A Need for Specialists and Generalists

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Science  10 Feb 2006:
Vol. 311, Issue 5762, pp. 743
DOI: 10.1126/science.311.5762.743a

No one disputes the agricultural importance of pollination, but what might happen if, under the current mass extinction, pollinator diversity were compromised? Fontaine et al. have measured the effect of pollinator diversity on plant yields in a 2-year experiment in caged plots at a site outside Paris. They created unmixed and mixed communities of plants with open or tubular flowers and pollinator insects with long (bumblebees) or short (syrphid hoverflies) proboscises, and they counted the number and species of fruits, seeds, and seedlings produced. As expected, the type of pollinator did have a significant effect: Bumblebees stimulated more fruit production overall, and the tubular flowers were unable to form fruits well if only syrphids were present. But there were unexpected effects: Although able to trigger fruit production, the bumblebees gave rise to fewer seeds per fruit for the open-flowered plants (possibly because they kept revisiting the same flowers, which is called geitonogamy), and when both types of pollinators were present, the overall recruitment of seedlings was enhanced, especially in the most complex of the communities. It appears that in mixed plots, the bumblebees show a preference for the tubular flowers and hence reduce their frequency of visits to the open flowers, which leaves the open flowers to the more efficient attentions of the syrphids. — CA

PLoS Biol. 4, e1 (2006).

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