SPACE, ENVIRONMENT, AND THEIR JOINT EFFECTS ON COMMUNITY ASSEMBLE OF NON-MARINE OSTRACODES ACROSS A NESTED SUBSET OF LAKES FROM THE BAHAMIAN ARCHIPELAGO

Spatial effects can confound the recognition of genuine ecological patterns. Lakes on Bahamian Islands provide a distinctive system to examine the role of space and environment in structuring ecological communities because they exist as nested subsets. Here we test the role of space in structuring non-marine ostracode communities across three islands to examine whether the same environmental gradients influence community assembly across the archipelago as on individual islands. We sampled ninety lakes across the three islands of New Providence, San Salvador, and Rum Cay for ostracode assemblages and environmental factors: electrical conductivity, lake area, depth, alkalinity, pH, water temperature, and dissolved oxygen. Using non-metric multidimensional scaling and multivariate fuzzy set ordination, we found that the abiotic environment is a main determinate of changes in ostracode assemblages on each island and across all three islands with electrical conductivity independently influencing community assembly across the three islands, on San Salvador, and on Rum Cay, but not on New Providence where community assembly is influenced by a complex multivariate abiotic gradient of correlated factors. However, on each island and across all three islands, Moran’s eigenvector mapping determined that spatial patterns also influence community assembly. While on San Salvador, these spatial patterns simply reflect the underlying spatial structure of the abiotic environment, on the other two islands spatial patterns have an effect independent of the abiotic environment on community assembly indicating that biotic factors, like ecological drift or incumbency effects, are important factors in structuring ostracode communities. Analysis of space at the island- and archipelago-scales show how geographic and environmental data can be combined to elucidate drivers of community assembly. In the process, we identify situations, such as San Salvador, where preserved ostracode assemblages are faithful records of paleoenvironmental change, and situations such as New Providence and Rum Cay, where preserved assemblages should be interpreted in light of spatial patterns as well as the abiotic environment.