Comparative thermal ecology of the high-altitude lizard Sceloporus grammicus on the eastern slope of the Iztaccihuatl Volcano, Puebla, Mexico

We studied the thermal ecology of Sceloporus grammicus occurring in very different thermal environments at 3700 and 4400 m elevation on the Iztaccihuatl Volcano, Mexico. Despite differences in the thermal environment between study sites, individual lizards maintained similar active body temperatures (around 31.5 degrees C). Similar body temperatures at the two study sites probably result in differences in the cost of the thermoregulatory behavior. Lizards at the high-altitude site, an open area with few predators or competitors, presumably incur a lower thermoregulatory cost than those at the low-altitude site, which has a considerable number of shaded spots and more predators and competitors. Lizards at the low-elevation site showed a greater resistance to high temperatures than those at the high-elevation site. Physiological, acclimatization to higher environmental temperatures at low elevation is likely to explain the greater heat tolerance. Freezing tolerance, thermoregulatory behavior, and low energy requirements permit S. grammicus to survive at high altitudes.