Coexistence among species with different competitive abilities and shared, limited resources has long been a focus of ecologists. Intraspecific spatial aggregation has been identified as one possible mechanism promoting coexistence in a variety of systems. It has been hypothesized that when competitors are aggregated, there are fewer interspecific encounters for weak competitors and increased competition among adjacent strong competitors. We tested this aggregation hypothesis of coexistence using scleractinian corals as a model system.

Results/Conclusions

In experiments using two common species of coral, one strong (Porites rus) and one weak competitor (Porites lobata), we found that within-patch aggregation of a strong coral competitor enhances the growth of a weaker coral competitor when space is limited. To test the importance of this effect over larger temporal and spatial scales, we constructed a cellular automata model (parameterized by the experimental data). We found that persistence of inferior competitors was increased when an aggregation benefit was applied in the model, consistent with hypotheses developed from empirical observations. Using results from our experimental and modeling approaches, we conclude that spatial aggregation may be an important mechanism contributing to species coexistence on coral reefs.