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Extreme Heat Drives North American, European Bumblebee Species Toward Extinction

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Extreme heat waves brought on by climate change have already driven some North American and European bumblebee species to the edge of extinction, according to a new study published last week in the journal Science.

“Climate change could increase species’ extinction risk as temperatures and precipitation begin to exceed species’ historically observed tolerances,” writes [1] a research team led by University of Ottawa biologist Peter Soroye. “Increasing frequency of hotter temperatures predicts species’ local extinction risk, chances of colonizing a new area, and changing species richness.”

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The impact is independent of land use changes, and the research method “explains observed patterns of geographical range loss and expansion across continents,” the scientists add in their research abstract. “Increasing frequencies of temperatures that exceed historically observed tolerances help explain widespread bumblebee species decline,” and “this mechanism may also contribute to biodiversity loss more generally.”

Citing the study, InsideClimate News notes that bumblebee populations “have been hardest hit in warming southern regions such as Spain and Mexico, where some species already live near the edge of their temperature range. Sometimes it just gets so hot that bees die and fall out of the sky.”

“Bumblebees are disappearing from areas eight times as fast as they are recolonizing others,” and “disappearing from areas where it’s getting hotter fast,” Soroye said. “They are the best pollinators in wild landscapes and really important for crops like tomatoes, squash, and berries.”

Although research in this field has been hampered by limited data, the latest study “analyzed more than half a million bumblebee observations of 66 species in Europe and North America from two time periods: 1901 to 1974, and 2000 to 2014,” InsideClimate writes. “The researchers mapped where the bees are now compared to where they used to be historically, and matched those records with changes in temperature and precipitation.”

They found the average probability of bumblebees occupying a particular site fell 46% in North America and 17% in Europe between the two time periods, indicating that “future warm extremes will continue to put the important pollinators under pressure,” ICN adds. “The new study also suggests that extreme heat poses risks for other species, including mammals, birds, and reptiles,” for which bumblebees are an indicator species.

“We were trying to answer the question, ‘Is climate change causing extinctions’? We decided to use bumblebees as a test example, and it turns out they work really well,” Soroye told InsideClimate. “In theory, these ideas are really universal for birds, reptiles, and mammals.”

University of British Columbia botanist and biodiversity researcher Jeanette Whitton, who was not involved in the study, said the findings point to a powerful way to determine the impact of warming and heavier precipitation on bumblebee populations. “We now have a stronger case linking changes in climate extremes to changes in abundance and distribution of bees,” she said. “We know that many plants rely on bees for their reproduction, so it’s not a big leap to say that this matters to plants. If bees decline, this won’t be good for the plants that rely on the bees.”

University of Sussex biologist and bumblebee specialist Dave Goulson said the results were no surprise. “Bumblebees thrive in cool, temperate climates. They are scarce in warmer regions where they tend to overheat in hot weather,” he said. “It seems likely that a rapidly warming future climate may be the final straw for many of them.”

In a related article in Science, University of Bristol ecologist and evolutionary geneticist Jon Bridle and University of Zurich evolutionary biologist Alexandra van Rensburg said the new study reinforces the link between climate change and biodiversity loss. The research “adds to a growing body of evidence for alarming, widespread losses of biodiversity and for rates of global change that now exceed the critical limits of ecosystem resilience,” they wrote. Soroye said the biodiversity crisis is “entirely driven by human activities,” making it crucial to understand where and why extinctions happen.

In addition to ending greenhouse gas emissions, scientists suggested a few steps to protect bees, like stopping the introduction of non-native populations to new areas, reducing pesticide use, restoring grasslands, and relying on citizen science to fill data gaps. “Homeowners can make their property more bee-friendly by using certain types of plants, and they can become advocates for bumblebee conservation by participating in community planning and decision-making to ensure there are bee-friendly areas like parks and highway medians,” InsideClimate adds.

Whitton also stressed the importance of political action. “If I was to say what people can do, I would say vote for people who recognize the importance of science as a basis for sound environmental, social, and other policies,” she said.