Latitudinal diversity gradient drives community response to heterogeneity and shapes marine biodiversity patterns at small scales

One of the clearest patterns in ecology is the latitudinal diversity gradient, where species richness increases at lower latitudes.  This large-scale gradient in regional diversity may also have important impacts on community dynamics and the maintenance of diversity at small scales.  Specifically, are community mechanisms that promote diversity as effective in latitudinal zones that harbor fewer species?  Habitat heterogeneity, specifically structural heterogeneity, can both promote community diversity and shape community composition.  Species themselves can create structural heterogeneity (e.g., coral reefs), and thus ‘engineer’ their environments.  We hypothesized that species-induced structural heterogeneity will increase diversity in tropical communities, while temperate communities remain unaffected.  In four regions of the North Atlantic Ocean and Caribbean Sea, we used mimics of ecosystem engineer species to manipulate structural heterogeneity in sessile marine invertebrate communities.  We deployed settlement panels in Connecticut, Virginia, Florida, and Belize with four treatments varying in their type of structural heterogeneity.  We monitored the experimental communities one and three months after deployment.  Results indicate that structural heterogeneity did not promote diversity in temperate regions.  In the tropics however, experimental structures harbored more species than adjacent areas of open space of equal surface area.  These exciting results support our hypothesis and will have important implications for the study of global patterns of marine biodiversity.