EcoSimR (version 0.1.0)

v_ratio: SchlutersVRatio Co-occurrence Metric

Description

Takes a binary presence-absence matrix or a matrix of abundances and returns Schluter's (1984) variance ratio.

Usage

v_ratio(m = matrix(rbinom(100, 1, 0.5), nrow = 10))

Arguments

m

a binary presence-absence matrix in which rows are species and columns are sites. The entries may be either abundances or occurrences of indivdual species.

Value

Returns the variance ratio of the matrix.

Details

The variance ratio is the ratio of the variance in species number among sites to the sum of the variance of the species occurrences. If the average covariation in abundance (or occurrence) of each species pair is close to zero, the expected value for this ratio is approximately 1.0. V-ratios larger than 1.0 imply positive average covariation in the abundance of species pairs, whereas V-ratios significantly smaller than 1.0 imply negative average covariation.

References

Schluter, D. 1984. A variance test for detecting species associations, with some example applications. Ecology 65: 998-1005.

McCulloch, C.E. 1985. Variance tests for species association. Ecology 66: 1676-1681.

Examples

varCScore <- v_ratio(m=matrix(rbinom(100,1,0.5),nrow=10))