Do spatial patterns of benthic diatom assemblages vary across regions and years?

Abstract

AbstractAuthors of several studies of the spatial distributions of microorganisms have shown strong geographical patterns and stressed the importance of considering the spatial component explicitly when studying assemblage–environment relationships. The processes underlying the patterns are still under debate because it is difficult to separate the unique roles of dispersal limitation and mass effects from spatially structured variation in environment. We analyzed correlations between assemblage dissimilarity and geographical and environmental distances in a large French diatom database, subdivided into regions, years, and different water-quality levels, with multiple regression on distance matrices (MRM) and partial Mantel correlograms. Before we applied MRM, we identified the strongest environmental predictors with the BIO-ENV procedure, which selects the best predictors after testing correlations between distance matrices including every possible set of variables. Environmental control of assemblages w...