Comparative ecology of sympatric Gonatodes (Squamata : Gekkonidae) in the western Amazon of Brazil

Two sphaerodactyline geckos, Gonatodes hasemani and G. humeralis were studi ed in eastern Rondonia, Brazil, to determine ecological factors allowing co existence. Gonatodes hasemani lives primarily on fallen logs in undisturbed forest, whereas G. humeralis lives primarily on tree trunks. Although both species occur in most forest patches, G. hasemani is more common within te rra firme (never flooded) forest, and G. humeralis is more common in forest adjacent to rivers. Gonatodes hasemani is slightly larger in body size and is more robust than the more arboreal G, humeralis. Both species are activ e at the same time during the day, maintain the same body temperatures, and are most frequently found in shade. Dietary overlaps based on numbers (0.8 31) and volumes (0.877) of prey types were high indicating relatively simil ar diets. Differences in prey types appear to reflect differences in microh abitat use, and both species eat prey of the same size. Reproductive charac teristics are similar but the larger bodied G. hasemani produces slightly l arger eggs. The niche axis on which these two lizards most clearly separate is microhabitat: G. hasemani uses lower perches with larger diameters in t he forest primarily because individuals typically are found on fallen logs, whereas G. humeralis uses big-her and thinner perches because individuals are typically found on tree trunks and vines. Limited data on snakes that p rey on small lizards in Amazon forest suggests the possibility that niche d ifferences between these Gonatodes species may be mediated by predators.