The Buzz about Biodiversity
Is bee species diversity actually important to pollination?
Jacob’s ladder, lacy phacelia, and wild bergamot were about to burst into blue, lavender, and pink and be swarmed by bees when a research group covered them with wedding favor bags. After the flowers opened, they removed the bags and waited. It did not take long for a bee to land.
Back in the lab, they counted the pollen grains the bee had deposited on the flower. Grain by grain, they were discovering how important bee species diversity is to pollination.
Ecologists have long thought — and found through experiments — that when ecosystems lose species, they function worse. Yet those experiments “don’t necessarily mimic the process by which species are lost under real circumstances,” said Emmett Duffy, a marine biodiversity and ecology researcher at the Smithsonian Environmental Research Center who was not involved in the study. This study did.
“They’re addressing the critical question of whether the species that are actually declining are leading to changes to ecosystem services that we really care about,” he said.
Rare and declining species have fewer individuals, and fewer individuals often mean a smaller impact on an ecosystem. Mark Genung, an ecologist at the University of Louisiana at Lafayette, wanted to measure this impact.
“We would love to conserve [rare and declining species] for their inherent value, but can we in good faith go out and tell people that it’s not just their inherent value but also things that are meaningful — tangible things that they contribute to?,” Genung remembered thinking.
To answer this question, Genung’s research group focused on rare and declining bee species. Their findings, recently published in Ecology, discovered those species have a surprisingly large impact.
They first had to determine which bee species were declining. The research group concentrated on New Jersey and Pennsylvania, one of the few regions with the necessary long-term data. They calculated how much each rare and declining species contributed to pollination by finding how often those species visited wildflowers and crops and how much pollen they deposited each visit. They used previously publish data on blueberry, cranberry, and watermelon plants at 16 commercial farms as well as the data they collected on Jacob’s ladder, lacy phacelia, and wild bergamot.
As part of that work, they identified which species visited the wildflowers. “Some bee species are really easy to identify — you could learn it in a few minutes,” Genung said. “Some would take your full professional dedication.”
Joel Gardner, a bee taxonomy PhD candidate at the University of Manitoba, was tasked with identifying the difficult bees, which ran the gamut. Some were smaller than an ant and others “a deep sapphire blue,” Gardner said.
Genung and his team discovered that, overall, rare and declining species did not contribute much to pollination in comparison to common species. Though they constituted half of the species, they only performed 15% of the pollination.
Yet at specific sites and during specific years, they performed as much as 86%. “Even if they’re not that important when you look across everything as a whole, in certain spots or at certain times, they can really step up and do a lot,” Genung said. If a common species is not able to contribute, rare species can fill their role. Rare species also often specialize in pollinating specific flowers. In sites where there are many of those flowers, rare species perform more pollination. To maintain wildflower and crop populations, they need to be pollinated each year and in each site. Rare and declining bee species make that possible.
If the research group had only looked at how much rare and declining species contributed to overall pollination, they would have missed that important finding. “Subjective decisions that you make as part of that process can really influence the story that we tell about what’s important for ecosystem function,” Genung said.
To tell a story that is closest to the truth, ecologists must develop studies that mimic real circumstances, as this one did. “It is very much informed by theory and the conceptual world of this biodiversity function,” Duffy said. “But it is also very much focused on how you address those things in the real world.”
