Biodiversity is a critical element of community properties and ecosystem processes. Both plant species richness and genetic diversity positively affect processes ranging from primary production, ecosystem stability, and the maintenance of diversity. In nature, it is likely that species diversity and genetic diversity interactively affect how communities are structured and ecosystems function. However, the relative contribution of species diversity and genetic diversity to ecological processes has been rarely documented, and potential interactions between the two levels of diversity have not been investigated. Here, I report results from a common garden experiment conducted in a coastal freshwater dune habitat at Sleeping Bear Dunes National Lakeshore in Empire, MI. I manipulated plant species diversity (0, 1, 3, or 6 species) and genetic diversity (0, 1, 3, or 6 populations) within a dominant, dune-building species (Ammophila breviligulata) to address how both levels of diversity simultaneously influence ecological properties and processes.

Results/Conclusions

In 2008, plant diversity influenced a wide range of ecological responses. Plant species diversity and genetic diversity within the dominant species synergistically increased above-ground biomass production, with biomass increasing the most with genetic diversity when there were 6 plant species present. A similar pattern was found for arthropod morphospecies richness and abundance. Separately, neither species diversity nor genetic diversity affected either biomass production or the arthropod community. Plant diversity also influenced below-ground properties and processes. For example, nematode abundance doubled with both increasing species diversity and genetic diversity, but there was no interaction between the two levels of diversity. These results suggest that interactions between levels of diversity are an important, but often overlooked, aspect of how diversity structures communities and mediates ecosystem processes and suggests that increasing awareness of these interactions may inform conservation and restoration strategies.