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Title: Cascading inter-trophic interactions in the provision of ecosystem services : a grassland experiment
Author: Orford , Katherine Anne
ISNI:       0000 0004 5915 3685
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Understanding how species' interactions impact upon the composition and functioning of ecological communities is central to conservation biology. The overarching objective of this thesis is to aid the enhancement of biodiversity and ecosystem services by investigation of bottom-up ecosystem processes in an agricultural context; specifically in conventionally managed grasslands. Grassland for livestock production is a dominant form of land-use throughout Europe. Its intensive management threatens biodiversity in agricultural landscapes. Given its extensive cover, modest increases to conventional grassland biodiversity could have considerable positive impacts on the provision of ecosystem services, such as pollination, to surrounding habitats. The impact of conventional grassland diversity and management on the functional diversity and ecosystem service provision of pollinator communities was investigated. This relationship was assessed using a field-scale experiment in which grassland seed mixes and sward management were manipulated. This was complemented by surveys on ten working farms which possessed a natural gradient of plant diversity within SW England and phytometer experiments (assessing fruit production and seed set of strawberry, broad bean and red campion). The impact of grassland diversity on the ecosystem service of herbivorous pest control was also investigated via a bio-assay experiment on the working farms which assessed parasitism of a surrogate pest; the firethom leaf minor. Increasing plant species richness, by the addition of both legumes and forbs, was associated with significant enhancements in the functional diversity of grassland pollinator communities. This was associated with increased temporal stability of flower-visitor interactions at the community level. Increased sward richness was correlated with an increase in the pollination of the phytometer species strawberry and red campion but not broad bean. Enhanced pollinator functional diversity of more diverse pastures was a potential mechanism for improved pollination of the strawberry phytometers. Increased sward richness under grazing management was associated with increased pollinator biomass and thereby potential resources for insectivores. Visitation networks revealed pasture species Taraxacum sp. and Cirsium arvense to have the highest pollinator visitation frequency and richness, though Cichorium intybus was highlighted as a potential target species for pasture seed mixes due to its agronomic benefits. Finally, increased pasture plant species richness was positively associated with parasitism of the surrogate pest by parasitoids. Results of this study further our understanding of the relationship between plant diversity and invertebrate community functioning, helping us to manage ecosystem services within agro-ecosystems. An additional objective was to assess the importance of different taxa in the pollination process following the observation that non-syrphid Diptera are frequently neglected in the literature. Data from 32 pollen-transport networks and 69 pollinator-visitation networks was analysed to compare the importance of various flower-visiting taxa as pollen-vectors. The non-syrphid Diptera and Syrphidae were compared in detail to determine if neglect of the former in the literature is justified. No significant difference in pollen loads was found between the syrphid and non-syrphid Diptera in terms of pollen count and specialisation. It was estimated that non-syrphid Diptera carry 87% of total pollen carried by farmland Diptera. As important pollinators such as bees and hoverflies have suffered serious declines, it would be prudent to improve our understanding of the role of non-syrphid Diptera as pollinators.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available