Examining the factors underpinning the differential success of wild bumble bee species and their responses to anthropogenic change
Open Access
- Author:
- Feuerborn, John
- Graduate Program:
- Biology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- September 29, 2024
- Committee Members:
- Heather M Hines, Thesis Advisor/Co-Advisor
Guilherme Becker, Committee Member
Elizabeth Mcgraw, Program Head/Chair
Christina M Grozinger, Thesis Advisor/Co-Advisor - Keywords:
- bumble bee
climate change
conservation
physiology
thermal tolerance
phenology
pollen macronutrients
distribution
floral visitation
habitat - Abstract:
- Several bumble bee species (Hymenoptera: Apidae: Bombus spp.) are showing significant declines in the U.S. and Europe. These declines have been associated with anthropogenic stressors such as climate change, habitat and floral resource loss, pesticide use, and pathogens and parasites. As the main pollinators in diverse natural ecosystems and efficient pollinators of many agricultural crops, bumble bee declines can negatively affect ecosystem function and agricultural production. However, not all bumble bee species are equally impacted, as some species are experiencing moderate to precipitous declines while others are stable or are even expanding their ranges. Identifying the causes of these species-specific differences in response to anthropogenic change requires understanding the diverse factors that limit these species. This thesis examines the role of phenology, habitat, floral resource use, macronutrient preferences, and heat stress resistance on the differential success of several bumble bee species in eastern Nearctic communities. First, baseline information is obtained on phenology, habitat distributions, relative abundances, and floral visitation patterns for bumble bee species across Pennsylvania. Species vary in their preference for forest versus open habitat, phenology, and season length, with the most abundant species, Bombus impatiens, having the latest phenology, the longest seasonality, and broadest habitat breadth. Floral visitation patterns of bumble bees in Pennsylvania indicate that non-native legumes (white clover and crown vetch) are most visited, and there is some evidence of species specialization, such as preference for asters by Bombus vagans and common milkweed by Bombus griseocollis. Second, this thesis examines whether bumble bee species differ in their pollen macro-nutrient preferences by assessing the protein and lipid content of pollen they collect. In field settings, species varied somewhat in protein levels collected, but P:L ratios were similar, averaging at 4.7:1. Bees collected the highest protein from the site with the highest plant diversity and highest available protein, and bees obtained higher ratios in sites in Oklahoma versus Pennsylvania due to an abundance of a protein-rich native legume, the partridge pea. Bumble bees typically collected higher protein pollen than the average of what was available from the plants flowering at the sites, while pollen lipid concentrations collected were more similar to what was available. These data suggest bumble bees selectively forage for higher protein but what they attain depends on what is available in the environment. Finally, the role of several biological factors with potential for contributing to heat stress resistance was examined in Pennsylvania bumble bees. Species that are common in warmer valleys and the lowest median latitudinal ranges were able to withstand heat stress for the longest period of time, whereas cooler-adapted boreal species were the least heat tolerant, suggesting heat tolerance is likely a key factor limiting their distribution. Many other biological factors were found to influence heat tolerance: queens were less heat tolerant than workers and males, recently eclosed adults were less heat tolerant than older bees, queens with activated ovaries were marginally less heat tolerant than queens with inactivated ovaries, larger bees were less heat tolerant in wild foragers, and higher levels of humidity decreased heat tolerance in both workers and queens. This thesis provides detailed analysis of multiple behavioral, physiological and nutritional factors that influence how different bumble bee species respond to variation in forage quality, habitat type, and weather. The insights gained from these studies can be used to develop habitat restoration strategies to support declining bumble bee species and diverse bumble bee communities.