Bumblebees and Honeybees Aren't the Only Key Bees

Less common bees play critical roles in ecosystems.

Ceratina bee visits a black-eyed Susan blossom
Ceratina bee visits a black-eyed Susan blossom.

Barry Rosenthall

Although bumblebees and honeybees get all the attention, there are other bees that are just as important to a blooming ecosystem.

Researchers recently uncovered the importance of pollinator diversity and it goes way beyond the bees that are most often in the spotlight. They found that less common bees are more critical to ecosystem health than previously believed.

“When my coauthors Lucia Weinman and Dylan Simpson started graduate school, they were both really intrigued by the fact that in different communities, different bee species seemed to play different roles,” University of Maryland entomologist Michael Roswell tells Treehugger. “It didn't totally fit with some emerging findings that the most common, or dominant species were doing almost all the work. So they dreamed up a way to explore the roles of rare and common species in more naturalistic contexts.”

For the study, researchers used data they collected from nearly a dozen locations in New Jersey over a one-year period. The plots included wild meadows and fields that had been seeded.

Michael Roswell

“Our study suggests that as ecosystems get more complex, biodiversity may get more important. The reason we found is simple: Ecosystem services and processes arise from lots of species, and these species contribute in a variety of (sometimes unique) ways.”

They found more than 180 species of bees making nearly 22,000 visits to more than 130 species of plants. Researchers used these visits to estimate the pollination roles each type of bee played with each plant. They did this because the bees that visit plants most often are usually its most critical pollinators.

They discovered that the more plant species there are in a location, the more the ecosystem depends on a diverse group of bees to pollinate them.

“It's funny, I think many people, and pollination ecologists, in particular, will not be surprised by these findings. We've known for a really long time that different species provide pollination services in different ways, at different times, to different plants,” Roswell says.

“But a huge, looming question for ecologists (and society) is what the consequences of changes and losses in biodiversity will be. Ecologists suspect that rare species are at greater risk of extinction. Because most species are rare, but many ecosystem processes are driven by common species, it is tempting to think that biodiversity loss could lead to relatively minor impacts on ecosystems.”

But the effects of biodiversity loss aren’t necessarily felt evenly.

“What our study showed was that species that, in aggregate, seem rare and probably not that important, are often playing particular roles in which they are much more so,” Roswell says.

The findings were published in the journal Proceedings of the Royal Society B Biological Sciences.

Finding the Full Picture

Researchers point out that earlier studies on the roles of bees as pollinators often focused on certain plants (such as crops) or all plants in an ecosystem, treating them as if they were one species. In these cases, the results often overemphasized the importance of common bees, particularly because 2% of bee species are responsible for 80% of crop pollination.

But they aren’t the only key bees.

“In New Jersey, there are likely over 400 species of wild bees. Fewer than 5% are bumblebee species,” Roswell says. “When I've sampled, I found that bumblebees make up a quarter to half the pollinators. We want to see the full picture.”

He points out that honeybees and bumblebees often make headlines because of population declines.

“Actually, honeybees are definitely not declining, neither in the U.S. nor globally. Bumblebees, which are very effective pollinators, are threatened globally and in this region, with clear declines in many species,” he says.

Less common bees are even more at risk of extinction from factors such as habitat loss, pollution, and climate change. While common bees are often studied because they are often so visible.

“Both bumblebees and honeybees are larger-bodied, social organisms that can have large colonies, so they often gather in large numbers on flowering resources, and they're easy to see and hear. They are, as you say, very effective pollinators in many systems,” Roswell says.

“But sweat bees and small carpenter bees, spring-flying miner bees and mason bees, and other bees are also important pollinators in both crops and wild systems... and these species may also be in trouble. Learning more about their ecology, and their role in pollination is a first step to conserving them and the ecosystems they support.”

Researchers say these findings are fascinating, but they are also important for future studies.

“In the past several decades, ecology has coalesced around findings from experiments that show that ecosystem functions increase with biodiversity—up to a certain level. We really want to know how those results scale up to real-world ecosystems, which are much more complex,” Roswell says.

“Our study suggests that as ecosystems get more complex, biodiversity may get more important. The reason we found is simple: Ecosystem services and processes arise from lots of species, and these species contribute in a variety of (sometimes unique) ways.”

View Article Sources
  1. "Many bee species, including rare species, are important for function of entire plant-pollinator networks." Proceedings of the Royal Society B, vol. 289, no. 1972, Apr. 2022. doi:10.1098/rspb.2021.2689

  2. Cutlip, Kimbra. "Research led in part by UMD reveals the importance of pollinator diversity, highlighting the role of rare bees in wild ecosystems." University of Maryland College of Agriculture and Natural Resources, 12 Apr. 2022.

  3. University of Maryland entomologist Michael Roswell