Bumblebee habitats are shrinking in response to climate change, in a way that differs from the responses of other organisms.

The area inhabited by bumblebees is shrinking, and scientists aren’t sure why. Image Credit: James Petts

“Picture a vise. Now picture the bumble bee habitat in the middle of the vise.”

Those words are from Jeremy Kerr, professor and university research chair in macroecology and conservation at the University of Ottawa. He is the lead researcher of a recent study that highlights how bumblebee habitats are being squeezed into a smaller and smaller area thanks to climate change.

The study, published in July in Science, looked at more than 400,000 population data points for 67 species of bumblebee in North America and Europe. The researchers measured the latitudinal and thermal limits of the bumblebees’ ranges and their mean elevation in three, 12-year periods between 1975 and 2010 and compared these periods to a larger baseline period (1901 to 1974).

The results: While bumblebee populations are moving the southern borders of their habitats northward in response to climate change, they have yet to move their northern borders northward as well, thus constraining themselves to an overall smaller habitable area.

As climate change warms the bumblebees’ habitat, the populations have moved their southern range limits further north by as much as 300 kilometers in both North America and Europe. Like other species, a similar northward shift of the northern range limit would be expected, as higher latitudes become warm enough to provide habitat for the bumblebees.

However, the researchers were surprised to find that the bumblebees don’t seem to be expanding their northern limits at all.

“Many other species groups like butterflies are generally expanding to the north and into colder areas,” Kerr tells the Calgary Herald, but “the bumblebees are doing something quite different.”

What exactly is preventing the bumblebees from moving their northern habitat borders to higher latitudes is unknown. The study says that the forces preventing the bumblebees’ northward expansion “require urgent evaluation.”

What the research does strongly indicate is that climate change appears to be the reason for this habitat squeeze. The researchers also included historical observations of land use and pesticide use in bumblebee habitats over the periods they surveyed, and neither was found to contribute significantly to this particular trend.

The importance of bees is hard to overstate. One-third of the human diet consists of plants pollinated by insects, and bees are responsible for the pollination of 80 percent of the world’s flowering plants, including 75 percent of fruits, nuts, and vegetables in the U.S. Crops directly and indirectly dependent on insect pollination contributed a total of $27 billion to the U.S. agricultural economy in 2009.

In May 2015, the White House released a strategy to encourage pollinator health in the U.S. The “Strategy to Promote the Health of Honey Bees and Other Pollinators” includes constructing gardens for pollinators and restoring pollinator habitat on federal land. With their habitat seemingly being compromised due to climate change, such measures may be critical for bumblebee survival.

Alec Drobac is a senior physics major at Middlebury College in Vermont. He hopes to pursue a career as a theoretical physicist, potentially in the field of astrophysics or cosmology. Originally from California, he is particularly concerned with water usage and conservation, as well as the advancement of technology in agriculture.