Assembly rules for Greater Antillean Anolis lizards : Competition and random models compared.

Abstract

Using previously published data, several models were constructed to predict the distribution of Anolis lizard species on a set of sites on Puerto Rico and Jamaica. The models form a series with increasing ecological detail. The simpler "null" models are based on randomly created species-site matrices using progressively greater dependency on the observed matrix. The remaining models hypothesize that competition is the most important biotic interaction determining the intra-island distribution of the lizards. "Simple" competition models test the predictive power of simple statistical descriptions relating intensity of competition and ecological variables such as niche overlap and body size ratios. More complicated models are based on the ecomorph model of Williams (1972) and use the lizard resourceuse data of several niche dimensions (e.g., perch diameter and height). These models are derived from Puerto Rican data and tested against Jamaican data. The primary statistical tool used to test the accuracy of these models in the kappa statistic (Fleiss 1973) which assesses the degree of agreement in a contingency table relative to that expected by chance. The model structure is based on generative grammars (Haefner 1981), but is also related to artificial intelligence expert systems. Model comparisons indicate the following. (1) Only those null models constrained by the marginals of the observed species-site matrix agree with observed data. (2) Simple competition models based on fixed size ratios and/or fixed levels of allowable overlap do not agree well. (3) A complex competition model developed for Puerto Rico also shows significant agreement with lizard distributions on Jamaica, but is not better than a constrained null model. (4) If allowance is made for the restricted distribution of A. sagrei, a recent colonist of Jamaica, agreement of the competition model increases dramatically. It is predicted that A. sagrei would persist following an experimental transplant to eastern Jamaica.