Consumer effects on establishment of grassland species

Herbivore and gastropod exclosure in coastal prairie at Pepperwood Preserve, CA. Photo Credit: C. Stein

How do small mammal and gastropod activity affect patterns of plant community structure and ecosystem function? Is establishment success of species and the impact of herbivores dependent on background diversity or productivity of the resident plant community? Do these interactions differ for exotic versus native plant species?

Understanding which ecological factors affect and control the establishment of native and exotic plant species is crucial to the development of successful restoration projects. Common restoration practices are implemented around the idea that native species are often seed limited, but often fail to take into account what other ecological factors may be contributing to the failure or success of species establishment.

The importance of generalist herbivores for the invasion of native grasslands by exotic plant species, and hence for the restoration success of native grasslands, is still poorly understood. Previous research has shown that plant species diversity and productivity within grasslands is strongly influenced by generalist herbivores, and the enemy release hypothesis further argues that exotic plants become invasive by being unpalatable or unrecognized by native herbivores. In contrast, the biotic resistance hypothesis predicts that native generalist herbivores suppress exotic plants that have not evolved traits to deter these herbivores. The goal of this project is to reconcile these different lines of research to develop a better framework for understanding when herbivores contribute to the success of an invasion and to the establishment of native species.

For this project we set up paired rodent and gastropod exclosures with exotic and native seed addition treatments to examine whether the effects of herbivory are similar within native and exotic grassland communities and how herbivory from different guilds may influence exotic success. We have set up this experiment within coastal grasslands at the Pepperwood Preserve in Santa Rosa, CA, as well in grassland sites in Montana and Germany to compare the performance of the exotic species in their home versus invasive range (Europe vs North America, respectively).

People involved: Claudia Stein, Lotte Korrell (visiting graduate student from Germany), Dr. Harald Auge, Helmholtz Centre for Environmental Research, Dr. John Maron, University of Montana, and Dr. Dean Pearson, Rocky Mountain Research Station