Floral Shape and bee communities

A honeybee on an open-shaped flower. Photo by George Gray. 

A bumblebee on a tube-shaped flower, photo by Brendan Zwelling.

This week's paper is published in Biology Letters, single-authored by Katherine Urban-Mead, a graduate student in the Department of Entomology at Cornell University. Urban-Mead used network analysis to examine how the shapes of flowers impacted bee species abundance in floral communities. In particular, Urban-Mead compared the availability of flowers with open corollas where the nectar is easily accessible to bees (especially short-tongued bees, but more on that later) with flowers with tube-shaped corollas where the nectar is at the base of the corolla requiring bees to enter the flower (and may therefore be easier for long-tongued bees). 

Urban-Mead worked in six meadows in Connecticut containing diverse flowering plants. In each meadow she selected three 3 x 6 m plots that had similar floral communities. In one plot she removed all the open flowers from one half of the plot, in the second plot she removed all the tube-shaped flowers from one half of the plot, and the third plot was left undisturbed. Urban-Mead then watched these floral plots and recorded the visits made be visiting bees of different morphospecies (bees are quite hard to identify to species in flight - so they are often lumped into identifiable groups). In total she saw more than 500 bees visit more than 3500 flowers. 

The bee community that visited open flowers in all plots was more diverse than the bee communities that visited tube-flowers. In the plots with the open flowers removed, the bees on the remaining tube flowers were not different from the bees on the tube flowers in the undisturbed plots. In the plots with the tube flowers removed, however, the bees on the open flowers were different from the bees on open flowers in undisturbed plots. Part of this shift appears to be due to tongue-length. Bees with longer tongues can more easily access nectar in tube-shaped flowers, and correspondingly, there is a higher proportion of long tongued bees in the control plots and plots with open flowers removed than in plots with tube-shaped flowers removed. It appears, therefore, that the availability of tube-shaped flowers is a more important predictor of bee communities than open flower shapes, but open flowers host higher bee diversity in general.