Responses of Bumblebees (Bombus) to Climate Change

Abstract

With over 1 million species facing extinction due to land use intensification and changing climatic patterns, the acceleration of extinction rates of flora and fauna worldwide is projected to continue to worsen. The swift pace of climate change limits opportunities for evolutionary adaptation, exposing species to conditions that challenge their ability to survive or fulfill essential functions. Bee populations, globally dwindling due to these environmental shifts, play a crucial role as wild pollinators responsible for over 80% of global pollination services. Of particular concern are declines in bumblebees (Bombus), a group of approximately 260 species. Rapid climate changes expose Bombus species to conditions surpassing their historical tolerances, with rising temperatures challenging thermoregulation, foraging, and reproduction efficiency. While models linking climate change to species losses rely on broad-scale observations and complex models, the interaction between climatic position and land use at both continent-wide and local scales remains understudied for bumblebees. This thesis investigates patterns in Bombus persistence across North America to elucidate the impacts of climate and land use on bumblebees and inform conservation initiatives. In Chapter 2, I identify broad-scale, continent-wide mechanisms behind Bombus climate vulnerability to involve spatio-temporal shifts. I find that shifts in activity timing, not only range shifts, have contributed to climate-driven bumblebee extirpations across North America for the last three decades. I determine that mechanisms of climate change and land use intensity vulnerability observed at a macroecological scale are relevant at a community scale in Southern Ontario, demonstrating the biological relevance of such drivers (Chapter 3). Then, I demonstrate that, among bumblebee species, vulnerabilities to these stressors have a quantifiable pattern with regards to life-history traits and evolutionary histories (Chapter 4). This work will improve predictions of how bumblebee species respond to changing environments and landscape and may suggest new avenues for conservation and management of these and other important pollinator species. By improving predictions of bumblebee responses to changing environments, this research offers insights for conservation and management strategies, with broader implications for understanding climate and land use change responses across taxa.