Impacts of plant diversity on arthropod communities and plant-herbivore network architecture

At the local scale, insect herbivore diversity is often limited by plant diversity, but little is known about how the network structure of plant and herbivore interactions changes across local plant diversity gradients. Ascertaining plant-herbivore interaction structure at the ecological community level is important for predicting responses of herbivores to plant species loss. We sampled arthropods and plants across three years, beginning in the fourth year of an experimental prairie restoration containing three treatment levels of sown plant diversity. Plots initially planted with higher plant diversity had higher arthropod species richness. Sown diversity treatments strongly affected plant-herbivore interaction structure: The increased sown diversity treatment decreased plant-herbivore connectance, increased average herbivore diet generalism, and increased herbivore robustness to plant species loss. Treatments diverged over time with the last year of sampling showing the greatest difference between treatments in plant and arthropod species richness, and plant-herbivore network structural properties. Network structural properties of the high sown diversity treatment were the least variable temporally. However, divergence of plant and arthropod between diversity treatments was not found in traditional ordinations of community taxonomic composition. While previous comparisons of plant-herbivore interaction networks across ecological gradients treated network size (biodiversity) as a confounding factor, we demonstrate that plant diversity can directly shape network structure, and higher plant diversity maintains less temporally variable ecological networks of herbivores and their host plants.