Comparative Biogeography of Marine and Terrestrial Microbes and Macrobiota Using Environmental DNA

AbstractQuantifying how patterns of biodiversity and underlying processes vary across diverse environments and ecological communities is a long-standing challenge in biogeography. The logistics of sampling entire communities over different geographic scales has been a barrier to developing biogeographic theory and conceptual integration at large scales. Here, we use environmental DNA (eDNA) to overcome these challenges and examine biogeography hypotheses contrasting diversity in marine versus terrestrial realms and unicellular versus multicellular organisms. We found that eDNA revealed both novel and familiar alpha diversity patterns. Marine diversity was lower than terrestrial diversity in multicellular biota although statistically indistinguishable in unicellular biota. Richness was modestly correlated within habitats and was routinely higher in unicellular than multicellular biota. Beta diversity was, unexpectedly, less similar within marine than terrestrial assemblages. Unicellular assemblages were consistently more similar than multicellular assemblages, and their beta diversity correlated with latitude. These patterns are consistent with predictions based on body size and nuanced effects of environmental heterogeneity. However, there was considerable heterogeneity in both datasets. Overall, eDNA provides a common currency for studying biodiversity patterns and underlying processes (e.g., drift, migration, selection) across diverse environments and complex communities and may be the foundation of a unifying macroecological framework.