LOCAL TO LANDSCAPES: THE INFLUENCE OF LANDSCAPES ACROSS SPATIAL SCALES ON BUMBLE BEE COMMUNITIES AND THEIR PATHOGENS
Open Access
- Author:
- Gratton, Elena
- Graduate Program:
- Entomology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 13, 2023
- Committee Members:
- Gary Felton, Program Head/Chair
Heather M Hines, Thesis Advisor/Co-Advisor
Frances E Buderman, Committee Member
Christina M Grozinger, Thesis Advisor/Co-Advisor - Keywords:
- Bumble Bee
Conservation
Disease Ecology
Community Ecology - Abstract:
- Bumble bees (Bombus spp) are critical pollinators contributing to native ecosystems as well as agricultural production. At least half of the studied bumble bee species in North America are experiencing population declines and range contractions due to interacting factors such as habitat loss, climate change, invasive species, and pathogens. Pathogens can cause disease, reduce fitness, and shorten lifespans. Moreover, infection rates are increased in bee populations that are stressed by poor nutrition or exposure to pesticides, and thus pathogen prevalence can serve as a broader bioindicator of poor conditions. Given the myriad of factors impacting bumble bees, a comprehensive approach is needed to assess which biotic and abiotic factors are most important for determining the health of bees across diverse landscapes. Through multi-state and multi-year analysis, I examine how environmental conditions affect bumble bee pathogen levels and communities at different spatial scales. First, I assess whether levels of four bumble bee pathogens and distributions of bumble bee species are driven by variation in habitat at a local scale by leveraging the replicated hill and valley system in Central Pennsylvania. I then evaluate if associations between pathogen levels, bumble bee species, and environmental conditions observed in Pennsylvania are also found in North Carolina. In Pennsylvania, I found that different communities of both pathogens and bumble bees were found between forested hills and developed valleys, with viral loads higher in valleys and loads of one pathogen, Crithidia bombi, higher in forests. Valley habitats were dominated by Bombus impatiens, a disturbance resilient bee, while the forest habitats hosted more diverse bumble bee communities. Through DNA barcoding I found that there has been significant misidentification of B. sandersoni as B. vagans or B. perplexus, all of which are found primarily in forested landscapes. The North Carolina data, consistent with data from Pennsylvania as well as other studies in the United States, demonstrate that bumble bee pathogen loads are higher in areas with more honey bees and developed land. However, across the broader datasets, there were variable effects of floral resources and bee community composition on pathogen loads. For example, areas with more floral resources were associated with decreased viral loads in honey bees in North Carolina and in bumble bees in Pennsylvania; but were associated with increased viral loads in North Carolina bumble bees. Moreover, these data show more floral resources support more diverse bumble bee communities, but more diverse communities may facilitate increased loads of some pathogens (e.g., Crithidia) for which some bumble bee species are more susceptible. Ultimately this thesis highlights several outstanding research issues and provides management recommendations. Pathogen transmission and prevalence can clearly be influenced by habitat type but the complexity of landscapes, changing bumble bee communities, and variable susceptibility of different bumble bee species means there is not a single, simple solution to reducing the effects or loads of pathogens for bumble bees. Generally, the presence of honey bees and increased disturbance lead to increased pathogen prevalence. Thus, management efforts should be targeted to improving habitat quality through increased floral and nesting resource quality, which reduces pathogen levels in both honey bees and bumble bees. Higher quality habitat can improve bumble bee community diversity, which can potentially reduce transmission rates, though this depends on the specific species involved. Future studies should focus on species showing declines, to better understand the disease dynamics. While there was partitioning of pathogens at a local scale, the overall loads of pathogens shift over larger regional scales, highlighting the value of examining effects from local to broader landscape scales.