Run a niche equivalency test (see Warren et al 2008) based on two species occurrence density grids.
ecospat.niche.equivalency.test (z1, z2, rep, alternative, ncores = 1)Species 1 occurrence density grid created by ecospat.grid.clim.
Species 2 occurrence density grid created by ecospat.grid.clim.
The number of replications to perform.
To indicate the type of test to be performed. It could be greater or lower.
The number of cores used for parallelisation.
a list with $obs = observed overlaps, $sim = simulated overlaps, $p.D = p-value of the test on D, $p.I = p-value of the test on I.
Compares the observed niche overlap between z1 and z2 to overlaps between random niches z1.sim and z2.sim, which are built from random reallocations of occurences of z1 and z2.
alternative specifies if you want to test for niche conservatism (alternative = "greater", i.e. the niche overlap is more equivalent/similar than random) or for niche divergence (alternative = "lower", i.e. the niche overlap is less equivalent/similar than random).
If you encounter a problem during your analyses, please first read the FAQ section of "Niche overlap" in http://www.unil.ch/ecospat/home/menuguid/ecospat-resources/tools.html
The arguments ncores allows choosing the number of cores used to parallelize the computation. The default value is 1. On multicore computers, the optimal would be ncores = detectCores() - 1.
Broennimann, O., M.C. Fitzpatrick, P.B. Pearman,B. Petitpierre, L. Pellissier, N.G. Yoccoz, W. Thuiller, M.J. Fortin, C. Randin, N.E. Zimmermann, C.H. Graham and A. Guisan. 2012. Measuring ecological niche overlap from occurrence and spatial environmental data. Global Ecology and Biogeography, 21, 481-497.
Warren, D.L., R.E. Glor and M. Turelli. 2008. Environmental niche equivalency versus conservatism: quantitative approaches to niche evolution. Evolution, 62, 2868-2883.