The hidden ecology of bumblebees: using classical and new methods to explore nest searching, floral resources and badger predation

Abstract

Bumblebees provide a crucial ecosystem service, and are experiencing worldwide declines due to a number of stressors, such as habitat loss and climate change. Populations are regulated through ‘bottom-up’ (resources) and ‘top-down’ (pesticides, disease and predation) processes. Bumblebees have been widely researched, but there are still aspects of their ecology which are understudied due to the difficulties associated with researching them. This is the case for nest locations and nest predation. This thesis aims to uncover some of these hidden aspects of bumblebee ecology, through the development and implementation of new techniques: thermal cameras as a tool to locate bumblebee nests (Chapter 3), artificial nests to study badger predation rates (Chapter 4 & 5), and the utilisation of model simulations to look at the potential combined impacts of badger predation and food availability on bumblebee populations (Chapter 5). Thermal cameras were found to be unsuccessful, due to their small viewing areas. However the artificial nest method was shown to be a successful way of studying the relative differences in predation rates between habitats and geographic locations, with high predation of bumblebee nests in areas of high badger densities. Model simulations also showed that under high badger predation rates a simulated bumblebee population produced significantly fewer hibernating queens, workers, and colonies. Thus, novel research tools were found to be a useful way of monitoring the effects of top-down and bottom-up effects on bumblebee populations. Alongside this, classical field techniques were used to study the use of botanical gardens and semi-natural farmland habitats by nest searching queens, and the foraging resources they provide across the flight season (Chapter 2). Residential gardens have been shown to be beneficial habitats for bumblebees, especially in urban environments. In Chapter 2 botanical gardens are looked at in a rural setting, which has not been done previously. Botanical gardens were found to contain a high number of nest searching queens, and experienced a peak of spring floral resources. However semi-natural habitats in farmland provided higher levels of floral resources in early and late summer. Therefore these two habitats may be providing complementary floral resources to pollinators. These results are discussed in terms of the importance of habitat heterogeneity for supporting pollinator populations.