The Diversity and Abundance of Lizards in Arid Australia: A New Hypothesis

Abstract

The vertebrate fauna of arid Australia is characterized by an extraordinarily rich assemblage of lizards, an ecological phenomenon first recognized and described by Pianka (1969a,b, 1972, 1973, 1981, 1982, 1986; Pianka and Pianka 1976). The extent of Australian lizard radiation remains a challenge to ecologists, because Pianka's (1975, 1986) careful comparisons of Australia, southern Africa, and North America demonstrate that individual arid ecosystems have disparate assemblages despite their superficially similar environments. Pianka recently concluded that the differences in ecologies of most lizard species among these three continental desert-lizard systems are much more striking than are similarities (1986, p. 23). Why are there so many species of lizards in local assemblages in arid Australia? Naturally, Pianka has devoted considerable thought to potential explanations, as have other workers (see, e.g., Milewski 1981a; Cogger 1984). We believe that proposed explanations are not completely convincing; in addition, recent research suggests that some aspects of Australian radiation are still not widely recognized. In this paper, we review published hypotheses for high local species diversity among lizards in Australia and then examine emerging concepts about edaphic, climatic, and biological characteristics of inland Australia that may assist in search for a more complete explanation. Finally, we advance a set of predictions that allows key segments of our hypothesis to be tested. Our principal interest lies in diversity of lizards that may be found at one site. We consider beta diversity only briefly, because we believe that Pianka (1972) has provided an adequate historical explanation.