custom header test
czekanowski(m = matrix(rpois(80, 1), nrow = 10))
Takes a resource utilization matrix as input and returns the average pairwise Czekanowki niche overlap index.
The Czekanowski niche overlap index is averaged over each unique species pair. The index measures the area of intersection of the resource utilization histograms of each species pair. Values of Czekanowski niche overlap index close to 0.0 reflect usage of exclusive resource categories, whereas values close to 1.0 reflect similar resource utilization spectra.
O_jk = O_kj = 1 - 0.5*sum|p_ij - p_ik|'
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.
Feinsinger, P., E.E. Spears, and R. Poole. 1981. A simple measure of niche breadth. Ecology 62: 27-32.
Winemiller, K.O. and E.R. Pianka. 1990. Organization in natural assemblages of desert lizards and tropical fishes. Ecological Monographs 60: 27-55.
obsOverlap <- czekanowski(m=matrix(rpois(40,0.5),nrow=8))
pianka niche overlap index.