Range, population abundance and conservation

Several patterns in the distribution and abundance of organisms have now been documented. They include broad (but not universal) positive correlations between range sizes and population abundances; a decline in the proportion of sites occupied and in average population densities from the centre to the edge of a species' range, with either unimodal or multimodal peaks of abundance and occupancy in the core of the range; and intriguing, but still poorly documented phylogenetic effects on both range size and abundance. All these patterns require further work to establish their generality, and all of them lack generally agreed explanations. They are important, however, not only theoretically but also practically, because of the constraints and opportunities they appear to provide for the management and conservation of species.