Occupancy-abundance relationships and spatial distribution: A review

One of the most general patterns in community ecology is the positive relationship between the number of sites or areas in which a species in a taxonomic assemblage occurs regionally and its local abundance. A number of hypotheses have been proposed to explain this interspecific occupancy-abundance relationship, but it has recently been argued that the pattern is most profitably viewed as a consequence of the spatial distribution of the individuals of each species. In this paper we explore the link between spatial distribution and the occupancy-abundance relationship, with particular reference to statistical models that have been suggested to describe the pattern, and discuss its connections with a broad understanding of how organisms are distributed in space. A range of models describe observed occupancy-abundance relationships reasonably well, but are commonly not well differentiated over the range of abundances implicit in such relationships. There is little evidence that species exhibit great commonality in the form of their aggregative behaviour, but this does not matter in terms of the generation of a positive interspecific occupancy-abundance relationship.