Mr Peter Soroye1, Dr Tim Newbold2, Dr Jeremy Kerr1
1University Of Ottawa, Ottawa, Canada, 2University College London, London, United Kingdom
Bumblebee (Bombus) species across North America and Europe are declining in range size and abundance across their ranges, linked in part to rapid recent climate change. Niche theory and physiology suggest that species’ physiological limits might define whether they persist in some areas and may help to inform predictions on climate change effects. Here, we develop a novel, spatially-explicit index for calculating species’ exposure to thermal and precipitation limits across their ranges. Using temporally and spatially explicit climate data, and a comprehensive occurrence dataset of 66 North American and European bumblebee species, we test whether a species’ or communities’ proximity to thermal or precipitation tolerance limits predicts local extinction, colonization, occupancy, and species richness change. We document declines in mean range size and likelihood of site occupancy by 40% and 27% since 1901. Local extinction events are 8 times more likely than colonization events. Models including environmental exposure predicted up to 54% of variation in site-specific local extinction, local colonization, occupancy, and species richness change. Using our index improved predictions over using models with simple climate variables (average temperature and total annual precipitation). Bumblebee occurrence and richness declines are significantly associated with regions where climate change has pushed species and communities towards or beyond their thermal or precipitation limits. Our results demonstrate that accumulating exposure to extreme climate conditions from climate change is linked with increasing extinction risk, and represent a step forward in our understanding of and ability to predict relatively local-scale climate change impacts on bumblebees.
Peter Soroye is a PhD student at the University of Ottawa. He is studying the direct and interactive impacts of climate change and land use change on pollinators.