The role of thermal biology in the co-occurrence of two endemic Liolaemus lizards from the temperate Pampas

Partitioning of thermal resources promotes coexistence among closely related lizard species, even with apparent niche overlap. Different thermoregulatory strategies, microhabitat use, and thermal physiology are frequently observed in syntopic lizard species, facilitating the partition of resources. This study investigated the thermal biology of Liolaemus absconditus and Liolaemus tandiliensis, two syntopic lizard species inhabiting the Tandilia Mountain Range. We examined the influence of intrinsic traits and environmental variables on thermoregulatory strategy, thermal parameters, and locomotor performance. Despite experiencing suboptimal thermal conditions during summer, both species were moderate thermoregulators. Both species exhibited significant overlap in body condition, microhabitat use, and thermoregulatory traits (field body temperature and thermal preference). However, they presented subtle differences in thermoregulatory strategy, thermal tolerance, and thermal performance. Liolaemus absconditus relied heavily on thigmothermy and exhibited a higher tolerance for maximum critical temperature but a narrower optimal temperature range for locomotion than the opportunistic L. tandiliensis, which alternated between thigmothermy and heliothermy. These subtle interspecific physiological differences may reduce competition for thermal resources of these Liolaemus lizards. However, L. tandiliensis likely has an advantage over L. absconditus under suboptimal thermal conditions. The predominance of L. tandiliensis over L. absconditus in the study site highlights the need for further investigation into other ecological factors and physiological traits drive their coexistence.