The influence of local and landscape factors on arthropod predator diversity in the Sundays River Valley, Eastern Cape, South Africa

Galloway, Alistair Duncan (2019-04)

Thesis (MScConsEcol)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Die landbou is wêreldwyd onder druk om die toenemende menslike bevolking te voed, wat lei tot groter extensivering en intensivering van die land. Dit het talle negatiewe impakte op beide gewasland en inheemse biodiversiteit, insluitend geleedpotige roofdiere (wat verwys na beide geleedpotige roofdiere en parasitoïede in hierdie studie). Baie van die navorsing wat die invloed van bestuurs- en landskapsfaktore op die roofdierkompleks ondersoek het, het plaasgevind in hoogs getransformeerde, minder-biodiverse ontwikkelde lande relatief tot ontwikkelende lande met hoë vlakke van biodiversiteit. Dit, in kombinasie met beide hoë bevolkingsgroeikoerse en klimaatsveranderings-impakte wat voorspel word vir ontwikkelende lande (veral Afrika suid van die Sahara), beklemtoon die behoefte aan groter navorsing in hierdie streke. Hierdie studie het dus daarop gemik om te bepaal of en in watter mate plaaslike en landskapsfaktore geleedpotige-roofdiere in die Sondagsriviervallei, Oos-Kaap, Suid-Afrika beïnvloed. Die roofdierkompleks tussen sitrusboorde (konvensioneel en organies) met en sonder naburige natuurlike plantegroei is, benewens invloedryke omgewingsveranderlikes, ondersoek. Die teenwoordigheid van natuurlike plantegroei langs langs sitrusboorde (konvensioneel of organies) is ook ondersoek om vas te stel of dit 'n invloed op die roofdierkompleks het oor die natuurlike plantegroei-sitrusboord grens. Die invloed van plaaslike plaasbestuur (organies en konvensioneel) was die grootste in eenvoudiger landskappe, waar organiese boerdery aansienlik geassosieer word met groter roofdierspesies-rykheid, talrykheid en diversiteit. Dit is geassosieer met 'n toename in dekkingsgewas en grondoppervlak heterogeniteit wat habitat, skuiling en voedselhulpbronne aan roofdiere bied. Natuurlike plantegroei het omgewings heterogeniteit op die landskapskaal verhoog en is gevolglik geassosieer met groter roofdiere spesiesrykheid in naburige konvensionele maar nie organiese boorde nie. Grense tussen natuurlike plantegroei en boorde het die roofdierkompleks van beide habitatte beïnvloed. Totale, mier- en wesp-spesies rykheid, en wesp-talrykheid het toegeneem teenoor die natuurlike plantegroei-grens, terwyl die kewerspesiesrykheid en diversiteit in natuurlike plantegroei naby die grens toegeneem het. Grense tussen natuurlike plantegroei en boorde kan dus nadelig wees vir inheemse biodiversiteit in naburige natuurlike plantegroei. Plaaslike- en landskaps-faktore is dus gevind om 'n aansienlike invloed op geleedpotige roofdiere te hê, met organiese boerdery tegnieke en die teenwoordigheid van natuurlike plantegroei wat verband hou met verbeterings in die roofdierkompleks. Bewaring en herstel van goed bestuurde en hoogs verbonde natuurlike plantegroei in die landbou landskap kan die roofdierkompleks in gewasland bevorder, terwyl negatiewe grenseffekte op inheemse biodiversiteit beperk word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105748
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