Projected climate change will reduce habitat suitability for bumble bees in the Pacific Northwest

Abstract

Global climate change is the greatest environmental challenge of the modern era. The impacts of climate change are increasingly well understood, and have already begun to materialize across diverse ecosystems and organisms. Bumble bees (Bombus) are suspected to be highly sensitive to climate change as they are predominately adapted to temperate and alpine environments. In this study, we determine which bumble bee species are most vulnerable to climate change in the Pacific Northwest. The Pacific Northwest is a topographically complex landscape that is punctuated by two major mountain ranges and a labyrinth of offshore islands in the Salish Sea. Using standardized survey methods, our study documents the occurrence of 15 bumble bee species across 23 field sites in seven federal parks, historical sites, and monuments. Our results show that bumble bee community richness and diversity increases along an altitude gradient in these protected areas. Furthermore, NMDS analysis reveals that high altitude environments are composed of a unique group of bumble bee species relative to low altitude environments. Finally, based on an analysis of species distributions models that aggregate bioclimatic data from global circulation climate models with preserved specimen records, we discover that 80% of the bumble bee species detected in our survey are poised to undergo habitat suitability (HS) loss within the next 50 years. Species primarily found in high altitude environments namely B. vandykei, B. sylvicola, and B. bifarius are projected to incur a mean HS loss of 63%, 59%, and 30% within the federally protected areas, respectively. While the implementation of climate change policies continue to be a significant challenge, the development of mitigation strategies to conserve the most vulnerable species may be a tractable option for land managers and stakeholders of protected areas. Our study meets this need by identifying which species and communities are most sensitive to climate change.