An Estimator of Species Overlap Using a Modified Beta-Binomial Model

A new species overlap measure is defined as the probability that, given a randomly selected species is present in at least one of the two communities, it is present in both communities. This measure can be thought of as a community analog of the Jaccard index for species overlap between two samples. Standard maximum likelihood methods are used to estimate the parameters of a modified beta-binomial' distribution. This leads directly to estimates of the community overlap measure. In an example from decapod communities on coral reefs, it is shown that this new estimate of community species overlap is 50% larger than the commonly used Jaccard measure of species overlap.