INTERSPECIFIC ABUNDANCE-OCCUPANCY RELATIONSHIPS - A TEST OF MECHANISMS USING MICROCOSMS

1, Several hypotheses have been proposed to account for the widely obs erved positive interspecific relationship between the local abundance and number of sites occupied, Here we provide a test of some of these hypotheses using data from microcosm communities of protists, in which sets of individual communities are linked by varying rates of dispers al. 2. Positive relationships between abundance and occupancy were fou nd over all the dispersal rate treatments, including those with no bet ween-community dispersal. 3, Species tended to be consistent in their position in the abundance-occupancy relationship, both within and betw een treatments. 4. The design of the experiment makes it unlikely that (i) sampling artefacts. (ii) geographical range position, (iii) niche breadth, (iv) resource availability, or (v) vital rates mechanisms ar e appropriate, or sole explanations for the observed patterns, though biotic heterogeneity complicates the interpretation of(ii)-(v), 5, The results fail to support the specific hypotheses based on metapopulati on dynamics, but suggest that occupancy may be driven be local abundan ce, combined with a very general (not specifically metapopulation-stru ctured) set of extinction and colonization processes.