Body-size differences in a colonizing amphipod-mollusc assemblage.

We examined body size patterns in a colonizing assemblage of marine amphipods and molluscs. We collected animals over a 25 day period from an archipelago of pits that were drilled in brick surfaces. The percent of pits occupied, abundance, species richness, and body size of colonists all increased significantly through time. We compared size ratios of coexisting species with two null models, one that randomized individuals and one that randomized species-populations. For both models, observed overlap ratios usually did not differ from randomness, although species richness was consistently lower than expected for later samples. Results were similar for a subset of the data, a guild of suspension/deposit feeding amphipod species. Some assemblages did show significant deviations from the null models, but the results were spotty and varied among replicates. Overall, the evidence for non-random overlap ratios in body sizes of colonizers was weak.