Diatom Diversity and Biogeography Across Tropical South America

Determining the mechanisms of community assembly forms the foundation of biogeography and community ecology. Studies of the biodiversity of Neotropical macro-organisms have recognized the roles of environmental, spatial, and historical factors in structuring communities at different spatial and temporal scales, but the influences on microorganisms are not well studied. Diatoms (unicellular siliceous algae) are a very species-rich group of algae, disperse widely, and respond rapidly and sensitively to environmental variation. In this chapter, we use a newly constructed database of tropical South American diatoms (8°N–30°S and 58–79°W) to analyze the distribution and diversity patterns of species across lentic and lotic environments, including predictors that describe local (limnology) and regional (geo-climatic) factors. We provide a conceptual framework that examines community responses (species composition and diversity) to environmental and spatial factors by applying paleolimnology and macroecological approaches (Theory of Island of Biogeography and metacommunity theory). Diatom biogeographic patterns emerge for (1) identifying regionally distinct floras with a significant association with geographic groups of lakes, (2) determining latitudinal gradients of species richness and community structure, and (3) estimating the joint contribution of environmental filtering and dispersal dynamics in affecting diatom community composition across time. We emphasize the potential for incorporating diatom ecology and paleolimnology into a macroecology framework to further develop multiple, interdisciplinary hypotheses on the mechanisms driving microbial diversity and community assembly in the Neotropics.