Thermal Ecology in Island Populations of Erhard's Wall Lizard, Podarcis erhardii

Abstract

Global climate change has already impacted the majority of natural ecosystems and is expected to lead to numerous extinctions. The effects will be particularly severe for populations that have been reduced and isolated through habitat fragmentation, an important mechanism of human-caused biodiversity loss. Despite the worldwide occurrence of both processes, we have a poor understanding of how habitat fragmentation (and the associated loss in genetic diversity) renders species increasingly susceptible to climate change. Elucidating this relationship is important if we are to conserve global biodiversity. In this study, we examined thermal ecology and physiology across Cycladic land bridge island populations of Erhard's Wall Lizard (Podarcis erhardii). Populations on land bridge islands have been isolated from the mainland by rising sea levels, a process that is similar to anthropogenic habitat fragmentation. Previous research has shown that P. erhardii populations in the Cyclades show a predictable gradient of genetic diversity according to island size and age, and this species is considered a model ectotherm for studies of thermal ecology. We quantified environmental conditions (Te), field body temperatures (Tb), preferred temperatures (Tpref), critical thermal maxima and minima (CTmax and CTmin) and evaporative water loss (EWL) across five populations that differed in either genetic structure (low vs. high genetic diversity) or site environmental characteristics (elevation and aspect). Our findings suggest that: 1) genetic diversity does not appear to underlie differences in physiology or variability in thermal ecology; and 2) while environmental differences do not affect thermal biology, they do shape the water retention ability of individuals in a population. These results have implications for the management of fragmented species under shifting climate conditions.