prabclus (version 1.0-2)

prabtest: Parametric bootstrap test for clustering in presence-absence matrices

Description

Parametric bootstrap test of a null model of i.i.d., but spatially autocorrelated species against clustering of the species' occupied areas (or alternatively nestedness). In spite of the lots of parameters, a standard execution will be prabmatrix <- prabinit(file="path/prabmatrixfile", neighborhood="path/neighborhoodfile") test <- prabtest(prabmatrix) summary(test) Note: Data formats are described on the prabinit help page. You may also consider the example datasets kykladspecreg.dat and nb.dat. Take care of the parameter rows.are.species of prabinit.

Usage

prabtest(x, teststat = "distratio", tuning=switch(teststat,distratio=0.25,
lcomponent=floor(3*ncol(x$distmat)/4),
isovertice=ncol(x$distmat),nn=4,NA), times = 1000, pd = NULL,
prange = c(0, 1), nperp = 4, step = 0.1, twostep = TRUE, sf.sim = FALSE,
sf.const = sf.sim, pdfnb=FALSE)

Arguments

x

an object of class prab (presence-absence data), as generated by prabinit.

teststat

string, indicating the test statistics. "isovertice": number of isolated vertices in the graph of tuning smallest distances between species. "lcomponent": size of largest connectivity component in thi

tuning

integer or (if teststat="distratio") numerical between 0 and 1. Tuning constant for test statistics, see teststat.

times

integer. Number of simulation runs.

pd

numerical between 0 and 1. The probability that a new region is drawn from the non-neighborhood of the previous regions belonging to a species under generation. If NA (the default), prabtest estimates this by function

prange

numerical range vector, lower value not smaller than 0, larger value not larger than 1. Range where pd is to be found. Used by function autoconst.

nperp

integer. Number of simulations per pd-value. Used by function autoconst.

step

numerical between 0 and 1. Interval length between subsequent choices of pd for the first simulation. Used by function autoconst.

twostep

logical. If TRUE, a first estimation step for pd is carried out in the whole prange, and then the final estimation is determined between the preliminary estimator -5*step2 and {+5*step2}.

sf.sim

logical. Indicates if the range sizes of the species are held fixed in the test simulation (TRUE) or generated from their empirical distribution in x (FALSE). See function randpop.nb.

sf.const

logical. Same as sf.sim, but for estimation of pd by autoconst.

pdfnb

logical. If TRUE, the probabilities of the regions are modified according to the number of neighboring regions in randpop.nb, see Hennig and Hausdorf (2002), p. 5. This is usually no improvement.

Value

• An object of class prabtest, which is a list with components
• results
  vector of test statistic values for all simulated populations.
• datac
  test statistic value for the original data.'
• p.value
  the p-value.
• tuning
  see above.
• pd
  see above.
• reg
  regression coefficients from autoconst.
• teststat
  see above.
• distance
  the distance measure chosen, see prabinit.
• times
  see above.
• pdfnb
  see above.

Details

From the original data, the distribution of the range sizes of the species, the autocorrelation parameter pd (estimated by autoconst) and the distribution on the regions induced by the relative species numbers are taken. With these parameters, times populations according to the null model implemented in randpop.nb are generated and the test statistic is evaluated. The resulting p-value is number of simulated statistic values more extreme than than the value of the original data+1 divided by times+1. "More extreme" means smaller for "lcomponent", "distratio", "nn", larger for "inclusions", and twice the smaller number between the original statistic value and the "border", i.e., a two-sided test for "isovertice". If pd=NA was specified, a diagnostic plot for the estimation of pd is plotted by autoconst. For details see Hennig and Hausdorf (2002) and the help pages of the cited functions.

References

Hennig, C. and Hausdorf, B. (2002) Distance-based parametric bootstrap tests for clustering of species ranges, submitted, http://stat.ethz.ch/Research-Reports/110.html.

Hausdorf, B. and Hennig, C. (2003) Biotic Element Analysis in Biogeography. To appear in Systematic Biology.

Hausdorf, B. and Hennig, C. (2003) Nestedness of nerth-west European land snail ranges as a consequence of differential immigration from Pleistocene glacial refuges. Oecologia 135, 102-109.

See Also

prabinit generates objects of class prab. autoconst estimates pd from such objects. randpop.nb generates populations from the null model. An alternative model is given by cluspop.nb.

Some more information on the test statistics is given in homogen.test, lcomponent, distratio, nn, incmatrix.

The simulations are computed by pop.sim.

Summary and print methods: summary.prabtest.

Examples

data(kykladspecreg)
# Note: If you do not use the installed package, replace this by
# kykladspecreg <- read.table("(path/)kykladspecreg.dat")
data(nb)
# Note: If you do not use the installed package, replace this by
# nb <- list()
# for (i in 1:34)
#   nb <- c(nb,list(scan(file="(path/)nb.dat",
#                   skip=i-1,nlines=1)))
set.seed(1234)
x <- prabinit(prabmatrix=kykladspecreg, neighborhood=nb)
# If you want to use your own ASCII data files, use
# x <- prabinit(file="path/prabmatrixfile",
# neighborhood="path/neighborhoodfile")
prabtest(x, times=100, pd=0.35)
# These settings are chosen to make the example execution
# a bit faster; usually you will use prabtest(kprab).