Even though physiological and behavioral processes are maximized within relatively narrow ranges of temperatures in amphibians and reptiles, individuals may not maintain activity at the optimum temperatures for performance because of the costs associated with doing so. Alternatively, activity can occur at suboptimal temperatures even when the costs are great. Theoretically, costs of activity at suboptimal temperatures must be balanced by gains of being active. For instance, the leatherback sea turtle will hunt during the time of day in which krill are abundant, even though the water is cooler and thus the turtle`s body temperature requires greater metabolic activity. In general, however, the cost of keeping a suboptimal body temperature, for reptiles and amphibians, is varied and not well understood; they include risk of predation, reduced performance, and reduced foraging success.
One reptile that scientists understand better is the desert lizard, which is active during the morning at relatively low body temperatures (usually 33.0 C), inactive during midday when external temperatures are extreme, and active in the evening at body temperatures of 37.0 C. Although the lizards engage in similar behavior (e.g., in morning and afternoon, social displays, movements, and feeding), metabolic rates and water loss are great and sprint speed is lower in the evening when body temperatures are high. Thus, the highest metabolic and performance costs of activity occur in the evening when lizards have high body temperatures. However, males that are active late in the day apparently have a higher mating success resulting from their prolonged social encounters. The costs of activity at temperatures beyond those optimal for performance are offset by the advantages gained by maximizing social interactions that ultimately impact individual fitness.