Evaluating temperature regulation by field-active ectotherms: the fallacy of the inappropriate question

We describe a research protocol for evaluating temperature regulation from data on small field-active ectothermic animals, especially lizards. The protocol requires data on body temperatures (Tb) of field-active ectotherms, on available operative temperatures (Te, "null temperatures" for nonregulating animals), and on the thermoregulatory set-point range (preferred body temperatures, Tset). These data are used to estimate several quantitative indexes that collectively summarize temperature regulation: the "precision" of body temperature (variance in Tb, or an equivalent metric), the "accuracy" of body temperature relative to the set-point range (the average difference between Tb and Tset), and the "effectiveness" of thermoregulation (the extent to which body temperatures are closer on the average to the set-point range than are operative temperatures). If additional data on the thermal dependence of performance are available, the impact of thermoregulation on performance (the extent to which performance is enhanced relative to that of nonregulating animals) can also be estimated. A sample analysis of the thermal biology of three Anolis lizards in Puerto Rico demonstrates the utility of the new protocol and its superiority to previous methods of evaluating temperature regulation. We also discuss several ways in which the research protocol can be extended and applied to other organisms.