Bee conservation and epidemiology across scales

Bees provide essential pollination services that support floral biodiversity and maintain global agricultural production. Bees also face numerous stressors and challenges to their conservation, including land-use change and increasing pressure from detrimental parasites and pathogens. Heavily modified landscapes often lack the nesting and/or foraging resources necessary to support a diverse community of bees, therefore anthropogenic land use change poses a major risk to the diversity and abundance of bee communities, and the health and long-term stability of their populations. Land use change alters the distribution and composition of plant and pollinator communities and their mutualistic interactions with plants. These interactions are especially critical given that many bee parasites are transmitted indirectly through shared use of flowers, as well as among nestmates of social bees. To better understand the stressors and conservation priorities for bees, I explore the drivers of parasite prevalence 1) at the landscape scale by surveying bumble bees across a 1000km gradient, 2) at regional scales by examining drivers of parasitism within urban gardens, and 3) at the local scale by studying shared parasitism across bee communities. As central place foragers, bees are tied to the local landscape, making them susceptible to land use and climate change, which alters the suitability and accessibility of local habitats. This has long-term consequences for gene flow, population structure, and genetic variation, with major consequences for parasitism. I incorporate spatially explicit environmental, biogeographic, and land-use data in combination with genetically derived host population data to conduct a large-scale epidemiological assessment of the drivers of parasite prevalence, finding that spatial patterns of parasitism are isolated by the same factors isolating host populations. At regional scales bee community composition varies greatly from patch to patch depending on nesting and foraging resource availability. The quality of resources and accessibility of local habitats determines the abundance and diversity of bees with direct impacts pathogen transmission. By studying bumble bees in urban gardens, I found that nest site limitations lead to higher parasite prevalence in local bumblebees, while certain gardens support more diverse bee communities which have lower pathogen pressure as a result. Lastly, at local scales, parasite prevalence varies greatly between species in the community, yet there is much we do not understand about parasite transmission across communities and whether parasite host ranges are related to functional differences in bee traits or foraging behavior. I use plant-pollinator networks to characterize bee foraging behavior, and map potential routes of interspecific parasite transmission through diet overlap. There is great potential for parasite sharing in these networks, with diet overlap and foraging specialization being key factors in addition to functional differences in species’ traits and life history. Overall, I provide evidence for many drivers of parasite prevalence across spatial and conceptual scales with impacts for conservation planning and landscape epidemiology.