Conservation of diverse parasitoid assemblages across agricultural mosaics within the Cape Floristic Region, South Africa

Thesis (MScConsEcol)--Stellenbosch University, 2018.

ENGLISH ABSTRACT: The ever-growing agricultural industry within the Cape Floristic Region (CFR) threatens many arthropod species, including functionally beneficial insects such as parasitoids. Damage caused by insect pests within agricultural landscapes may be reduced by these important natural enemies. Various other vital ecosystem services and functions may be provided by maintaining structurally diverse agricultural landscapes as habitat heterogeneity promotes biodiversity. Here, I aim to investigate changes in parasitoid assemblages between various biotopes and across seasons within the CFR winelands. Firstly, I assess whether parasitoid richness and assemblage structure differs between five dominant biotope types within CFR agricultural mosaics. I also investigate which environmental variables influence changes in diversity. The biotopes were vineyards, old fields, riparian vegetation, remnant natural vegetation, and areas invaded by alien trees. I found that parasitoid assemblage structure differed significantly among all biotopes, with the undisturbed habitats supporting highest parasitoid diversity. Each biotope type made a unique contribution to overall parasitoid diversity. Structural diversity and botanical diversity, as well as the amount of untransformed habitat in the landscape, influenced parasitoids. Various spatial scales are therefore important when conserving these organisms. By maintaining a diversity of biotope types, farmers will be able to promote parasitoid biodiversity across farmland mosaics. Secondly, I assess the changing parasitoid assemblage structure and diversity across these biotope types over three seasons. Sample seasons were autumn, spring and summer. I found that parasitoid assemblage structure differed between the biotope types across the three seasons, with different biotopes having differential importance between seasons. Spatial and temporal turnover of species therefore takes place across agricultural landscapes in response to changing environmental conditions across various seasons. It is therefore necessary for farmers to preserve a variety of biotope types to promote species movement and re-establishment throughout farmland mosaics. To conserve these functionally important insects, we need to consider movement of parasitoids throughout landscapes, and over larger spatial and temporal time-scales. Here I show that habitat heterogeneity is an important consideration for future farmland design and planning for human-induced disturbances.

AFRIKAANSE OPSOMMING: Die steeds groeiende landboubedryf in die Kaapse Floristiese Streek bedreig groot hoeveelhede geleedpotige spesies, insluitende voordelige insekte soos parasitoïede. Skade wat veroorsaak word deur insekteplae in landboulandskappe kan deur hierdie belangrike natuurlike vyande verminder word. Verskeie ander belangrike ekosisteemdienste en -funksies kan voorsien word deur die handhawing van uiteenlopende landboulandskappe, aangesien habitat-heterogeniteit biodiversiteit bevorder. Hier ondersoek ek die verandering in parasitoïede samestellings tussen verskillende biotope en oor seisoene binne die CFR-wynlande. Eerstens het ek vasgestel of die parasitoïede rykheid en samestellingstruktuur verskil tussen vyf dominante biotoopsoorte binne CFR-landboumosaïeke. Ek het ook ondersoek ingestel na watter omgewingsveranderlikes veranderinge in diversiteit beïnvloed het. Die biotope was wingerde, ou velde, oewerplantegroei, oorblywende natuurlike plantegroei en gebiede wat deur indringerbome oorgeneem is. Parasitoïede samestellingstruktuur het aansienlik verskil tussen alle biotope, met die onverstoorde habitatte wat die hoogste parasitoïede diversiteit ondersteun. Elke biotooptipe het 'n unieke bydrae gelewer tot die algehele parasitoïede diversiteit. Strukturele diversiteit en botaniese diversiteit, sowel as die hoeveelheid ongetransformeerde habitatte in die landskap, het parasitoïede beïnvloed. Verskeie ruimtelike skale is dus belangrik wanneer hierdie organismes bewaar word. Deur die verskaffing van 'n verskeidenheid biotooptipes, kan boere volhoubare parasitoïede bevolkings oor landmosaïeke bevorder. Tweedens, oor drie seisoene, het ek die veranderende parasitoïede samestellingstruktuur en diversiteit oor bogenoemde biotoopsoorte geassesseer. Steekproefseisoene was herfs, lente en somer. Parasitoïede samestellingstrukture het tussen die drie seisoene tussen die biotoopsoorte verskil. Ruimtelike en temporale omset van spesies vind dus plaas binne landboulandskappe in reaksie op veranderende omgewingstoestande oor verskillende seisoene. Om af te sluit, dit is nodig vir boere om 'n verskeidenheid biotope te bewaar ten einde spesiebeweging te bevorder in landskappe. Navorsing gefokus op die beweging van voordelige natuurlike vyande dwarsdeur landskappe, en oor langer tydskale, kan toekomstige landbougrondontwerp beïnvloed en beplanning van mensgeïnduseerde versteurings beïnvloed.

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