Comparative field responses to diel and annual thermal regimens among Sceloporine lizards, with specific reference to <i>Sceloporus malachiticus</i>

Abstract

Sceloporus malachiticus is a diurnal iguanid lizard occupying upland and montane areas through much of Mexico and Central America. In Costa Rica, where field observations were made, this species utilizes various habitats between elevations from about 600 to more than 3,000 meters. In response to the diel march of temperature, activity usually demonstrated a unimodal peak in the late morning hours, prior to the onset of cloud caver. Body temperatures generally exceed those of both ambient air and substratum; active animals exhibit a greater differential than inactive ones. Body temperatures range from 8.4 °C to 34.4 °C, of which the voluntary activity range is 22.0 to 34.4 °C (X28.6 °C). No significant differences were found among different size or sex groupings. Basking behavior is common throughout the range of activity in all groups. Neither hibernation nor acclimation is exhibited in montane S. malachiticus.

In comparing these thermal responses with other sceloporines, the most conspicuous feature of this population of S. malachiticus is its low thermal preferendum. Among the collective voluntary activity ranges and preferenda reported for other members of the genus there is an obvious contrast with the results obtained. Further evidence acquired during this study indicates that thermal preferenda among sceloporines are more characteristic of their autecology than their phylogeny.