Ecophysiology and vulnerability to warming of Whorl-tail Iguanas (Tropidurinae: Stenocercus) from the Tropical Andes of Ecuador

Introduction: Environmental changes can significantly affect the performance of ectotherms, as nearly all aspects of their life history are intricately linked to temperature conditions in their habitats. One approach to quantify ectothermic physiological performance is to assess traits that define their thermal tolerance. Research integrating thermophysiological traits of terrestrial ectotherms with environmental data has shown that tropical ectothermic species face a higher risk of extinction compared to their temperate counterparts because they live near their physiological thermal optimum and exhibit limited plasticity to adapt to changing conditions. Methods: In this study we measured the preferred body temperature (T_pref), critical thermal minimum (CT_min), and critical thermal maximum (CT_max) of seven Stenocercus populations inhabiting high-altitude tropical ecosystems in the Ecuadorian Andes, between 2093 and 4046 m asl. Field-based experiments were conducted on adult lizards to determine these thermophysiological traits. We combined these data with environmental records and operative temperature models (OTMs) to characterise the thermal conditions of each population's microhabitat and to evaluate vulnerabilty under current and future warming scenarios. Results: Our findings support the hypothesis that habitats with greater daily temperature variability and structurally complex vegetation allow lizards to exhibit broader thermal tolerance ranges and higher tolerance to warming. For instance, Stenocercus lizards from paramo ecosystems are unlikely to be physiologically constrained by projected temperature increases. In contrast, warming is likely to restrict the activity of Inter-Andean lizards because their microhabitats already reach temperatures close to their physiological optimum. Discussion: These results highlight the importance of access to suitable thermal microhabitats and the role of behavioural strategies in reducing the risk of overheating.