Collaborative Proposal: The Contribution of Specialist Pollinators to Generalist Plants: When Do Specialists Matter?

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Interactions among species remain an understudied part of biodiversity that is crucial to predicting the structure of natural communities and how they will sustain themselves in a changing world. Pollination by bees stands out as a key interaction on which most plants in natural systems and agriculture depend. In this collaborative project, researchers and students from two U.S. universities, a women's college, and Mexico will investigate the roles played by different native bees in the pollination of desert plants and how their roles change depending on the types of other plants and pollinators in the natural community. Bees are an unusual pollinator group because many species are very selective in the plants they visit (these are known as "specialized" pollinators), while others are generalized, visiting a wide variety of plants. Historically, it was assumed that specialized pollinators would pollinate only plants with elaborate flowers that were difficult for other pollinators to use. Surprisingly, the investigators of this project have found that specialist bees most often go to plants with simple flowers that are also visited by many generalized pollinators. In such cases, the contributions of specialists to their favored plant may be overwhelmed by those of the numerous generalists. Using a set of focal plants, we address the questions: Are these specialized bee species truly important to their host plants? And, if so, does their importance change in concert with the blooming periods of different groups of flowering plants and generalist pollinators? We will assess the importance of specialists and generalist pollinators by measuring the numbers of visits that each bee species makes to the plant and the number of pollen grains transferred during these visits. These data will help reveal not simply how the identities of species change in response to others in the community, but how their functional roles change and what mechanisms underlie these shifts. The answers are central to understanding the structure of pollinator-plant interactions and how they vary in the face of changing environments.