Habitat use and activity influence thermoregulation in a tropical lizard, Ameiva exsul

We examined the contributions of alterations in daily activity and behavioral selection of microhabitat to thermoregulation in a population of the lizard, Ameiva exsul (Teiidae), by combining data on lizard activity with data on the availability of sun-shade patches and operative temperatures (T_e). By comparing T_e distributions predicted by “no thermoregulation” and “only thermoregulation” hypotheses to those predicted by random use of thermal habitat, we assessed the relative contributions of microhabitat selection and daily activity to regulation of body temperature (T_b). Over the course of a day lizards maintained T_b very close to optimal temperature (T_sel) despite T_es that deviated substantially from T_sel. Data demonstrating a unimodal daily activity pattern reject the hypothesis of uniform activity throughout the day. Also, lizard activity was not positively correlated with the proportion of T_es within T_sel nor negatively correlated with the absolute deviation of available T_e from T_sel (d_e) (“only thermoregulation”). Microsite use by A. exsul deviated significantly from predictions of the “no thermoregulation” hypothesis, but our data could not reject predictions of the “only thermoregulation” hypothesis that lizards would use sun-shade patches relative to the proportion of microsites where T_e is within T_sel. Also, lizards appeared to actively select sunlit and partially shaded microsites at different times of day. Thus, despite thermal constraints imposed by the habitat, A. exsul maintained high and relatively constant T_bs throughout its daily activity period and thermoregulated effectively. This appears to be generally representative of West Indian species of Ameiva.