Insect herbivory affects plant survival and establishment in post-restoration plant communities
Insect herbivory can regulate plant populations and structure plant communities in natural systems. Much less is known about the effect insect herbivory has on plants in early seral post-disturbance habitats, such as those subject to restoration. In addition, invasion by exotic plant species can have dramatic impacts on native plants and restoration success can be limited by pressure from invasive plant species. Though invasive species may be superior competitors for space and resources, it is also possible that their dominance is enhanced by native insect herbivores, particularly if native plants are more preferred food sources than invasive plants. There is pressing need to understand ecological relationships between insect herbivores and invasive plants, particularly with regard to their potential for impacting restoration success. This study assessed impacts of grasshopper herbivory and the invasive grass Bromus tectorum (cheatgrass) on mortality and growth of 17 native plant species. Field and greenhouse experiments were conducted using moderate densities of a ubiquitous generalist grasshopper (Melanoplus bivittatus).
The presence of grasshoppers had stronger and more consistent impacts on plants in both field and greenhouse studies than cheatgrass. After six weeks in the greenhouse, grasshoppers were associated with 36% mortality over all native species compared to 2% when grasshoppers were absent. Herbivory was also associated with an approximately 50% decrease in native plant biomass in both greenhouse and field studies. However, effects of herbivory varied among plant species. Artemisia tridentata, Chrysothamnus viscidiflorus, and Coreopsis tinctoria were among the most negatively impacted species when exposed to grasshoppers, while Oenothera pallida, Pascoyrum smithii, Leymus cinerus were unaffected. These findings suggest that grasshopper herbivory can have a large impact on the trajectory of plant community development following disturbance and can influence the successful establishment of target restoration species such as A. tridentata.