A nonparametric estimator of species overlap

For two communities, species overlap has been defined by Smith, Solow, and Preston (1996, Biometrics 52, 1472-1477) as the probability that a randomly selected species is present in both communities given that it is present i n at least one community. Species overlap can thus be used to describe the similarity of two communities. In contrast with the parametric estimator of Smith et al., we propose a nonparametric maximum likelihood estimator (NPM LE). We prove that the NPMLE is consistent and asymptotically normally dist ributed and show that computation of the NPMLE and its standard error is st raightforward. We also compare the NPMLE and the estimator of Smith et al. for a variety of situations.