Native oak diversity increases herbivory to non-native oaks

Background/Question/Methods

There is often an inverse relationship between the diversity of a plant community and the invasibility of that community by non-native plants.  Native herbivores that colonize novel plants may contribute to diversity-invasibility relationships by limiting the relative success of non-native plants, but this idea has rarely been tested.  At the same time, herbivores often tend to colonize non-native plants that are similar to their native hosts, but there is considerable variation in this trend between sites and systems.  We surveyed herbivore damage to large collections of non-native oak trees at sites across the United States.  

Results/Conclusions

Non-native oaks introduced to regions with greater oak species richness accumulated greater leaf damage than in regions with low oak diversity.  Underlying this trend was the ability of herbivores to exploit non-native plants that were close relatives to their native host.  In diverse oak communities, non-native trees were on average more closely related to native trees and received greater leaf damage than those in depauperate oak communities.  Because insect herbivores colonize non-native plants that are phylogenetically similar to their native hosts, in communities with greater native plant diversity, non-natives experience greater herbivory.  This fulfills the first step of herbivory as a mechanism behind diversity-invasibility relationships.  Future work can relate these trends in herbivore damage to non-native plant fitness and population growth in order to show dinifitively that herbivores are one mechanism behind diversity-invasibility relationships.