Population Densities and Structural Habitats in Lowland Populations of Anolis Lizards on Grenada

Abstract

In June 2002, we examined populations of Grenadian anoles at four ecologically different sites to: (1) test the general applicability of previously published hypotheses that Anolis richardii is more abundant in densely shaded areas and that adult male A. richardii perch higher than smaller conspecifics and all age classes of A. aeneus, and (2) evaluate the structural niche breadths of both species and the degree of similarity (e.g., structural niche overlaps) between them in different habitats. Estimated population densities for A. richardii and A. aeneus, respectively, were 830 and > 5,600/ha in mangrove forest, 2,170 and about 5,000/ha in dry scrub, > 5,000 and > 9,200/ha in dry woodland, and about 12,500 and > 2000/ha in streamside forest, generally supporting the contention that A. richardii is more abundant in densely shaded areas. For the most part, larger individuals of both species in all habitats perched higher than smaller individuals. Perch heights of A. aeneus in streamside forest were significantly higher than those used elsewhere, presumably reflecting an effort to exploit higher, more fully insolated, and warmer perches. Anolis richardii perched significantly higher than A. aeneus in dry scrub, whereas A. aeneus perched higher in streamside forest. Our data did not support the assumption that adult male A. richardii consistently perch higher than A. aeneus. Perch diameters of both species generally indicated a preference for larger trunks and were smallest in the dry scrub, where these were least abundant. Niche breadths based on both perch heights and diameters were generally indicative of habitat generalists, and niche overlaps approached values indicating syntopy in dry scrub and dry woodlands. These data reaffirm the impression that, with the exception of A. richardii pre- ferring or better tolerating cooler, shaded conditions, structural habitat utilization by both Grenadian species essentially reflects the locally available suite of perch heights and diameters.