Climate change is imperiling bumblebees in the US and Europe

Jul 27, 2015

A recent report in the journal Science says climate change has caused bumblebee habitat to shrink by as much as 180 miles in the last 40 years — a pace researchers say is quite alarming.

Jeremy Kerr, the lead author on the study and a professor of biology at the University of Ottawa, says the bumblebee is caught in a kind of vice: its habitat is not extending northward to adjust to changing temperatures and the habitat in its southern range is diminishing.

“The geographical range of a species ... looks a little like a big rug if you were to spread it out on a giant map of North America or Europe,” Kerr says. “What we're effectively doing with climate change, our best measurements suggest, is rolling that rug up from the south. And since the bumblebee, unlike may other species, is not tracking north to areas that are getting warmer, the net effect is that their ranges are constricting through time."

What’s more, Kerr adds, the phenomenon is global. “These effects are happening at exactly the same pace and with very similar timing across continents,” he says. The study looked at 67 bumblebee species over a period of 110 years, comprising about 423,000 observations across both Europe and North America.

Kerr says the researchers had access to very good data on the effects of pesticides on bumblebee populations in the US, which allowed them essentially to eliminate pesticides as a primary cause of the habitat change.

“We know from multiple lines of evidence that pesticide and habitat losses kill bees. Those facts are not in dispute,” he says. “Particularly dangerous [is a] group of pesticides directly designed to kill insects called neonicotinoids. [But] we found that, at the boundaries of where you find species, the habitat loss predates the use of neonicotinoids.”

The researchers also found that, statistically speaking, bumblebee species at the boundaries of their range are just as likely to have fared well or poorly in places where neonicotinoid use is high.

In addition, they looked at changing land use “as carefully as the data would let [them] do,” and found no effect that would account for their observations. There is no doubt, Kerr says, that “we’re seeing a climate change-related signal.”

Kerr suspects the bumblebee’s distinctive evolutionary origin explains why they are not moving northward like other pollinators. Scientists know from research done in the US that bumblebees evolved in cool, temperate conditions in Eurasia.

“We tested for an evolutionary signal among our bumblebee species in this study to see whether or not closely related species responded in similar ways to shifting climatic conditions,” he explains. “We found that the more closely related bumblebee species are, the more likely it is that they share an intolerance for extreme heat conditions.”

Some scientists have proposed the idea of ‘assisted migration’ for bumblebees — literally relocating the bees to areas where they might thrive. Kerr says this is something to consider, but advises cautions, as there could be unintended consequences.

“Bumblebee species, unlike honeybees, are wild animals and tend to have much smaller colonies,” Kerr says. “Just picking up those colonies and moving them to the north is quite a different sort of prospect with bumblebee species, because they don't live in boxes with tens of thousands of individuals in them. Their natural history is very different and colonies don't persist in a general sense from one year into the next.”

But while researchers investigate this idea “we also have an opportunity to do a better job managing areas where bumblebee species are currently found,” Kerr says.

“We can think about reducing unnecessary applications of pesticides, maintaining field margins with wild flowers, which are great nectar and pollen resources for bumblebees, and planting native wild flowers in our own gardens,” he says. “All of these things will help hold onto the pollinators and buy us some time while we come to grips with the question of assisted migration — and the much more important problem, ultimately, of dealing with climate change as though we actually wanted to solve that problem."

This article is based on an interview that aired on PRI's Science Friday with Ira Flatow