Community level impacts of Microstegium vimineum on arthropod community structure and foodweb dynamics in a temperate deciduous forest.

Invasion by non-native primary producers are generally expected to lead to a decline in native species richness, however in some cases, these invasions can actually lead to an increase in diversity and abundance of certain groups of organisms. Arthropods are extremely sensitive to changes in the plant community, particularly herbivores, and the response of these primary consumers can influence predator populations. Microstegium vimineum is an invasive C4 grass that has developed strong populations in the understory of temperate deciduous forests along the east coast of the U.S. This work evaluates the influence that this invader may have on insect and spider abundance and diversity, including changes at the trophic group and functional guild levels. Additionally we evaluate the impacts of both an increase in invasion density and a decrease in native plant diversity on arthropod community structure. In general, we find a significant increase in herbivore abundance, primarily as a result in the increased abundances of concealed chewers, free-living chewers and free-living sap feeders. Free-living sap-feeders also showed an increase in biomass. Spider abundance and diversity also increased in association with invasion by M. vimineum. Both active hunters and sit-and-wait predators showed significant increases in invaded sites. The ratio of adult:immature spiders however had a negative relationship with invasion. These changes in the arthropod community appear to be related to both changes in vegetation structure as well as changes in plant biomass. We found increased abundances in our treatments in which invasion density increased and decreases in the arthropod community in sites where native plants were removed from the system. We also show some support for the idea that carnivores, specifically spiders, may respond more strongly to changes in vegetative complexity, while herbivores, specifically leaf hoppers, may respond more strongly to changes in plant biomass