metricTester (version 1.3.6)

FDis: Calculate functional dispersion (FDis)

Description

Calculate the functional dispersion of clouds of multivariate points.

Usage

FDis(ordination.results, road.map)

Arguments

ordination.results

Matrix of ordination results, e.g. the $x element from a prcomp object, or the $points element from a metaMDS object in vegan. Could also be raw trait values, but cannot currently handle categorical variables.

road.map

Identical to the input for the 'a' argument in the dbFD function of the FD package, and to the picante.cdm argument used elsewhere in this package. Thus, this is a matrix or data frame containing the abundance of each 'species' in the ordination results. Rows are "sites" and columns are "species". Rather than abundances, the values can simply be presence/absences. Moreover, sites could be species and species could be individuals. See details.

Value

Named numeric with FDis values.

Details

The definition of FDis provided by Laliberte and Legendre (2010) and implemented in the dbFD function of the FD package is geared towards calculating the functional diversity of a community, given a set of species with an array of traits. Another useful way in which FDis might be implemented is as a measure of a species' niche breadth. In this case, ordination.results would be measures (e.g. foraging observations) of multiple individuals of multiple species', and road.map would be a matrix describing which observations belong to which species. The abundances in the matrix in this case would describe how much weight to assign to each individual observation. Regardless of the scale of calculation (either across species within a community or across individuals within a species), this function determines the weighted centroid of each cloud of points and then determines the weighted mean absolute deviation from each centroid.

References

Miller, E. T. 2016. Random thoughts, though please cite metricTester via our 2016 Ecography paper.

Laliberte, E. & P. Legendre. 2010. A distance-based framework for measuring functional diversity from multiple traits. Ecology 91:299-305.

Examples

# NOT RUN {
#example of how to calculate the FDis of a series of plots based on the trait values
#of a set of species. begin by simulating a phylogeny with a birth-death process
tree <- geiger::sim.bdtree(b=0.1, d=0, stop="taxa", n=50)

#create a log-normal abundance distribution
sim.abundances <- round(rlnorm(5000, meanlog=2, sdlog=1)) + 1

#simulate a community data matrix, with species as columns and sites as rows
cdm <- simulateComm(tree, richness.vector=10:25, abundances=sim.abundances)

#simulate two traits and combine into a matrix. because species are sometimes absent
#from the cdm, also exclude any species from the trait data frame that are not in the
#cdm (to avoid errors), then ordinate with a PCA
traits <- evolveTraits(tree)[[2]]
traits <- traits[row.names(traits) %in% colnames(cdm),]
ord <- prcomp(traits)

#the FDis of the species in each plot
FDis(ordination.results=ord$x, road.map=cdm)

#now an example of how to calculate the FDis of a series of species based on the trait
#values of a set of individuals. begin by simulating trait data for a series of
#individuals. to illustrate the point, simulate varying numbers of individuals per
#species, and where there are varying degrees of variance in traits per species. 
traits2 <- data.frame(trait1=c(rnorm(n=30, sd=1), rnorm(n=60, sd=2), rnorm(n=120,sd=4)),
trait2=c(rnorm(n=30, sd=1), rnorm(n=60, sd=2), rnorm(n=120, sd=4)))

#ordinate the traits. could readily use another ordination here, e.g. nmds with gower
ord2 <- prcomp(traits2)

#create a road.map where species are rows and individual observations are columns. the
#first 30 observations belong to sp1, the following 60 to sp2, and the following 120
#to sp3.
cdm2 <- matrix(nrow=3, ncol=dim(traits2)[1], 0)
colnames(cdm2) <- row.names(traits2)
row.names(cdm2) <- c("sp1", "sp2", "sp3")
cdm2[1,1:30] <- 1
cdm2[2,31:90] <- 1
cdm2[3,91:210] <- 1

#the FDis of each species (i.e. niche breadth)
FDis(ordination.results=ord2$x, road.map=cdm2)
# }