Abstract

Microhabitat selection is critical to thermoregulation in ectotherms, particularly in small-bodied organisms for which low thermal inertia can impose rapid acquisition of thermal equilibrium with the environment. Although thermal microhabitat selection is often included in studies of niche partitioning among lizard species these investigations typically address only adult thermoregulation and, therefore, potentially neglect age classes in which thermal microhabitat selection could be especially consequential. We measured thermal time constants for juveniles of the lizard Anolis carolinensis and compared thermal microhabitat selection of this species with that of an invasive co-occurring congener, Anolis sagrei. In keeping with the exceptionally low mass of these lizards, heating and cooling rates were found to be extremely high and more similar to those of some insects than to other terrestrial vertebrates. On laboratory thermal gradients juvenile A. carolinensis tended to select warmer temperatures than A. sagrei, a pattern that is opposite to that observed for adults of these species. Because the rate of core temperature change was found to be an order of magnitude higher in juveniles than in adults and because the interspecific pattern of temperature selection is categorically different, these results suggest that investigation of juvenile anole thermoregulation could be of particular importance in developing an accurate characterization of resource partitioning among these model species.