The invasion of non-native plants into novel ecosystems has the potential to alter ecological dynamics across multiple trophic levels from the individual to community scale. The interaction between insect herbivores and invasive plants may contribute to invasive success and alter herbivore and predator abundance and community composition. Euonymus alatus (burning bush) and E. europaeus (spindle tree) are two related invasive plants that occur in natural areas in North America. To evaluate the contribution of plant-herbivore interactions to the potential invasiveness of these non-native species, we measured in field herbivory rates as well as the performance of a model generalist herbivore (H. cunea) on these plants compared to a native congener (E. atropurpureus, eastern wahoo). In addition to altering interactions with herbivores, invasive plants can have major impacts on native vegetation and can drastically alter the structure of forest ecosystems. Similarly, overgrazing by deer alters forests through the modification of vegetation composition and structure. Invasion by non-native plants and deer herbivory have the potential to drastically alter predator assemblages, including spiders. We established exclosures in burning bush invaded and native areas to determine the impacts and potential drivers of plant invasion and deer herbivory on shrub- and ground-dwelling spiders.
Results/Conclusions
Both spindle tree and burning bush had eight times less damage compared to the native eastern wahoo. However, the model herbivore fed, grew, and pupated at similar rates on spindle tree and eastern wahoo, while exhibiting slow growth and low survival on burning bush. Low herbivory rates and poor herbivore survival are suggestive of enemy release, which may contribute to invasiveness for both Euonymus species. In addition, the inability for a generalist to use burning bush in the lab and for any herbivore to use either non-native as a host in the field suggests that the invasion of these plant species may contribute to reduced herbivore success in invaded areas. Shrub-dwelling spiders were more abundant in native plant dominated areas. The defoliation of burning resulted in the recovery of spider abundance. This was likely due to the resulting structure, which more closely resembled that of the native vegetation. Ground-dwelling spiders were more abundant in areas protected from deer herbivory. These results were not be explained by litter depth or plant cover, but may relate to prey availability. The interaction between non-native plants and white-tailed deer herbivory can alter a predator community through alterations in vegetation structure and prey availability.