Species Richness of Reef-Building Corals Determined by Local and Regional Processes

Abstract

Species richness in ecological communities has traditionally been explained in terms of species interactions, especially competition, operating within the local community over relatively short periods of time. Recently, it has become clear that ecological communities can be organized by a variety of processes operating at different spatial and temporal scales. Since local communities are imbedded within larger geographic regions, regional/historical phenomena and local processes may influence local richness jointly and should be analysed simultaneously. Here we perform such an analysis by comparing assemblages of hermatypic scleractinian corals from different regions sampled at over 100 sites around the world. Using multiple regression analysis, we find that local richness is as sensitive to regional richness as it is to each of two variables (depth and habitat) that subsume much of the local variability at a site. Our results indicate that although coral assemblages are believed to be intensely interactive, they are, nevertheless, regionally enriched and show no evidence of saturation. Multi-scale effects on local richness demand further investigation to clarify causal relationships, and to enlighten policy decisions over issues of biodiversity, habitat loss and fragmentation, and ecological restoration.