Grasshopper herbivory affects native plant diversity and abundance in a grassland dominated by the exotic grass Agropyron cristatum

Authors: Branson, David - Dave; Sword, Gregory

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2007
Publication Date: 1/3/2009
Citation: Branson, D.H., Sword, G.A. 2009. Grasshopper Herbivory Affects Native Plant Diversity and Abundance in a Grassland Dominated by the Exotic Grass Agropyron cristatum. Restoration Ecology. 17(1):89-96.

Interpretive Summary: The effects of exotic plant species on native plant and animal diversity is of increasing concern. Crested wheatgrass is the most common exotic grass in western North America. Crested wheatgrass communities are invasive, resistant to colonization by native plant species and often remain relatively stable for decades, which impose problems for the restoration of native grasslands. Grasshopper population densities are often high in plant communities dominated by crested wheatgrass, and field observations suggested that native grasshoppers in crested wheat grass dominated habitats commonly fed on emerging plant seedlings. As such, grasshopper herbivory on plants other than crested wheatgrass could play an important role in determining plant community structure. Grasshopper herbivory in a crested wheatgrass dominated community led to a reduction in both native plant species richness and abundance. The observed effects of grasshopper herbivory on native plant abundance and diversity are likely to apply to crested wheatgrass dominated areas across the northern Great Plains. These findings illustrate the importance of understanding the impact of invertebrate herbivores such as grasshoppers on the relationships between exotic and native plants.

Technical Abstract: The indirect effects of native generalist insect herbivores on interactions between exotic and native grassland plants have received limited attention. Crested wheatgrass (Agropyron cristatum) is the most common exotic grass in western North America. Crested wheatgrass communities are resistant to colonization by native plant species and often remain relatively stable for decades, imposing problems for the restoration of native grasslands. Grasshoppers are generalist herbivores that are often abundant in crested wheatgrass dominated sites in the northern Great Plains. We conducted two manipulative experiments in a crested wheatgrass dominated grassland in western North Dakota to test the hypothesis that grasshopper herbivory influences local crested wheatgrass community composition by impeding the recruitment of native seedlings. Grasshopper herbivory negatively affected the species richness, numerical abundance and Shannon diversity of native plants in three of four years. Although additional research is needed to determine if grasshoppers actively select native plants relative to crested wheatgrass, the effects of grasshopper herbivory may nonetheless be an important consideration in the restoration of crested wheatgrass areas in northern Great Plains. The findings illustrate the importance of understanding the impact of native generalist invertebrate herbivores on the relationships between exotic and native plants.