Thermal Ecology of the Desert Dragon Amphibolurus inermis

Amphibolurus inermis occurs throughout Australia except for the eastern third of the continent, the north—central coast, and the southwestern tip. It inhabits sandy soils. Body temperature rises in the morning, levels off and remains rather constant between 1000 and 1600 hr, and falls after 1600 hr. Thermoregulation involves changes in location and posture, color change, basking, burrowing, shade—seeking, and panting. The level of temperature maintained depends on geographic locality and immediate weather conditions and may depart widely from the temperature preferred in a laboratory gradient. The relative importance of specific behavioral responses varies with locality; burrowing and shade—seeking may be interchangeable. Amphibolurus inermis functions either as a thigmotherm or a heliotherm depending on local conditions and time of day. It is one of the most heat—resistant species known; the mean body temperature which causes loss of coordination is 48.5° C, and the lethal temperature is 49.3° C. Because of the extreme environments it occupies, A. inermis has narrow minimum thermal safety margins even though it has high temperature tolerances. Burrows tend to be located near thermoregulatory perches. When the sun—perch and the shade—perch are close together, an individual may have only one burrow; if the perches are further apart, a burrow will usually be located near each. If widely separated, auxiliary burrows may occur between the two types of perches. Burrows sometimes become too hot to serve in thermoregulation. Active individuals are found at all hours between sunrise and sunset in summer. However, individuals may seek shelter at midday. In winter the activity period is restricted to a few hours at midday. It is suggested that preferred temperatures may shift during the day, but that these levels cannot always be maintained. Head temperatures may be regulated more precisely than those of the body.