A heterogeneidade ambiental das savanas amazônicas determina a distribuição local de lagartos cnemidophorus cryptus (SQUAMATA: TEIIDAE)

Abstract

The spatial distribution of organisms may be directly and indirectly affected by multiple environmental gradients. Environmental heterogeneity often causes variation in local habitat quality and levels of competition, which may lead to environmental filtering changing population density over a species geographic range. In this study we test the generalized hypothesis that savannas in Amazonia may contain enough environmental heterogeneity that lizard density estimates are not homogeneous across space. In a protected area we sampled 26 plots, each of which covering 1500 m2 (250m long, 6 m wide), to test the influence of air temperature, altitude, number of termite mounds, shrub cover, canopy openness, competitor density, and interactions between some of these gradients on Cnemidophorus cryptus (Squamata, Teiidae) density. We found positive effects of number of termite mounds and shrub cover on C. cryptus densities. These findings suggest that high availability of refuge sites from the high temperatures (up to 40 ºC) experienced by midday savannas favor high densities. Additionally, we found negative effects of altitude and temperature on the estimated densities, which suggests environmental filtering at thermally unsuitable sites. However, an interaction plot showed that altitude effects on C. cryptus density are only significant under mild temperatures. Overall, our findings suggest that C. cryptus does not homogeneously occupy available habitats, but environmental filtering may emerge from lack of shelter and inefficient thermoregulation toward body heat loss at relatively low altitudes (< 104 m), and heat gain at relatively high temperatures (> 104 m). We discuss our findings from ecological and biodiversity conservation perspectives