Integration of local and regional perspectives on the species richness of coral assemblages

We have evaluated the relationship between regional species richness and the number of species occurring within local, quantitatively sampled assemblages of scleractinian corals. Our data have been extracted from the published literature describing richness patterns from over 100 locations around the world. In general, we find a positive relationship between local and regional richness. Local richness is not independent of regional richness as posited by conventional theory and there is no hard upper limit indicating saturation, Instead, local coral assemblages are regionally enriched. This result suggests that these assemblages are open to regional sources of species. The degree of regional enrichment is geographically variable. In the Indo-Pacific, assemblages in speciose regions appear to be less open and much more sensitive to local depth and habitat gradients than those in more depauperate regions. Other large-scale geographical and historical effects on local richness in tbe Indo-Pacific include the degree of isolation from high-diversity regions and distance from the equator. In contrast, local richness in the relatively homogeneous and depauperate western Atlantic is insensitive to the large-scale variables we examined. As in most ecological communities, membership in local assemblages of corals is not absolutely limited (by biotic interactions or local environmental factors) nor is it totally open to regional pools of species. Understanding the dynamics of coral communities will require integrating the local ecological perspective with large-scale phenomena (i.e., physical TECO processes [Myers, 1994] and evolutionary history [Hugueny et al. 1997]), Such an integration will necessarily encompass multiple spatial and temporal scales.