Characterizing the pollinator communities & pollination sustainability of four economically important crops in Great Britain

Bees provide a critical ecosystem service for agricultural production by contributing to the pollination of the majority of leading global crops. A growing body of research indicates that species rich pollinator communities benefit the yields and stability of insect-pollinated crops. Additionally, species rich communities may promote more resilient crop pollination services, which is particularly imperative due to increasing rates of anthropogenic induced environmental changes. However, this ecosystem service is being compromised due to declines in bee species, driven by a loss of floral and nesting resources due to agricultural land expansion and intensification. Whilst agri-environment schemes have been implemented across Europe to halt biodiversity losses, recent evidence suggests that they predominantly benefit common bumblebee species, and are of limited value to solitary species, which also provide important crop pollination services. Currently there is limited information on which species provide crop pollination services to guide management and monitoring, and preserve pollination services. Identifying crop pollinating bee species, monitoring their populations in agricultural landscapes and understanding how crop pollinator communities vary across time and space have recently been identified as key research objectives for national and international policy and monitoring programmes. Focusing on Great Britain, which has comprehensive data on its bee fauna, and considering four of its most economically important crops – apples, field bean, oilseed rape and strawberries – this thesis aimed to address key knowledge gaps in our understanding of bee crop pollinator communities. The first objective of this thesis was to produce national lists of bee pollinators for each of the four focal crops. Building upon this information the second objective was to evaluate the capacity of different survey methods to sample bee species in each of these crops. The final objective was to investigate how pollinator community composition, and pollinator species richness, may affect the stability of crop pollinator occurrence. The results of chapter 2 indicate that whilst a smallsuite of common species may make a disproportionate contribution to flower visitation to our focal crops, at least a quarter of bee species in Great Britain, including some rare and specialist ones, could act as potential pollinators of these crops. These findings indicate that current agri-environment schemes, which have been predominantly developed around the needs of bumblebees, may not be as effective at supporting pollination service in crops such as apples and oilseed, which are also visted by a diverse range of solitary bees. Chapter 3 revealed that different survey methods sample distinct components of crop pollinator communities, and that the efficacy of different survey methods to sample bee crop pollinators may be contingent upon the guild and crop being targeted. Transect walks were superior at measuring both abundance and richness of bumblebees in all crops, and may be sufficient to sample bee pollinators in crops such as field bean, which are almost exclusively visited by bumblebees. Pan traps, notably yellow ones, detected the greatest abundance and species richness of solitary bees in apple, oilseed and strawberry crop sites, and may be an essential complementary sampling technique in crops for which solitary bees are key pollinators. These findings can be used to inform national pollinator monitoring schemes which aim to sample crop pollinators in agricultural areas. Finally, the results of chapter 4 indicate that bee crop pollinator communities composed of a small number of closely related species, such as field bean, are likely to exhibit more synchronized inter-annual occupancy dynamics, and show a greater variance in mean occupancy, compared to crop pollinator communities comprised of a more diverse set of bee species, such as oilseed. Additional analyses also indicate that more species rich pollinator communities may result in greater stability of crop pollinator occurrence over time, which could have positive benefits for the resilience of crop pollination services under future environmental changes. The outcomes of this thesis show that agri-environment schemes need to be adapted to cater for the resource requirements of a wider diversity of bee species than at present, and strategies to achieve this are discussed within the context of the wider literature. The implications of differences in the capacity of different survey methods to sample and monitor crop pollinating bee species are also discussed. Additionally, a consideration of how management in agricultural landscapes can promote stable bee populations in and around cropped areasis also provided. Together these recommendations provide an overview of how species-rich and stable bee crop pollinator populations could be protected and promoted in agricultural landscapes in order to safeguard production of insect pollinated crops.