Bees ‘betray’ their flowers when pollinator species decline
Remove even one bumblebee species from an ecosystem and the impact is swift and clear: their floral “sweethearts” produce significantly fewer seeds. The results show how reduced competition among pollinators disrupts floral fidelity, or specialization, among the remaining bees in the system, leading to less successful plant reproduction. The alarming trend suggests that global declines in pollinators could have a bigger impact on flowering plants and food crops than was previously realized.
July 22, 2013 — Remove even one bumblebee species from an ecosystem and the impact is swift and clear: Their floral “sweethearts” produce significantly fewer seeds, a new study finds.The study, to be published by the Proceedings of the National Academy of Sciences, focused on the interactions between bumblebees and larkspur wildflowers in Colorado’s Rocky Mountains. The results show how reduced competition among pollinators disrupts floral fidelity, or specialization, among the remaining bees in the system, leading to less successful plant reproduction.”We found that these wildflowers produce one-third fewer seeds in the absence of just one bumblebee species,” says Emory University ecologist Berry Brosi, who led the study. “That’s alarming, and suggests that global declines in pollinators could have a bigger impact on flowering plants and food crops than was previously realized.”The National Science Foundation (NSF) funded the study, co-authored by ecologist Heather Briggs of the University of California-Santa Cruz.About 90 percent of plants need animals, mostly insects, to transfer pollen between them so that they can fertilize and reproduce. Bees are by far the most important pollinators worldwide and have co-evolved with the floral resources they need for nutrition.During the past decade, however, scientists have reported dramatic declines in populations of some bee species, sparking research into the potential impact of such declines.Some studies have indicated that plants can tolerate losing most pollinator species in an ecosystem as long as other pollinators remain to take up the slack. Those studies, however, were based on theoretical computer modeling.Brosi and Briggs were curious whether this theoretical resilience would hold up in real-life scenarios. Their team conducted field experiments to learn how the removal of a single pollinator species would affect the plant-pollinator relationship.”Most pollinators visit several plant species over their lifetime, but often they will display what we call floral fidelity over shorter time periods,” Brosi explains. “They’ll tend to focus on one plant while it’s in bloom, then a few weeks later move on to the next species in bloom. You might think of them as serial monogamists.”Floral fidelity clearly benefits plants, because a pollinator visit will only lead to plant reproduction when the pollinator is carrying pollen from the same plant species. “When bees are promiscuous, visiting plants of more than one species during a single foraging session, they are much less effective as pollinators,” Briggs says.The researchers conducted their experiments at the Rocky Mountain Biological Laboratory near Crested Butte, Colorado. Located at 9,500 feet, the facility’s subalpine meadows are too high for honeybees, but they are buzzing during the summer months with bumblebees. …
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