Browsing by Author "Kietzka, Gabriella Joy"

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    Dragonflies as bioindicators and biodiversity surrogates for freshwater ecosystems
    (Stellenbosch : Stellenbosch University, 2019-12) Kietzka, Gabriella Joy; Pryke, James S.; Samways, Michael J.; Gaigher, Rene; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Biological indicators (bioindicators) are useful for rapid and cost-effective ecosystem assessments. Dragonflies are valued for their potential as bioindicators in freshwater ecosystems. My dissertation aims to assess and expand on their use as bioindicators in transformed landscapes and as surrogates for other aquatic biodiversity. Of the three bioindicator categories (environmental, ecological and biodiversity), biodiversity indicators and their application are poorly understood. The umbrella species concept is a biodiversity surrogacy method that aims to conserve a large number of species in an ecosystem by focusing on a select group of co-occurring species. I used the umbrella index, which quantitatively identified a group of seven dragonfly species and a group of eight Ephemeroptera, Plecoptera and Trichoptera (EPT) species, any of which could be used as biodiversity surrogates (Chapter 2). Adult dragonflies can only be surveyed on warm, windless days during summer, but are easily identifiable. On the other hand, their larvae can be sampled under any weather conditions and are also sensitive bioindicators. I showed that the interchangeability of the life stages for assessments was dependent on landscape spatial scale, coupled with the specific question asked (Chapter 3). Comprehensive biodiversity surveys at fine ecological scales should sample both adults and larvae. However, at larger spatial scales with coarser ecological questions, either adults or larvae can be used. To mitigate the detrimental effects caused by forestry, ecological networks (ENs) are integrated into plantation landscapes. These comprise grassland corridors connected to protected areas (PAs), which often include rivers. They aim to conserve biodiversity by creating habitats or facilitating dispersal of grassland species. I showed that water quality and adult dragonfly diversity did not differ between EN corridors and PAs (Chapter 4). Therefore, the EN approach is an effective method for conserving dragonfly diversity and river ecosystem integrity in plantation landscapes. In the Pietermaritzburg Botanical Gardens, an insect conservation pond was built along a degraded stream. Dragonfly species richness and abundance significantly increased, as both lentic and lotic species were able to colonize the area. Over time, the pond became overgrown and siltation reverted it back to a stream, which negatively affected dragonfly diversity. Shortly after extensive restoration efforts, the dragonfly assemblage had almost completely recovered and closely resembled that of the original pond. This was linked to alien plant removal, decreased vegetation cover and the inclusion of a range of microhabitats. This indicates that conservation ponds need to be actively maintained to keep their function as biodiversity reservoirs. This highlights the value of dragonflies as indicators of habitat quality in aquatic restoration projects. Throughout the thesis, adult dragonflies continuously demonstrated their success as bioindicators. The umbrella index validated the use of dragonflies as biodiversity indicators and surrogates for some of the most sensitive aquatic taxa (the EPT). Although dragonfly larvae and adults are both indicators of water quality, they are not always interchangeable, in terms of sampling at the species level. Their interchangeability depends on the specific question asked and the scale used. I also successfully monitored dragonfly assemblage responses in agricultural lotic and urban lentic environments, which highlighted their benefits for good aquatic conservation planning in transformed landscapes.
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    The natural drivers and the effects of landscape transformation for dragonflies of the Cape Floristic Region
    (Stellenbosch : Stellenbosch University, 2016-03) Kietzka, Gabriella Joy; Pryke, James S.; Samways, Michael J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The Cape Floristic Region (CFR) is a biodiversity hotspot. The region has three established biosphere reserves, which all aim to alleviate the impacts that land transformation has on ecosystem integrity, without jeopardizing basic human needs. In addition to its unique plant diversity, the CFR has high endemism levels of other taxa, including dragonflies. Dragonflies are useful bioindicators of freshwater quality, which has led to the development of the Dragonfly Biotic Index (DBI), a biomonitoring tool for freshwater. The combined pressures of urbanisation and agricultural expansion in the CFR are a major concern for rare, endemic dragonfly species, as well as for overall river ecosystem integrity. In view of this, my study aims to determine which variables drive lotic dragonfly diversity in the CFR, and to assess the effects that land transformation has on this diversity. I first determined which environmental parameters were consistently important so that they could be used as mesofilters to conserve dragonfly diversity (Chapter 2). Dragonfly assemblages and various environmental variables were recorded along the untransformed reaches of three CFR rivers. Heterogeneity of water parameters was found to be the most crucial variables for dragonfly assemblages and for affecting species richness. Here, heterogeneity is defined by the natural spatial and temporal variation of water temperature, dissolved oxygen, conductivity and pH. This differed from previous studies, which strongly suggest vegetation-related variables are the primary drivers of dragonfly diversity. However, these studies took place in transformed landscapes where the strong effects related to anthropogenic disturbances could override the importance of other more subtle natural variables. The maintenance of a gradient of water parameters, which accounts for the natural range of each of the selected water variables, would thus aid in the conservation of dragonflies in the CFR. I also investigated the effects of urbanization and agricultural development on dragonfly diversity and DBI scores. Land transformation homogenized dragonfly assemblages as some endemic species could not persist in these areas. However, species richness was not always reduced, because disturbance allowed for additional widespread, generalist species to enter the system. Dragonfly assemblages differed between agricultural and urban sites but these sites were more similar to each other than to undisturbed sites. Each river supported a unique dragonfly assemblage, making it important to conserve each individual river. Mitigating the adverse influences of landscape transformation is essential for the conservation of rare and endemic taxa, particularly in areas of high conservation value, and the DBI provided an effective way to assess ecosystem integrity in the region. In conclusion, land transformation negatively affects dragonfly diversity and ecosystem integrity in CFR rivers. Conservation efforts should aim to rehabilitate the natural heterogeneity of riparian ecosystems. However, conservation plans should not only focus on restoration of riparian vegetation, but also incorporate variation in water quality parameters. There is not a high possibility of reducing land transformation, with the requirements of an ever-increasing human population. An important alternative option, as I show here, is to protect ecological integrity within a biosphere reserve. The proclamation of more biosphere reserves in the CFR, that include other, additional river catchments, will allow for the conservation of more rare, endemic dragonflies and other taxa. Dragonfly assemblages and the DBI should be used in future monitoring programs and to guide conservation actions.