RA2 Niche Overlap Randomization Algorithm


ra2(speciesData = matrix(rpois(80, 1), nrow = 10))


a resource utilization matrix (rows = species, columns = discrete resource states) filled with non-negative real numbers.


Returns a random utilization matrix with the same dimensions as the input matrix.


Randomizes a numeric utilization matrix speciesData by replacing all non-zero elements with a random uniform [0,1] value.


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 retains the number and position of zero states in the original matrix. However, all non-zero values are again replaced by a random [0,1] value, which tends to inflate niche breadths of the simulated assemblage. Although the results are not as severe as for RA1, this algorithm is still prone to Type I errors, and is not recommended for niche overlap analysis.


Kobayashi, S. 1991. Interspecific relations in forest floor coleopteran assemblages: niche overlap and guild structure. Researches in Population Ecology 33: 345-360.

Winemiller, K.O. and E.R. Pianka. 1990. Organization in natural assemblages of desert lizards and tropical fishes. Ecological Monographs 60: 27-55.


ranUtil <- ra2(speciesData=matrix(rpois(40,0.5),nrow=8))