Bumblebees are struggling to adapt to global warming and are simply dying rather than migrating northward to cooler climes, said a study Thursday that raised new concerns about these important pollinators.
The report in the journal Science is the first of its kind to point to the role of climate change in worldwide bee decline, which until now has largely been blamed on pesticide use, parasites, disease and loss of areas for habitat.
"Picture a vice. Now picture the bumblebee habitat in the middle of the vice," said lead author Jeremy Kerr, professor of macroecology and conservation at the University of Ottawa.
"As the climate warms, bumblebee species are being crushed as the 'climate vice' compresses their geographical ranges," he added.
"The result is widespread, rapid declines of pollinators across continents, effects that are not due to pesticide use or habitat loss."
Bumblebees help pollinate plants, wildflowers and fruit trees as well as important crops like blueberries and tomatoes, providing an invaluable service to agriculture and wildlife.
By examining nearly a half million records from museums and citizen scientists on 67 bumblebee species in North America and Europe beginning in 1900, researchers were able to track changes in the bumblebees' range over time.
They found that bumblebees have lost as many as 185 miles (300 kilometers) of their historical southern range in North America and Europe.
"This is a huge loss, and it has happened very quickly," said Kerr.
"We are looking at rates of loss of about nine kilometers per year from those southern areas," he told reporters.
Meanwhile, bumblebees are "generally failing" to move north and are instead gong locally extinct in some areas.
"They just aren't colonizing new areas and establishing new populations fast enough to track rapid human caused climate change," Kerr said.
The failure of bumblebees to adapt is in contrast to the behavior of butterflies, which have been shown to change their migration patterns in response to warming temperatures.
- Not pesticides, climate -
Researchers said the current paper shows no indication that bumblebee decline is linked to human land development or to insect-killing chemicals that protect crops, known as neonicotinoids.
"Bumblebee range losses began before neonicotinoids were in wide use," said co-author Alana Pindar, also of the University of Ottawa.
"This cannot be interpreted to mean that neonicotinoids do not and cannot harm bees, just that they do not affect our results," she said.
Bumblebees are believed to have originated some 35 million years ago. Since they are natives of cooler areas than tropical butterflies, scientists think bumblebees may be not be as well-equipped to cope with warming temperatures.
Ways to help the bees survive should include reducing global greenhouse gas emissions, as well as helping them establish populations in northern latitudes, a process known as assisted migration, researchers said.
The study did not examine population density, so it did not delve into the health of bumblebee populations. Some species are known to be coping better than others.
- New direction -
According to science director of the International Bee Research Association, Norman Carreck, who was not involved in the research, the study is "important," because it points researchers in a new direction.
Until now, "scientists have been fairly relaxed about the effects of climate change, arguing that since pollinators can fly, if confronted by changing and hostile conditions, they would simply move to more suitable conditions, perhaps shifting northwards," said Carreck, who is also a researcher at the University of Sussex.
"However, this paper reveals that the true picture is more complex, and that this does not appear to be happening."
Given the losses that have been seen so far, researchers expect the problem will only get worse, and more bumblebees will disappear in the coming decades unless human-caused climate change can be stopped.
The decline in pollination could make food more expensive and some crops harder to grow, researchers said.
"Impacts are large and they are underway. They are not just something to worry about at some vague, future time," Kerr said.