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How an explosion in urban beekeeping coincided with a decline in wild pollinators

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How an explosion in urban beekeeping coincided with a decline in wild pollinators

"Just as we wouldn’t advocate keeping backyard chickens to save the birds, we shouldn’t look to beekeeping to save the bees,” say researchers.
May 10, 2023

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Much like growing vegetables in front yards, rooftops and abandoned lots, raising honey bees in in cities is enjoying a surge in popularity. The growing interest in local food production, concern about a decline in pollinator numbers and a more general fascination with fusing city living and nature all deserve credit.

But while city-dwelling bee wranglers might feel like they are adding to their neighborhood’s nature-friendly features, it isn’t that simple. The proliferation of hives might be taking a toll on the other pollinators living there.

“Urban beekeeping is often falsely marketed as a solution to biodiversity loss,” says Carly Ziter, a biology professor at Concordia University in Montreal, Canada. “Just as we wouldn’t advocate keeping backyard chickens to save the birds, we shouldn’t look to beekeeping to save the bees.”

Ziter was part of a group of Montreal scientists who set out to see how an explosion in honey bee hives within their city might be affecting the more than 150 species of wild bees sharing space with 2 million people in this eastern Canada city.

The number of honey bee colonies there recorded by government officials rose from 238 in 2013 to nearly 3,000 by 2020. With as many as 50,000 honey bees in a single hive, that’s a lot of insects scouring neighborhood flowers for pollen. The researchers wondered if this infusion of honey bees might be creating a food shortage for their bee brethren.

 

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To figure that out, they replicated a 2013 survey of bees in the city. They descended on 15 different pollination hotspots – community gardens, cemeteries and nature parks. Using insect traps and nets, they spent the summer and early fall of 2020 collecting bees while navigating the restrictions of the early months of the COVID-19 pandemic. All told they captured more than 6,200 bees.

When they compared their catch to seven years earlier, a few things stood out. There were a lot more honey bees. And a lot fewer species of wild bees. Seven years earlier, bee-seekers counted roughly the same total number of bees – nearly 5,300. But just 122 of those were honey bees, compared to 2,291 honey bees in 2020. Meanwhile, the number of different types of wild bees fell from 163 species to 120, the scientists reported recently in the journal PeerJ.

It doesn’t look like a coincidence. “We found that the sites with the largest increase in honey bee populations across sites and years also had the fewest wild bee species,” said Gail MacInnis, the study’s lead author, formerly a Concordia postdoctoral researcher who is now with the National Bee Diagnostic Centre in Alberta.

The scientists found some clues about why this might be happening. White clover flowers sampled from sites with more honey bees had less pollen, suggesting the domesticated bees were hoovering up more of the food.

The small species of wild bees were the hardest hit. So the effect is being felt by the types of bees most limited by the distance they can travel to find more flowers.  

The scientists have a few suggestions on ways to reduce the toll beekeeping takes on wild pollinators. For starters, there is no government agency tracking where beehives are located, making it hard to know if honey bees are concentrating in particular hotspots in numbers that raise the risk of a disease outbreak among the insects.

Also, if people want to make life sweeter for wild bees, they might want to turn their attention from beekeeping to gardening. “If our goal is to increase urban biodiversity,” says Ziter, “We’re much better off planting pollinator gardens than adding more urban hives.”

MacInnis, et. al. “Decline in wild bee species richness associated with honey bee (Apis mellifera L.) abundance in an urban ecosystem.” PeerJ, Feb. 3, 2023.

Image: via Flickr

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