Density and diversity of bees in the Midwestern agricultural landscape: Influence of surrounding agricultural land use and local plant community characteristics

After over a century of large-scale agricultural development in the Midwestern corn-belt of the United States, many wild bee pollinator populations are in rapid decline or extirpated from their historic range. Large-bodied species, such as Bombus spp. are especially threatened, but are also valuable as efficient natural pollinators that are capable of effectively pollinating many economically important crops. Bees, therefore, have high conservation value, and pollination research has shifted focus from community inventory to population recovery efforts. These efforts include reducing the effects of habitat fragmentation and destruction using ecological restoration as well as integrating conservation strategies into agricultural land management. This thesis investigates both strategies by analyzing local and landscape-scale vegetation effects on wild bee populations. At the local scale, I sampled and analyzed bee populations on land planted with perennial tallgrass prairie plants utilized for alternative bioenergy production at the University of Northern Iowa’s Cedar River Ecological Research Site. These plantings ranged in diversity from a switchgrass monoculture to a diverse 32-species biofuel feedstock mixture. At the landscape scale, I used existing remote sensing products to examine the effect of surrounding land cover on bee community indices at small organic farming operations throughout Iowa. I found at the local scale that both bee abundance and diversity increased with plant species richness in biofuel crops, and that temporal stability of floral resources may be a more important factor than sheer abundance of flowering plants. Temporal stability in floral resources refers to the change in abundance of floral food sources for pollinators as well as the degree of overlap in flowering times throughout the growing season. Diverse biofuel feedstocks have a positive effect on the wild bee community and at a site level are capable of supporting a pollinator community similar diversity to small remnant tallgrass prairie communities. At the landscape scale, bee diversity responded positively to surrounding natural land cover and negatively to agricultural row crops like corn and soy. I was unable, however, to link wild bee abundance to surrounding land cover, perhaps because finescale, on-farm factors may have a greater influence on bee abundance, especially for smaller, less mobile species. I conclude that increasing floral abundance and diversity in the landscape is an important step toward recovery of wild bee pollinator communities. It is evident that both degree of isolation from suitable habitat as well as local habitat quality influence pollinator communities of conservation concern