On the Relationship between Abundance and Distribution of Species

How environmental conditions and population processes determine the abundance and distribution of species is a central problem of ecology and biogeography. Although it has long been recognized that abundance and distribution are intimately interrelated, the nature of this relationship has not been investigated systematically over the range of spatial scales from local populations to entire geographic ranges of species. On a local scale, i.e., the small habitat patches that constitute most ecologists' study areas, the relationship between population density and spatial distribution of individuals has been studied by many population and community ecologists (e.g., Andrewartha and Birch 1954; Krebs 1978, and numerous references therein). Distribution on a large geographic scale has usually been regarded as the special province of biogeography, whose practitioners often have little experience or interest in population ecology (but see, e.g., Grinnell 1922; MacArthur 1972; Walter 1979; Rapoport 1982; Brown and Gibson 1983). Thus few investigators have systematically studied variation in population density over the geographic range of species. Recently, however, several authors have presented data that suggest a general relationship between local population density and spatial distribution on a geographic scale (e.g., Rabinowitz 1981; Hanski 1982a, 1982b, 1982c; Bock and Ricklefs 1983; J. T. Emlen et al., MS). Here I reanalyze and synthesize some of the diverse information available on the relationship between abundance and distribution. These data suggest extremely general patterns within and among species that appear to hold for organisms as diverse as vascular plants, intertidal invertebrates, terrestrial arthropods, planktonic crustaceans, and terrestrial vertebrates. I develop a general theory to explain these relationships. This conceptual construct and the empirical observations that motivated it focus attention on problems that span the boundaries between the traditional disciplines of population ecology, community ecology, biogeography, population genetics, and evolution. Clarification of terminology should facilitate understanding of what follows. The paper is concerned with the relationship between two attributes of populations and species: the density of individuals within a local area and the extent of the distribution of individuals in space. I shall often use the term abundance to