Night-time warming and prey availability interact to influence physiology in prairie lizards (Sceloporus consobrinus)

Among ectotherms, temperature and food availability are drivers of individual and population characteristics. Increasing night-time temperatures due to climate change can increase energetic demands, potentially amplified or mitigated by prey consumption. Few studies examine night-time temperatures specifically, and consequences of co-occurring changes in the abiotic and biotic environment. Thus, we examined interactions between warming night-time temperatures and prey availability (as a proxy of foraging time and effectiveness), and how they affect food consumption, digestive passage time, metabolizable energy intake (MEI), assimilated energy, and fecal and urate production in a model organism, prairie lizards (Sceloporus consobrinus). Three temperature treatments (current conditions, +2°C night-time increase and +4°C night-time increase) and three levels of prey availability (low, moderate and high) were used to examine multiple scenarios. Prey and warming interacted in non-linear and unpredictable ways to influence food consumption, passage time and MEI. For example, lizards consumed the most food under 2°C warming yet excreted a high proportion of energy resulting in low MEI in comparison to current temperatures. The combined effects of prey availability and night-time warming will be missed by studies only considering single treatment effects. Moreover, physiological processes can have different thermal sensitivities to night-time temperatures, which can vary in unpredictable ways with combined biotic changes. Complex interactions between thermal sensitivities and multiple concurrent environmental changes may be common among ectotherms, complicating our understanding of responses to a shifting climate.