For many species, geographical ranges are expanding toward the poles in response to climate change, while remaining stable along range edges nearest the equator. Using long-term observations across Europe and North America over 110 years, we tested for climate change–related range shifts in bumblebee species across the full extents of their latitudinal and thermal limits and movements along elevation gradients.
To investigate bumblebees' responses to climate change, researchers from Canada, Belgium, Germany, UK and US first generated a database of geotagged observations of 67 European and North American bumblebee species from 1901 to 2010.
They compared changes in individual bee species' northward movements in recent decades, against baseline bumblebee activity from 1901 to 1974, when the climate was cooler. To their surprise, bumblebees in recent, warmer decades didn't shift their ranges north. Simultaneously, bumblebee populations disappeared from the southernmost and hottest parts of their ranges, with bumblebees in those locations moving to higher, cooler elevations, where possible. The colleagues also evaluated the roles of factors such as land use and pesticide application, in causing bumblebee range losses - finding no significant correlation.
Bumblebee disappearances from warm, southern areas are just as likely when there is no pesticide use and little agriculture. But we know that increasingly frequent weather extremes, like heat waves, can hit bumblebee species hard, and climate change poses threats that are already being felt.
Global warming has trapped bumblebee species in a kind of climate vise - the result is dramatic losses of bumblebee species from the hottest areas across two continents. For species that evolved under cool conditions, like bumblebees, global warming might be the kind of threat that causes many of them to disappear for good. Unlike so many other species, bumblebees generally haven't expanded into more northern areas. We may need to help these species establish new colonies to the north and at continental scales.
Here is a York university video about this study featuring two of the co-authors, Sheila Colla from Wildlife Preservation Canada and old friend Laurence Packer, world renowned expert on everything Apoidea.