Print PageOur planet shows striking gradients in the species richness of plants and animals, from high biodiversity in the tropics to low biodiversity in polar and high-mountain regions. Recently, similar patterns have been described for some groups of microorganisms, but the large-scale biogeographical distribution of freshwater phytoplankton diversity is still largely unknown. We examined the species diversity of freshwater phytoplankton sampled from 527 lakes and reservoirs distributed across the continental United States using structural equation modeling.
Results/Conclusions
We found strong latitudinal, longitudinal and altitudinal gradients in phytoplankton biodiversity. Our results thus provide support for the idea that microorganisms can show substantial geographic variation in biodiversity. These large-scale biodiversity gradients in freshwater phytoplankton diversity were largely driven by local environmental factors. Specifically, we found that phytoplankton species richness increased with water temperature and lake surface area, and was a unimodal function of lake chlorophyll concentration, resembling effects of temperature, habitat area and productivity on diversity patterns commonly observed for macroorganisms. These local environmental factors, in turn, varied along latitudinal, longitudinal and altitudinal gradients. These results imply that changes in land use or climate that affect these local environmental factors are likely to have major impacts on large-scale biodiversity patterns of freshwater phytoplankton.
