Geographic range size and speciation

Abstract No species is distributed ubiquitously across the Earth. Indeed, the sizes of global geographic ranges vary by at least 12 orders of magnitude (Brown et al.1996). At one extreme lie those species constrained, by ecology or by history, to occupy small, isolated islands of habitat or very scarce sets of environmental conditions. At the other extreme lie those species which are distributed across multiple biogeographic regions. This interspecific variance in geographic range sizes has stimulated a host of investigations of the constraints on the occurrences of more narrowly distributed species, and of the mechanisms which enable the more widely distributed to become so (e.g. for references and reviews see Woodward 1987; Hengeveld 1990). On the contrary, little interest has been directed toward broad interspecific patterns in the determinants and consequences of this variation (for reviews see Kunin and Gaston 1993, 1997; Gaston 1994a; Brown 1995).Perhaps the most basic summary of, and pattern in, the variation of geographic range sizes exhibited by a taxonomic assemblage is the species-range size distribution and its associated statistics. The frequency distribution of the geographic range sizes of species in a taxonomic assemblage tends to be unimodal with a strong right-skew.