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It takes all kinds: the underestimated role of rare pollinators

How many pollinators are needed to pollinate all the species in a given community of plants? This question is the focus of a study by a team of researchers including University of Maryland entomologist Michael Roswell. 

Previous research on pollinator bees has over-emphasized the contribution of the most common bees, especially since only two percent of bee species provide 80 percent of pollination. The new study helped to demonstrate that less common bees are much more important for ecosystem health than previously documented.

The answer: Many bees are needed to pollinate a meadow of flowers – far more than just the honeybees and bumblebees that most people are familiar with.

The research shows that when there are more plant species, more bee species are needed for pollination. It was found that less common bees visited specific plants that other bees didn’t. 

“Our work shows that things that are rare in general, like infrequent visitors to a meadow, can still serve really important functions, like pollinating plants no one else pollinates,” said Roswell.  “And that’s a really good argument for why biodiversity matters.”

The researchers surveyed 10 plots that included wild meadows over one year. They observed bees from over 180 species making nearly 22,000 visits to over 130 different plant species. These visits were used to estimate the pollination services each type of bee provided to each plant. This is because a plant’s most frequent visitors are typically its most important pollinators.

The findings showed that an entire meadow community relied on 2 ½ to 7 ½ times more bee species for pollination than a single typical plant species does. The study also found that locally rare species accounted for up to 25 percent of pollinator species. This was greatest in meadows with the most plant diversity. When these findings are applied to an entire ecosystem, the number of locally rare species important for pollination is even greater.

“We were looking at meadows that might be a few acres in size,” said Roswell, “but a typical bee flies over a couple of square miles, which is a really large and complicated landscape filled with lots of different kinds of plants that flower at different times and are visited by different insects. At that scale, even more diversity of pollinators is likely to be important.”

The research sheds new light on the role of rare species in ecosystems that must be protected. Rare species are most at risk of extinction from habitat loss, pollution, climate change and other factors. 

The study is published in the journal Proceedings of the Royal Society B Biological Sciences.

By Katherine Bucko, Staff Writer

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