Plant invasion impacts on arthropod abundance, diversity and feeding consistent across environmental and geographic gradients

Abstract

Exotic plant invasion not only changes native plant communities, it also alters associated arthropod community diversity and structure. These impacts often are contradictory and context-specific by study location. M. vimineum is an Asian grass currently invading the eastern United States that generally escapes herbivory. The invasion impacts on arthropod communities are mixed, and the effects on arthropod food webs are largely unknown. Because M. vimineum has a unique δ13C value, its carbon flow can be resolved from native plants in recipient food webs. We investigate arthropod communities at M. vimineum-invaded sites along a 100-km geographic and environmental gradient in the southeastern U.S. We investigate M. vimineum impacts on arthropod abundance and diversity, how M. vimineum-derived carbon contributes to arthropod biomass and how environmental variation modifies invasion effects on arthropod communities. We find that M. vimineum invasion corresponds with increased arthropod diversity and abundance, but reduced evenness. Herbivore damage to leaves is equivalent between native species and M. vimineum, but the type of herbivore damage is not the same between the native and invader plants. We also find that herbivores derive 37 % of their biomass-carbon from the exotic plant but predators almost none (4 %). Detritivores derive exotic carbon (9 %) proportional to M. vimineum in the litter layer. Whereas exotic plant impacts on arthropod communities often seem idiosyncratic by site, we find no context-dependent invasion effects of M. vimineum by study location. The consistency suggests that the impacts may be broadly generalizable, at least within well-established parts of the invasion range.