Browsing by Author "Galloway, Alistair Duncan"

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    The influence of local and landscape factors on arthropod predator diversity in the Sundays River Valley, Eastern Cape, South Africa
    (Stellenbosch : Stellenbosch University, 2019-04) Galloway, Alistair Duncan; Pryke, James S.; Gaigher, Rene; Seymour, Colleen L.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Globally, agriculture is under pressure to feed the increasing human population, leading to greater cropland extensification and intensification. This has numerous negative impacts on both cropland and native biodiversity, including arthropod predators (which refer to both arthropod predators and parasitoids within this study). Much of the research investigating the influence of management and landscape factors on the predator complex has taken place in highly transformed, less-biodiverse developed countries relative to biodiverse developing countries. This, in combination with both high population growth rates and climate change impacts predicted for developing countries (particularly sub-Saharan Africa), emphasises the need for greater research in these regions. This study therefore aimed to determine whether, and to what extent, local and landscape factors influence arthropod predators in the Sundays River Valley, Eastern Cape, South Africa. The predator complex between citrus orchards (conventional and organic) with and without neighbouring natural vegetation was investigated, in addition to their environmental drivers. The presence of natural vegetation bordering alongside citrus orchards (either conventional or organic) was also investigated to determine whether it has an influence on the predator complex across the natural vegetation-orchard edge. The influence of local farm management (organic and conventional) was greatest in simpler landscapes, where organic farming was significantly associated with greater predator species richness, abundance and diversity. This was associated with an increase in cover crop and soil surface heterogeneity which provides habitat, shelter and food resources to predators. Natural vegetation, interestingly, increased environmental heterogeneity at the landscape scale and subsequently was associated with greater predator species richness in neighbouring conventional but not organic orchards. Edges between natural vegetation and orchards influenced the predator complex of both habitats. Total, ant and wasp species richness, and wasp abundance increased towards the natural vegetation-orchard edge, whilst beetle species richness and diversity increased in natural vegetation near the edge. Edges between natural vegetation and orchards can therefore be detrimental for native biodiversity in neighbouring natural vegetation. Local and landscape factors were thus found to significantly influence arthropod predators, with organic farming techniques and the presence of natural vegetation being associated with improvements in the predator complex. Conservation and restoration of well-managed and highly connected natural vegetation in the agricultural landscape can promote the predator complex in cropland whilst limiting negative edge effects on native biodiversity.