Estimating and Interpreting Body-Size Growth in Some Anolis Lizards

Abstract

This paper derives several models to describe growth in body size and applies those models to data from Bahamian Anolis lizards. Nonlinear regression equations that give size at the end of a time interval as a function of size at the beginning of that interval and its duration show that a logistic-by-weight model fits data far better than the Von Bertalanffy Model or a logistic-by-length model. Application of this model to 25 data sets comprising 4 species from 7 sites on Bimini and Abaco shows: 1) Males and females have the same characteristic growth rate (r), but their usually very different asymptotic sizes cause males to grow absolutely faster than similarly sized females. 2) Significant differences in growth rates exist between Abaco A. sagrei populations only a few hundred meters apart. Growth rates are directly correlated with population density in these populations as well as in nearly all comparisons of Bimini species. We speculate that food density is higher in areas of more rapid growth and that lizards do not, and should not, diffuse sufficiently to such places to compensate exactly for that greater density. 3) Male A. distichus, and to a lesser extent female A. carolinensis and both sexes of A. angusticeps, all arboreal species, grow more rapidly than the trunk-ground A. sagrei. Unlike A. sagrei, they also grow more rapidly than several common West Indian species, suggesting less food pressure upon these relatively low-density species. 4) Male A. sagrei on a one-species island (Abaco) grow more rapidly than on a 4-species island (Bimini); females show no difference. We speculate this is because females but not males have a relatively exclusive structural habitat on Bimini.