INTERSPECIFIC ABUNDANCE RANGE SIZE RELATIONSHIPS - AN APPRAISAL OF MECHANISMS

1. Positive relationships between the local abundance and the range si ze of the species in a taxonomic assemblage are very general. 2. Expla nations for these relationships typically focus on two mechanisms, bas ed on differences in the niche breadths of species, or metapopulation dynamics. Others have, however, also been suggested. 3. Here we identi fy and clarify all the principal mechanisms proposed to explain positi ve interspecific abundance-range size relationships. We critically ass ess the assumptions and predictions that they make, and the evidence i n support of them. 4. A number of predictions are common to all of the biological (as opposed to artefactual) mechanisms, but the combinatio n of predictions and assumptions made by each is unique, suggesting th at, in principle, conclusive tests of all of the mechanisms are possib le. 5. On present evidence, no single mechanism has unequivocal suppor t. We discuss reasons why this might be the case.