Browsing by Author "Theron-De Bruin, Natalie"

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    Mite (acari) ecology within protea communities in the Cape Floristic Region, South Africa
    (Stellenbosch : Stellenbosch University, 2018-03) Theron-De Bruin, Natalie; Roets, F.; Dreyer, L. L.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Protea is a key component in the Fynbos Biome of the globally recognised Cape Floristic Region biodiversity hotspot, not only because of its own diversity, but also for its role in the maintenance of numerous other organisms such as birds, insects, fungi and mites. Protea is also internationally widely cultivated for its very showy inflorescences and, therefore, has great monetary value. Some of the organisms associated with these plants are destructive, leading to reduced horticultural and floricultural value. However, they are also involved in intricate associations with Protea species in natural ecosystems, which we still understand very poorly. Mites, for example, have an international reputation to negatively impact crops, but some taxa may be good indicators of sound management practices within cultivated systems. Their role in natural systems is even less well-understood. In this dissertation I explore the role of mites within Protea populations in both natural and cultivated systems, focussing on assemblages from inflorescences, infructescences and soil. Protea inflorescences and infructescences provide a niche for a unique assemblage of mites that have associations with a group of arthropod-associated fungi, the ophiostomatoid fungi. The mites feed on the fungi and carry their spores to new inflorescences as phoretic partners of Protea-pollinating beetles. As it was shown that some of the fungi have a panmictic population genetic structure over as much as 1000 km, it was assumed that organisms other than beetles must be responsible for this extremely long-range dispersal. Here I present the first concrete evidence of the ability of birds to vector spore-carrying mites to new Protea trees. I also provide evidence for a newly discovered mite-fungus mutualism within ornithophilous Protea neriifolia inflorescences between a Glycyphagus sp. mite and various species within the ophiostomatoid genus Sporothrix. New mite-mite commensalisms between the Proctolaelaps vandenbergi flower mite and the Glycyphagus sp. mite was also discovered and documented. In this intriguing system the Glycyphagus sp. mites have a mutualistic association with species in the fungal genus Sporothrix. These small mites are phoretic on the larger P. vandenbergi mites that, in turn, are phoretic on Protea pollinating birds, explaining genetic evidence for the long distance dispersal of the fungi. It is well-known that flower-associated mites such as Proctolaelaps kirmsei are nectar and pollen thieves of hummingbird pollinated plants in America. These mites reduce nectar and pollen rewards for pollinators, which influences pollinator visitation patterns and decreases available pollen for dispersal, thereby negatively influencing seed-set and plant population dynamics. This phenomenon has, however, not been investigated in similar systems in other parts of the world. I, therefore, set out to determine the possible role of P. vandenbergi flower mites, the most abundant flower mite within Protea inflorescences, as pollen and nectar thieves and as secondary pollinators of P. neriifolia. I provide the first evidence that P. vandenbergi feeds on nectar and pollen and that its reproduction is strongly linked to pollen availability. Nectar consumption rates of P. vandenbergi likely have little effect on total nectar availability for pollinators, but they can significantly reduce available pollen in inflorescences and may ultimately negatively influence seed set. This is exacerbated by the fact that I could show that they do not contribute to Protea pollination. There is rising global concern about the negative impact of land transformation on natural ecosystems. With the increase in land transformation for agriculture, natural flora is replaced by intensively managed exotic crops. This has devastating effects on biodiversity and ecosystem services. Ecologically more friendly management systems are thus urgently required. One proposed such system is the production of native plants as crops, as these can provide known niche space for native organisms including beneficial ones, which may reduce required management inputs. Protea is of high ecological significance and economic value as it is harvested for export within both natural and cultivated systems in South Africa. Although mites associated with these plants can be beneficial, they are usually regarded as pests and/or organisms that pose significant phytosanitary risks. I, therefore, investigated the impact of Protea repens cultivation on the mite assemblages associated with inflorescences, infructescences (the crop products where the presence of mites pose agricultural risks) and the rhizosphere (where most of the agriculturally beneficial mite species would reside). I show that this indigenous crop may well be able to maintain a large native mite biodiversity component in all three of these niches. However, essential environmental services such as the maintenance of sound soil ecology may be hindered even with very low management intensity. Results also indicated that current intensive pest management strategies do not effectively control mites associated with inflorescences. Continued improvement of post-harvest pest management practices, as difficult as these are for sensitive and fresh produce, are urgently needed. Less reliance on intensive management systems during the production phases of Protea inflorescences would also help preserve some natural ecological processes, such as the ones discovered and described in this dissertation.