adehabitatHS (version 0.3.18)

randtest.enfa: Randomisation Test for the Ecological Niche Factor Analysis

Description

randtest.enfa performs a randomisation test for the Ecological Niche Factor analysis (ENFA).

Usage

# S3 method for enfa
randtest(xtest, nrepet = 999, ...)

Value

returns a list of class randtest

Arguments

xtest

an object of class enfa

nrepet

the number of iterations for the randomisation test

...

further arguments to be passed to the generic function randtest

Author

Clement Calenge

Details

This test is carried out by simulating a random distribution of the species occurrences in the pixels of a map.

At each step of the randomisation procedure, the test randomly allocates the nk occurrences (where nk is the sum of the occurrence vector pr of the object of class enfa) in the Ik pixels of the focus area (where Ik is the length of this occurrence vector).

At each step of the procedure, the first eigenvalue of the ENFA performed on the randomised data set is recomputed. This value provides a criterion to test the pertinence of the ENFA analysis.

References

Manly, B.F.J. (1997) Randomization, Bootstrap and Monte Carlo Methods in Biology. London: Chapman & Hall.

Hirzel, A.H., Hausser, J., Chessel, D. and Perrin, N. (2002) Ecological-niche factor analysis: How to compute habitat suitability maps without absence data? Ecology, 83, 2027--2036.

See Also

enfa

Examples

if (FALSE) {
data(chamois)
locs <- chamois$locs
map <- chamois$map

## prepare the data
tab <- slot(map, "data")
tab$Vegetation <- NULL
pr <- slot(count.points(locs, map), "data")[,1]

en <- enfa(dudi.pca(tab, scannf=FALSE), pr, scannf = FALSE)
(tutu <- randtest(en, nrepet = 100))
plot(tutu)

}