Interspecific Abundance-Occupancy Relationships: A Test of Mechanisms Using Microcosms

Abstract

1. Several hypotheses have been proposed to account for the widely observed 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 dispersal. 2. Positive relationships between abundance and occupancy were found over all the dispersal rate treatments, including those with no between-community dispersal. 3. Species tended to be consistent in their position in the abundance-occupancy relationship, both within and between 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 are 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 metapopulation dynamics, but suggest that occupancy may be driven by local abundance, combined with a very general (not specifically metapopulation-structured) set of extinction and colonization processes.