Sympatry of Desert Lizards (Ctenotus) in Western Australia

Abstract

Seven species of congeneric lizards (Ctenotus) frequently occur in ecologic sympatry in the Australian desert. The ecologies of these and seven other species are described and compared, with particular reference to niche differences. Adult Ctenotus range from 45 to 118 mm in snout—vent length. Larger species take larger prey items than smaller ones. Six species do most of their foraging in the open spaces between plants, while six others forage mostly within the dense tussocks of porcupine grass (Triodea). The former have proportionately longer hindlegs than the latter. It is demonstrated that hindleg and head proportions are good morphological indicators of the place niche and the food niche, respectively, and that body temperature reflects the time niche in a useful way. Lizards with higher body temperatures are usually active later in the day than those with lower body temperatures. Whereas the species which forage in the open show a poor correlation between air temperature and body temperature, those that forage in shady places within vegetation have body temperatures closely correlated with ambient air temperatures. The former are dependent upon direct solar and/or substrate heat, while the latter appear not to substantially exploit these heat sources. After analyzing the ways in which the lizards subdivide habitat space and environmental resources, it is concluded that there are at least three dimensions to the Ctenotus niche: place, food, and time. An analysis is presented which demonstrates that Ctenotus are ecologically rather tightly "packed," and it is suggested that the overall differences between pairs may represent minimal ecologic distances.