ra4(speciesData = matrix(rpois(80, 1), nrow = 10))
Randomizes a numeric utilization matrix speciesData by reshuffling the non-zero elements within each row.
The resource utilization matrix (rows = species, columns = discrete resource categories) may include zeroes, but no negative numbers or missing values. Relative resource within a species is first calculated, so the rows need not sum to 1.0.
This algorithm is similar to RA3, but adds the additional constraint of retaining the positions of all of the zero elements of the matrix, and reshuffling only the non-zero elements of the matrix within each row. It is more conservative than RA3, but has a low Type I error rate, and, along with RA3, is recommended for null model analysis of niche overlap.
Winemiller, K.O. and E.R. Pianka. 1990. Organization in natural assemblages of desert lizards and tropical fishes. Ecological Monographs 60: 27-55.
ranUtil <- ra4(speciesData=matrix(rpois(40,0.5),nrow=8))Warning message: number of items to replace is not a multiple of replacement length