer with NA
, and tries to find shortest
paths between all sites using remaining dissimilarities. Several
dissimilarity indices are semi-metric which means that they do not
obey the triangle inequality , and shortest path algorithm can replace these
dissimilarities as well, even when they are shorter than
toolong
.
De'ath (1999) suggested a simplified method known as extended
dissimilarities, which are calculated with path = "extended"
.
In this method, dissimilarities that are
toolong
or longer are first made NA
, and then the function
tries to replace these NA
dissimilarities with a path through
single stepping stone points. If not all NA
could be
replaced with one pass, the function will make new passes with updated
dissimilarities as long as
all NA
are replaced with extended dissimilarities. This mean
that in the second and further passes, the remaining NA
dissimilarities are allowed to have more than one stepping stone site,
but previously replaced dissimilarities are not updated. Further, the
function does not consider dissimilarities shorter than toolong
,
although some of these could be replaced with a shorter path in
semi-metric indices, and used as a part of other paths. In optimal
cases, the extended dissimilarities are equal to shortest paths, but
they may be longer.
As an alternative to defining too long dissimilarities with parameter
toolong
, the input dissimilarities can contain NA
s. If
toolong
is zero or negative, the function does not make any
dissimilarities into NA
. If there are no NA
s in the
input and toolong = 0
, path = "shortest"
will find shorter paths for semi-metric indices, and path = "extended"
will do nothing. Function no.shared
can be
used to set dissimilarities to NA
.
If the data are disconnected or there is no path between all points,
the result will
contain NA
s and a warning is issued. Several methods cannot
handle NA
dissimilarities, and this warning should be taken
seriously. Function distconnected
can be used to find
connected groups and remove rare outlier observations or groups of
observations.
Alternative path = "shortest"
uses Dijkstra's method for
finding flexible shortest paths, implemented as priority-first search
for dense graphs (Sedgewick 1990). Alternative path = "extended"
follows De'ath (1999), but implementation is simpler
than in his code.
Function returns an object of class dist
with extended
dissimilarities (see functions vegdist
and
dist
).
The value of path
is appended to the method
attribute.
The function changes the original dissimilarities, and not all like this. It may be best to use the function only when you really must: extremely high beta diversity where a large proportion of dissimilarities are at their upper limit (no species in common).
Semi-metric indices vary in their degree of violating the triangle
inequality. Morisita and Horn–Morisita indices of
vegdist
may be very strongly semi-metric, and shortest
paths can change these indices very much. Mountford index violates
basic rules of dissimilarities: non-identical sites have zero
dissimilarity if species composition of the poorer site is a subset of
the richer. With Mountford index, you can find three sites so that
and
, but
. The results of
stepacross
on Mountford index can be very weird. If stepacross
is needed,
it is best to try to use it with more metric indices only.
Jari Oksanen
Bradfield, G.E. & Kenkel, N.C. (1987). Nonlinear ordination using flexible shortest path adjustment of ecological distances. Ecology 68, 750–753.
De'ath, G. (1999). Extended dissimilarity: a method of robust estimation of ecological distances from high beta diversity data. Plant Ecol. 144, 191–199.
Sedgewick, R. (1990). Algorithms in C. Addison Wesley.
Williamson, M.H. (1978). The ordination of incidence data. J. Ecol. 66, 911-920.
Function distconnected
can find connected groups in
disconnected data, and function no.shared
can be used to
set dissimilarities as NA
. See swan
for an
alternative approach. Function stepacross
is an essential
component in isomap
and cophenetic.spantree
.
# There are no data sets with high beta diversity in vegan, but this # should give an idea. data(dune) dis <- vegdist(dune) edis <- stepacross(dis) plot(edis, dis, xlab = "Shortest path", ylab = "Original") ## Manhattan distance have no fixed upper limit. dis <- vegdist(dune, "manhattan") is.na(dis) <- no.shared(dune) dis <- stepacross(dis, toolong=0)
# There are no data sets with high beta diversity in vegan, but this # should give an idea. data(dune) dis <- vegdist(dune) edis <- stepacross(dis) plot(edis, dis, xlab = "Shortest path", ylab = "Original") ## Manhattan distance have no fixed upper limit. dis <- vegdist(dune, "manhattan") is.na(dis) <- no.shared(dune) dis <- stepacross(dis, toolong=0)
Functions plot ordination distances in given number of dimensions
against observed distances or distances in full space in eigenvector
methods. The display is similar as the Shepard diagram
(stressplot
for non-metric multidimensional scaling
with metaMDS
or monoMDS
), but shows the
linear relationship of the eigenvector ordinations. The
stressplot
methods are available for wcmdscale
,
rda
, cca
, capscale
,
dbrda
, prcomp
and princomp
.
## S3 method for class 'wcmdscale' stressplot(object, k = 2, pch, p.col = "blue", l.col = "red", lwd = 2, ...)
## S3 method for class 'wcmdscale' stressplot(object, k = 2, pch, p.col = "blue", l.col = "red", lwd = 2, ...)
object |
Result object from eigenvector ordination ( |
k |
Number of dimensions for which the ordination distances are displayed. |
pch , p.col , l.col , lwd
|
Plotting character, point colour and line colour like in
default |
... |
Other parameters to functions, e.g. graphical parameters. |
The functions offer a similar display for eigenvector
ordinations as the standard Shepard diagram
(stressplot
) in non-metric multidimensional
scaling. The ordination distances in given number of dimensions are
plotted against observed distances. With metric distances, the
ordination distances in full space (with all ordination axes) are
equal to observed distances, and the fit line shows this
equality. In general, the fit line does not go through the points,
but the points for observed distances approach the fit line from
below. However, with non-Euclidean distances (in
wcmdscale
, dbrda
or
capscale
) with negative eigenvalues the ordination
distances can exceed the observed distances in real dimensions; the
imaginary dimensions with negative eigenvalues will correct these
excess distances. If you have used dbrda
,
capscale
or wcmdscale
with argument
add
to avoid negative eigenvalues, the ordination distances
will exceed the observed dissimilarities.
In partial ordination (cca
, rda
, and
capscale
with Condition
in the formula), the
distances in the partial component are included both in the observed
distances and in ordination distances. With k=0
, the
ordination distances refer to the partial ordination. The exception is
dbrda
where the distances in partial, constrained and
residual components are not additive, and only the first of these
components can be shown, and partial models cannot be shown at all.
Functions draw a graph and return invisibly the ordination distances or the ordination distances.
Jari Oksanen.
stressplot
and stressplot.monoMDS
for
standard Shepard diagrams.
data(dune, dune.env) mod <- rda(dune) stressplot(mod) mod <- rda(dune ~ Management, dune.env) stressplot(mod, k=3)
data(dune, dune.env) mod <- rda(dune) stressplot(mod) mod <- rda(dune ~ Management, dune.env) stressplot(mod, k=3)
Function finds indices of taxonomic diversity and distinctness, which are averaged taxonomic distances among species or individuals in the community (Clarke & Warwick 1998, 2001)
taxondive(comm, dis, match.force = FALSE) taxa2dist(x, varstep = FALSE, check = TRUE, labels)
taxondive(comm, dis, match.force = FALSE) taxa2dist(x, varstep = FALSE, check = TRUE, labels)
comm |
Community data. |
dis |
Taxonomic distances among taxa in |
match.force |
Force matching of column names in |
x |
Classification table with a row for each species or other basic taxon, and columns for identifiers of its classification at higher levels. |
varstep |
Vary step lengths between successive levels relative to proportional loss of the number of distinct classes. |
check |
If |
labels |
The |
Clarke & Warwick (1998, 2001) suggested several alternative indices of
taxonomic diversity or distinctness. Two basic indices are called
taxonomic diversity () and distinctness (
):
|
|
The equations give the index value for a single site, and summation
goes over species and
. Here
are taxonomic
distances among taxa, and
are species abundances, and
is the total abundance for a site.
With presence/absence data both indices reduce to the same index
, and for this index Clarke & Warwick (1998) also have
an estimate of its standard deviation. Clarke & Warwick (2001)
presented two new indices:
is the product of species
richness and
, and index of variation in
taxonomic distinctness (
) defined as
|
The dis
argument must be species dissimilarities. These must be
similar to dissimilarities produced by dist
. It is
customary to have integer steps of taxonomic hierarchies, but other
kind of dissimilarities can be used, such as those from phylogenetic
trees or genetic differences. Further, the dis
need not be
taxonomic, but other species classifications can be used.
Function taxa2dist
can produce a suitable dist
object
from a classification table. Each species (or basic taxon) corresponds
to a row of the classification table, and columns give the
classification at different levels. With varstep = FALSE
the
successive levels will be separated by equal steps, and with
varstep = TRUE
the step length is relative to the proportional
decrease in the number of classes (Clarke & Warwick 1999).
With check = TRUE
, the function removes classes which are distinct for all
species or which combine all species into one class, and assumes that
each row presents a distinct basic taxon. The function scales
the distances so that longest path length between
taxa is 100 (not necessarily when check = FALSE
).
Function plot.taxondive
plots against Number of
species, together with expectation and its approximate 2*sd
limits. Function
summary.taxondive
finds the values and
their significances from Normal distribution for
.
Function returns an object of class taxondive
with following items:
Species |
Number of species for each site. |
D , Dstar , Dplus , SDplus , Lambda
|
|
sd.Dplus |
Standard deviation of |
ED , EDstar , EDplus
|
Expected values of corresponding statistics. |
Function taxa2dist
returns an object of class "dist"
, with
an attribute "steps"
for the step lengths between successive levels.
The function is still preliminary and may change. The scaling of
taxonomic dissimilarities influences the results. If you multiply
taxonomic distances (or step lengths) by a constant, the values of all
Deltas will be multiplied with the same constant, and the value of
by the square of the constant.
Jari Oksanen
Clarke, K.R & Warwick, R.M. (1998) A taxonomic distinctness index and its statistical properties. Journal of Applied Ecology 35, 523–531.
Clarke, K.R. & Warwick, R.M. (1999) The taxonomic distinctness measure of biodiversity: weighting of step lengths between hierarchical levels. Marine Ecology Progress Series 184: 21–29.
Clarke, K.R. & Warwick, R.M. (2001) A further biodiversity index applicable to species lists: variation in taxonomic distinctness. Marine Ecology Progress Series 216, 265–278.
## Preliminary: needs better data and some support functions data(dune) data(dune.taxon) # Taxonomic distances from a classification table with variable step lengths. taxdis <- taxa2dist(dune.taxon, varstep=TRUE) plot(hclust(taxdis), hang = -1) # Indices mod <- taxondive(dune, taxdis) mod summary(mod) plot(mod)
## Preliminary: needs better data and some support functions data(dune) data(dune.taxon) # Taxonomic distances from a classification table with variable step lengths. taxdis <- taxa2dist(dune.taxon, varstep=TRUE) plot(hclust(taxdis), hang = -1) # Indices mod <- taxondive(dune, taxdis) mod summary(mod) plot(mod)
Species tolerances and sample heterogeneities.
tolerance(x, ...) ## S3 method for class 'cca' tolerance(x, choices = 1:2, which = c("species","sites"), scaling = "species", useN2 = TRUE, hill = FALSE, ...) ## S3 method for class 'decorana' tolerance(x, data, choices = 1:4, which = c("sites", "species"), useN2 = TRUE, ...)
tolerance(x, ...) ## S3 method for class 'cca' tolerance(x, choices = 1:2, which = c("species","sites"), scaling = "species", useN2 = TRUE, hill = FALSE, ...) ## S3 method for class 'decorana' tolerance(x, data, choices = 1:4, which = c("sites", "species"), useN2 = TRUE, ...)
x |
object of class |
choices |
numeric; which ordination axes to compute tolerances and heterogeneities for. Defaults to axes 1 and 2. |
which |
character; one of |
scaling |
character or numeric; the ordination scaling to
use. See |
hill |
logical; if |
useN2 |
logical; should the bias in the tolerances / heterogeneities be reduced via scaling by Hill's N2? |
data |
Original input data used in |
... |
arguments passed to other methods. |
Function to compute species tolerances and site heterogeneity measures from unimodal ordinations (CCA & CA). Implements Eq 6.47 and 6.48 from the Canoco 4.5 Reference Manual (pages 178–179).
Function wascores
with stdev = TRUE
uses the same
algebra, but bases the standard deviations on weighted averages
scores instead of linear combinations scores of tolerance
.
Matrix of tolerances/heterogeneities with some additional
attributes: which
, scaling
, and N2
, the latter of
which will be NA
if useN2 = FALSE
or N2
could not
be estimated.
Gavin L. Simpson and Jari Oksanen (decorana
method).
data(dune) data(dune.env) mod <- cca(dune ~ ., data = dune.env) ## defaults to species tolerances tolerance(mod) ## sample heterogeneities for CCA axes 1:6 tolerance(mod, which = "sites", choices = 1:6) ## average should be 1 with scaling = "sites", hill = TRUE tol <- tolerance(mod, which = "sites", scaling = "sites", hill = TRUE, choices = 1:4) colMeans(tol) apply(tol, 2, sd) ## Rescaling tries to set all tolerances to 1 tol <- tolerance(decorana(dune)) colMeans(tol) apply(tol, 2, sd)
data(dune) data(dune.env) mod <- cca(dune ~ ., data = dune.env) ## defaults to species tolerances tolerance(mod) ## sample heterogeneities for CCA axes 1:6 tolerance(mod, which = "sites", choices = 1:6) ## average should be 1 with scaling = "sites", hill = TRUE tol <- tolerance(mod, which = "sites", scaling = "sites", hill = TRUE, choices = 1:4) colMeans(tol) apply(tol, 2, sd) ## Rescaling tries to set all tolerances to 1 tol <- tolerance(decorana(dune)) colMeans(tol) apply(tol, 2, sd)
Functional diversity is defined as the total branch length in a trait dendrogram connecting all species, but excluding the unnecessary root segments of the tree (Petchey and Gaston 2006). Tree distance is the increase in total branch length when combining two sites.
treedive(comm, tree, match.force = TRUE, verbose = TRUE) treeheight(tree) treedist(x, tree, relative = TRUE, match.force = TRUE, ...)
treedive(comm, tree, match.force = TRUE, verbose = TRUE) treeheight(tree) treedist(x, tree, relative = TRUE, match.force = TRUE, ...)
comm , x
|
Community data frame or matrix. |
tree |
A dendrogram which for |
match.force |
Force matching of column names in data
( |
verbose |
Print diagnostic messages and warnings. |
relative |
Use distances relative to the height of combined tree. |
... |
Other arguments passed to functions (ignored). |
Function treeheight
finds the sum of lengths of connecting
segments in a dendrogram produced by hclust
, or other
dendrogram that can be coerced to a correct type using
as.hclust
. When applied to a clustering of species
traits, this is a measure of functional diversity (Petchey and Gaston
2002, 2006), and when applied to phylogenetic trees this is
phylogenetic diversity.
Function treedive
finds the treeheight
for each site
(row) of a community matrix. The function uses a subset of
dendrogram for those species that occur in each site, and excludes
the tree root if that is not needed to connect the species (Petchey
and Gaston 2006). The subset of the dendrogram is found by first
calculating cophenetic
distances from the input
dendrogram, then reconstructing the dendrogram for the subset of the
cophenetic distance matrix for species occurring in each
site. Diversity is 0 for one species, and NA
for empty
communities.
Function treedist
finds the dissimilarities among
trees. Pairwise dissimilarity of two trees is found by combining
species in a common tree and seeing how much of the tree height is
shared and how much is unique. With relative = FALSE
the
dissimilarity is defined as , where
and
are heights of component trees and
is the height of the combined tree. With
relative = TRUE
the dissimilarity is .
Although the latter formula is similar to
Jaccard dissimilarity (see
vegdist
,
designdist
), it is not in the range , since combined tree can add a new root. When two zero-height
trees are combined into a tree of above zero height, the relative
index attains its maximum value
. The dissimilarity is zero
from a combined zero-height tree.
The functions need a dendrogram of species traits or phylogenies as an
input. If species traits contain factor
or
ordered
factor variables, it is recommended to use Gower
distances for mixed data (function daisy
in
package cluster), and usually the recommended clustering method
is UPGMA (method = "average"
in function hclust
)
(Podani and Schmera 2006). Phylogenetic trees can be changed into
dendrograms using function as.hclust.phylo
in the
ape package.
It is possible to analyse the non-randomness of tree diversity
using oecosimu
. This needs specifying an adequate Null
model, and the results will change with this choice.
A vector of diversity values or a single tree height, or a
dissimilarity structure that inherits from dist
and
can be used similarly.
Jari Oksanen
Lozupone, C. and Knight, R. 2005. UniFrac: a new phylogenetic method for comparing microbial communities. Applied and Environmental Microbiology 71, 8228–8235.
Petchey, O.L. and Gaston, K.J. 2002. Functional diversity (FD), species richness and community composition. Ecology Letters 5, 402–411.
Petchey, O.L. and Gaston, K.J. 2006. Functional diversity: back to basics and looking forward. Ecology Letters 9, 741–758.
Podani J. and Schmera, D. 2006. On dendrogram-based methods of functional diversity. Oikos 115, 179–185.
Function treedive
is similar to the phylogenetic
diversity function pd
in the package picante, but
excludes tree root if that is not needed to connect species. Function
treedist
is similar to the phylogenetic similarity
phylosor
in the package picante, but excludes
unneeded tree root and returns distances instead of similarities.
taxondive
is something very similar from another bubble.
## There is no data set on species properties yet, and we demonstrate ## the methods using phylogenetic trees data(dune) data(dune.phylodis) cl <- hclust(dune.phylodis) treedive(dune, cl) ## Significance test using Null model communities. ## The current choice fixes numbers of species and picks species ## proportionally to their overall frequency oecosimu(dune, treedive, "r1", tree = cl, verbose = FALSE) ## Phylogenetically ordered community table dtree <- treedist(dune, cl) tabasco(dune, hclust(dtree), cl) ## Use tree distances in distance-based RDA dbrda(dtree ~ 1)
## There is no data set on species properties yet, and we demonstrate ## the methods using phylogenetic trees data(dune) data(dune.phylodis) cl <- hclust(dune.phylodis) treedive(dune, cl) ## Significance test using Null model communities. ## The current choice fixes numbers of species and picks species ## proportionally to their overall frequency oecosimu(dune, treedive, "r1", tree = cl, verbose = FALSE) ## Phylogenetically ordered community table dtree <- treedist(dune, cl) tabasco(dune, hclust(dtree), cl) ## Use tree distances in distance-based RDA dbrda(dtree ~ 1)
Function tsallis
find Tsallis diversities with any scale or the corresponding evenness measures. Function tsallisaccum
finds these statistics with accumulating sites.
tsallis(x, scales = seq(0, 2, 0.2), norm = FALSE, hill = FALSE) tsallisaccum(x, scales = seq(0, 2, 0.2), permutations = 100, raw = FALSE, subset, ...) ## S3 method for class 'tsallisaccum' persp(x, theta = 220, phi = 15, col = heat.colors(100), zlim, ...)
tsallis(x, scales = seq(0, 2, 0.2), norm = FALSE, hill = FALSE) tsallisaccum(x, scales = seq(0, 2, 0.2), permutations = 100, raw = FALSE, subset, ...) ## S3 method for class 'tsallisaccum' persp(x, theta = 220, phi = 15, col = heat.colors(100), zlim, ...)
x |
Community data matrix or plotting object. |
scales |
Scales of Tsallis diversity. |
norm |
Logical, if |
hill |
Calculate Hill numbers. |
permutations |
Usually an integer giving the number
permutations, but can also be a list of control values for the
permutations as returned by the function |
raw |
If |
subset |
logical expression indicating sites (rows) to keep:
missing values are taken as |
theta , phi
|
angles defining the viewing
direction. |
col |
Colours used for surface. |
zlim |
Limits of vertical axis. |
... |
Other arguments which are passed to |
The Tsallis diversity (also equivalent to Patil and Taillie diversity) is a one-parametric generalised entropy function, defined as:
where is a scale parameter,
the number of species in
the sample (Tsallis 1988, Tothmeresz 1995). This diversity is concave
for all
, but non-additive (Keylock 2005). For
it
gives the number of species minus one, as
tends to 1 this
gives Shannon diversity, for
this gives the Simpson index
(see function
diversity
).
If norm = TRUE
, tsallis
gives values normalized by the
maximum:
where is the number of species. As
tends to 1, maximum
is defined as
.
If hill = TRUE
, tsallis
gives Hill numbers (numbers
equivalents, see Jost 2007):
Details on plotting methods and accumulating values can be found on
the help pages of the functions renyi
and
renyiaccum
.
Function tsallis
returns a data frame of selected
indices. Function tsallisaccum
with argument raw = FALSE
returns a three-dimensional array, where the first dimension are the
accumulated sites, second dimension are the diversity scales, and
third dimension are the summary statistics mean
, stdev
,
min
, max
, Qnt 0.025
and Qnt 0.975
. With
argument raw = TRUE
the statistics on the third dimension are
replaced with individual permutation results.
Péter Sólymos,
[email protected], based on the code of Roeland Kindt and
Jari Oksanen written for renyi
Tsallis, C. (1988) Possible generalization of Boltzmann-Gibbs statistics. J. Stat. Phis. 52, 479–487.
Tothmeresz, B. (1995) Comparison of different methods for diversity ordering. Journal of Vegetation Science 6, 283–290.
Patil, G. P. and Taillie, C. (1982) Diversity as a concept and its measurement. J. Am. Stat. Ass. 77, 548–567.
Keylock, C. J. (2005) Simpson diversity and the Shannon-Wiener index as special cases of a generalized entropy. Oikos 109, 203–207.
Jost, L (2007) Partitioning diversity into independent alpha and beta components. Ecology 88, 2427–2439.
Plotting methods and accumulation routines are based on
functions renyi
and renyiaccum
. An object
of class tsallisaccum
can be displayed with dynamic 3D function
rgl.renyiaccum
in the vegan3d package. See also settings for
persp
.
data(BCI) i <- sample(nrow(BCI), 12) x1 <- tsallis(BCI[i,]) x1 diversity(BCI[i,],"simpson") == x1[["2"]] plot(x1) x2 <- tsallis(BCI[i,],norm=TRUE) x2 plot(x2) mod1 <- tsallisaccum(BCI[i,]) plot(mod1, as.table=TRUE, col = c(1, 2, 2)) persp(mod1) mod2 <- tsallisaccum(BCI[i,], norm=TRUE) persp(mod2,theta=100,phi=30)
data(BCI) i <- sample(nrow(BCI), 12) x1 <- tsallis(BCI[i,]) x1 diversity(BCI[i,],"simpson") == x1[["2"]] plot(x1) x2 <- tsallis(BCI[i,],norm=TRUE) x2 plot(x2) mod1 <- tsallisaccum(BCI[i,]) plot(mod1, as.table=TRUE, col = c(1, 2, 2)) persp(mod1) mod2 <- tsallisaccum(BCI[i,], norm=TRUE) persp(mod2,theta=100,phi=30)
The varespec
data frame has 24 rows and 44 columns. Columns
are estimated cover values of 44 species. The variable names are
formed from the scientific names, and are self explanatory for anybody
familiar with the vegetation type.
The varechem
data frame has 24 rows and 14 columns, giving the
soil characteristics of the very same sites as in the varespec
data frame. The chemical measurements have obvious names.
Baresoil
gives the estimated cover of bare soil, Humdepth
the thickness of the humus layer.
data(varechem) data(varespec)
data(varechem) data(varespec)
Väre, H., Ohtonen, R. and Oksanen, J. (1995) Effects of reindeer grazing on understorey vegetation in dry Pinus sylvestris forests. Journal of Vegetation Science 6, 523–530.
data(varespec) data(varechem)
data(varespec) data(varechem)
The function partitions the variation in community data or community
dissimilarities with respect to two, three, or four explanatory
tables, using adjusted in redundancy analysis
ordination (RDA) or distance-based redundancy analysis. If response
is a single vector, partitioning is by partial regression. Collinear
variables in the explanatory tables do NOT have to be removed prior
to partitioning.
varpart(Y, X, ..., data, chisquare = FALSE, transfo, scale = FALSE, add = FALSE, sqrt.dist = FALSE, permutations) ## S3 method for class 'varpart' summary(object, ...) showvarparts(parts, labels, bg = NULL, alpha = 63, Xnames, id.size = 1.2, ...) ## S3 method for class 'varpart234' plot(x, cutoff = 0, digits = 1, ...)
varpart(Y, X, ..., data, chisquare = FALSE, transfo, scale = FALSE, add = FALSE, sqrt.dist = FALSE, permutations) ## S3 method for class 'varpart' summary(object, ...) showvarparts(parts, labels, bg = NULL, alpha = 63, Xnames, id.size = 1.2, ...) ## S3 method for class 'varpart234' plot(x, cutoff = 0, digits = 1, ...)
Y |
Data frame or matrix containing the response data table or
dissimilarity structure inheriting from |
X |
Two to four explanatory models, variables or tables. These can
be defined in three alternative ways: (1) one-sided model formulae
beginning with |
... |
Other parameters passed to functions. NB, arguments after dots cannot be abbreviated but they must be spelt out completely. |
data |
The data frame with the variables used in the formulae in
|
chisquare |
Partition Chi-square or the inertia of Correspondence
Analysis ( |
transfo |
Transformation for |
scale |
Should the columns of |
add |
Add a constant to the non-diagonal values to euclidify
dissimilarities (see |
sqrt.dist |
Take square root of dissimilarities. This often
euclidifies dissimilarities. NB., the argument name cannot be
abbreviated. The argument has an effect only when |
permutations |
If |
parts |
Number of explanatory tables (circles) displayed. |
labels |
Labels used for displayed fractions. Default is to use the same letters as in the printed output. |
bg |
Fill colours of circles or ellipses. |
alpha |
Transparency of the fill colour. The argument takes
precedence over possible transparency definitions of the
colour. The value must be in range |
Xnames |
Names for sources of variation. Default names are |
id.size |
A numerical value giving the character expansion factor for the names of circles or ellipses. |
x , object
|
The |
cutoff |
The values below |
digits |
The number of significant digits; the number of decimal places is at least one higher. |
The functions partition the variation in Y
into components
accounted for by two to four explanatory tables and their combined
effects. If Y
is a multicolumn data frame or matrix, the
partitioning is based on redundancy analysis (RDA, see
rda
) or on constrained correspondence analysis if
chisquare = TRUE
(CCA, see cca
). If Y
is a single variable, the partitioning is based on linear
regression. If Y
are dissimilarities, the decomposition is
based on distance-based redundancy analysis (db-RDA, see
dbrda
) following McArdle & Anderson (2001). The
input dissimilarities must be compatible to the results of
dist
. Vegan functions vegdist
,
designdist
, raupcrick
and
betadiver
produce such objects, as do many other
dissimilarity functions in R packages. Partitioning will be made
to squared dissimilarities analogously to using variance with
rectangular data – unless sqrt.dist = TRUE
was specified.
The function primarily uses adjusted to assess
the partitions explained by the explanatory tables and their
combinations (see
RsquareAdj
), because this is the
only unbiased method (Peres-Neto et al., 2006). The raw
for basic fractions are also displayed, but
these are biased estimates of variation explained by the explanatory
table. In correspondence analysis (
chisquare = TRUE
), the
adjusted are found by permutation and they vary
in repeated analyses.
The identifiable fractions are designated by lower case alphabets. The
meaning of the symbols can be found in the separate document (use
browseVignettes("vegan")
), or can be displayed graphically
using function showvarparts
.
A fraction is testable if it can be directly expressed as an RDA or
db-RDA model. In these cases the printed output also displays the
corresponding RDA model using notation where explanatory tables
after |
are conditions (partialled out; see rda
for details). Although single fractions can be testable, this does
not mean that all fractions simultaneously can be tested, since the
number of testable fractions is higher than the number of estimated
models. The non-testable components are found as differences of
testable components. The testable components have permutation
variance in correspondence analysis (chisquare = TRUE
), and
the non-testable components have even higher variance.
An abridged explanation of the alphabetic symbols for the individual
fractions follows, but computational details should be checked in the
vignette (readable with browseVignettes("vegan")
) or in the
source code.
With two explanatory tables, the fractions explained
uniquely by each of the two tables are [a]
and
[b]
, and their joint effect
is [c]
.
With three explanatory tables, the fractions explained uniquely
by each of the three tables are
[a]
to [c]
, joint fractions between two tables are
[d]
to [f]
, and the joint fraction between all three
tables is [g]
.
With four explanatory tables, the fractions explained uniquely by each
of the four tables are [a]
to [d]
, joint fractions between two tables are [e]
to
[j]
, joint fractions between three variables are [k]
to
[n]
, and the joint fraction between all four tables is
[o]
.
summary
will give an overview of unique and and overall
contribution of each group of variables. The overall contribution
(labelled as “Contributed”) consists of the unique contribution
of the variable and equal shares of each fraction where the variable
contributes. The summary tabulates how each fraction is divided
between the variables, and the contributed component is the sum of all
these divided fractions. The summary is based on the idea of Lai et
al. (2022), and is similar to the output of their rdacca.hp
package.
There is a plot
function that displays the Venn diagram and
labels each intersection (individual fraction) with the adjusted R
squared if this is higher than cutoff
. A helper function
showvarpart
displays the fraction labels. The circles and
ellipses are labelled by short default names or by names defined by
the user in argument Xnames
. Longer explanatory file names can
be written on the varpart output plot as follows: use option
Xnames=NA
, then add new names using the text
function. A
bit of fiddling with coordinates (see locator
) and
character size should allow users to place names of reasonably short
lengths on the varpart
plot.
Function varpart
returns an
object of class "varpart"
with items scale
and
transfo
(can be missing) which hold information on
standardizations, tables
which contains names of explanatory
tables, and call
with the function call
. The
function varpart
calls function varpart2
,
varpart3
or varpart4
which return an object of class
"varpart234"
and saves its result in the item part
.
The items in this object are:
SS.Y |
Sum of squares of matrix |
n |
Number of observations (rows). |
nsets |
Number of explanatory tables |
bigwarning |
Warnings on collinearity. |
fract |
Basic fractions from all estimated constrained models. |
indfract |
Individual fractions or all possible subsections in
the Venn diagram (see |
contr1 |
Fractions that can be found after conditioning on single explanatory table in models with three or four explanatory tables. |
contr2 |
Fractions that can be found after conditioning on two explanatory tables in models with four explanatory tables. |
Items fract
,
indfract
, contr1
and contr2
are all data frames with
items:
Df
: Degrees of freedom of numerator of the -statistic
for the fraction.
R.square
: Raw . This is calculated only for
fract
and this is NA
in other items.
Adj.R.square
: Adjusted .
Testable
: If the fraction can be expressed as a (partial) RDA
model, it is directly Testable
, and this field is
TRUE
. In that case the fraction label also gives the
specification of the testable RDA model.
You can use command browseVignettes("vegan")
to display
document which presents Venn diagrams showing the fraction names in
partitioning the variation of Y with respect to 2, 3, and 4 tables of
explanatory variables, as well as the equations used in variation
partitioning.
The functions frequently give negative estimates of variation.
Adjusted can be negative for any fraction;
unadjusted
of testable fractions of variances
will be non-negative. Non-testable fractions cannot be found
directly, but by subtracting different models, and these subtraction
results can be negative. The fractions are orthogonal, or linearly
independent, but more complicated or nonlinear dependencies can
cause negative non-testable fractions. Any fraction can be negative
for non-Euclidean dissimilarities because the underlying db-RDA
model can yield negative eigenvalues (see
dbrda
). These negative eigenvalues in the underlying
analysis can be avoided with arguments sqrt.dist
and
add
which have a similar effect as in dbrda
:
the square roots of several dissimilarities do not have negative
eigenvalues, and no negative eigenvalues are produced after Lingoes
or Cailliez adjustment, which in effect add random variation to the
dissimilarities.
A simplified, fast version of RDA, CCA adn dbRDA are used (functions
simpleRDA2
, simpleCCA
and simpleDBRDA
). The
actual calculations are done in functions varpart2
to
varpart4
, but these are not intended to be called directly by
the user.
Pierre Legendre, Departement de Sciences Biologiques, Universite de Montreal, Canada. Further developed by Jari Oksanen.
(a) References on variation partitioning
Borcard, D., P. Legendre & P. Drapeau. 1992. Partialling out the spatial component of ecological variation. Ecology 73: 1045–1055.
Lai J., Y. Zou, J. Zhang & P. Peres-Neto. 2022. Generalizing hierarchical and variation partitioning in multiple regression and canonical analysis using the rdacca.hp R package. Methods in Ecology and Evolution, 13: 782–788.
Legendre, P. & L. Legendre. 2012. Numerical ecology, 3rd English edition. Elsevier Science BV, Amsterdam.
(b) Reference on transformations for species data
Legendre, P. and E. D. Gallagher. 2001. Ecologically meaningful transformations for ordination of species data. Oecologia 129: 271–280.
(c) Reference on adjustment of the bimultivariate redundancy statistic
Peres-Neto, P., P. Legendre, S. Dray and D. Borcard. 2006. Variation partitioning of species data matrices: estimation and comparison of fractions. Ecology 87: 2614–2625.
(d) References on partitioning of dissimilarities
Legendre, P. & Anderson, M. J. (1999). Distance-based redundancy analysis: testing multispecies responses in multifactorial ecological experiments. Ecological Monographs 69, 1–24.
McArdle, B.H. & Anderson, M.J. (2001). Fitting multivariate models to community data: a comment on distance-based redundancy analysis. Ecology 82, 290-297.
For analysing testable fractions, see rda
and
anova.cca
. For data transformation, see
decostand
. Function inertcomp
gives
(unadjusted) components of variation for each species or site
separately. Function rda
displays unadjusted
components in its output, but RsquareAdj
will give
adjusted that are similar to the current
function also for partial models.
data(mite) data(mite.env) data(mite.pcnm) # Two explanatory data frames -- Hellinger-transform Y mod <- varpart(mite, mite.env, mite.pcnm, transfo="hel") mod summary(mod) ## Use fill colours showvarparts(2, bg = c("hotpink","skyblue")) plot(mod, bg = c("hotpink","skyblue")) ## Test fraction [a] using partial RDA, '~ .' in formula tells to use ## all variables of data mite.env. aFrac <- rda(decostand(mite, "hel"), mite.env, mite.pcnm) anova(aFrac) ## RsquareAdj gives the same result as component [a] of varpart RsquareAdj(aFrac) ## Partition Bray-Curtis dissimilarities varpart(vegdist(mite), mite.env, mite.pcnm) ## Three explanatory tables with formula interface mod <- varpart(mite, ~ SubsDens + WatrCont, ~ Substrate + Shrub + Topo, mite.pcnm, data=mite.env, transfo="hel") mod summary(mod) showvarparts(3, bg=2:4) plot(mod, bg=2:4) ## Use RDA to test fraction [a] ## Matrix can be an argument in formula rda.result <- rda(decostand(mite, "hell") ~ SubsDens + WatrCont + Condition(Substrate + Shrub + Topo) + Condition(as.matrix(mite.pcnm)), data = mite.env) anova(rda.result) ## Four explanatory tables mod <- varpart(mite, ~ SubsDens + WatrCont, ~Substrate + Shrub + Topo, mite.pcnm[,1:11], mite.pcnm[,12:22], data=mite.env, transfo="hel") mod summary(mod) plot(mod, bg=2:5) ## Show values for all partitions by putting 'cutoff' low enough: plot(mod, cutoff = -Inf, cex = 0.7, bg=2:5)
data(mite) data(mite.env) data(mite.pcnm) # Two explanatory data frames -- Hellinger-transform Y mod <- varpart(mite, mite.env, mite.pcnm, transfo="hel") mod summary(mod) ## Use fill colours showvarparts(2, bg = c("hotpink","skyblue")) plot(mod, bg = c("hotpink","skyblue")) ## Test fraction [a] using partial RDA, '~ .' in formula tells to use ## all variables of data mite.env. aFrac <- rda(decostand(mite, "hel"), mite.env, mite.pcnm) anova(aFrac) ## RsquareAdj gives the same result as component [a] of varpart RsquareAdj(aFrac) ## Partition Bray-Curtis dissimilarities varpart(vegdist(mite), mite.env, mite.pcnm) ## Three explanatory tables with formula interface mod <- varpart(mite, ~ SubsDens + WatrCont, ~ Substrate + Shrub + Topo, mite.pcnm, data=mite.env, transfo="hel") mod summary(mod) showvarparts(3, bg=2:4) plot(mod, bg=2:4) ## Use RDA to test fraction [a] ## Matrix can be an argument in formula rda.result <- rda(decostand(mite, "hell") ~ SubsDens + WatrCont + Condition(Substrate + Shrub + Topo) + Condition(as.matrix(mite.pcnm)), data = mite.env) anova(rda.result) ## Four explanatory tables mod <- varpart(mite, ~ SubsDens + WatrCont, ~Substrate + Shrub + Topo, mite.pcnm[,1:11], mite.pcnm[,12:22], data=mite.env, transfo="hel") mod summary(mod) plot(mod, bg=2:5) ## Show values for all partitions by putting 'cutoff' low enough: plot(mod, cutoff = -Inf, cex = 0.7, bg=2:5)
These functions are provided for compatibility with older versions of vegan only, and may be defunct as soon as the next release.
## moved to vegan3d package: install from CRAN orditkplot(...) ## use toCoda instead as.mcmc.oecosimu(x) as.mcmc.permat(x)
## moved to vegan3d package: install from CRAN orditkplot(...) ## use toCoda instead as.mcmc.oecosimu(x) as.mcmc.permat(x)
x |
object to be transformed. |
... |
Other arguments passed to the functions. |
orditkplot
was moved to vegan3d (version
1.3-0). Install that package from CRAN and use in the old way.
as.mcmc
functions were replaced with toCoda
.
The function computes dissimilarity indices that are useful for or
popular with community ecologists. All indices use quantitative data,
although they would be named by the corresponding binary index, but
you can calculate the binary index using an appropriate argument. If
you do not find your favourite index here, you can see if it can be
implemented using designdist
. Gower, Bray–Curtis,
Jaccard and Kulczynski indices are good in detecting underlying
ecological gradients (Faith et al. 1987). Morisita, Horn–Morisita,
Binomial, Cao and Chao indices should be able to handle different
sample sizes (Wolda 1981, Krebs 1999, Anderson & Millar 2004), and
Mountford (1962) and Raup-Crick indices for presence–absence data
should be able to handle unknown (and variable) sample sizes. Most of
these indices are discussed by Krebs (1999) and Legendre & Legendre
(2012), and their properties further compared by Wolda (1981) and
Legendre & De Cáceres (2012). Aitchison (1986) distance
is equivalent to Euclidean distance between CLR-transformed samples
("clr"
) and deals with positive compositional data.
Robust Aitchison distance by Martino et al. (2019) uses robust
CLR ("rlcr"
), making it applicable to non-negative data
including zeroes (unlike the standard Aitchison).
vegdist(x, method="bray", binary=FALSE, diag=FALSE, upper=FALSE, na.rm = FALSE, ...)
vegdist(x, method="bray", binary=FALSE, diag=FALSE, upper=FALSE, na.rm = FALSE, ...)
x |
Community data matrix. |
method |
Dissimilarity index, partial match to
|
binary |
Perform presence/absence standardization before analysis
using |
diag |
Compute diagonals. |
upper |
Return only the upper diagonal. |
na.rm |
Pairwise deletion of missing observations when
computing dissimilarities (but some dissimilarities may still be
|
... |
Other parameters. These are ignored, except in
|
Jaccard ("jaccard"
), Mountford ("mountford"
),
Raup–Crick ("raup"
), Binomial and Chao indices are discussed
later in this section. The function also finds indices for presence/
absence data by setting binary = TRUE
. The following overview
gives first the quantitative version, where
refer to the quantity on species (column)
and sites (rows)
and
. In binary versions
and
are the numbers of species on compared sites, and
is
the number of species that occur on both compared sites similarly as
in
designdist
(many indices produce identical binary
versions):
euclidean
|
|
binary:
|
|
manhattan
|
|
binary:
|
|
gower
|
|
binary:
|
|
where is the number of columns (excluding missing
values)
|
|
altGower
|
|
where is the number of non-zero columns excluding
double-zeros (Anderson et al. 2006).
|
|
binary:
|
|
canberra
|
|
where is the number of non-zero entries.
|
|
binary:
|
|
clark
|
|
where is the number of non-zero entries.
|
|
binary:
|
|
bray
|
|
binary:
|
|
kulczynski
|
|
binary:
|
|
morisita
|
, where
|
|
|
binary: cannot be calculated | |
horn
|
Like morisita , but
|
binary:
|
|
binomial
|
,
|
where
|
|
binary:
|
|
cao
|
,
|
where is the number of species in compared sites and
|
Jaccard index is computed as , where
is
Bray–Curtis dissimilarity.
Binomial index is derived from Binomial deviance under null hypothesis that the two compared communities are equal. It should be able to handle variable sample sizes. The index does not have a fixed upper limit, but can vary among sites with no shared species. For further discussion, see Anderson & Millar (2004).
Cao index or CYd index (Cao et al. 1997) was suggested as a minimally
biased index for high beta diversity and variable sampling intensity.
Cao index does not have a fixed upper limit, but can vary among sites
with no shared species. The index is intended for count (integer)
data, and it is undefined for zero abundances; these are replaced with
arbitrary value following Cao et al. (1997). Cao et
al. (1997) used
, but the current function uses
natural logarithms so that the values are approximately
times higher than with 10-based logarithms. Anderson & Thompson (2004)
give an alternative formulation of Cao index to highlight its
relationship with Binomial index (above).
Mountford index is defined as where
is the parameter of Fisher's logseries assuming that the compared
communities are samples from the same community
(cf.
fisherfit
, fisher.alpha
). The index
is found as the positive root of equation
, where
is the number of species occurring in
both communities, and
and
are the number of species
in each separate community (so the index uses presence–absence
information). Mountford index is usually misrepresented in the
literature: indeed Mountford (1962) suggested an approximation to be
used as starting value in iterations, but the proper index is
defined as the root of the equation above. The function
vegdist
solves with the Newton method. Please note
that if either
or
are equal to
, one of the
communities could be a subset of other, and the dissimilarity is
meaning that non-identical objects may be regarded as
similar and the index is non-metric. The Mountford index is in the
range
.
Raup–Crick dissimilarity (method = "raup"
) is a probabilistic
index based on presence/absence data. It is defined as , or based on the probability of observing at least
species in shared in compared communities. The current function uses
analytic result from hypergeometric distribution
(
phyper
) to find the probabilities. This probability
(and the index) is dependent on the number of species missing in both
sites, and adding all-zero species to the data or removing missing
species from the data will influence the index. The probability (and
the index) may be almost zero or almost one for a wide range of
parameter values. The index is nonmetric: two communities with no
shared species may have a dissimilarity slightly below one, and two
identical communities may have dissimilarity slightly above zero. The
index uses equal occurrence probabilities for all species, but Raup
and Crick originally suggested that sampling probabilities should be
proportional to species frequencies (Chase et al. 2011). A simulation
approach with unequal species sampling probabilities is implemented in
raupcrick
function following Chase et al. (2011). The
index can be also used for transposed data to give a probabilistic
dissimilarity index of species co-occurrence (identical to Veech
2013).
Chao index tries to take into account the number of unseen species
pairs, similarly as in method = "chao"
in
specpool
. Function vegdist
implements a
Jaccard, index defined as
;
other types can be defined with function
chaodist
. In Chao
equation, ,
and
is similar except for site index
.
is the total number of individuals in the
species of site
that are shared with site
,
is the total number of individuals at site
,
(and
) are the number of species
occurring in site
that have only one (or two) individuals in
site
, and
is the total number of individuals
in the species present at site
that occur with only one
individual in site
(Chao et al. 2005).
Morisita index can be used with genuine count data (integers) only. Its Horn–Morisita variant is able to handle any abundance data.
Mahalanobis distances are Euclidean distances of a matrix where columns are centred, have unit variance, and are uncorrelated. The index is not commonly used for community data, but it is sometimes used for environmental variables. The calculation is based on transforming data matrix and then using Euclidean distances following Mardia et al. (1979). The Mahalanobis transformation usually fails when the number of columns is larger than the number of rows (sampling units). When the transformation fails, the distances are nearly constant except for small numeric noise. Users must check that the returned Mahalanobis distances are meaningful.
Euclidean and Manhattan dissimilarities are not good in gradient separation without proper standardization but are still included for comparison and special needs.
Chi-square distances ("chisq"
) are Euclidean distances of
Chi-square transformed data (see decostand
). This is
the internal standardization used in correspondence analysis
(cca
, decorana
). Weighted principal
coordinates analysis of these distances with row sums as weights is
equal to correspondence analysis (see the Example in
wcmdscale
). Chi-square distance is intended for
non-negative data, such as typical community data. However, it can
be calculated as long as all margin sums are positive, but warning
is issued on negative data entries.
Chord distances ("chord"
) are Euclidean distance of a matrix
where rows are standardized to unit norm (their sums of squares are 1)
using decostand
. Geometrically this standardization
moves row points to a surface of multidimensional unit sphere, and
distances are the chords across the hypersphere. Hellinger distances
("hellinger"
) are related to Chord distances, but data are
standardized to unit total (row sums are 1) using
decostand
, and then square root transformed. These
distances have upper limit of .
Bray–Curtis and Jaccard indices are rank-order similar, and some
other indices become identical or rank-order similar after some
standardizations, especially with presence/absence transformation of
equalizing site totals with decostand
. Jaccard index is
metric, and probably should be preferred instead of the default
Bray-Curtis which is semimetric.
Aitchison distance (1986) and robust Aitchison distance (Martino et al. 2019) are metrics that deal with compositional data. Aitchison distance has been said to outperform Jensen-Shannon divergence and Bray-Curtis dissimilarity, due to a better stability to subsetting and aggregation, and it being a proper distance (Aitchison et al., 2000).
The naming conventions vary. The one adopted here is traditional
rather than truthful to priority. The function finds either
quantitative or binary variants of the indices under the same name,
which correctly may refer only to one of these alternatives For
instance, the Bray
index is known also as Steinhaus, Czekanowski and
Sørensen index.
The quantitative version of Jaccard should probably called
Ružička index.
The abbreviation "horn"
for the Horn–Morisita index is
misleading, since there is a separate Horn index. The abbreviation
will be changed if that index is implemented in vegan
.
Function is a drop-in replacement for dist
function and
returns a distance object of the same type. The result object adds
attribute maxdist
that gives the theoretical maximum of the
index for sampling units that share no species, or NA
when
there is no such maximum.
The function is an alternative to dist
adding some
ecologically meaningful indices. Both methods should produce similar
types of objects which can be interchanged in any method accepting
either. Manhattan and Euclidean dissimilarities should be identical
in both methods. Canberra index is divided by the number of variables
in vegdist
, but not in dist
. So these differ by
a constant multiplier, and the alternative in vegdist
is in
range (0,1). Function daisy
(package
cluster) provides alternative implementation of Gower index that
also can handle mixed data of numeric and class variables. There are
two versions of Gower distance ("gower"
, "altGower"
)
which differ in scaling: "gower"
divides all distances by the
number of observations (rows) and scales each column to unit range,
but "altGower"
omits double-zeros and divides by the number of
pairs with at least one above-zero value, and does not scale columns
(Anderson et al. 2006). You can use decostand
to add
range standardization to "altGower"
(see Examples). Gower
(1971) suggested omitting double zeros for presences, but it is often
taken as the general feature of the Gower distances. See Examples for
implementing the Anderson et al. (2006) variant of the Gower index.
Most dissimilarity indices in vegdist
are designed for
community data, and they will give misleading values if there are
negative data entries. The results may also be misleading or
NA
or NaN
if there are empty sites. In principle, you
cannot study species composition without species and you should remove
empty sites from community data.
Jari Oksanen, with contributions from Tyler Smith (Gower index), Michael Bedward (Raup–Crick index), and Leo Lahti (Aitchison and robust Aitchison distance).
Aitchison, J. The Statistical Analysis of Compositional Data (1986). London, UK: Chapman & Hall.
Aitchison, J., Barceló-Vidal, C., Martín-Fernández, J.A., Pawlowsky-Glahn, V. (2000). Logratio analysis and compositional distance. Math. Geol. 32, 271–275.
Anderson, M.J. and Millar, R.B. (2004). Spatial variation and effects of habitat on temperate reef fish assemblages in northeastern New Zealand. Journal of Experimental Marine Biology and Ecology 305, 191–221.
Anderson, M.J., Ellingsen, K.E. & McArdle, B.H. (2006). Multivariate dispersion as a measure of beta diversity. Ecology Letters 9, 683–693.
Anderson, M.J & Thompson, A.A. (2004). Multivariate control charts for ecological and environmental monitoring. Ecological Applications 14, 1921–1935.
Cao, Y., Williams, W.P. & Bark, A.W. (1997). Similarity measure bias in river benthic Auswuchs community analysis. Water Environment Research 69, 95–106.
Chao, A., Chazdon, R. L., Colwell, R. K. and Shen, T. (2005). A new statistical approach for assessing similarity of species composition with incidence and abundance data. Ecology Letters 8, 148–159.
Chase, J.M., Kraft, N.J.B., Smith, K.G., Vellend, M. and Inouye,
B.D. (2011). Using null models to disentangle variation in community
dissimilarity from variation in -diversity.
Ecosphere 2:art24 doi:10.1890/ES10-00117.1
Faith, D. P, Minchin, P. R. and Belbin, L. (1987). Compositional dissimilarity as a robust measure of ecological distance. Vegetatio 69, 57–68.
Gower, J. C. (1971). A general coefficient of similarity and some of its properties. Biometrics 27, 623–637.
Krebs, C. J. (1999). Ecological Methodology. Addison Wesley Longman.
Legendre, P. & De Cáceres, M. (2012). Beta diversity as the variance of community data: dissimilarity coefficients and partitioning. Ecology Letters 16, 951–963. doi:10.1111/ele.12141
Legendre, P. and Legendre, L. (2012) Numerical Ecology. 3rd English ed. Elsevier.
Mardia, K.V., Kent, J.T. and Bibby, J.M. (1979). Multivariate analysis. Academic Press.
Martino, C., Morton, J.T., Marotz, C.A., Thompson, L.R., Tripathi, A., Knight, R. & Zengler, K. (2019) A novel sparse compositional technique reveals microbial perturbations. mSystems 4, 1.
Mountford, M. D. (1962). An index of similarity and its application to classification problems. In: P.W.Murphy (ed.), Progress in Soil Zoology, 43–50. Butterworths.
Veech, J. A. (2013). A probabilistic model for analysing species co-occurrence. Global Ecology and Biogeography 22, 252–260.
Wolda, H. (1981). Similarity indices, sample size and diversity. Oecologia 50, 296–302.
Function designdist
can be used for defining
your own dissimilarity index. Function betadiver
provides indices intended for the analysis of beta diversity.
data(varespec) vare.dist <- vegdist(varespec) # Orlóci's Chord distance: range 0 .. sqrt(2) vare.dist <- vegdist(decostand(varespec, "norm"), "euclidean") # Anderson et al. (2006) version of Gower vare.dist <- vegdist(decostand(varespec, "log"), "altGower") # Range standardization with "altGower" (that excludes double-zeros) vare.dist <- vegdist(decostand(varespec, "range"), "altGower")
data(varespec) vare.dist <- vegdist(varespec) # Orlóci's Chord distance: range 0 .. sqrt(2) vare.dist <- vegdist(decostand(varespec, "norm"), "euclidean") # Anderson et al. (2006) version of Gower vare.dist <- vegdist(decostand(varespec, "log"), "altGower") # Range standardization with "altGower" (that excludes double-zeros) vare.dist <- vegdist(decostand(varespec, "range"), "altGower")
Functions vegemite
and tabasco
display compact
community tables. Function vegemite
prints text tables where
species are rows, and each site takes only one column without
spaces. Function tabasco
provides interface for
heatmap
for a colour image
of the
data. The community table can be ordered by explicit indexing, by
environmental variables or results from an ordination or cluster
analysis.
vegemite(x, use, scale, sp.ind, site.ind, zero=".", select, diagonalize = FALSE, ...) tabasco(x, use, sp.ind = NULL, site.ind = NULL, select, Rowv = TRUE, Colv = TRUE, labRow = NULL, labCol = NULL, scale, col = heat.colors(12), ...) coverscale(x, scale=c("Braun.Blanquet", "Domin", "Hult", "Hill", "fix","log"), maxabund, character = TRUE)
vegemite(x, use, scale, sp.ind, site.ind, zero=".", select, diagonalize = FALSE, ...) tabasco(x, use, sp.ind = NULL, site.ind = NULL, select, Rowv = TRUE, Colv = TRUE, labRow = NULL, labCol = NULL, scale, col = heat.colors(12), ...) coverscale(x, scale=c("Braun.Blanquet", "Domin", "Hult", "Hill", "fix","log"), maxabund, character = TRUE)
x |
Community data. |
use |
Either a numeric vector or a classification factor, or an
object from |
sp.ind , site.ind
|
Species and site indices. In |
zero |
Character used for zeros. |
select |
Select a subset of sites. This can be a logical vector
( |
diagonalize |
Try to re-order |
Rowv , Colv
|
Re-order factors or dendrograms for the rows (sites)
or columns (species) of |
labRow , labCol
|
character vectors with row and column labels
used in the |
scale |
In |
col |
A vector of colours used for above-zero abundance values. |
maxabund |
Maximum abundance used with |
character |
Return character codes suitable for tabulation in
|
... |
Arguments passed to |
The function vegemite
prints a traditional community table.
The display is transposed, so that species are in rows and sites in
columns. The table is printed in compact form: only one character
can be used for abundance, and there are no spaces between
columns. Species with no occurrences are dropped from the table.
Function tabasco
produces a similar table as vegemite
using heatmap
, where abundances are coded by
colours. The function scales the abundances to equal intervals for
colour palette, but either rows or columns can be scaled to equal
maxima, or the coverscale
class systems can be used. The
function can also display dendrograms for sites (columns) or species
if these are given as an argument (use
for sites,
sp.ind
for species).
The parameter use
will be used to re-order output. The
use
can be a vector or an object from hclust
or
agnes
, a dendrogram
or any
ordination result recognized by scores
(all ordination
methods in vegan and some of those not in vegan). The
hclust
, agnes
and
dendrogram
must be for sites. The dendrogram is
displayed above the sites in tabasco
, but is not shown in
vegemite
. In tabasco
the species dendrogram can be
given in sp.ind
.
If use
is a numeric vector, it is used for ordering sites,
and if it is a factor, it is used to order sites by classes. If
use
is an object from ordination, both sites and species are
arranged by the first axis (provided that results are available also
for species). When use
is an object from
hclust
, agnes
or a
dendrogram
, the sites are ordered similarly as in the
cluster dendrogram. Function tabasco
re-orders the
dendrogram to give a diagonal pattern if Rowv =
TRUE
. Alternatively, if Rowv
is a vector its values are used
to re-order dendrogram. With diagonalize = TRUE
the
dendrogram will be re-ordered in vegemite
to give a diagonal
pattern. If use
is a factor, its levels and sites within
levels will be reordered to give a diagonal pattern if
diagonalize = TRUE
in vegemite
or Rowv = TRUE
in tabasco
. In all cases where species scores are missing,
species are ordered by their weighted averages
(wascores
) on site order or site value.
Species and sites can be ordered explicitly giving their indices or
names in parameters sp.ind
and site.ind
. If these are
given, they take precedence over use
. A subset of sites can
be displayed using argument select
, but this cannot be used
to order sites, but you still must give use
or
site.ind
. However, tabasco
makes two exceptions:
site.ind
and select
cannot be used when use
is
a dendrogram (clustering result). In addition, the sp.ind
can
be an hclust
tree, agnes
clustering or a dendrogram
, and in that case the
dendrogram is plotted on the left side of the
heatmap
. Phylogenetic trees cannot be directly used,
but package ape has tools to transform these to
hclust
trees.
If scale
is given, vegemite
calls coverscale
to
transform percent cover scale or some other scales into traditional
class scales used in vegetation science (coverscale
can be
called directly, too). Function tabasco
can also use these
traditional class scales, but it treats the transformed values as
corresponding integers. Braun-Blanquet and Domin scales are
actually not strict cover scales, and the limits used for codes
r
and +
are arbitrary. Scale Hill
may be
inappropriately named, since Mark O. Hill probably never intended
this as a cover scale. However, it is used as default “cut levels”
in his TWINSPAN
, and surprisingly many users stick to this
default, and this is a de facto standard in publications.
All traditional scales assume that values are cover percentages with
maximum 100. However, non-traditional alternative log
can be
used with any scale range. Its class limits are integer powers of
1/2 of the maximum (argument maxabund
), with +
used
for non-zero entries less than 1/512 of the maximum (log
stands alternatively for logarithmic or logical). Scale fix
is intended for “fixing” 10-point scales: it truncates scale values
to integers, and replaces 10 with X
and positive values below
1 with +
.
The functions are used mainly to display a table, but they return
(invisibly) a list with items species
for ordered species
index, sites
for ordered site index, and table
for the
final ordered community table.
These items can be used as arguments sp.ind
and site.ind
to reproduce the table, or the table
can be further edited. In
addition to the table, vegemite
prints the numbers of species
and sites and the name of the used cover scale.
The name vegemite
was chosen because the output is so
compact, and the tabasco
because it is just as compact, but
uses heat colours.
Jari Oksanen
The cover scales are presented in many textbooks of vegetation science; I used:
Shimwell, D.W. (1971) The Description and Classification of Vegetation. Sidgwick & Jackson.
cut
and approx
for making your
own ‘cover scales’ for vegemite
. Function
tabasco
is based on heatmap
which in turn is
based on image
. Both functions order species with
weighted averages using wascores
.
data(varespec) ## Print only more common species freq <- apply(varespec > 0, 2, sum) vegemite(varespec, scale="Hult", sp.ind = freq > 10) ## Order by correspondence analysis, use Hill scaling and layout: dca <- decorana(varespec) vegemite(varespec, dca, "Hill", zero="-") ## Show one class from cluster analysis, but retain the ordering above clus <- hclust(vegdist(varespec)) cl <- cutree(clus, 3) sel <- vegemite(varespec, use=dca, select = cl == 3, scale="Br") ## Re-create previous vegemite(varespec, sp=sel$sp, site=sel$site, scale="Hult") ## Re-order clusters by ordination clus <- as.dendrogram(clus) clus <- reorder(clus, scores(dca, choices=1, display="sites"), agglo.FUN = mean) vegemite(varespec, clus, scale = "Hult") ## Abundance values have such a wide range that they must be rescaled tabasco(varespec, dca, scale="Braun") ## Classification trees for species data(dune, dune.taxon) taxontree <- hclust(taxa2dist(dune.taxon)) plotree <- hclust(vegdist(dune), "average") ## Automatic reordering of clusters tabasco(dune, plotree, sp.ind = taxontree) ## No reordering of taxonomy tabasco(dune, plotree, sp.ind = taxontree, Colv = FALSE) ## Species cluster: most dissimilarity indices do a bad job when ## comparing rare and common species, but Raup-Crick makes sense sptree <- hclust(vegdist(t(dune), "raup"), "average") tabasco(dune, plotree, sptree)
data(varespec) ## Print only more common species freq <- apply(varespec > 0, 2, sum) vegemite(varespec, scale="Hult", sp.ind = freq > 10) ## Order by correspondence analysis, use Hill scaling and layout: dca <- decorana(varespec) vegemite(varespec, dca, "Hill", zero="-") ## Show one class from cluster analysis, but retain the ordering above clus <- hclust(vegdist(varespec)) cl <- cutree(clus, 3) sel <- vegemite(varespec, use=dca, select = cl == 3, scale="Br") ## Re-create previous vegemite(varespec, sp=sel$sp, site=sel$site, scale="Hult") ## Re-order clusters by ordination clus <- as.dendrogram(clus) clus <- reorder(clus, scores(dca, choices=1, display="sites"), agglo.FUN = mean) vegemite(varespec, clus, scale = "Hult") ## Abundance values have such a wide range that they must be rescaled tabasco(varespec, dca, scale="Braun") ## Classification trees for species data(dune, dune.taxon) taxontree <- hclust(taxa2dist(dune.taxon)) plotree <- hclust(vegdist(dune), "average") ## Automatic reordering of clusters tabasco(dune, plotree, sp.ind = taxontree) ## No reordering of taxonomy tabasco(dune, plotree, sp.ind = taxontree, Colv = FALSE) ## Species cluster: most dissimilarity indices do a bad job when ## comparing rare and common species, but Raup-Crick makes sense sptree <- hclust(vegdist(t(dune), "raup"), "average") tabasco(dune, plotree, sptree)
Computes Weighted Averages scores of species for ordination configuration or for environmental variables.
wascores(x, w, expand = FALSE, stdev = FALSE) eigengrad(x, w) ## S3 method for class 'wascores' scores(x, display = c("wa", "stdev", "var", "se", "n2", "raw"), ...)
wascores(x, w, expand = FALSE, stdev = FALSE) eigengrad(x, w) ## S3 method for class 'wascores' scores(x, display = c("wa", "stdev", "var", "se", "n2", "raw"), ...)
x |
Environmental variables or ordination scores, or for
|
w |
Weights: species abundances. |
expand |
Expand weighted averages so that they have the same weighted variance as the corresponding environmental variables. |
stdev |
Estimate weighted standard deviation of WA scores. |
display |
Type of scores returned. |
... |
Other arguments passed to functions (currently ignored). |
Weighted Averages are a classical way of estimating the species
optima along continuous environmental variables
(a.k.a. gradients). Function wascores
is a simple function
that is mainly designed to add species scores to unimodal
ordinations (metaMDS
, sppscores
) or
ordering rows or columns to give diagonal pattern of tabulation
(vegemite
, tabasco
). It can also be used
to find species “optima” or sampling unit calibrations for
community data. For this purpose, specialized packages such
analogue are recommended (but see
calibrate.cca
).
First argument of wascores
is the variable or a matrix of
variables for which weighted averages are needed, and the second
argument is the matrix of weights. In classical approaches weights are
a community matrix, where taxon abundances define the weights. The
number of rows must match. If the first argument is for taxa
(columns), community weight matrix must be transposed.
Weighted averages “shrink”: they cannot be more extreme than
values used for calculating the averages. With expand = TRUE
,
the function “deshrinks” the weighted averages making their
weighted variance equal to the weighted variance of the
corresponding input variable. Specialized packages (such as
analogue) offer a wider range of deshrinking alternatives, but
deshrinking can also made after the analysis (see
Examples). Function eigengrad
returns the strength of
expansion as attribute shrinkage
of the wascores
result for each environmental gradient. The shrinkage equal to the
constrained eigenvalue of cca
when only this one
gradient was used as a constraint, and describes the strength of the
gradient.
With stdev = TRUE
the function estimates the unbiased
weighted standard deviation of the WA estimates using
cov.wt
. For unbiased standard deviation the virtual
number of observations is equal to inverse Simpson index of
diversity also known as Hill number N2 (see
diversity
). The numeric results can be accessed with
scores
function. Function tolerance
uses the
same algebra for weighted standard deviation, but bases the variance
on linear combination scores (constaints) variables instead of the
weighted averages of the sites like wascores
.
Weighted averages are closely linked to correspondence analysis
(ca
, cca
). Repeated use of
wascores
will converge to the first axis of unconstrained
correspondence analysis (ca
) which therefore is also
known as Reciprocal Averaging (Hill 1973). Constrained
correspondence analysis (cca
) is equivalent to
weighted averages and calibrate.cca
will return
weighted averages of the constraint with different deshrinking.
If stdev = TRUE
, function returns an object of class
"wascores"
with items
wa |
A matrix of weighted averages with. If
|
stdev |
a matrix of weighted standard deviations |
n2 |
effective sample sizes which are equal to inverse Simpson diversity or Hill number N2 |
If stdev = FALSE
(default), only the plain matrix wa
is returned. Function eigengrad
returns only the
shrinkage
attribute. With stdev = TRUE
only a brief
summary of the result is printed, and the individvual scores can be
accessed with scores
function.
Jari Oksanen
Hill, M.O. (1973) Reciprocal averaging: An eigenvector method of ordination. Journal of Ecology 61, 237–249.
calibrate.cca
, tolerance.cca
,
sppscores
.
data(mite, mite.env) ## add species points to ordination mod <- monoMDS(vegdist(mite)) plot(mod) ## add species points; sppscores does the same and can also add the ## species scores to mod points(wascores(scores(mod), mite, expand = TRUE), pch="+", col=2) ## Get taxon optima for WatrCont head(wascores(mite.env$WatrCont, mite)) ## WA calibration: site WA from species WA; NB using transpose for site WA spwa <- wascores(mite.env$WatrCont, mite, expand = TRUE) wacalib <- wascores(spwa, t(mite), expand = TRUE) plot(wacalib ~ WatrCont, data=mite.env) abline(0, 1) ## use traditional 'inverse' regression deshrinking instead of wascores ## 'expand' wareg <- fitted(lm(WatrCont ~ wacalib, data=mite.env)) head(cbind("WatrCont" = mite.env$WatrCont, "expand" = drop(wacalib), "regression" = wareg)) ## Reciprocal Averaging algorithm for Correspondence Analysis ## start with random values u <- runif(nrow(mite)) ## repeat the following steps so long that the shrinkage converges v <- wascores(u, mite, expand = TRUE) u <- wascores(v, t(mite), expand = TRUE) attr(u, "shrinkage") # current estimate of eigenvalue ## The strengths of two continuous variables in the data set eigengrad(mite.env[, 1:2], mite)
data(mite, mite.env) ## add species points to ordination mod <- monoMDS(vegdist(mite)) plot(mod) ## add species points; sppscores does the same and can also add the ## species scores to mod points(wascores(scores(mod), mite, expand = TRUE), pch="+", col=2) ## Get taxon optima for WatrCont head(wascores(mite.env$WatrCont, mite)) ## WA calibration: site WA from species WA; NB using transpose for site WA spwa <- wascores(mite.env$WatrCont, mite, expand = TRUE) wacalib <- wascores(spwa, t(mite), expand = TRUE) plot(wacalib ~ WatrCont, data=mite.env) abline(0, 1) ## use traditional 'inverse' regression deshrinking instead of wascores ## 'expand' wareg <- fitted(lm(WatrCont ~ wacalib, data=mite.env)) head(cbind("WatrCont" = mite.env$WatrCont, "expand" = drop(wacalib), "regression" = wareg)) ## Reciprocal Averaging algorithm for Correspondence Analysis ## start with random values u <- runif(nrow(mite)) ## repeat the following steps so long that the shrinkage converges v <- wascores(u, mite, expand = TRUE) u <- wascores(v, t(mite), expand = TRUE) attr(u, "shrinkage") # current estimate of eigenvalue ## The strengths of two continuous variables in the data set eigengrad(mite.env[, 1:2], mite)
Weighted classical multidimensional scaling, also known as weighted principal coordinates analysis.
wcmdscale(d, k, eig = FALSE, add = FALSE, x.ret = FALSE, w) ## S3 method for class 'wcmdscale' plot(x, choices = c(1, 2), display = "sites", type = "t", ...) ## S3 method for class 'wcmdscale' scores(x, choices = NA, display = "sites", tidy = FALSE, ...)
wcmdscale(d, k, eig = FALSE, add = FALSE, x.ret = FALSE, w) ## S3 method for class 'wcmdscale' plot(x, choices = c(1, 2), display = "sites", type = "t", ...) ## S3 method for class 'wcmdscale' scores(x, choices = NA, display = "sites", tidy = FALSE, ...)
d |
a distance structure such as that returned by |
k |
the dimension of the space which the data are to be
represented in; must be in |
eig |
indicates whether eigenvalues should be returned. |
add |
an additive constant |
x.ret |
indicates whether the doubly centred symmetric distance matrix should be returned. |
w |
Weights of points. |
x |
The |
choices |
Axes to be returned; |
display |
Kind of scores. Normally only |
type |
Type of graph which may be |
tidy |
Return scores that are compatible with ggplot2:
scores are in a |
... |
Other arguments passed to graphical functions. |
Function wcmdscale
is based on function
cmdscale
(package stats of base R), but it uses
point weights. Points with high weights will have a stronger
influence on the result than those with low weights. Setting equal
weights w = 1
will give ordinary multidimensional scaling.
With default options, the function returns only a matrix of scores
scaled by eigenvalues for all real axes. If the function is called
with eig = TRUE
or x.ret = TRUE
, the function returns
an object of class "wcmdscale"
with print
,
plot
, scores
, eigenvals
and
stressplot
methods, and described in section Value.
The method is Euclidean, and with non-Euclidean dissimilarities some
eigenvalues can be negative. If this disturbs you, this can be
avoided by adding a constant to non-diagonal dissimilarities making
all eigenvalues non-negative. The function implements methods
discussed by Legendre & Anderson (1999): The method of Lingoes
(add="lingoes"
) adds the constant to squared
dissimilarities
using
and the method of Cailliez (
add="cailliez"
) to
dissimilarities using . Legendre & Anderson (1999)
recommend the method of Lingoes, and base R function
cmdscale
implements the method of Cailliez.
If eig = FALSE
and x.ret = FALSE
(default), a
matrix with k
columns whose rows give the coordinates of
points corresponding to positive eigenvalues. Otherwise, an object
of class wcmdscale
containing the components that are mostly
similar as in cmdscale
:
points |
a matrix with |
eig |
the |
x |
the doubly centred and weighted distance matrix if
|
ac , add
|
additive constant and adjustment method used to avoid
negative eigenvalues. These are |
GOF |
Goodness of fit statistics for |
weights |
Weights. |
negaxes |
A matrix of scores for axes with negative eigenvalues
scaled by the absolute eigenvalues similarly as
|
call |
Function call. |
Gower, J. C. (1966) Some distance properties of latent root and vector methods used in multivariate analysis. Biometrika 53, 325–328.
Legendre, P. & Anderson, M. J. (1999). Distance-based redundancy analysis: testing multispecies responses in multifactorial ecological experiments. Ecology 69, 1–24.
Mardia, K. V., Kent, J. T. and Bibby, J. M. (1979). Chapter 14 of Multivariate Analysis, London: Academic Press.
The function is modelled after cmdscale
, but adds
weights (hence name) and handles negative eigenvalues differently.
eigenvals.wcmdscale
and
stressplot.wcmdscale
are some specific methods. Species
scores can be added to the result with sppscores
. Other
multidimensional scaling methods are monoMDS
, and
isoMDS
and sammon
in package
MASS.
## Correspondence analysis as a weighted principal coordinates ## analysis of Euclidean distances of Chi-square transformed data data(dune) rs <- rowSums(dune)/sum(dune) d <- dist(decostand(dune, "chi")) ord <- wcmdscale(d, w = rs, eig = TRUE) ## Ordinary CA ca <- cca(dune) ## IGNORE_RDIFF_BEGIN ## Eigevalues are numerically similar ca$CA$eig - ord$eig ## Configurations are similar when site scores are scaled by ## eigenvalues in CA procrustes(ord, ca, choices=1:19, scaling = "sites") ## IGNORE_RDIFF_END plot(procrustes(ord, ca, choices=1:2, scaling="sites")) ## Reconstruction of non-Euclidean distances with negative eigenvalues d <- vegdist(dune) ord <- wcmdscale(d, eig = TRUE) ## Only positive eigenvalues: cor(d, dist(ord$points)) ## Correction with negative eigenvalues: cor(d, sqrt(dist(ord$points)^2 - dist(ord$negaxes)^2))
## Correspondence analysis as a weighted principal coordinates ## analysis of Euclidean distances of Chi-square transformed data data(dune) rs <- rowSums(dune)/sum(dune) d <- dist(decostand(dune, "chi")) ord <- wcmdscale(d, w = rs, eig = TRUE) ## Ordinary CA ca <- cca(dune) ## IGNORE_RDIFF_BEGIN ## Eigevalues are numerically similar ca$CA$eig - ord$eig ## Configurations are similar when site scores are scaled by ## eigenvalues in CA procrustes(ord, ca, choices=1:19, scaling = "sites") ## IGNORE_RDIFF_END plot(procrustes(ord, ca, choices=1:2, scaling="sites")) ## Reconstruction of non-Euclidean distances with negative eigenvalues d <- vegdist(dune) ord <- wcmdscale(d, eig = TRUE) ## Only positive eigenvalues: cor(d, dist(ord$points)) ## Correction with negative eigenvalues: cor(d, sqrt(dist(ord$points)^2 - dist(ord$negaxes)^2))