THERMOREGULATION AND ECCRITIC BODY TEMPERATURES IN MEXICAN LIZARDS OF THE GENUS SCELOPORUS

Resumen

Ten species and subspecies of the iguanid genus Sceloporus were studied under field conditions in the United States, Mexico, and Honduras, between the latitudes of 14° and 33° in North America, and at elevations varying from 60 meters to 2200 meters. Means for the normal activity ranges, or eccritic body temperatures, of the ten varied from only 32.9° C. for a cloud forest species in Honduras, to 36.9° for a species in the tropical lowlands of San Luis Potosí. When abroad and active the majority of these heliothermic lizards maintain the body temperature within extremes scarcely more than 4° C. above or below a mean that approximates 34° to 35° C. Although there are slight differences between species, the lizards of the genus evidently maintain body temperatures within a zone of preference ranging from 29.6° to 40.0° C. Eccritic body temperatures are not closely correlated with those of the air or substratum, nor with altitude or latitude. The maintenance of relatively constant body temperatures is primarily a reflection of the lizard's ability to regulate the absorption of solar heat by means of its behavior, although habitat selection, probably coupled with adaptive modifications in the morphology and in the breeding cycle of individual populations, permits each species to maintain a thermal level that is more or less characteristic of its genus.