Ornate tree lizards (Urosaurus ornatus) thermoregulate less accurately in habitats of high thermal quality.

Abstract

Temperature plays a critical role for ectotherm performance and thus for fitness. Ectotherms, since unable to regulate their body temperature internally, use behavioural thermoregulation to maintain their body temperature within a range that maximizes performance. According to the cost-benefit model of thermoregulation, investment into thermoregulation is dictated by the trade-off between the costs and benefits of thermoregulating. The thermal quality of the environment is a major cost of thermoregulation because it directly affects the amount of time and energy that must be invested by an individual to achieve and maintain an optimal body temperature. Thus, in habitats of poor thermal quality, lizards should thermoregulate less. Using Urosaurus ornatus living at 10 sites each straddling two adjacent habitats (wash and upland), we tested the hypothesis that investment in thermoregulation is dependent on the thermal quality of the habitat. We found that the wash habitat had higher thermal quality indicated by a longer duration when optimal body temperatures could be reached. Lizards had more accurate body temperatures in the upland despite its poorer thermal quality. These results suggest that discrepancies in thermal quality between adjacent habitats affect investment in thermoregulation by lizards, but in a direction opposite to the main prediction of the cost-benefit model of thermoregulation.