How Important are Regional Processes in Determining the Local Species Richness of Marine Communities

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This study investigates the relationship between the number of species in biogeographic regions (spatial scale of 10' to 1W kms ) and the number occurring in local communities (spatial scale of 1 to 10'm's) of sessile epifaunal invertebrates from 11 biogeographic regions comprising at least 33 local sites. The main predictions to be tested are: if local communities are simply a sink from the biogeographic (regional) species pool, then local species richness will be positively and linearly related to regional species richness over a broad range of diversities. Alternatively, if ecological interactions limit the number of species coexisting in local habitats, then regressions of local richness on regional richness will level off or saturate. We propose to test these hypotheses by sampling the species richness of epifaunal communities in different biogeographic regions with quantitative photographic techniques. Local diversity will be quantified from 35 mm photo quadrats (0.25m ) taken at random locations along transects placed horizontally across subtidal rock walls at approximately 10 m depth. Quadrat photos will be analyzed until a plot of the cumulative number of species at each location asymptotes, which will comprise our measure of local species richness. Regional species richness will be estimated from published species lists and by consulting local experts at each site. Regression techniques are developed herein to test the predictions of regional influence vs. local saturation. In addition, four related questions will be investigated to increase our understanding of 1) the relationship between body (or colony) size and local species richness 2) the ability of larval dispersal mode to explain the degree of regional influence an local richness, 3) the relation between species density, local species richness and regional species richness and 4) how the nature of the relationship between local and regional richness varies among different taxa. The preservation of biological diversity is one of the most pressing environmental issues of the present and next century. Accurately identifying the nature of threats to Earth's biotic diversity and designing and implementing sound conservation strategies requires an understanding of the forces that shape spatio temporal patterns of biodiversity. The results of the proposed research will greatly enhance our ability to critically assess the importance of regional processes in structuring shallow marine hard substrate communities.