INFLUENCE OF BEHAVIORAL THERMOREGULATION ON MICROHABITAT USE BY 2 SCELOPORUS LIZARDS

Sceloporus occidentalis and S. graciosus were studied along a 1300 m elevational gradient in the San Gabriel Mountains, S California. These species occupy different, but overlapping, elevational ranges, with S. graciosus occurring at higher elevations. Because their ranges differ, the species experience different thermal environments, but they are nearly identical in several measures of thermal physiology. Body temperatures of active lizards varied little with altitude, although air temperatures decrease substantially over this range. Both species compensated behaviorally for variation in thermal environments by varying basking frequency and microhabitat use. By thermoregulating, lizards maintained body temperatures that favor high levels of locomotor performance and other physiological functions. S. occidentalis was almost completely arboreal at low elevation; lizards of both species were partly arboreal, partly terrestrial at intermediate elevation; and S. graciosus was mainly terrestrial at high elevations. Thus, the species converged in microhabitat use where sympatric. These shifts in microhabitat use parallel altitudinal changes in the spatial location of thermally suitable microhabitats and in habitat structure. Behavioral thermoregulation, thus appears to be an important determinant of habitat use in these lizards. -from Author