What’s the buzz?: a dual-scale assessment of Kansas bumble bee species to inform future conservation efforts

Abstract

The decline of bumble bee (genus Bombus) populations across North America, attributed to factors such as habitat loss/ fragmentation, increasing use of pesticides, and climate change, poses significant concerns for both natural ecosystems and agricultural productivity. Two bumble bee species found in the Great Plains are imperiled, which necessitates further research exploring where they are located, how their habitats differ from species that are stable, and what land management techniques can be implemented to benefit the bumble bee community as a whole. In this thesis, I used experimental and modeling methodologies to assess how Kansas bumble bee species are affected by environmental factors on two different scales. On a local scale (Chapter 1), I take an experimental approach by conducting a two-year field study to investigate the direct and indirect effects of bison (Bison bison) grazing and fire frequency (common grassland management strategies) on bumble bee abundance, community composition, and plant interactions. I found that the presence of bison indirectly increases total bumble bee abundance by means of increasing floral resource availability; there were interactive effects with fire frequency. Community composition did not differ significantly between grazing treatments; however, there were differences in host-plant interactions among bumble bee species. On a state-wide scale (Chapter 2), I use species distribution models to understand differences in habitat selection and spatial distributions between common and threatened species in Kansas. While most findings were species-specific and not characteristic of “common” or “threatened” groups as a whole, one species of least-concern deviated the most in terms of habitat associations. In general, all species were negatively associated with monoculture crop coverage. Climate factors appeared to be less important drivers of distribution than landscape factors. Model-predicted maps created from each species’ most significant set of predictor variables display hotspots where individuals are most likely to be detected across Kansas. Such maps are crucial for designating priority areas for threatened species protection. Overall, this research provides valuable insights into the ways in which grassland management, land cover, and climate factors affect bumble bee species for the purposes of assisting with targeted conservation efforts across Kansas and the entire Great Plains.