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Effects of the availability of floral resources on plant-pollinator interactions and the implications for the long-term survival of plant populations Tracie M Evans Thesis presented for the degree of Doctor of Philosophy The University of Edinburgh 2017 For Matt Evans Declaration All methods and analyses described in this thesis were performed by the author unless stated otherwise. No part of this thesis has been submitted for any other degree or qualification. Acknowledgements First and foremost, I would like to thank David Gill for tolerating hearing about my work every day over the course of this PhD. He has provided endless support and interest; my experience during this PhD would not have been the same without him. I would like to extend this deep gratitude to my supervisors; Professor Matt Heard, Dr Adam Vanbergen, Dr Stephen Cavers and Professor Richard Ennos: all of whom I have the deepest admiration and respect. Professor Matt Heard has taught me so much through endless hours of support and advice and has always been there to listen and subtly reroute me back down to earth. Dr Adam Vanbergen has been extremely approachable and always been there when I have needed help. He has always managed to reduce my stress levels and I have learnt so much from his in-depth knowledge of pollinators. I have learnt everything I know about microsatellites and plant genetics from Dr Stephen Cavers, who has been extremely helpful over the course of this PhD, managing to interpret my convoluted and sometimes, confused, lengthy, emails and reply with sense. Professor Richard Ennos has been extremely approachable, always providing efficient and timely feedback, to which he continually provided sound advice. He has shared so much of his knowledge surrounding plant genetics, for which I am extremely grateful. To all my friends and colleagues at the Centre for Ecology and Hydrology, who have been there to help me with every obstacle. Lucy Hulmes, Sarah Hulmes and Nadine Mitschunas have made this PhD possible, particularly in keeping my plants alive; a debt to which I owe so much gratitude. I wouldn’t have results if it wasn’t for their care and diligence and all their endless knowledge. Anna Oliver and Lindsay Newbold were there for me in my most stressful period. Their knowledge and kindness was invaluable and they provided me with so much help and support. My thanks extends to all of my other colleagues who have been so helpful during the course of this PhD and made everything run smoothly; Kath Turvey, Caroline Wills-Wright, John Redhead, Steven Freeman, Alex Robinson and to all of the PhD students, past and present, who have made working at CEH such a pleasurable experience. Also, to Ivan Wright for all of his help verifying my bee identifications and all of the landowners and research institutes who have made my experiments possible. This PhD would not have been possible without all of this help and support and all of my family and friends who have put up with me over the last four years Abstract 1. Insect pollinators have been shown to alter their foraging patterns in response to habitat and landscape composition, particularly in relation to changes in the availability of floral resources which provide essential pollen and nectar provisions. Changes to pollinator behaviour and community composition, may alter the distance, directness and frequency of pollen movement and thus, the compatibility and genetic relatedness of pollen transferred between plants. We still lack good understanding of how variation in the spatial and temporal availability of floral resources drives pollinator responses and in turn, affects the fitness of outcrossing plants. Knowledge in this area could contribute to improved management interventions to enhance pollination services for plant conservation. 2. Through a combination of habitat and landscape scale field experiments, I explored how the availability of floral resources at different spatial scales affected plant-pollinator interactions, pollen transfer and mating success in plant populations, particularly those isolated from conspecifics. This involved introducing different species of plants in experimental arrays across a range of study systems that varied in structure and floral availability. Over the course of the thesis, I measured the community composition and behaviour of pollinators visiting experimental arrays; focusing on traits considered important for pollen transfer (e.g. Inter-tegular (‘IT’) span). Pollen movement was quantified within and between populations (5-150m) and the resulting plant outcrossing rates were measured using different methods including paternity analysis and the use of a dominance inheritance system. In addition, the implications of variations in pollinator foraging and pollination services can be attributed to pollen and gene flow and subsequently the reproduction and fitness of plants were assessed as a means of predicting the impacts on longer-term plant survival. 3. Findings from this thesis demonstrate reductions in the activity density (the abundance of actively foraging pollinators) and richness of pollinators and thus, the potential for plant visitation in response to a high abundance of floral resources within a habitat. This led to disruptions in pollen transfer, illustrated through a lower incidence of intra and inter-population pollen movement, and ultimately, reduced plant outcrossing rates. In parallel, plant seed set and germination rates were also reduced in habitats with high resource availability. Changes to pollinator communities and pollination services varied with the spatial scale at which floral resources were measured. Pollinator communities (activity density, richness and IT span) were most affected by floral resource abundance at a local scale (1-50m), particularly within a 20m radius of a plant population. Intra-population pollen movement was similarly affected by floral resources at a local spatial scale (within a 1m radius of a plant population). In contrast, no effect was observed on pollinator communities, intra-population pollen movement or plant reproduction when floral resources were measured at a landscape scale (within a 100-1500m radius of a plant population). However, findings were variable across different experiments at the same scale of measurement. For instance, the availability of floral resources at a local scale did not always elicit an effect on plant reproduction. This reflects differences in plant species identity and the effects of breeding system and floral traits, illustrated through variations in visitation rates between plant species. Inconsistencies were further observed with pollinator activity density and richness, which were not related to floral resources at a habitat scale in one chapter. 4. This thesis highlights the importance of the availability of floral resources at a local scale on plant-pollinator interactions and pollination services to plants. Co-flowering plants within florally rich habitats compete for pollinators and subsequently, visitation and pollen transfer between individuals of low density plant populations is diluted rather than facilitated. This suggests that although pollinator abundance and diversity may be enhanced through florally rich habitats (e.g. habitats implemented under the agri-environment scheme), pollination services are not automatically improved for plants which are present at low frequency in the landscape. This needs to be considered when designing and implementing management for threatened or isolated plants where plants may instead benefit from focused interventions. For instance, pollination services may be increased by efforts to maximise the facilitative effect of surrounding habitats, while increasing the ability of threatened or isolated plants to withstand competition from co- flowering plants. Lay summary Insect pollinators (including bees, butterflies and hoverflies) play a vital role in the sexual reproduction of flowering plants, inadvertently transferring pollen from male to female flowers, as they forage between plants in their search for an energy and nutrient rich reward of nectar and/or pollen. From an individual plant’s perspective, successful sexual reproduction depends on pollen being delivered to or from another plant of the same species. How far a pollinator travels between two plants of the same species is also significant; greater distance travelled tends to lead to sexual reproduction between less closely related parent plants and therefore greater exchange of unique genes. However, pollinators are not trying to help plants; where, how far, how often and from which plants they choose to forage is based