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Dr. Berry Brosi, Emory University – Flowers and Bee Fidelity

In today’s Academic Minute, Dr. Berry Brosi of Emory University explores the impact of pollinator loss on bee behavior and fidelity to their favorite flowers. 

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Dr. Berry Brosi, Emory University – Flowers and Bee Fidelity
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Berry Brosi is an assistant professor of environmental studies at Emory University where his research program seeks to understand the causes and implications of bee declines. His lab explores topics such as the effects of land-use change on bee communities, the impacts of bee species losses on plant pollination, and understanding and managing disease threats in bees.  He holds a Ph.D. from Stanford University.

About Dr. Brosi

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Dr. Berry Brosi, Emory University – Flowers and Bee Fidelity

In this study, we investigated what will happen to native plants when we lose a single pollinator species from an ecosystem.  On the one hand, this sounds almost trivial: pollinator species losses must be bad for plants, right?  On the other hand, computer simulation models suggest that plant communities will actually be very resilient to pollinator species losses, because most plants are visited by multiple pollinator species, so there is backup when one species is lost.

We were skeptical, however, that we would find the same thing in real ecosystems, because the simulations assume that after a pollinator species loss, the remaining pollinators would behave exactly as they had done before.  By contrast, previous research suggests that when species are lost and competition is reduced, remaining species tend to become more generalized.

And that could be bad, because pollination requires specialization.  Plants need pollen from the same species to become successfully pollinated.  We call pollinator specialization “floral fidelity”, and we hypothesized that it would be reduced when we lose a pollinator species from an ecosystem, with negative impacts on plants.  

a bumble bee (Bombus nevadensis) foraging on the study's target plant species, tall larkspur (Delphinium barbyei).

To test this hypothesis, we studied bumble bees in wildflower meadows at the Rocky Mountain Biological Laboratory in Colorado.  We set up 20 meter square plots and studied each one in a “control” state, with all of its bee species present, and compared that to a “manipulated” state, in which we removed a single bumble bee species.  To conduct the species removals, we captured bees of the target species using butterfly nets; after the experiments, we released them unharmed.  We quantified floral fidelity by following the foraging movements of individual bees.   We also studied the pollen loads that bees were carrying, the pollen that they deposited on flowers, and the seeds that were ultimately produced as a result.

Our results supported our hypothesis.  We found that in the manipulated state, bees showed reduced floral fidelity relative to bees in the control state.  Flowers in the manipulated state had more pollen from other species deposited on them, and ultimately produced fewer seeds compared to the control. These results suggest that plants may be sensitive to losing even a single pollinator species from an ecosystem.  

Production support for the Academic Minute comes from Newman’s Own, giving all profits to charity and pursuing the common good for over 30 years, and from Mount Holyoke College.

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