Thermoregulatory Behavior of the North American Lizards Cnemidophorus velox and Sceloporus undulatus

Abstract The patterns of thermoregulation of Cnemidophorus velox and Sceloporus undulatus were compared and related to their foraging modes. In nature, C. velox are widely foraging lizards and most individuals actively shuttled in the temperature enclosures to regulate Tb. Sceloporus undulatus are wait-and-ambush predators and were relatively inactive in the enclosures. The terms active and inactive thermoregulation were used to describe these categories of behavior. There were no intraspecific differences between active/ inactive individuals, either in choice of Tb or precision of regulation of Tb. Cnemidofihorus velox (Tb = 37.2 C) was more thermophilic than S. ursdulatus (Tb = 35.9 C), however, the other thermoregulatory attributes of the species were similar. Both species regulated Tb with equal precision and the between individual variability in Tb was essentially the same for the two species. The wave characteristics of the thermoregulation curves were similar in amplitude (a measure of precision), however, there were interspecific differences in period of the curve. Cnemidophorus velox shuttled more frequently in order to achieve the same precision as S. undulatus. Thermoregulation in two different temperature enclosures was compared, one a sun/shade enclosure, and the other an IR thermal gradient. Both species thermoregulated similarly in the two enclosures. Thus both species used the complex thermal environments with equal facility and no gradient specific characteristics were observed.