Conservation Implications of Georaphic Range Size—Body Size Relationships

The oft-cited statement that 'big fierce animals are rare' (Colinvaux 1978) is, like most such generalizations in ecology, only partially correct. Animals with large bodies, fierce or otherwise, do have lower densities than smaller species, at least in studies based on compendia of data drawn from the literature (for example, Damuth 1981, 1987, 1993; Peters & Wassenberg 1983; Currie 1993; Silva & Downing 1994); conclusions may be rather different when based on sampling whole assemblages of taxonomically similar animals e.g. Brown & Maurer 1987; Morse et al. 1988; Cotgreave 1993; Blackburn & Lawton 1994). However, a growing body of work has documented positive relationships between the geographic range size and the body size of animal species (Table 1). In terms of geographic range size, within taxonomic assemblages (such as North American mammals) big animals are often rather common; geographic range size is a dimension of the rare-common axis equally as valid, and perhaps as widely applied, as density or population size (Rabinowitz 1981; Rabinowitz et al. 1986; Reed 1992; McCoy & Mushinsky 1992; Fiedler & Ahouse 1992; Gaston 1994). Moreover, at least amongst terrestrial mammals, the big fierce species may tend to have particularly large geographic range sizes; carnivores have larger geographic ranges on average than species in other terrestrial mammalian orders (Brown 1981; Rapoport 1982; Pagel et al. 1991; Letcher & Harvey 1994). The relationship between interspecific geographic range size and body size has attracted attention primarily in the context of macroecology and may explain how species partition space and resources (Brown & Maurer 1987, 1989; Gaston & Lawton 1988b; Gaston 1994; Lawton et al. 1994; Taylor & Gotelli 1994). It also has some potentially important consequences for conservation (as do various other macroecological patterns) (Lawton 1993; Gaston 1994; Gaston & Blackburn 1995a,b). We limit ourselves here to consideration of interspecific range size to body size relationships from studies on assemblages at large geographic scales, such that all or most of the geographic ranges of the species in the assemblage are considered. It is on global, rather than local, scales that the conservation status of species is most important. At more restricted scales the form of the range size to body size relationship is less clear (see for example Gaston 1988; Gaston & Lawton 1988a,b).