Plant invasions are known to have negative effects on native plant communities, yet their effects on higher trophic levels have not been well documented. Past studies documenting the effects of invasive plants on arthropod communities have been largely observational in nature and thus lack the ability to tease apart whether differences in arthropods are a cause or consequence of the invasion. Observational studies are also unable to distinguish whether these differences result from pre-existing variabilites in environmental conditions in invaded vs. uninvaded areas.  In addition, understanding how plant traits and composition change in invaded habitats may increase our ability to predict when and where invasive plants will have effects that cascade to arthropods. Here, we experimentally introduced a non-native plant (Microstegium vimineum, Japanese stilt grass) to evaluate its effects on arthropods. We additionally investigated possible mechanisms through which the invader could affect associated arthropods, including changes in native plant species richness, aboveground plant biomass, light availability, and vegetation height.  

Results/Conclusions

In experimentally invaded plots, arthropod abundance was significantly reduced by 39%, and richness by 19%. Interestingly, carnivores experienced greater reductions than herbivores (61% versus 31% reduction). Nonmetric multidimensional scaling analysis showed that arthropod composition differed between experimentally invaded and control plots, and SIMPER analysis identified particular species belonging to the insect families Aphididae, Formicidae and Leiodidae as contributing the most to compositional differences. Among the mechanisms we investigated, only the reduction in native plant species richness was strongly correlated with the declines in total arthropod abundance and arthropod species richness. In sum, our results demonstrate negative impacts of M. vimineum invasion on higher trophic levels and suggest that these effects may occur, in part, indirectly through invader-mediated reductions in the richness of the native plant community.