TRACY, C. R.; CHRISTIAN, K. A.; TRACY, C. R.; Univ. of Nevada, Reno; Charles Darwin Univ., Northern Territory, Australia; Charles Darwin Univ., Northern Territory, Australia: Evaluating thermoregulation in large reptiles: null modeling

Hertz et al. (1993) presented protocols for evaluating thermoregulation in reptiles. Their approach employs comparisons of thermoregulatory performance with null models of the body temperatures achievable in particular environments. Their approach assesses the precision, accuracy, and effectiveness of thermoregulation, and they suggest means to assess the ecological impact of thermoregulation on performance measures for individuals. The approach requires measuring, or calculating, operative temperatures as a means to create null models of achievable body temperatures. However, large reptiles have significant thermal inertia and this means that operative temperatures are really not necessarily achievable body temperatures. The operative temperature is the body temperature that a reptile would achieve, if the real animal had no mass. However, for large reptiles the achievable body temperature is simultaneously a function of the operative temperature, the heat capacitance of the animal, physiological adaptations for controlling heat gain and loss, and the thermal history of the animal. Christian and Weavers attempted to evaluate thermoregulation in large Varanid lizards, but neither they nor anybody else has incorporated the necessary variables to calculate achievable body temperatures for large reptiles in a manner that would allow calculation of null models and application of the Hertz et al. protocols. We have used models to understand the mechanistic relationships among the variables that determine achievable body temperatures in large reptiles, and we show how difficult it is to apply the Hertz et al. protocols for large reptiles.