The Ecology of Moloch horridus (Lacertilia: Agamidae) in Western Australia

Abstract

Observations on the ecology of the Australian agamid, Moloch horridus, are described, and the literature on the species is reviewed. Its geographic distribution, which embraces most of the desert interior of Australia, corresponds closely to the distribution of sandy soils. With respect to food, Moloch is among the most specialized of lizards, since analysis of the stomach contents of 103 specimens revealed almost nothing but very small ants (Iridomyrmex). Moloch has a bimodal seasonal pattern of activity, with reduced activity in mid-winter and mid-summer. Evidence is presented for a spring breeding season, during which time individuals travel over great distances, probably increasing their chances of making mating contacts. At least some ovarian eggs become enlarged and yolked in autumn, but, since there is no evidence for autumnal oviducal eggs or egg laying, either sperm storage or arrested embryonic development may occur during the winter. Egg deposition occurs in the spring or early summer. Clutch size varies from three to ten, with a mode of eight. Females reach nearly twice the body weight of males. Natural longevity is often at least six years. Predators on the species include aborigines, bustards, and probably raptors and snakes. The ecology of Moloch is compared with that of its North American ecological analogue Phrynosoma platyrhinos. Although these two ant specialists are morphologically similar, there are a number of striking differences in their ecologies, which can be explained, in part, by the differences between the Australian and the American desert environments.