metricTester (version 1.3.6)

synthComm: Create synthetic community niche space

Description

Create niche spaces with similar characteristics to input.

Usage

synthComm(ordination.results, road.map, cov.matrix = NULL)

Arguments

ordination.results

Total niche space, e.g. the $x element of a PCA object. This should be a matrix. If it is not, it will be converted to one. This means categorical variables will not be handled well.

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 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 and examples.

cov.matrix

Optional covariance matrix, e.g. from a larger total trait space.

Value

Dataframe with the coordinates and species identities of the new niche space.

Details

This function is totally untested and may not do what I think it does. Use with care! In theory, it takes the points that describe the total trait space of a community (or multiple communities, depending upon the analysis) and a community road map, optionally a cov.matrix, and will return a new total trait space with the same number of species (or sites) and observations per species (or community) as the input. It works by first simulating a multivariate normal distribution with centroids like those from ordination.results. It bases the positions of these centroids on the covariance matrix of the input ordination.results unless a different covariance matrix (e.g., from a larger trait space) is provided. Points (either akin to multiple individuals or species, depending on the level of analysis) are then distributed around those points with multivariate normal distributions like those in the input.

References

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

Examples

# NOT RUN {
#generate six species' niche spaces of 20 observations each in 3 dimensions. first
#define the centroids of their distributions
centroids <- matrix(nrow=6, ncol=3, rep(seq(from = -2, to = 2, length.out=6), 3))

#brute force the points into a list and reduce back into a large simulated
#ordination.results object

output <- list()

for(i in 1:6)
{
	temp1 <- rnorm(n=20, mean=centroids[i,1], sd=1/i)
	temp2 <- rnorm(n=20, mean=centroids[i,2], sd=1/i)
	temp3 <- rnorm(n=20, mean=centroids[i,3], sd=1/i)
	output[[i]] <- data.frame(temp1, temp2, temp3)
}

totalNiche <- Reduce(rbind, output)

#add a species then color column to totalNiche then scramble to simulate real data
totalNiche$species <- sort(rep(paste("species", 1:6, sep=""),20))

toMerge <- data.frame(species=paste("species", 1:6, sep=""), color=1:6)

totalNiche <- merge(totalNiche, toMerge)

totalNiche <- totalNiche[sample(row.names(totalNiche)),]

#plot the points to give some sense of what it looks like (not run, but works)
#plot(totalNiche[,3]~totalNiche[,2], col=totalNiche$color, pch=20)

#create a road map identifying which points belong to which species
roadMap <- matrix(nrow=6, ncol=120, 0)

row.names(roadMap) <- paste("species", 1:6, sep="")
colnames(roadMap) <- 1:120
roadMap[1,][row.names(totalNiche)[totalNiche$species=="species1"]] <- 1
roadMap[2,][row.names(totalNiche)[totalNiche$species=="species2"]] <- 1
roadMap[3,][row.names(totalNiche)[totalNiche$species=="species3"]] <- 1
roadMap[4,][row.names(totalNiche)[totalNiche$species=="species4"]] <- 1
roadMap[5,][row.names(totalNiche)[totalNiche$species=="species5"]] <- 1
roadMap[6,][row.names(totalNiche)[totalNiche$species=="species6"]] <- 1

roadMap <- as.data.frame(roadMap)

#now run the synthComm null model. exclude 1st and 5th columns since these are species
#names and color, which are not normal inputs
temp <- synthComm(totalNiche[,c(-1,-5)], roadMap)

#plot the points to give some sense of what it looks like (not run, but works)
#plot(temp[,3]~temp[,2], col=temp$species, pch=20)
# }