Pollinator Community Homogenization and Pollination Services in Agroecosystems

Pollination, or the transfer of pollen to plant stigmas, is an essential part of plant reproduction. The term “pollination system” refers to the floral phenotype and pollinator of a given plant. Although angiosperms exhibit a variety of different pollination systems, most rely partially or completely on animals, particularly insects, to vector their pollen. In agricultural systems, understanding the pollination system of the crop species is necessary to produce an economically valuable yield. Moreover, agricultural management may affect pollination systems by altering the abundance, diversity, or function of the pollinator community. In natural ecosystems, there is a great diversity of pollinating insects. This pollinator diversity may be vulnerable to global change and land use. One concern is that land use change may homogenize these pollinator communities, which in turn might affect their pollination service to angiosperms. To better understand the effect of agriculture on the homogenization of pollinator communities, we conducted a survey of pollinator diversity in different land-use types in eastern Tennessee. We sampled flower-visiting (pollinating) insects from the landscape around experimental plots of plants native to Tennessee. We found that the plots represent a subset of the pollinator diversity at the landscape level at most of our sites but found no effect of land-use type of pollinator community homogenization. To complement this landscape survey, we also evaluated pollination services in a focal agricultural crop. First, we conducted a greenhouse study to evaluate biotic effects of tree health and pollen donor on fruit set. We found that tree identity and size affected the probability of fruit set in greenhouse cacao trees. Another way to evaluate the effect of management on agricultural pollination services is to measure fruit set in different management scenarios. For example, agroforestry is a more sustainable way to grow cacao (Theobroma cacao), an extremely important crop world-wide; however, the effects of agroforestry on cacao pollination are unknown. In addition, pollination may affect the varietal purity of cacao, thereby affecting its market value. We conducted a hand-pollination experiment on Criollo and Trinitario cacao grown within an agroforestry setting in Punta Gorda, Belize. We examined the self-pollination and cross-variety compatibility of these cacao varieties. We found that the Criollo variety can self-pollinate whereas the Trinitario variety cannot. However, both varieties are compatible with one another, leading to implications for pure heirloom chocolate production where they are grown in close proximity.