Evaluating the ecosystem function of selected dipteran families and their role as indicators of farm habitat quality in Ireland
Ahmed, Karzan Sabah D.
Ahmed, Karzan Sabah D.
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Identifiers
http://hdl.handle.net/10379/16976
https://doi.org/10.13025/17995
https://doi.org/10.13025/17995
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Publication Date
2021-09-27
Type
Thesis
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Abstract
Biodiversity has undergone significant declines worldwide as a result of human activities. This trend is particularly apparent in agricultural ecosystems where farming intensification is recognised as one of the primary causes of rapid decline in farmland biodiversity particularly in insects with multiple ecosystem services including pollination, biological pest control and nutrient cycling. While the positive role of results-based agri-environment payment schemes in protecting and enhancing farmland biodiversity and increasing habitat quality has been recognised in recent years, there are still gaps in knowledge regarding how farmland habitats should be assessed particularly in relation to non-iconic invertebrates. Two dipteran taxa selected for this study, Syrphidae and Sciomyzidae, have a range of ecosystem functions. These include pollination, biocontrol and nutrient cycling (Syrphidae) and biocontrol of molluscs (Sciomyzidae), Both families co-exist within many of the same habitats but have markedly different ecological requirements and ecosystem functions, making them good indicators of farm habitat quality. This study comprises three major elements conducted at different scales as follows: 1) an investigation of the ecosystem function/biocontrol potential of Tetanocera elata (Diptera: Sciomyzidae) which feeds on pestiferous slugs; 2) an examination of the contribution of linear habitats across a range of farming intensities to both Syrphidae and Sciomyzidae diversity and abundance; and 3) an exploration of how variables (at local and landscape level) could be used to incorporate hoverfly functional groups in rapid farmland biodiversity assessments. The results of laboratory experiments investigating the biocontrol potential of T. elata demonstrated that larval survival outcomes depend on prey slug species with neonate and third instar larvae appearing to prioritise different predatory strategies. Of particular note is that successful pupariation in T. elata is reduced for larvae fed on slugs exposed to Phasmarhabditis hermaphrodita (Rhabditida: Rhabditidae), a slug parasitic nematode. This potentially negative effect of P. hermaphrodita (which can be purchased in Europe for the control of pestiferous slugs) on T. elata survival has implications for protecting wild populations of T. elata and for how biological control of slugs is undertaken in the future. The contribution of farm linear habitats across a gradient of farming intensities to Syrphidae and Sciomyzidae abundance and diversity was investigated in Co. Sligo (Ireland) using bi-directional malaise traps. Overall, Syrphidae and Sciomyzidae species richness and community composition reflected a farming intensity gradient with significantly greater species richness for both families on extensively managed farms. In addition, although their abundance and species richness were greatest in dense hedgerows with adjacent watercourses, Syrphidae showed no significant difference overall between linear habitat types. This is in contrast to Sciomyzidae where open hedgerows with adjacent watercourses had significantly more Sciomyzidae species and individuals than dense or open hedgerows without adjacent watercourses. Syrphidae species richness was also significantly correlated with the flowering plant species richness of linear habitats while Sciomyzidae species richness was correlated with a habitat quality score for grasslands adjacent to the linear habitats. The results suggest that while low intensity farming appears to support species richness of both taxa, universal management prescriptions for a farmland linear habitat (such as a hedgerow) may not benefit all dipteran taxa equally. This has implications for future agri-environmental schemes and is discussed in the context of how the conservation value of linear habitats on farmlands is currently assessed. Given that detailed field surveys of invertebrates at landscape scale are extensive and time-consuming, determining the best habitat features (reflecting Syrphidae ecosystem services) that can be rapidly measured through high resolution satellite imagery rather than field survey, is crucial for national agri-environmental payment schemes. With this in mind, selected habitat features that best reflect hoverfly requirements and their associated ecosystem services were investigated at local and landscape scale using pan traps in two study regions with contrasting farming conditions (Cos. Sligo and Wexford, Ireland). Predatory and non-predatory species dominated the Syrphidae in Cos. Wexford and Sligo respectively. In addition, results indicate that at landscape scale, hedgerows and tree lines (irrespective of county and farming conditions) are the most important driving factors positively affecting hoverfly abundance/richness, with other linear habitat features showing variable results within and between each study region. The implications of these results in the context of selecting the best explanatory variables that can be incorporated in rapid assessments for agri-environmental payment schemes are discussed with particular reference to total lengths of hedgerows/tree lines on farms.
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NUI Galway