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Ectotherms are especially susceptible to changing temperature conditions within their environment. To limit temperature fluctuations they must behaviorally regulate body temperature by moving between microhabitats of different ambient temperatures. By actively selecting specific substrate temperatures within a heterogeneous thermal environment, an individual could attain preferred body temperature and approach internal thermal homeostasis for periods of time. Ambient temperature dependence should thus force an individual to select those microhabitats that present optimal thermal conditions. Because dynamic thermal microhabitat structure is difficult to assess, the extent to which lizards employ behavioral thermoregulation is not well understood. Therefore, there is a need to better assess thermal habitat structure and how it relates to behavioral thermoregulation. In this study, thermal imaging was used to evaluate the dynamics in thermal microhabitat structure, lizard body temperature, and substrate preference during the warm season (July and August). Despite a broad range of microhabitat temperatures surrounding lizards (1-2 m2 of surface showed a mean range of 11°C), mean lizard temperature varied within a narrow range (36 to 38°C). A variety of hypotheses exist for why Uta strongly prefer body temperatures of 37°C, such as optimization of physiological processes. Lizards selected sites with temperatures that differed slightly yet significantly from the mean temperature around them, indicating that individuals do exhibit behavioral thermoregulation. Furthermore, lizards make use of radiative heat gain to regulate their body temperature significantly above that of their perch (mean difference of 2.6°C). Regulation differed throughout the day. Lizard body temperature differences from before and after short-and long-distance switches in position accounted for only 15% of the variation in body temperature. These findings show that lizards are able to maintain fairly constant body temperatures for extended periods of time, during the warm season, by combining selection of a thermally favorable microhabitat with radiative regulation. Habitat structural complexity differs across the geographical range of Uta stansburiana, and therefore provides variable opportunity for thermoregulation. Impacts of change in temperature due to climate change may therefore vary based upon population. Our results indicate that, although Uta may go locally extinct due to the effects of climate change, the study population, living as it does in an area of extraordinary thermal heterogeneity, may actually benefit.

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Biology Commons



Faculty Mentor

Susannah S. French

Departmental Honors Advisor

Kimberly Sullivan