Microhabitat Use and Thermal Ecology of Two Narrowly Sympatric Sceloporus (Phrynosomatidae) Lizards

Abstract

I studied the microhabitat use of two narrowly sympatric Sceloporus lizards, Sceloporus occidentalis and S. undulatus, to evaluate the relationship between microhabitat features and microen- vironmental temperature, and to determine if interspecific differences in microhabitat use could be related to differences in thermoregulation. Sceloporus undulatus were found on, or near, taller rocks and in rockier microhabitats than were S. occidentalis. Sceloporus occidentalis were found closer to trees and shrubs, and in microhabitats with larger trees and shrubs than those of S. undulatus. Principal components analysis indicated that the major source of variation in lizard microhabitats reflected these interspecific differences. Sceloporus occidentalis moved closer to trees or shrubs, and were found near large trees and shrubs at higher ambient temperatures. Variation in these microhabitat features had a significant effect on the environmental temperatures experienced by S. occidentalis. Sceloporus undulatus did not appear to ther- moregulate by selecting variable features of the structural microhabitat, but thermoregulated on a finer scale by moving between the exposed and shaded portions of large rocks. Interspecific differences in thermoregulatory behavior exhibited a profound influence on interspecific microhabitat differences.