Mentor: Dr. Neal Williams
More than 66% of the crops worldwide are insect pollinated with bees often being the most important pollinator. Although honey bees have been considered the cornerstone of agricultural pollination in the USA, an increasing number of studies suggest that native bees also provide pollination services. Because these species are not managed, their contribution to crop pollination may vary with the area and the proximity of natural habitat to farm sites. Studies in California suggest that the amount and stability of pollination from native bees increased with the area of upland habitat 1. Surveys of bees from central Europe show that the overall species richness and abundance of native bee species decrease as more land is lost to commercial or residential development.2 As the colonies of managed European honeybees (Apis mellifera) steadily decline3 in the US, the importance of native bees as crop pollinators increases. Because natural habitat provides nesting resources for native bees, potentially the dependency of crops on bee pollinators might provide viable incentives for the conservation of natural areas to procure the needed pollination services from native bees.
Given the importance of Pennsylvania and New Jersey for agriculture and the loss of natural habitat in the region due to development pressure, my research, as a part of an ongoing project of Professor Neal Williams and his collaborators, will focus on the change of contributions of native bees to crop pollination as a function of the landscape matrix. For this study I will visit 20 farm sites in Bucks and Montgomery, PA, Hunterdon and Mercer counties, NJ. Watermelon (Citrullus lanatus) and cherry tomato (Lycopersicon esculentum), the target crops of this study, have specific flower morphology that requires bees for pollination and, hence, fruit formation. To determine the pollination efficiency of native bees, I will measure visitation rates by native bees on the two crops and quantify the pollen deposition by each bee species on watermelon in addition to my work with GPS (Global Positioning System) and GIS (Geographic Information System) to help prepare a landscape use map of the area around farms.
Based on the findings of previous studies, my hypothesis is that the pollination services of native bees decrease as a function of the area and proximity of natural habitat surrounding the farm site. Also, I expect to find that diversity in the natural habitat enhances the complexity of pollination webs and population sizes of individual species since it can provide a wider array of nesting resources2. These predictions have implications for the degree of substitutability of A. mellifera with native pollinators, for amount of crop yields and for the conservation of natural areas.
1. Kremen, C., Williams, N.M & Thorp, R.W. (2002). Crop pollination from native bees at risk from agricultural intensification. Proc. Natl. Acad. Sci. USA, 99, 16182-16186
2. Steffan-Dewenter, I., Münzenberg, U., Bürger, C., Thies, C. & Tscharnitke, T. (2002). Scale-dependent effects of landscape context on three pollinator guilds. Ecology, 83(5), 1421-1432
3. Kremen, C., Williams, N.M., Bugg, R.L., Fay, J.P. & Thorp, R.W. (2004). The area requirements of an ecosystem service: crop pollination by native bee communities in California. Ecology Letters, 7, 1109-1119