Takes a resource utilization matrix as input and
returns the average pairwise Pianka's niche overlap index.
Usage
pianka(m = matrix(rpois(80, 1), nrow = 10))
Arguments
m
a matrix of resource utilization values.
Value
Returns the average pairwise niche overlap.
Details
Pianka's niche overlap index is averaged
over each unique species pair. The index is symmetric,
with a normalization term in the denominator for the overlap
between species 1 and 2. Values of Pianka's niche overlap index close to 0.0
reflect usage of exclusive resource categories, whereas values close to 1.0
reflect similar resource utilization spectra.
$$O_{jk} = O_{kj} = \frac{\sum_{n}^{i}p_{ij}p_{jk}}{\sqrt{\sum_{n}^{i}p_{ij}^2\sum_{n}^{i}p_{ik}^2}}$$
References
Pianka, E. 1973. The structure of lizard communities.
Annual Review of Ecology and Systematics 4:53-74.
Winemiller, K.O. and E.R. Pianka. 1990. Organization in natural assemblages
of desert lizards and tropical fishes. Ecological Monographs 60: 27-55.