Navigating the risk-reward landscape : bumblebee movement, resource use, and health in agroecosystems

Agricultural intensification disrupts the availability, quality, and configuration of floral and nesting resources for pollinators, resulting in the declines of many species. However, closely related taxa often exhibit variable population trends, suggesting that they differ in their capacity to buffer themselves against environmental change. Understanding the mechanisms underlying this variation would facilitate both targeted conservation interventions and more accurate predictions of future pollinator communities under different management scenarios. Here, I investigate the effects of landscape composition and configuration on bumblebee abundance, health, and behaviour in an agricultural region of southwestern British Columbia, Canada. I first show that native bumblebee abundance and total community richness—but not abundance of an introduced species, B. impatiens—decline in landscapes dominated by an intensively managed crop (high-bush blueberry). Surprisingly, native bumblebee microparasite prevalence followed a similar trend, suggesting that landscape context shapes disease dynamics independently of host density. I next explored how sensitivity to land use change may be linked to species’ behaviours. B. impatiens had a broader foraging range and more expansive nesting habitat niche than native B. mixtus, potentially contributing to a ten-fold difference in the rates of lineage continuity between the two species. Both pollinators travelled further to reach locally abundant resource patches dominated by a single floral species, a pattern reflected in B. mixtus pollen loads, which were more flower-constant when the local and landscape-scale abundance of each forager’s “major” plant was high. Conversely, in more configurationally complex landscapes B. mixtus shortened its foraging range yet collected a greater richness of pollens, suggesting that landscape complexity is associated with behavioural shifts which are potentially mediated by spatiotemporal resource complementation of different habitat types. This flexibility appeared sufficient to buffer colony success across a gradient of landscape complexity, as habitat configuration had no effect on colony abundance of either species. I conclude by synthesizing results, highlighting methodological limitations, and discussing how pollinator behaviours can inform our understanding of the pressures associated with agricultural intensification.