Using citizen science to monitor bumblebee populations

Bumblebees are important pollinators of crops and wildflowers and are currently in global decline. The main drivers of decline include agricultural intensification, climate change, invasive species, pesticides, parasites and pathogens and it is thought that these multiple stressors act together to impact populations. However, their relative importance is unknown and there are wide knowledge gaps in relation to the current status of species populations and their response to environmental variables such as climate, habitat and land use change. Citizen science offers a potential method of collecting data at a broad enough scale to measure species population responses to environmental stressors and it has successfully been applied to other taxa, particularly UK birds and butterflies. This thesis investigates the use of citizen science to address the current knowledge gaps in the status of UK bumblebee populations by analysing volunteer-collected data on current distribution and abundance trends in relation to habitat and climate change. Results are compared to previous studies to infer long-term changes in population dynamics. The value of applying citizen science methods to bumblebee monitoring is highlighted, revealing evidence for decline of some common species and the recent retraction of rare species to their climatic optima. The main findings reveal a potential impact of climate on the distribution of winter-active bumblebees. They also indicate that, while urban parks and gardens provide refuge for bumblebees in an otherwise impoverished landscape, urbanisation may favour short-tongued generalist species over long-term specialists. The outcomes of this thesis have important management implications for UK bumblebee populations including the need for reassessment of the conservation status of B. soroeensis and the sympathetic management of urban parks and gardens for longtongued specialists through the provision of suitable forage material