Ecology of the Agamid Lizard Amphibolurus isolepis in Western Australia

The geographic distribution of Amphibolurus isolepis covers much of the desert interior of Australia, except for certain rocky areas. A. isolepis gularis usually occurs in desert habitats with a sandy, reddish colored substrate. Ants constitute most of its food, but numerous other arthropods, various plant materials, and an occasional lizard are also taken. Foraging individuals usually sit-and-wait in the open spaces between shrubs where they make short forays after prey items. Actvity is year around; in warm months, daily activity is distinctly bimodal, whereas in colder months the lizards are most active during midday. Cloacal body temperatures average 100 C higher than ambient air temperatures, indicating that these reptiles employ incident radiation and the substrate to maintain their body temperature. Both air and body temperatures recorded for lizards in the shade when first sighted are significantly higher than those recorded for animals in the sun. Body temperatures of active lizards show a decided seasonality, being much lower during winter. Females lay at least two clutches of eggs each season, with late clutches averaging nearly one egg larger than early clutches. Eggs are laid from September through early February. Clutch size is correlated with female body size. Hatchlings grow rapidly, reaching adult size and breeding in their first spring at an age of from six to nine months. There may be an annual turnover of adults, but this is still uncertain. Potential predators and competitors are described and briefly discussed. Certain ecological similarities and differences between A. isolepis and Uta stansburiana and Callisaurus draconoides are indicated, and it is suggested that the the former two species are both relatively r selected.