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The diversity of bees is important for maintaining

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image: A bee of the genus Ceratina on a plant of the genus Ipomoea (morning glory).
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Credit: Joe Zientek

Rutgers scientists assessing the level of bee species diversity needed to sustain wild plant populations have concluded that ecosystems depend on many bee species to thrive, not just a few dominant ones.

The report, published in The Proceedings of the Royal Society Bsupports the fundamental idea that biodiversity is essential for sustaining life on Earth, especially at a time when species are rapidly disappearing due to the pressures of climate change and human development.

“This is one of the strongest demonstrations to date of the importance of bee diversity and rare bee species in maintaining healthy ecosystems,” said Dylan Simpson, author and doctoral student on the program. Graduate Studies in Ecology and Evolution from Rutgers. “It’s important because pollination is essential for plant reproduction. And life on earth ultimately depends on plants.

The researchers conducted their investigation by analyzing data from extensive field surveys recording bees visiting flowers in 10 wilderness settings and an experimental garden of native plant species in New Jersey. In the surveys, the researchers directly observed bee-plant interactions, identified the bee species and flower species visited, and tracked the frequency of interactions between specific bee and plant species.

There are about 400 species of bees in New Jersey alone – some familiar ones, like the common eastern bumblebee (Bombus impatiens), but others rarely seen. “There are a lot more bees than you think,” Simpson said. “Many are small, some are metallic and shiny, some are dark, unscratched and inconspicuous.”

While the sightings were all made in open grassland habitats, the bee species observed included those associated with both forests and human-dominated habitats. Pollinated plants included some of the following plants: Black-eyed Susan (Rudbeckia hirta); bee balm (Fistulous monarda); different species of goldenrod (of the genus Solidago); New England Aster (Symphyotrichum novae-angliae); species of milkweed (of the genus Asclepias); and common weeds, such as white clover (Trifolium repens) and red clover (T. pratense).

Researchers were trying to establish how many species of bees are needed to pollinate distinct segments of nature. Using this as a framework for investigation, they also wanted to understand the function of rare species in this landscape.

“There is a moral and ethical imperative to try to manage ecosystems to keep communities as they are, so they don’t disappear,” Simpson said. “But there’s also the practical argument to be made to come to a better understanding – much of our food comes from animal-pollinated crops.”

Based on their analysis of the data, the authors found:

  • Different species of bees are often important for different plant species. Accordingly, while only a few bee species are important for a particular plant species, the number of bee species needed to support a large plant community must be equally large.
  • A significant portion of the bees that pollinated the plants were rare species.

Much of the past research has generally focused on single-species crops and concluded that pollination often depends on a few honey bees.

“In contrast, this study focused on a wider variety of plants and found that even rare bees can be important for particular plants,” Simpson said. “These findings suggest that ecologists have likely underestimated the importance of bee diversity for pollination in various natural ecosystems.”

Other authors on the paper include: Rachael Winfree, a professor in the Rutgers Department of Ecology, Evolution and Natural Resources; Lucia Weinman, Michael Roswell, and Molly McLeod, all from Rutgers’ graduate program in ecology and evolution; and Mark Genung of the University of Louisiana at Lafayette.


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