Abundance-occupancy relationships

1. The abundance and distribution of species tend to be linked, such that s pecies declining in abundance often tend also to show declines in the numbe r of sites they occupy, while species increasing in abundance tend also to be increasing in occupancy. Therefore, intraspecific abundance-occupancy re lationships are commonly positive. 2. The intraspecific pattern is mirrored by more general positive interspec ific abundance-occupancy relationships: widespread species tend to be abund ant, and narrowly distributed species rare. 3. Here, we review recent research on these patterns based on the flora and fauna of the British Isles. We assess their generality, describe what is c urrently known about their structure, and summarize the results of tests of the several hypotheses proposed to explain their existence. 4. The positive form generally exhibited by abundance-occupancy relationshi ps, intraspecific or interspecific, has consequences for several areas of a pplied ecology, including conservation, harvesting, biological invasions an d biodiversity inventorying. These implications are discussed briefly.