THE ECOLOGICAL CONSEQUENCES OF HABITAT AND MICROHABITAT USE IN LIZARDS:: A REVIEW

Abstract

We review the ecological consequences of habitat and microhabitat use in lizards. Different habitats have different biotic and abiotic properties and thus are likely to have different consequences for the lizards that occur in them. Individual performance and life histories are influenced by habitat use, particularly when habitats differ in thermal characteristics that may influence physiological processes or constrain activity. We know relatively little about how the effects of habitat use on individual performance translate into population dynamics. We do know that the ability of lizards to use particular habitats can influence the persistence of populations in the face of habitat changes. Community-level processes (e.g., competition) and community structure (e.g., diversity) can be influenced by habitat use in lizards, often by habitat use facilitating co-existence of two or more potentially competing species. We know relatively little about how other community processes, such as predation and parasitism, are influenced by habitat use. Why do animals occur where they do? Beyond the basic requirement that an individual must be able to survive, different locations or habitats may provide different conditions for an individual's existence. Thus, another question arises: What are the consequences of the choice of habitat or microhabitat on the biology and ecology of the organism being considered? From an ecological point of view, habitat selection can influence physiological processes (Huey, 1991), population dynamics (Holt, 1987; Pulliam and Danielson, 1991), and community level processes (Morris, 1988; Rosenzweig, 1991). Lizards are an excellent group of organisms with which to examine the ecological consequences of habitat and microhabitat use. First, there is a relatively long history of studying habitat and microhabitat use in lizards, at least qualitatively (reviewed by Heatwole, 1977). Second, lizard ecology and physiology is well studied, at least for some species (see papers in Milstead, 1967; Gans and Pough, 1982a,b; Huey et al., 1983; Gans and Huey, 1988; Vitt and Pianka, 1994). Finally, recent studies have begun to examine the relationship between lizards and their environments in greater detail (see below) and provide a means to assess the role of habitat and microhabitat use in a lizard’s ecology. There is also a practical reason for looking at the ecological consequences of habitat and microhabitat use in lizards, and that is the on-going alterations of the environment by humans. We need to understand the role of habitat and microhabitat use in lizard ecology to be able to assess the potential impacts of such environmental changes and to suggest possible conservation measures. Before we begin our review of habitat use in lizards, it is necessary for us to define what we mean by "habitat". Habitat can mean a number of things and its meaning can depend heavily on the scale one is considering (see Morris, 1987a,b, 1992 for discussions of the interaction of scale and habitat use). For the majority of this review, habitat is used in a broader sense to include the general type of area in which an individual occurs (e.g., woodland or desert). However, in some instances, we use habitat and microhabitat synonymously to mean the actual substrate or perch on which an individual occurs. We feel our use of habitat in both these contexts is appropriate for our review because we believe that the general consequences of habitat (or microhabitat) use at any scale will be the same for a given species (i.e., certain requirements must be met for an individual or population to be successful). CONSEQUENCES OF HABITAT AND MICROHABITAT USE The consequences of living in a particular habitat can be manifested at several levels, ranging from effects on the individual to effects on an entire community. Below we discuss the implications of using different habitats for (1) individuals, (2) populations, and (3) communities.