The alarming rate of decline of bumblebees—key pollinators of crops and wildflowers across the world and an essential part of a healthy environment— has been at the forefront of scientific news for the past several years. To date, most of the bee die-off has been attributed to changes in agricultural practices and the use of bee-killing pesticides such as neonicotinoids. Recent study, however, adds another dimension to the decline of bumblebees. Kerr et al. (2015) used over 100 years of observations across European and North American continents to test for climate-change related range shifts in bumblebee species across their latitudinal and thermal limits. Using Global Biodiversity Information Facility (GBIF), Bumblebees of North America, and the Status and Trends of European Pollinators Collaborative Project, Kerr et al. assembled a database of over 420,000 observations for over 65 species of bumblebees. Using these observations, they measured differences in species’ northern and southern range boundaries, their thermal limits (i.e., the warmest or coolest temperatures where the species were found), and species’ mean elevations in three periods (1975 to 1986, 1987 to 1998, and 1999 to 2010) and compared those to the baseline conditions between 1901 and 1974.
Kerr et al.’s findings suggest that bumblebees have been unsuccessful in tracking changing climatic conditions: While species have experienced significant losses from southern range boundaries, there has been no corresponding expansion of range limits to the north. Shifts to higher elevations were restricted to southern species. Kerr et al. (2015) tested for effects of changing land uses and pesticide applications, but found that those factors did not contribute to the observed changes. Climate change thus appears to have contributed distinctively to the observed range compression among bumblebee species. To mitigate these range losses, the authors suggest assisted colonization of bumblebee colonies into new, climatically-suitable areas.
Kerr J.T. et al. 2015. Climate change impacts on bumblebees converge across continents. Science, 349, 177-180.