INTERSPECIFIC ABUNDANCE-RANGE SIZE RELATIONSHIPS - RANGE POSITION ANDPHYLOGENY

A number of mechanisms have been proposed to explain the widely observ ed positive interspecific relationship between local abundance and ext ent of geographic distribution in animals. Here, we use data on Britis h birds to assess two of these hypotheses: that the relationship resul ts from the relative position of a study area with respect to the geog raphic ranges of the species which occur there, and that the relations hip results from a simple difference between taxonomic groups, rather than any general tendency for more abundant species to have larger ran ge sizes. We find support for neither hypothesis. Phylogenetically con trolled comparative analyses reveal that the positive abundance-range size relationship is consistently found within taxa, even when abundan ce and range size are calculated at a variety of spatial and temporal scales. Analyses both across species and within taxa show that bird sp ecies for which Britain is near to the centre of their distribution in Europe tend to have larger British range sizes and higher abundances than do species where Britain is close to the edge of their range in E urope. However, these relationships do not cause that between abundanc e and range size, because this latter relationship persists within dif ferent range position categories. Whether a species is near the centre or edge of its geographic range in Britain may affect its position on the abundance-range size relationship, but does not produce the relat ionship. Range position in Britain does, however, seem to be related t o the magnitude of temporal changes in the range sizes of British bird s. There is some evidence to suggest that species for which Britain is nearer to their European range centre have shown smaller changes in d istribution over the period 1970-1990 than have species for which Brit ain is close to their European range edge.