Assistant Professor Goucher College, United States
Abstract: Humans affect local biodiversity in many ways, leading to decreased community stability or changes in species interactions. Loss of species diversity has often been the primary focus of studies of biodiversity loss, but diversity within species is also consequential, from both evolutionary and ecological perspectives. Despite its importance, the magnitude of the effect of intraspecific diversity loss on species interactions relative to other ecologically important factors is still not well understood. To help fill this gap, I investigated the relative impacts of intraspecific diversity and nutrient addition on plant growth and herbivory in a common garden experiment. I factorially manipulated nutrient addition and genotypic diversity (monoculture or polyculture) of Solidago sempervirens, seaside goldenrod. Both variables affected plant growth but in different ways. Diversity led to taller plants with fewer shoots, while nutrients led to more herbivory. Nutrients and diversity interactively affected the number of leaves on a plant, and polyculture pots had more leaves than monoculture pots only in high nutrient conditions. Similarly, the effect size of diversity was larger for some plant measures while nutrient effects were larger for others, and in some cases, the effects were nearly the same magnitude. These results suggest that the impact of intraspecific diversity on plant growth and herbivory can be comparable in magnitude to the effect of nutrient addition. More broadly, this suggests that efforts to conserve intraspecific diversity would have important ecological impacts in at least some situations, in addition to their already well-known evolutionary impacts on species’ long-run survival. Further research broadening our understanding of the importance of intraspecific diversity relative to other ecologically important factors would be valuable.
