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Abstract

LATITUDINAL DIVERSITY GRADIENT DRIVES COMMUNITY RESPONSE TO HETEROGENEITY AND SHAPES MARINE BIODIVERSITY AT SMALL SCALES.

Amy L. Freestone and Richard W. Osman
Smithsonian Environmental Research Center
Bio

One of the clearest patterns in ecology is the latitudinal diversity gradient, where species diversity 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. Recent studies have shown that in sessile marine invertebrate systems, communities in less diverse higher latitudes are more ‘regionally enriched,’ that is communities at small scales are more representative of the regional species pools. More diverse tropical environments, however, tend to have a smaller percentage of the regional species pool represented at small scales. Therefore, we hypothesized that at temperate latitudes, if species are more uniformly distributed, then a diversity-promoting mechanism will have less of an effect than in tropical latitudes where there are proportionately more species available to colonize local habitats. 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, but not in temperate communities. In four regions of the North Atlantic Ocean and Caribbean Sea, we used mimics of ecosystem engineering species to manipulate structural heterogeneity in sessile marine invertebrate communities. We deployed settlement panels in Connecticut, Virginia, Florida (SMSFP), and Belize (Carrie Bow Cay) with four treatments varying in their type of structural heterogeneity. We monitored diversity of the experimental communities up to one year after deployment. As hypothesized, we found a striking and consistent latitudinal gradient in the effect of structural heterogeneity on community diversity, ranging from a negative effect in our northern-most region to a positive effect in our southern-most region. These exciting results represent one of the first large-scale experimental demonstrations that marine community dynamics shift with latitude, differentially shaping biodiversity patterns.