Bee, butterfly and plant species diversity in northeastern Illinois tallgrass prairie restorations
Pollinators not only are essential for production of a substantial portion of the world’s food supply, but also provide key ecosystem services in natural ecosystems. In the Midwestern United States tallgrass prairies likely function as refugia for many native pollinator species; however, less than 1% of the original area of tallgrass prairie remains. Tallgrass prairie restoration is increasingly practiced to increase the extent of this natural ecosystem. Characterization of relationships among plant and pollinator species is needed to better understand and gauge the success of tallgrass prairie restorations. In this study the hypothesis that plant species diversity is positively linked with pollinator species diversity was tested in ten tallgrass prairie restorations in northeastern Illinois. During July and August 2013 we quantified number of species of plants, bees and butterflies along two 100-m transects in each prairie restoration. We then conducted separate correlation analyses for plant species diversity vs. bee species diversity, plant species diversity vs. butterfly species diversity and plant species diversity vs. all pollinator (bees and butterflies combined) diversity.
Unexpectedly, plant species diversity was negatively correlated with bee species diversity. Further analysis showed that the proportion of honeybees (Apis mellifera) at sites was positively correlated with plant species diversity and had a strongly negative correlation with native bee species diversity. While the main hypothesis of this study was refuted, results of the study demonstrate a relationship exists between plant species diversity and bee species diversity and there is evidence for competition between honey bees and native bees.