Changes in arthropod community structure associated with invasion by Microstegium vimineum

Background/Question/Methods

The potential for invasive species to alter regional biota and cause native species decline is a cause for much concern.  Microstegium vimineum is an invasive annual C4 grass that thrives in disturbed environments and is dominant in many eastern deciduous forests.  Because this grass plays an important role in determining the plant community structure in the understory of these forests, it also has the potential to significantly alter arthropod community structure.  Here we present data from a study evaluating the impact of a relatively new invasion of Microstegium vimineum on arthropod communities in a disturbed forest in North Central Kentucky.  Arthropod community samples were collected from 24 sites (12 invaded/12 uninvaded) once per month during the growing season (May-October 2010, 2011) using pitfall traps and sweep nets.   Arthropods were identified to family, assigned to morpho-group, trophic group and functional guild, counted and weighed.  ANOVA was used to evaluate differences in abundance, Shannon diversity, evenness and family richness between the treatments.  NMS and MRPP analysis were used to assess overall differences in community structure between the treatments.

Results/Conclusions

Arthropods showed a significant treatment (invaded vs. uninvaded) effect with a 57% higher abundance in invaded sites.  Family richness and Shannon diversity differed between treatments, with invaded sites containing 27% more families, and a 16% higher Shannon diversity index.  Trophic group analysis showed significantly higher abundances of herbivores that included increases in concealed chewer, free-living chewer and free-living sap-feeder functional guilds.  In terms of biomass, herbivore biomass increased in the presence of M. vimineum, however this increase was limited to free-living sap feeders at the functional guild level.  Forb abundance, which serves as the primary food source for herbivorous arthropods in this system, showed significant reductions in sites invaded with Microstegium vimineum.  Microstegium vimineum invasion was also associated with significant increases in aboveground standing crop biomass which was nearly 50% greater in invaded sites.  These results indicate that the arthropod community may be responding to the increased biomass rather than a change in the food availability in this system.