Invasive plant species can alter dynamics of pollinator communities, attracting higher numbers of pollinators as compared to native species through more prolific floral display. This can in turn facilitate further spread of the invasive plant species. Our study compared plant-pollinator dynamics between the invasive L. cuneata and three native congeners, all sympatric, in the Flint Hills region of the North American tallgrass prairie. Using in situ populations of the four Lespedeza species in seven field sites over two years, we compared peak floral displays and insect visitation rates among randomly selected plants. Additionally, we collected and analyzed data on insect visitor taxa during timed observation periods to assess whether the plant species relied on similar insect taxa, and whether the invasive is more generalist pollinated than the native species. 

Results/Conclusions

Lespedeza cuneata produced five times as many showy flowers per plant as any of the native Lespedeza species, and demonstrated significantly higher insect visitation rates per plant in both years. Positive correlations were found between floral density and visitation rate per plant in all the native species, although not in the invasive L. cuneata. Rarefaction curve analysis on insect taxa data indicated that while there was a higher species richness of insect visitors to L. cuneata in both years, the difference was not significant. Similarity indices also indicated a majority of visiting insect taxa were common between plant species. However, the taxonomic breakdown of insects visiting each plant species showed the primary visitor to the invasive L. cuneata was the common honeybee, Apis mellifera, which was in fact never observed visiting any of the native Lespedeza species. In conclusion, this study showed that L. cuneata attracts a significantly greater number of insect visitors, likely through its prolific floral display; and that while it relies generally on the same insect communities visiting the native species, it is also singularly and primarily visited by A. mellifera.