Impacts of African elephant feeding on white rhinoceros foraging opportunities
- Authors: Prinsloo, Dominique
- Date: 2017
- Subjects: Herbivores -- Ecology -- South Africa , Grassland ecology -- South Africa Animal-plant relationships -- South Africa Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/13768 , vital:27306
- Description: In this study, I investigated the interaction between two megaherbivores, the African elephant and white rhinoceros, that has the potential to impact grazing lawns of which white rhino are the creators and maintainers and elephants are potentially the modifiers. I hypothesized that as elephants browse, they discard a variety of coarse woody debris onto the ground; should this woody debris (of varying amounts and sizes) fall onto grazing lawns, white rhino either move them, consume grass around the woody debris or abandon the lawn entirely. If high levels of woody debris are deposited here, grazing by white rhino is likely to be prevented, at which time I predicted that mesoherbivores would have a competitive advantage in accessing forage that white rhino cannot. I examined the mechanistic links between different levels of elephant-deposited woody debris and grass response at a point scale and feeding patch spatial scale of grazing lawns in an African savanna. In addition, I assessed the response of mesoherbivores in terms of vigilance behaviour with increasing levels of predation risk posed by increasing levels of woody debris. I present the first evidence of an indirect effect of elephant on white rhino foraging behaviour. I demonstrate how increasing levels of woody debris lead to a decreasing probability of foraging by white rhino. I also demonstrate how the probability of foraging by mesoherbivores increases as the amount of forage increases. However, since this study took place during a severe drought where resources are extremely limited, I was unable to properly separate the effects of elephant-deposited woody debris from the severe lack of rainfall on grass response and subsequently herbivore foraging behaviour. Due possibly to the drought, mesoherbivores responded less or not at all to risk factors such as woody debris therefore woody debris was not a predictor of vigilance behaviour in my study. This study contributes to our understanding of how the impacts of elephants, as ecosystem engineers, have cascading effects on savanna ecosystems. My study showed that elephant impact mediates the foraging behaviour of white rhino during a drought. However, under average rainfall periods, my original hypothesized effect of the indirect impacts of elephants on white rhino foraging and grazing lawn dynamics could still hold. This key hypothesis that I was unable to test under ‘normal’ conditions due to the drought is still valid and functionally important for understanding the ecosystem processes driving grazing lawn formation, persistence and composition in African savannas where elephants and white rhinos coexist.
- Full Text:
- Date Issued: 2017
- Authors: Prinsloo, Dominique
- Date: 2017
- Subjects: Herbivores -- Ecology -- South Africa , Grassland ecology -- South Africa Animal-plant relationships -- South Africa Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/13768 , vital:27306
- Description: In this study, I investigated the interaction between two megaherbivores, the African elephant and white rhinoceros, that has the potential to impact grazing lawns of which white rhino are the creators and maintainers and elephants are potentially the modifiers. I hypothesized that as elephants browse, they discard a variety of coarse woody debris onto the ground; should this woody debris (of varying amounts and sizes) fall onto grazing lawns, white rhino either move them, consume grass around the woody debris or abandon the lawn entirely. If high levels of woody debris are deposited here, grazing by white rhino is likely to be prevented, at which time I predicted that mesoherbivores would have a competitive advantage in accessing forage that white rhino cannot. I examined the mechanistic links between different levels of elephant-deposited woody debris and grass response at a point scale and feeding patch spatial scale of grazing lawns in an African savanna. In addition, I assessed the response of mesoherbivores in terms of vigilance behaviour with increasing levels of predation risk posed by increasing levels of woody debris. I present the first evidence of an indirect effect of elephant on white rhino foraging behaviour. I demonstrate how increasing levels of woody debris lead to a decreasing probability of foraging by white rhino. I also demonstrate how the probability of foraging by mesoherbivores increases as the amount of forage increases. However, since this study took place during a severe drought where resources are extremely limited, I was unable to properly separate the effects of elephant-deposited woody debris from the severe lack of rainfall on grass response and subsequently herbivore foraging behaviour. Due possibly to the drought, mesoherbivores responded less or not at all to risk factors such as woody debris therefore woody debris was not a predictor of vigilance behaviour in my study. This study contributes to our understanding of how the impacts of elephants, as ecosystem engineers, have cascading effects on savanna ecosystems. My study showed that elephant impact mediates the foraging behaviour of white rhino during a drought. However, under average rainfall periods, my original hypothesized effect of the indirect impacts of elephants on white rhino foraging and grazing lawn dynamics could still hold. This key hypothesis that I was unable to test under ‘normal’ conditions due to the drought is still valid and functionally important for understanding the ecosystem processes driving grazing lawn formation, persistence and composition in African savannas where elephants and white rhinos coexist.
- Full Text:
- Date Issued: 2017
Ecology of key cerithioidean gastropods in the mangroves of the iSimangaliso Wetland Park, KwaZulu-Natal South Africa
- Authors: Raw, Jacqueline Leoni
- Date: 2017
- Subjects: Gastropoda -- South Africa -- KwaZulu-Natal Mangrove ecology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11942 , vital:27009
- Description: Gastropods are one of the most diverse species groups in mangrove habitats, however, many of their specific roles in relation to ecological patterns and processes are currently largely unknown. The overall aim of this research project was to provide basic ecological information for key gastropod species from subtropical mangroves within a protected area. South African mangroves cover relatively small areas and are restricted to estuaries, these habitats therefore present unique opportunities and challenges to the species that occur in them. Three gastropod species, Terebralia palustris, Cerithidea decollata, and Melanoides tuberculata, all occur at their natural southernmost range limit within South Africa and were selected based on their prominence and occurrence in mangrove habitats of the iSimangaliso Wetland Park, a UNESCO World Heritage Site. Trophic linkages and resource partitioning, resource utilization rates, and ecological resilience were investigated respectively using: 1) a stable isotope (δ15N and δ13C) approach; 2) an experimental approach to quantify feeding dynamics (ingestion rate, consumption/digestion efficiency and grazing impact); and 3) a mixed-effects modelling approach to relate population responses to environmental variables. The diet of T. palustris was seasonally variable and a number of sources were incorporated by different sized snails, but their grazing impact on microphytobenthos was not significant. The results also indicated an ontogenetic shift in the dietary niche for T. palustris through robust partitioning of resources between different size classes. The diets of C. decollata and M. tuberculata were dominated by different primary resources as a function of where they occurred in the mangroves. Melanoides tuberculata consumed a wide variety of primary resources, a typical trait of an opportunistic generalist species. The ingestion rate of M. tuberculata was not dependent on the availability of microphytobenthos, and was highest when conditions were oligotrophic. The resilience of C. decollata was related to the tree-climbing behaviour of this species and its occurrence was best explained by sediment conductivity. These responses were considered in conjunction to what has previously been reported on the resilience of the mangrove trees. The results of this research project have provided new basic ecological information for all three gastropod species in this data-deficient subtropical region. This information can potentially be used in comparative studies for these species in other regions or in broader scale ecological studies. Terebralia palustris has recently experienced a range contraction along the South African coastline. This research project has shown that the diet of this species is highly variable and that food limitation and competition for resources should be considered as potential drivers of the local decline. Cerithidea decollata has in contrast expanded its distributional range in this region. This research project has shown that this species has a generalist diet and exhibits traits in relation to tolerance that are expected to have facilitated its expansion into temperate saltmarsh habitats that occur in dynamic estuaries. Melanoides tuberculata is a globally invasive species, and as South African populations are within its native range, ecological information from this region is valuable as it can be used to investigate the potential ecological effects following introduction into new habitats beyond the native range. Biological drivers have a significant impact on mangrove ecosystem functioning, particularly in relation to recycling and the retention of organic carbon generated through primary productivity. Understanding the ecological linkages that maintain ecological functioning and stability is therefore an important step towards conserving and sustainably managing threatened ecosystems such as mangrove forests.
- Full Text:
- Date Issued: 2017
- Authors: Raw, Jacqueline Leoni
- Date: 2017
- Subjects: Gastropoda -- South Africa -- KwaZulu-Natal Mangrove ecology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11942 , vital:27009
- Description: Gastropods are one of the most diverse species groups in mangrove habitats, however, many of their specific roles in relation to ecological patterns and processes are currently largely unknown. The overall aim of this research project was to provide basic ecological information for key gastropod species from subtropical mangroves within a protected area. South African mangroves cover relatively small areas and are restricted to estuaries, these habitats therefore present unique opportunities and challenges to the species that occur in them. Three gastropod species, Terebralia palustris, Cerithidea decollata, and Melanoides tuberculata, all occur at their natural southernmost range limit within South Africa and were selected based on their prominence and occurrence in mangrove habitats of the iSimangaliso Wetland Park, a UNESCO World Heritage Site. Trophic linkages and resource partitioning, resource utilization rates, and ecological resilience were investigated respectively using: 1) a stable isotope (δ15N and δ13C) approach; 2) an experimental approach to quantify feeding dynamics (ingestion rate, consumption/digestion efficiency and grazing impact); and 3) a mixed-effects modelling approach to relate population responses to environmental variables. The diet of T. palustris was seasonally variable and a number of sources were incorporated by different sized snails, but their grazing impact on microphytobenthos was not significant. The results also indicated an ontogenetic shift in the dietary niche for T. palustris through robust partitioning of resources between different size classes. The diets of C. decollata and M. tuberculata were dominated by different primary resources as a function of where they occurred in the mangroves. Melanoides tuberculata consumed a wide variety of primary resources, a typical trait of an opportunistic generalist species. The ingestion rate of M. tuberculata was not dependent on the availability of microphytobenthos, and was highest when conditions were oligotrophic. The resilience of C. decollata was related to the tree-climbing behaviour of this species and its occurrence was best explained by sediment conductivity. These responses were considered in conjunction to what has previously been reported on the resilience of the mangrove trees. The results of this research project have provided new basic ecological information for all three gastropod species in this data-deficient subtropical region. This information can potentially be used in comparative studies for these species in other regions or in broader scale ecological studies. Terebralia palustris has recently experienced a range contraction along the South African coastline. This research project has shown that the diet of this species is highly variable and that food limitation and competition for resources should be considered as potential drivers of the local decline. Cerithidea decollata has in contrast expanded its distributional range in this region. This research project has shown that this species has a generalist diet and exhibits traits in relation to tolerance that are expected to have facilitated its expansion into temperate saltmarsh habitats that occur in dynamic estuaries. Melanoides tuberculata is a globally invasive species, and as South African populations are within its native range, ecological information from this region is valuable as it can be used to investigate the potential ecological effects following introduction into new habitats beyond the native range. Biological drivers have a significant impact on mangrove ecosystem functioning, particularly in relation to recycling and the retention of organic carbon generated through primary productivity. Understanding the ecological linkages that maintain ecological functioning and stability is therefore an important step towards conserving and sustainably managing threatened ecosystems such as mangrove forests.
- Full Text:
- Date Issued: 2017
A sedimentological and structural study of the lower Ecca Group, with a focus on facies analysis of the Collingham Formation, north of Grahamstown, SE Karoo Basin, South Africa
- Authors: Slamang, Shereen
- Date: 2017
- Subjects: Formations (Geology) -- South Africa -- Grahamstown Facies (Geology) -- South Africa -- Grahamstown
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21099 , vital:29439
- Description: A study of the Collingham Formation was conducted in the area of the Ecca Pass and Committees Drift Road some 20km north of Grahamstown, Eastern Cape. The study incorporates outcrops of the lower Ecca Group, with a focus on the Collingham Formation. The structural and sedimentological characteristics have been documented, and a detailed description and facies outcrop characterization of the Collingham Formation has been undertaken. The combined thickness of the Prince Albert (~55m), Whitehill (~12m), and Collingham (~20m) Formations is approximately 85m. These formations are composed of fine grained parallel laminated mudrocks of mostly silt- and clay-size particles. A general north-easterly dip direction is recorded with three prominent joint directions striking NNE, NNW, and ESE. Intense small scale folding is evident in the Whitehill Formation, and is likely linked to local décollement structures; while north-verging duplex faults in the Prince Albert Formation is possibly linked to a sole thrust/detachment fault rooted in rocks of the Cape Supergroup. The foreland model has been proposed for these deformational structures. Six lithofacies have been recognised in the Collingham Formation, namely; claystone facies, mudstone facies, siltstone facies, chert facies, tuff facies, and shale facies. The Collingham Formation is comprised of an upward fining sequence of sediments; seen from the gradual change from siltstone facies in the lower layers, to mudstone facies, and claystone facies in the upper layers. This was created in a delta environment whereby clay particles were held in suspension in a hypopycnal mouth bar, and slowly settled to form claystone facies. An influx of sediment caused silt particles to settle further out to sea under the influence of gravity in a hyperpycnal mouth bar, thereby forming siltstone facies. Mudstone facies formed as the sediment supply gradually depleted, subsequently reducing the concentration of silt particles. The dominance of clay particles present suggests deposition to have occurred in tranquil waters, in a possible intracratonic basin setting, where the water depth is known to be a lot shallower. An upward decrease in organic content is seen by the colour change of mudrocks from dark grey near the base to dark green grey in the upper layers. Chlorite is commonly found in thin section, SEM, and XRD, and is an indication that the formation was later subject to low grade greenschist facies metamorphism.
- Full Text:
- Date Issued: 2017
- Authors: Slamang, Shereen
- Date: 2017
- Subjects: Formations (Geology) -- South Africa -- Grahamstown Facies (Geology) -- South Africa -- Grahamstown
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21099 , vital:29439
- Description: A study of the Collingham Formation was conducted in the area of the Ecca Pass and Committees Drift Road some 20km north of Grahamstown, Eastern Cape. The study incorporates outcrops of the lower Ecca Group, with a focus on the Collingham Formation. The structural and sedimentological characteristics have been documented, and a detailed description and facies outcrop characterization of the Collingham Formation has been undertaken. The combined thickness of the Prince Albert (~55m), Whitehill (~12m), and Collingham (~20m) Formations is approximately 85m. These formations are composed of fine grained parallel laminated mudrocks of mostly silt- and clay-size particles. A general north-easterly dip direction is recorded with three prominent joint directions striking NNE, NNW, and ESE. Intense small scale folding is evident in the Whitehill Formation, and is likely linked to local décollement structures; while north-verging duplex faults in the Prince Albert Formation is possibly linked to a sole thrust/detachment fault rooted in rocks of the Cape Supergroup. The foreland model has been proposed for these deformational structures. Six lithofacies have been recognised in the Collingham Formation, namely; claystone facies, mudstone facies, siltstone facies, chert facies, tuff facies, and shale facies. The Collingham Formation is comprised of an upward fining sequence of sediments; seen from the gradual change from siltstone facies in the lower layers, to mudstone facies, and claystone facies in the upper layers. This was created in a delta environment whereby clay particles were held in suspension in a hypopycnal mouth bar, and slowly settled to form claystone facies. An influx of sediment caused silt particles to settle further out to sea under the influence of gravity in a hyperpycnal mouth bar, thereby forming siltstone facies. Mudstone facies formed as the sediment supply gradually depleted, subsequently reducing the concentration of silt particles. The dominance of clay particles present suggests deposition to have occurred in tranquil waters, in a possible intracratonic basin setting, where the water depth is known to be a lot shallower. An upward decrease in organic content is seen by the colour change of mudrocks from dark grey near the base to dark green grey in the upper layers. Chlorite is commonly found in thin section, SEM, and XRD, and is an indication that the formation was later subject to low grade greenschist facies metamorphism.
- Full Text:
- Date Issued: 2017
Using computer vision to categorize tyres and estimate the number of visible tyres in tyre stockpile images
- Authors: Eastwood, Grant
- Date: 2017
- Subjects: Tires -- Specifications Tires -- Recycling , Tires -- Maintenance and repair
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/16022 , vital:28313
- Description: Pressures from environmental agencies contribute to the challenges associated with the disposal of waste tyres, particularly in South Africa. Recycling of waste tyres in South Africa is in its infancy resulting in the historically undocumented and uncontrolled existence of waste tyre stockpiles across the country. The remote and distant locations of such stockpiles typically complicate the logistics associated with the collection, transport and storage of waste tyres prior to entering the recycling process. In order to optimize the logistics associated with the collection of waste tyres from stockpiles, useful information about such stockpiles would include estimates of the types of tyres as well as the quantity of specific tyre types found in particular stockpiles. This research proposes the use of computer vision for categorizing individual tyres and estimating the number of visible tyres in tyre stockpile images to support the logistics in tyre recycling efforts. The study begins with a broad review of image processing and computer vision algorithms for categorization and counting objects in images. The bag of visual words (BoVW) model for categorization is tested on two small data sets of tread tyre images using a random sub-sampling holdout method. The categorization results are evaluated using performance metrics for multiclass classifiers, namely the average accuracy, precision, and recall. The results indicated that corner-based local feature detectors combined with speeded up robust features (SURF) descriptors in a BoVW model provide moderately accurate categorization of tyres based on tread images. Two feature extraction methods for extracting features for use in training neural networks (NNs) for tyre count estimations in tyre stockpiles are proposed. The two feature extraction methods are used to describe images in terms of feature vectors that can be used as input for NNs. The first feature extraction method uses the BoVW model with histograms of oriented gradients (HOG) features collected from overlapping sub-images to create a visual vocabulary and describe the images in terms of their visual word occurrence histogram. The second feature extraction method uses the image gradient magnitude, gradient orientation, and edge orientations of edges detected using the Canny edge detector. A concatenated histogram is constructed from individual histograms of gradient orientations and gradient magnitude. The histograms are then used to train NNs using backpropogation to approximate functions from the feature vectors describing the images to scalar count estimations. The accuracy of visible object count predictions are evaluated using NN evaluation techniques to determine the accuracy of predictions and the generalization ability of the fit model. The count estimation experiments using the two feature extraction methods for input to NNs showed that fairly accurate count estimations can be obtained and that the fit model could generalize fairly well to unseen images.
- Full Text:
- Date Issued: 2017
- Authors: Eastwood, Grant
- Date: 2017
- Subjects: Tires -- Specifications Tires -- Recycling , Tires -- Maintenance and repair
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/16022 , vital:28313
- Description: Pressures from environmental agencies contribute to the challenges associated with the disposal of waste tyres, particularly in South Africa. Recycling of waste tyres in South Africa is in its infancy resulting in the historically undocumented and uncontrolled existence of waste tyre stockpiles across the country. The remote and distant locations of such stockpiles typically complicate the logistics associated with the collection, transport and storage of waste tyres prior to entering the recycling process. In order to optimize the logistics associated with the collection of waste tyres from stockpiles, useful information about such stockpiles would include estimates of the types of tyres as well as the quantity of specific tyre types found in particular stockpiles. This research proposes the use of computer vision for categorizing individual tyres and estimating the number of visible tyres in tyre stockpile images to support the logistics in tyre recycling efforts. The study begins with a broad review of image processing and computer vision algorithms for categorization and counting objects in images. The bag of visual words (BoVW) model for categorization is tested on two small data sets of tread tyre images using a random sub-sampling holdout method. The categorization results are evaluated using performance metrics for multiclass classifiers, namely the average accuracy, precision, and recall. The results indicated that corner-based local feature detectors combined with speeded up robust features (SURF) descriptors in a BoVW model provide moderately accurate categorization of tyres based on tread images. Two feature extraction methods for extracting features for use in training neural networks (NNs) for tyre count estimations in tyre stockpiles are proposed. The two feature extraction methods are used to describe images in terms of feature vectors that can be used as input for NNs. The first feature extraction method uses the BoVW model with histograms of oriented gradients (HOG) features collected from overlapping sub-images to create a visual vocabulary and describe the images in terms of their visual word occurrence histogram. The second feature extraction method uses the image gradient magnitude, gradient orientation, and edge orientations of edges detected using the Canny edge detector. A concatenated histogram is constructed from individual histograms of gradient orientations and gradient magnitude. The histograms are then used to train NNs using backpropogation to approximate functions from the feature vectors describing the images to scalar count estimations. The accuracy of visible object count predictions are evaluated using NN evaluation techniques to determine the accuracy of predictions and the generalization ability of the fit model. The count estimation experiments using the two feature extraction methods for input to NNs showed that fairly accurate count estimations can be obtained and that the fit model could generalize fairly well to unseen images.
- Full Text:
- Date Issued: 2017
The investigation of chemical variation in the stems and rhizomes of cissampelos capensis l. f. (menispermaceae) the Eastern Cape medicinal plant
- Authors: Latolla, Nehemiah Solomon
- Date: 2017
- Subjects: Plants -- Composition Medicinal plants Endemic plants
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/13970 , vital:27362
- Description: Cissampelos capensis L. f. (Menispermaceae) commonly known as “Mayisake” (Xhosa) and “Dawidjieswortel” (Afrikaans) is the most commonly used medicinal plant of the Menispermaceae family in South Africa. The rhizomes of Cissampelos capensis are the most used part of the plant to treat illnesses. This poses a threat to the ongoing conservation of this valuable endemic species. Thus, we studied the chemical variation and subsequently the bioactivity in the stems and rhizomes of Cissampelos capensis, the Eastern Cape medicinal plant, to suggest the possible use of the stems for medicinal purposes. We studied the variation in the chemical composition in the stems and the rhizomes by employing four different extraction methods; the methanolic-, non-polar-, alkaloidal- and Total Tertiary Alkaloidal (TTA) to extract compounds from Cissampelos capensis. Employing various chromatographic techniques, HPLC, NMR and LC/MS to investigate the chemical variation and the in vitro assays for the crude materials of the stems and rhizomes of Cissampelos capensis. We successfully documented a library of the phytochemicals content in Cissampelos capensis from three different regions in the Eastern Cape. We could profile different extraction methods, with the TTA extraction delivering the best comparative profile. Employing LC/MS and HPLC we identified eleven known alkaloidal compounds in the stems and rhizomes. We also isolated a known alkaloid, pronuciferine, from the TTA extract and a crystal structure of proto-quericitol from the methanolic extract, which was isolated for the first time from Cissampelos capensis. Preliminary in vitro results suggested anti-inflammatory activity in the methanolic extracts of the stems and rhizomes, while the TTA extracts showed some cytotoxicity. Finally, through analytical HPLC analysis this study found as high as 31% similarity between the chemical variation of the stems and rhizomes, but key alkaloids were not always present, indicating more work is needed before the stems can be recommended as a replacement for the rhizomes.
- Full Text:
- Date Issued: 2017
- Authors: Latolla, Nehemiah Solomon
- Date: 2017
- Subjects: Plants -- Composition Medicinal plants Endemic plants
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/13970 , vital:27362
- Description: Cissampelos capensis L. f. (Menispermaceae) commonly known as “Mayisake” (Xhosa) and “Dawidjieswortel” (Afrikaans) is the most commonly used medicinal plant of the Menispermaceae family in South Africa. The rhizomes of Cissampelos capensis are the most used part of the plant to treat illnesses. This poses a threat to the ongoing conservation of this valuable endemic species. Thus, we studied the chemical variation and subsequently the bioactivity in the stems and rhizomes of Cissampelos capensis, the Eastern Cape medicinal plant, to suggest the possible use of the stems for medicinal purposes. We studied the variation in the chemical composition in the stems and the rhizomes by employing four different extraction methods; the methanolic-, non-polar-, alkaloidal- and Total Tertiary Alkaloidal (TTA) to extract compounds from Cissampelos capensis. Employing various chromatographic techniques, HPLC, NMR and LC/MS to investigate the chemical variation and the in vitro assays for the crude materials of the stems and rhizomes of Cissampelos capensis. We successfully documented a library of the phytochemicals content in Cissampelos capensis from three different regions in the Eastern Cape. We could profile different extraction methods, with the TTA extraction delivering the best comparative profile. Employing LC/MS and HPLC we identified eleven known alkaloidal compounds in the stems and rhizomes. We also isolated a known alkaloid, pronuciferine, from the TTA extract and a crystal structure of proto-quericitol from the methanolic extract, which was isolated for the first time from Cissampelos capensis. Preliminary in vitro results suggested anti-inflammatory activity in the methanolic extracts of the stems and rhizomes, while the TTA extracts showed some cytotoxicity. Finally, through analytical HPLC analysis this study found as high as 31% similarity between the chemical variation of the stems and rhizomes, but key alkaloids were not always present, indicating more work is needed before the stems can be recommended as a replacement for the rhizomes.
- Full Text:
- Date Issued: 2017
Foraging ecology of gentoo penguins pygoscelis papua at the Falkland Islands
- Authors: Handley, Jonathan Murray
- Date: 2017
- Subjects: Gentoo penguin -- Food -- Falkland Islands Gentoo penguin -- Ecology
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/14113 , vital:27431
- Description: Marine top predators often occupy broad geographical ranges that encompass varied habitats. Therefore, a pre-requisite towards conserving these animals is to determine the components of their realized niche, and investigate whether a species is a specialist or a generalist. For generalist species, it is also necessary to understand if local specialisation occurs. Uncovering these components can allow us to build models of a species realized niche that may then be used to infer habitat use in unsampled locations. However, fully understanding the components of a marine top predators realized niche is challenging owing to the limited opportunity for in situ observations. Overcoming these limitations is a key step in marine top predator research. It will enhance our understanding of trophic coupling in marine systems, and aid in the development of tools to better study these predators in their dynamic environment. Seabirds, penguins (Spheniscids) in particular, are a group of animals for which investigating their realized niche is of vital importance. This is because numerous species face growing uncertainty in the Anthropocene, and in a time of rapid environmental change there is furthermore a need to better understand the potential use of these birds as indicators of ecosystem health. The aim of this thesis, therefore, is to investigate the foraging ecology of gentoo penguins (Pygoscelis papua) at the Falkland Islands. At the Falkland Islands, limited historical information exists regarding this species foraging ecology, with most information coming from a single location at the Falklands. As the Falkland Islands have the world’s largest population of gentoo penguins, elucidating factors influencing this population will have global relevance. Furthermore, historical information indicated potential competition with fisheries, and with prospecting for hydrocarbons and an inshore fishery, there is a need to understand the distribution of these birds across the islands. Penguins are also well suited to carry biologging devices allowing for in situ observations of inter and intraspecific interactions, as well as habitat specific interactions. In this study, I sampled birds over three breeding seasons, from four breeding colonies - chosen for their varied surrounding at sea habitat - across the Falkland Islands. I investigated the diet with stomach content and stable isotope analysis, the at-sea distribution with GPS and time depth recorders, and how these birds behaved at sea using custom made animal-borne camera loggers. Furthermore, I developed a method to recognise prey encounter events from back mounted accelerometers, using a supervised machine learning approach. As part of the first species specific description of diet at this scale for the Falklands, I revealed six key prey items for the birds: rock cod (Patagonotothen spp.), lobster krill (Munida spp.), Falkland herring (Sprattus fuegensis), Patagonian squid (Doryteuthis gahi), juvenile fish (likely all nototheniids), and southern blue whiting (Micromesistius australis). The use of animal-borne camera loggers verified that not only do gentoo penguins consume a diverse array of prey items, but they adopted various methods to capture and pursue prey, with evidence of birds following optimal foraging theory. Prey composition varied significantly between study sites with the at-sea distribution and habitat use of penguins reflecting that of local prey. Birds from colonies close to gently sloping, shallow waters, foraged primarily in a benthic manner and had larger niche widths. However, those at a colony surrounded by steeply sloping, deeper waters, typically foraged in a pelagic manner. Contrasting diet patterns were also prevalent from stable isotope data, and the niche widths of birds relating to both stomach content and stable isotope data were larger at colonies where benthic foraging was prevalent. Therefore, it was clear that surrounding bathymetry played a key role in shaping this species’ foraging ecology, and that at the population level at the Falkland Islands birds are generalists. However, at individual colonies some specialisation occurs to take advantage of locally available prey. I developed habitat distribution models - via boosted regression trees – which transferred well in time but poorly across space. Reasons for poor model transfer might relate to the generalist foraging nature of these birds and the reduced availability of environmental predictors owing to the limited range of these birds. I furthermore developed a method to identify prey encounter events that can also, to a degree, distinguish between prey items. This method will be a promising approach to refine habitat distribution models in future. These habitat distribution models could potentially contribute to marine spatial planning at the Falkland Islands. Footage from animal-borne camera loggers clearly showed that prey behaviour can significantly influence trophic coupling in marine systems and should be accounted for in studies using marine top predators as samplers of mid to lower trophic level species. Ultimately, flexibility in foraging strategies and inter-colony variation will play a critical role when assessing factors such as interspecific competition or overlap with anthropogenic activities.
- Full Text:
- Date Issued: 2017
- Authors: Handley, Jonathan Murray
- Date: 2017
- Subjects: Gentoo penguin -- Food -- Falkland Islands Gentoo penguin -- Ecology
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/14113 , vital:27431
- Description: Marine top predators often occupy broad geographical ranges that encompass varied habitats. Therefore, a pre-requisite towards conserving these animals is to determine the components of their realized niche, and investigate whether a species is a specialist or a generalist. For generalist species, it is also necessary to understand if local specialisation occurs. Uncovering these components can allow us to build models of a species realized niche that may then be used to infer habitat use in unsampled locations. However, fully understanding the components of a marine top predators realized niche is challenging owing to the limited opportunity for in situ observations. Overcoming these limitations is a key step in marine top predator research. It will enhance our understanding of trophic coupling in marine systems, and aid in the development of tools to better study these predators in their dynamic environment. Seabirds, penguins (Spheniscids) in particular, are a group of animals for which investigating their realized niche is of vital importance. This is because numerous species face growing uncertainty in the Anthropocene, and in a time of rapid environmental change there is furthermore a need to better understand the potential use of these birds as indicators of ecosystem health. The aim of this thesis, therefore, is to investigate the foraging ecology of gentoo penguins (Pygoscelis papua) at the Falkland Islands. At the Falkland Islands, limited historical information exists regarding this species foraging ecology, with most information coming from a single location at the Falklands. As the Falkland Islands have the world’s largest population of gentoo penguins, elucidating factors influencing this population will have global relevance. Furthermore, historical information indicated potential competition with fisheries, and with prospecting for hydrocarbons and an inshore fishery, there is a need to understand the distribution of these birds across the islands. Penguins are also well suited to carry biologging devices allowing for in situ observations of inter and intraspecific interactions, as well as habitat specific interactions. In this study, I sampled birds over three breeding seasons, from four breeding colonies - chosen for their varied surrounding at sea habitat - across the Falkland Islands. I investigated the diet with stomach content and stable isotope analysis, the at-sea distribution with GPS and time depth recorders, and how these birds behaved at sea using custom made animal-borne camera loggers. Furthermore, I developed a method to recognise prey encounter events from back mounted accelerometers, using a supervised machine learning approach. As part of the first species specific description of diet at this scale for the Falklands, I revealed six key prey items for the birds: rock cod (Patagonotothen spp.), lobster krill (Munida spp.), Falkland herring (Sprattus fuegensis), Patagonian squid (Doryteuthis gahi), juvenile fish (likely all nototheniids), and southern blue whiting (Micromesistius australis). The use of animal-borne camera loggers verified that not only do gentoo penguins consume a diverse array of prey items, but they adopted various methods to capture and pursue prey, with evidence of birds following optimal foraging theory. Prey composition varied significantly between study sites with the at-sea distribution and habitat use of penguins reflecting that of local prey. Birds from colonies close to gently sloping, shallow waters, foraged primarily in a benthic manner and had larger niche widths. However, those at a colony surrounded by steeply sloping, deeper waters, typically foraged in a pelagic manner. Contrasting diet patterns were also prevalent from stable isotope data, and the niche widths of birds relating to both stomach content and stable isotope data were larger at colonies where benthic foraging was prevalent. Therefore, it was clear that surrounding bathymetry played a key role in shaping this species’ foraging ecology, and that at the population level at the Falkland Islands birds are generalists. However, at individual colonies some specialisation occurs to take advantage of locally available prey. I developed habitat distribution models - via boosted regression trees – which transferred well in time but poorly across space. Reasons for poor model transfer might relate to the generalist foraging nature of these birds and the reduced availability of environmental predictors owing to the limited range of these birds. I furthermore developed a method to identify prey encounter events that can also, to a degree, distinguish between prey items. This method will be a promising approach to refine habitat distribution models in future. These habitat distribution models could potentially contribute to marine spatial planning at the Falkland Islands. Footage from animal-borne camera loggers clearly showed that prey behaviour can significantly influence trophic coupling in marine systems and should be accounted for in studies using marine top predators as samplers of mid to lower trophic level species. Ultimately, flexibility in foraging strategies and inter-colony variation will play a critical role when assessing factors such as interspecific competition or overlap with anthropogenic activities.
- Full Text:
- Date Issued: 2017
The effects of terpenoids on the expression and function of cytokines and adipokines in pre-adipocytes and differentiated adipocytes
- Authors: Bloom, Carri-Ann
- Date: 2017
- Subjects: Terpenes , Cytokines , Fat cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/9208 , vital:26479
- Description: CURRENTLY UNDER EMBARGO UNTIL THE 26/4/2019: Type 2 diabetes is a metabolic disorder characterised by inflammation, insulin resistance and the inability of pancreatic β-cells to secrete enough insulin to produce a physiological effect. Obesity and high levels of triacylglycerol’s are associated with the development of Type 2 diabetes. Adipose tissue is an active endocrine organ that secretes various protein and peptide hormones, known as adipokines, which mediate important metabolic functions. In an insulin resistant and hyperglycaemic state, levels of anti-inflammatory adipokines, adiponectin, are reduced, whereas levels of pro-inflammatory cytokines, interleukin-6 and interleukin-1β, are elevated; this results in a shift from an anti- to a pro-inflammatory state that is accompanied by dysfunction and apoptosis of the pancreatic β-cells. Cannabis sativa L. has been traditionally used as an anti-inflammatory agent in Southern Africa, specifically treating snakebites, fever and malaria. Δ9-tetrahydrocannabinol is the main psychoactive compound derived from C. sativa, whereas the other major cannabinoids, cannabinol and cannabidiol, have shown anti-inflammatory and sedative properties respectively. Marrubiin is a compound derived from the plant Leonotis leonurus L. and has been traditionally used as an anti-inflammatory and anti-diabetic agent. To determine the effects of these compounds in a hyperglycaemic state, pre- and differentiated mouse adipocytes (3T3-L1 cells) were exposed for seven and fourteen days to the following treatments: Δ9-tetrahydrocannabinol, cannabidiol, cannabinol, marrubiin, anandamide (an endogenous endocannabinoid) and cannabis extract, individually and in combination, under normal glucose and hyperglycaemic conditions. Levels of adiponectin, interleukin-6, leptin, tumour-necrosis factor-α and interleukin-1β were quantified using mouse enzyme-linked immunosorbent assay kits and Oil Red O staining was carried out to determine lipid distribution and lipid droplet characteristics. Results indicate that various cannabinoids, in combination, mediate an anti-inflammatory effect by decreasing the expression of various pro-inflammatory cytokines, which may have allowed for a shift from a pro- to an anti-inflammatory state by these compounds, and may also contribute to the reduction of lipid, which may be used as a supplementary option to current diabetic treatment regimes.
- Full Text: false
- Date Issued: 2017
- Authors: Bloom, Carri-Ann
- Date: 2017
- Subjects: Terpenes , Cytokines , Fat cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/9208 , vital:26479
- Description: CURRENTLY UNDER EMBARGO UNTIL THE 26/4/2019: Type 2 diabetes is a metabolic disorder characterised by inflammation, insulin resistance and the inability of pancreatic β-cells to secrete enough insulin to produce a physiological effect. Obesity and high levels of triacylglycerol’s are associated with the development of Type 2 diabetes. Adipose tissue is an active endocrine organ that secretes various protein and peptide hormones, known as adipokines, which mediate important metabolic functions. In an insulin resistant and hyperglycaemic state, levels of anti-inflammatory adipokines, adiponectin, are reduced, whereas levels of pro-inflammatory cytokines, interleukin-6 and interleukin-1β, are elevated; this results in a shift from an anti- to a pro-inflammatory state that is accompanied by dysfunction and apoptosis of the pancreatic β-cells. Cannabis sativa L. has been traditionally used as an anti-inflammatory agent in Southern Africa, specifically treating snakebites, fever and malaria. Δ9-tetrahydrocannabinol is the main psychoactive compound derived from C. sativa, whereas the other major cannabinoids, cannabinol and cannabidiol, have shown anti-inflammatory and sedative properties respectively. Marrubiin is a compound derived from the plant Leonotis leonurus L. and has been traditionally used as an anti-inflammatory and anti-diabetic agent. To determine the effects of these compounds in a hyperglycaemic state, pre- and differentiated mouse adipocytes (3T3-L1 cells) were exposed for seven and fourteen days to the following treatments: Δ9-tetrahydrocannabinol, cannabidiol, cannabinol, marrubiin, anandamide (an endogenous endocannabinoid) and cannabis extract, individually and in combination, under normal glucose and hyperglycaemic conditions. Levels of adiponectin, interleukin-6, leptin, tumour-necrosis factor-α and interleukin-1β were quantified using mouse enzyme-linked immunosorbent assay kits and Oil Red O staining was carried out to determine lipid distribution and lipid droplet characteristics. Results indicate that various cannabinoids, in combination, mediate an anti-inflammatory effect by decreasing the expression of various pro-inflammatory cytokines, which may have allowed for a shift from a pro- to an anti-inflammatory state by these compounds, and may also contribute to the reduction of lipid, which may be used as a supplementary option to current diabetic treatment regimes.
- Full Text: false
- Date Issued: 2017
Tribocorrosion properties of friction stir welded and laser welded titanium alloy
- Authors: Davoren, Brandon Hilton
- Date: 2017
- Subjects: Chemistry, Technical -- Research Materials -- Mechanical properties , Aluminum alloys
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/33250 , vital:32605
- Description: Titanium alloy Ti6Al4V has extensive uses in aerospace, dentistry and the biomedical industry. When used in these applications there is often a need to weld two or more pieces of titanium alloy together. This can be done by either friction stir weld or laser weld methods. These welded regions are often exposed to corrosive environments in addition to factors such as induced additional mechanical wear. Thus to accurately report on the viability of the material in a specific application, the corrosion, wear and their synergistic effects need to be studied. Friction stir welding, which is a well-suited method for joining plates of Ti6Al4V, creates regions in the material that are affected differently. These regions can be described as the parent material, advancing side, retreating side and the weld zone. The tribological properties of the different friction stir weld regions were analysed in air using different loads, frequencies, experimental duration and surrounding environments. When the applied load was increased some of the weld regions showed an increase in the specific wear rate. For example, the weld zone region showed a decrease when compared to the parent material. In this tribology study the effect of the counter material was evaluated. E52100, Si3N4, SS 316 and alumina counter materials were used in the test procedure which was conducted in air on the weld regions. The parent material was found to have the highest average specific wear rates with the four counter materials when compared to the weld zone samples. The regions affected by the friction stir weld process all showed, on average, lower specific wear rates than the parent material. For the various tested samples, the coefficient of friction and material compatibility that was found to be the most stable, was the alumina ball. Owing to this as well as its chemical stability, alumina was determined to be the best material for further tribocorrosion studies. The friction stir welded samples, that were cut from a cross section of a friction stir weld plate, were analyzed in 3.5% NaCl and dilute Harrison’s solution respectively. The effect of wear on the electrochemical properties was studied under open circuit voltage (OCV) and fixed 0.2 V and 0.4 V applied potential conditions respectively. The effect of wear on the corrosion properties was studied using potentiodynamic polarization. From analyzing the friction stir weld regions in both a wear and wear-free environment, the synergistic properties, namely the effect of wear on corrosion and the effect of corrosion on wear, were able to be calculated. The first electrochemical study was performed under OCV conditions. In the presence of applied wear, the open circuit potential of the friction stir weld samples, in both 3.5% NaCl and dilute Harrison’s solution, was found to decrease from the initial stabilized value. Of interest was the rate at which the OCV recovered. It was found to follow a second order repassivation growth model which was explained in terms of an initial film growth stage, followed by a film thickening stage that results in a new OCV. The second synergized electrochemical-wear study was under fixed 0.2 V and 0.4 V applied potential conditions. In both solutions, 3.5% NaCl and dilute Harrison’s solution, a large increase in the current was observed during the applied wear experiment. The samples submerged in 3.5% NaCl were found to have higher average currents during the wear experiment than those in dilute Harrison’s solution. The rapid decrease in the current, after the applied wear ceased, was found to also follow the second order repassivation model. The electrochemical-wear synergism was done by using potentiodynamic polarization tests. The friction stir weld regions as well as the laser samples were analysed in a wear as well as a wear-free environment in order to determine the effect that wear had on the corrosion properties. In both 3.5% NaCl and dilute Harrison’s solution the corrosion rates were found to increase by 100-fold when the wear was present. The effect of the wear process on corrosion could also be described by synergistic factor, where values close to 1 would imply that applied wear had little effect on the corrosion properties and vice versa. The synergistic factors showed that the corrosion rate was greatly affected by the presence of wear with corrosion synergistic factors of 20 and upward for the friction stir welded samples. The results showed that the weld zone region had a lower corrosion rate than the parent material. This implied that the main weld zone was shown to have the least effect of wear on corrosion and would therefore show the lowest likelihood of failure due to corrosion when compared to the parent material. The wear synergistic factor was found to be between 1 and 1.6 for the friction stir weld regions. This implied that the wear rates of the friction stir welded samples were slightly affected by the presence of a corrosive environment and that the wear properties of the laser welded samples were enhanced by the presence of a corrosive environment. Similar studies performed on laser welded samples showed unusually different results due to the small nature of the laser weld region, with inconclusive results when compared to the friction stir welded samples.
- Full Text:
- Date Issued: 2017
- Authors: Davoren, Brandon Hilton
- Date: 2017
- Subjects: Chemistry, Technical -- Research Materials -- Mechanical properties , Aluminum alloys
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/33250 , vital:32605
- Description: Titanium alloy Ti6Al4V has extensive uses in aerospace, dentistry and the biomedical industry. When used in these applications there is often a need to weld two or more pieces of titanium alloy together. This can be done by either friction stir weld or laser weld methods. These welded regions are often exposed to corrosive environments in addition to factors such as induced additional mechanical wear. Thus to accurately report on the viability of the material in a specific application, the corrosion, wear and their synergistic effects need to be studied. Friction stir welding, which is a well-suited method for joining plates of Ti6Al4V, creates regions in the material that are affected differently. These regions can be described as the parent material, advancing side, retreating side and the weld zone. The tribological properties of the different friction stir weld regions were analysed in air using different loads, frequencies, experimental duration and surrounding environments. When the applied load was increased some of the weld regions showed an increase in the specific wear rate. For example, the weld zone region showed a decrease when compared to the parent material. In this tribology study the effect of the counter material was evaluated. E52100, Si3N4, SS 316 and alumina counter materials were used in the test procedure which was conducted in air on the weld regions. The parent material was found to have the highest average specific wear rates with the four counter materials when compared to the weld zone samples. The regions affected by the friction stir weld process all showed, on average, lower specific wear rates than the parent material. For the various tested samples, the coefficient of friction and material compatibility that was found to be the most stable, was the alumina ball. Owing to this as well as its chemical stability, alumina was determined to be the best material for further tribocorrosion studies. The friction stir welded samples, that were cut from a cross section of a friction stir weld plate, were analyzed in 3.5% NaCl and dilute Harrison’s solution respectively. The effect of wear on the electrochemical properties was studied under open circuit voltage (OCV) and fixed 0.2 V and 0.4 V applied potential conditions respectively. The effect of wear on the corrosion properties was studied using potentiodynamic polarization. From analyzing the friction stir weld regions in both a wear and wear-free environment, the synergistic properties, namely the effect of wear on corrosion and the effect of corrosion on wear, were able to be calculated. The first electrochemical study was performed under OCV conditions. In the presence of applied wear, the open circuit potential of the friction stir weld samples, in both 3.5% NaCl and dilute Harrison’s solution, was found to decrease from the initial stabilized value. Of interest was the rate at which the OCV recovered. It was found to follow a second order repassivation growth model which was explained in terms of an initial film growth stage, followed by a film thickening stage that results in a new OCV. The second synergized electrochemical-wear study was under fixed 0.2 V and 0.4 V applied potential conditions. In both solutions, 3.5% NaCl and dilute Harrison’s solution, a large increase in the current was observed during the applied wear experiment. The samples submerged in 3.5% NaCl were found to have higher average currents during the wear experiment than those in dilute Harrison’s solution. The rapid decrease in the current, after the applied wear ceased, was found to also follow the second order repassivation model. The electrochemical-wear synergism was done by using potentiodynamic polarization tests. The friction stir weld regions as well as the laser samples were analysed in a wear as well as a wear-free environment in order to determine the effect that wear had on the corrosion properties. In both 3.5% NaCl and dilute Harrison’s solution the corrosion rates were found to increase by 100-fold when the wear was present. The effect of the wear process on corrosion could also be described by synergistic factor, where values close to 1 would imply that applied wear had little effect on the corrosion properties and vice versa. The synergistic factors showed that the corrosion rate was greatly affected by the presence of wear with corrosion synergistic factors of 20 and upward for the friction stir welded samples. The results showed that the weld zone region had a lower corrosion rate than the parent material. This implied that the main weld zone was shown to have the least effect of wear on corrosion and would therefore show the lowest likelihood of failure due to corrosion when compared to the parent material. The wear synergistic factor was found to be between 1 and 1.6 for the friction stir weld regions. This implied that the wear rates of the friction stir welded samples were slightly affected by the presence of a corrosive environment and that the wear properties of the laser welded samples were enhanced by the presence of a corrosive environment. Similar studies performed on laser welded samples showed unusually different results due to the small nature of the laser weld region, with inconclusive results when compared to the friction stir welded samples.
- Full Text:
- Date Issued: 2017
Identification and classification of micro-estuaries using selected abiotic and biotic characteristics along the Eastern Cape coast, South Africa
- Authors: Naidoo, Lyndle Sherae
- Date: 2017
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11920 , vital:27007
- Description: Many of the larger estuaries along the South African coastline are highly degraded due to human impacts, highlighting the need to conserve pristine systems. There are approximately 100 micro-estuaries along our coastline which have not yet been identified or classified and hence their ecological functioning is unknown. The aim of this study was to identify and classify micro-estuaries along the Eastern Cape coast. Specific objectives of the study were to: 1) map the distribution of estuarine habitats in a selection of micro-estuaries and assess changes over time; 2) measure the physico-chemical characteristics of the micro-estuaries in the field; 3) investigate the distribution of vegetation, identify macrophyte species and habitat integrity and classify the micro-estuaries sampled using abiotic and botanical characteristics. A total of 30 systems were identified of which 10 were selected for sampling which took place seasonally (2015-2016). A relationship between open water surface area and short term rainfall was only evident in Cunge, Sandy Bottom and Ichabana. In the field it was observed that after heavy rainfall, open water surface area increased and mouth breaching occurred. Salinity was the only water column characteristic that showed differences; salinity increased in response to over wash events. Sand was dominant in all systems and there were no differences in sediment characteristics. A total of 8 macroalgal species, 16 estuarine macrophyte species, six freshwater species and 72 riparian plant species were found. Seed bank reserves were low in all systems despite them being vegetated. Only abiotic characteristics were used for classification using Principle Components Analysis since there were no botanical differences between systems. Micro-estuaries were larger (> 0.03 ha), had a higher salinity (oligohaline, mesohaline and polyhaline conditions) and a constant water body. Micro-outlets were smaller (< 0.03 ha), had a lower salinity (oligohaline conditions were most common) and showed periods of drying. Five micro-estuaries (Shelbertsstroom, Kwesani, Cunge, Mtwendwe and Mtendwe) and five micro-outlets (Stromatolite, Sandy Bottom, Ichabana, Palm Tree and Black Rock) were classified. This study has shown that the micro-estuaries along the Eastern Cape coast are pristine (i.e. intact riparian zone and catchment), untouched and highly dynamic systems (i.e. great variation in water surface area and mouth condition) highlighting their need for protection.
- Full Text:
- Date Issued: 2017
- Authors: Naidoo, Lyndle Sherae
- Date: 2017
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11920 , vital:27007
- Description: Many of the larger estuaries along the South African coastline are highly degraded due to human impacts, highlighting the need to conserve pristine systems. There are approximately 100 micro-estuaries along our coastline which have not yet been identified or classified and hence their ecological functioning is unknown. The aim of this study was to identify and classify micro-estuaries along the Eastern Cape coast. Specific objectives of the study were to: 1) map the distribution of estuarine habitats in a selection of micro-estuaries and assess changes over time; 2) measure the physico-chemical characteristics of the micro-estuaries in the field; 3) investigate the distribution of vegetation, identify macrophyte species and habitat integrity and classify the micro-estuaries sampled using abiotic and botanical characteristics. A total of 30 systems were identified of which 10 were selected for sampling which took place seasonally (2015-2016). A relationship between open water surface area and short term rainfall was only evident in Cunge, Sandy Bottom and Ichabana. In the field it was observed that after heavy rainfall, open water surface area increased and mouth breaching occurred. Salinity was the only water column characteristic that showed differences; salinity increased in response to over wash events. Sand was dominant in all systems and there were no differences in sediment characteristics. A total of 8 macroalgal species, 16 estuarine macrophyte species, six freshwater species and 72 riparian plant species were found. Seed bank reserves were low in all systems despite them being vegetated. Only abiotic characteristics were used for classification using Principle Components Analysis since there were no botanical differences between systems. Micro-estuaries were larger (> 0.03 ha), had a higher salinity (oligohaline, mesohaline and polyhaline conditions) and a constant water body. Micro-outlets were smaller (< 0.03 ha), had a lower salinity (oligohaline conditions were most common) and showed periods of drying. Five micro-estuaries (Shelbertsstroom, Kwesani, Cunge, Mtwendwe and Mtendwe) and five micro-outlets (Stromatolite, Sandy Bottom, Ichabana, Palm Tree and Black Rock) were classified. This study has shown that the micro-estuaries along the Eastern Cape coast are pristine (i.e. intact riparian zone and catchment), untouched and highly dynamic systems (i.e. great variation in water surface area and mouth condition) highlighting their need for protection.
- Full Text:
- Date Issued: 2017
Bush clumps as indicators of thresholds of change in Arid Thicket mosaic piospheres
- Authors: Schmidt, Anton George
- Date: 2017
- Subjects: Biodiversity conservation Ecological processes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20811 , vital:29403
- Description: In the literature, Arid Thicket transformation by domestic meso-herbivores is purported to follow a state-and-transition model, whereby the ecosystem is initially resilient to herbivory until some threshold is crossed, where after there is a rapid shift to a new alternative stable state. My study represents a first attempt to verify this hypothesis by searching for evidence of stable ecosystem states separated by structural, functional and degradation thresholds in Pruim-Spekboomveld, a variation of Arid Thicket found in the southern Cape of South Africa. In this variation, thicket bush clumps ranging in size from approximately 1 m2 to 100 m2 are interspersed in a matrix of Succulent Karoo vegetation. I correlate structural and functional attributes of the thicket bush clumps and the soil environment beneath them (indicators of ecosystem function) to distance from artificial watering points in four piosphere treatments that have had a different rangeland management history. I mostly fit linear, exponential and sigmoid regression models to my data and use Akaike’s Information Criterion to select the best fitting model. When analysing data on changes in the variation of vegetation production with distance from water using the Normalized Difference Vegetation Index, I additionally fit Generalized Additive Models to the data to take into account more complex predicted patterns of change. Furthermore, I compare the end regions of my data in the piosphere treatments to each other and to similar data collected in a transformed and untransformed reference site. I use both the pattern and extent of transformation within and between the treatments and the reference sites, to verify the existence of stable states and structural, functional and degradation thresholds. I also subject my entire dataset to multivariate analysis using ordination and permutation procedures, in an attempt to corroborate my results from the univariate analysis and to assess the response of bush clump community composition to herbivory. My results indicate that at the scale of a bush clump, a threshold reduction in species richness, functional type diversity, succulent shrub redundancy and cover, palatable shrub cover and bush clump leaf mass below 1.5 m occurs in regions intensively used by domestic meso-herbivores. Furthermore, at the landscape scale there is a threshold reduction in canopy tree cover and bush clump density. In addition to these structural threshold changes, results from a Landscape Function Analysis indicate that soil nutrient cycling, soil water infiltration and soil stability thresholds are crossed at the landscape scale. The soil nutrient cycling threshold is affirmed by soil chemical analyses which indicate that the most rested treatment in the study area has low carbon and nitrogen levels. Furthermore, the keystone species, Portulacaria afra, is unable to re-establish itself in any of the treatments. High pH and potassium levels in all the treatments, relative to the untransformed reference site, indicate that Portulacaria afra (which prefers moderate soil conditions) is unlikely to re-establish in the study area. This finding suggests that all my treatments have crossed a degradation threshold and therefore represent an alternative stable state to the untransformed reference site. My multivariate analysis supports this finding and further indicates that the sampling zones within 25 m of the watering points in the most utilized treatments have crossed a second degradation threshold. This finding is supported by my results that indicate that structural and function thresholds (related to the size, density and ability of bush clumps to capture and retain soil resources) have been crossed. Furthermore, excessively high concentrations of base cations in these sampling zones, relative to the untransformed reference site, affirm the crossing of a degradation threshold. My results on the changes in the variation of vegetation production with distance from water using the Normalized Difference Vegetation Index, support the growing body of evidence in the literature that suggests that increases in the variance of ecosystem processes and services are important indicators of impending ecological thresholds. In general, my findings support the prediction in the literature that domestic meso-herbivore induced transformation of Arid Mosaic Thicket will follow a state-andtransition model.
- Full Text:
- Date Issued: 2017
- Authors: Schmidt, Anton George
- Date: 2017
- Subjects: Biodiversity conservation Ecological processes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20811 , vital:29403
- Description: In the literature, Arid Thicket transformation by domestic meso-herbivores is purported to follow a state-and-transition model, whereby the ecosystem is initially resilient to herbivory until some threshold is crossed, where after there is a rapid shift to a new alternative stable state. My study represents a first attempt to verify this hypothesis by searching for evidence of stable ecosystem states separated by structural, functional and degradation thresholds in Pruim-Spekboomveld, a variation of Arid Thicket found in the southern Cape of South Africa. In this variation, thicket bush clumps ranging in size from approximately 1 m2 to 100 m2 are interspersed in a matrix of Succulent Karoo vegetation. I correlate structural and functional attributes of the thicket bush clumps and the soil environment beneath them (indicators of ecosystem function) to distance from artificial watering points in four piosphere treatments that have had a different rangeland management history. I mostly fit linear, exponential and sigmoid regression models to my data and use Akaike’s Information Criterion to select the best fitting model. When analysing data on changes in the variation of vegetation production with distance from water using the Normalized Difference Vegetation Index, I additionally fit Generalized Additive Models to the data to take into account more complex predicted patterns of change. Furthermore, I compare the end regions of my data in the piosphere treatments to each other and to similar data collected in a transformed and untransformed reference site. I use both the pattern and extent of transformation within and between the treatments and the reference sites, to verify the existence of stable states and structural, functional and degradation thresholds. I also subject my entire dataset to multivariate analysis using ordination and permutation procedures, in an attempt to corroborate my results from the univariate analysis and to assess the response of bush clump community composition to herbivory. My results indicate that at the scale of a bush clump, a threshold reduction in species richness, functional type diversity, succulent shrub redundancy and cover, palatable shrub cover and bush clump leaf mass below 1.5 m occurs in regions intensively used by domestic meso-herbivores. Furthermore, at the landscape scale there is a threshold reduction in canopy tree cover and bush clump density. In addition to these structural threshold changes, results from a Landscape Function Analysis indicate that soil nutrient cycling, soil water infiltration and soil stability thresholds are crossed at the landscape scale. The soil nutrient cycling threshold is affirmed by soil chemical analyses which indicate that the most rested treatment in the study area has low carbon and nitrogen levels. Furthermore, the keystone species, Portulacaria afra, is unable to re-establish itself in any of the treatments. High pH and potassium levels in all the treatments, relative to the untransformed reference site, indicate that Portulacaria afra (which prefers moderate soil conditions) is unlikely to re-establish in the study area. This finding suggests that all my treatments have crossed a degradation threshold and therefore represent an alternative stable state to the untransformed reference site. My multivariate analysis supports this finding and further indicates that the sampling zones within 25 m of the watering points in the most utilized treatments have crossed a second degradation threshold. This finding is supported by my results that indicate that structural and function thresholds (related to the size, density and ability of bush clumps to capture and retain soil resources) have been crossed. Furthermore, excessively high concentrations of base cations in these sampling zones, relative to the untransformed reference site, affirm the crossing of a degradation threshold. My results on the changes in the variation of vegetation production with distance from water using the Normalized Difference Vegetation Index, support the growing body of evidence in the literature that suggests that increases in the variance of ecosystem processes and services are important indicators of impending ecological thresholds. In general, my findings support the prediction in the literature that domestic meso-herbivore induced transformation of Arid Mosaic Thicket will follow a state-andtransition model.
- Full Text:
- Date Issued: 2017
Foraging behaviour and thermal physiology of Cape sugarbirds: sex-specific responses to temperature
- Authors: Molepo, Mokgatla Jerry
- Date: 2017
- Subjects: Sexual dimorphism (Animals) , Sex differences Birds -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/19124 , vital:28775
- Description: Body size (Mb) determines an animal’s energy and water demands for thermoregulation. Sexual dimorphism in Mb is common across many species, but its physiological consequences (e.g. energy and water demands) remain poorly understood. In this study, I determined if the sexually dimorphic Cape Sugarbird (Promerops cafer)–males are up to 15% larger than females, show sex-specific foraging patterns and physiological responses. To determine intraspecific variability behavioural in response to temperature, I compared flower visitation rates between male and female Cape Sugarbirds at different times of the day, and among days that varied in maximum air temperature. A total of 1207 males and 561 females were observed. Female Cape Sugarbirds visited flowers more often and continued to feed especially on hot days. Males generally dominated flower resources throughout the day, except on hot days. I also compared physiological responses in EWL, RMR and Tb between males and females at high air temperatures. There were no significant differences between the two sexes. Aggression which was overlooked appeared to have a high influence on foraging behaviour of Cape Sugarbirds. These results suggest that female Cape Sugarbirds will be more prone to energy and water stress during hot and dry summers in the Fynbos region because of resource dominance by male Cape Sugarbirds. Endemic birds, such as the Cape Sugarbird, warrant a conservation priority, especially since they are the dominant pollinator of the Protea plants in the Fynbos biome. The findings of this study will provide insights into population persistence of Cape Sugarbirds in response to predicted heat waves and rise in global temperatures.
- Full Text:
- Date Issued: 2017
- Authors: Molepo, Mokgatla Jerry
- Date: 2017
- Subjects: Sexual dimorphism (Animals) , Sex differences Birds -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/19124 , vital:28775
- Description: Body size (Mb) determines an animal’s energy and water demands for thermoregulation. Sexual dimorphism in Mb is common across many species, but its physiological consequences (e.g. energy and water demands) remain poorly understood. In this study, I determined if the sexually dimorphic Cape Sugarbird (Promerops cafer)–males are up to 15% larger than females, show sex-specific foraging patterns and physiological responses. To determine intraspecific variability behavioural in response to temperature, I compared flower visitation rates between male and female Cape Sugarbirds at different times of the day, and among days that varied in maximum air temperature. A total of 1207 males and 561 females were observed. Female Cape Sugarbirds visited flowers more often and continued to feed especially on hot days. Males generally dominated flower resources throughout the day, except on hot days. I also compared physiological responses in EWL, RMR and Tb between males and females at high air temperatures. There were no significant differences between the two sexes. Aggression which was overlooked appeared to have a high influence on foraging behaviour of Cape Sugarbirds. These results suggest that female Cape Sugarbirds will be more prone to energy and water stress during hot and dry summers in the Fynbos region because of resource dominance by male Cape Sugarbirds. Endemic birds, such as the Cape Sugarbird, warrant a conservation priority, especially since they are the dominant pollinator of the Protea plants in the Fynbos biome. The findings of this study will provide insights into population persistence of Cape Sugarbirds in response to predicted heat waves and rise in global temperatures.
- Full Text:
- Date Issued: 2017
Devulcanization of model compounds by a variety of diphenyldisulfides
- Authors: Boyce, Annemè
- Date: 2017
- Subjects: Rubber -- Recycling Rubber, Reclaimed , Rubber -- Standards -- South Africa Rubber -- Research Chromatographic analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14730 , vital:27834
- Description: Improvements to the properties of recycled rubber, by developing a more selective breakdown process, is an important issue and a global challenge. Devulcanization is the most promising way to achieve this. It is a process which aims to totally or partially cleave monosulfidic (C-S-C), disulfidic (C-S-S-C) and polysulfidic (C-Sx-C) crosslinks of vulcanized rubber. In this study, the devulcanization of sulfur-vulcanized natural rubber with a variety of diphenyldisulfides has been studied using 2,3-dimethyl-2-butene and squalene as model compounds, vulcanized by sulfur and 2-bisbenzothiazole-2,2’-disulfide. 2-aminodiphenyldisulfide; 4-amino-diphenyldisulfide; bis(2-benzamido-)diphenyldisulfide and 2,2’-bithiosalicylic acid were used as aromatic disulfides devulcanization agents. Thermal analysis was used to investigate interactions between various combinations of curatives in the vulcanization systems in the absence of model compounds. Thermogravimetric analysis was used to detect mass changes during vulcanization and whether the samples decompose/evaporate so as not to contaminate differential scanning calorimetry instrumentation. Differential scanning calorimetry was used to investigate reactions occurring between curatives. Comparison of reversing and non-reversing signals in modulated experiments are suggestive of reactions between devulcanization agents and sulfur, and accelerators Vulcanization of the model compounds were performed in 10m evacuated sealed glass ampoules placed in an oil bath at 160 °C and agitated for the duration of vulcanization. After 60 min the ampoules were removed and quenched. These were then devulcanized by exposure to a devulcanization agent in a sealed ampoule at 180 for 60 min. Crosslinked 2,3-dimethyl-2-butene species were isolated and analysed by reversed phase high performance liquid chromatography. Particular attention was paid to changes in the number of sulfur atoms in the crosslinks. Results indicate that of the devulcanization agents tested 4-amino-diphenyldisulfide was the most effective. No detrimental effect on devulcanization efficiency was caused by the substitution of a basic amino group with an acidic carboxylic acid group Gel permeation chromatography was performed on devulcanized squalene crosslinks using a tetrahydrofuran eluent. GPC investigations with squalene were less effective than HPLC experiments with 2,3-dimethyl-2-butene at evaluating the relative efficiency of individual devulcanization agents. Results were, however, consistent with 4-amino-diphenyldisulfide again being the most efficient devulcanization agent.
- Full Text:
- Date Issued: 2017
- Authors: Boyce, Annemè
- Date: 2017
- Subjects: Rubber -- Recycling Rubber, Reclaimed , Rubber -- Standards -- South Africa Rubber -- Research Chromatographic analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14730 , vital:27834
- Description: Improvements to the properties of recycled rubber, by developing a more selective breakdown process, is an important issue and a global challenge. Devulcanization is the most promising way to achieve this. It is a process which aims to totally or partially cleave monosulfidic (C-S-C), disulfidic (C-S-S-C) and polysulfidic (C-Sx-C) crosslinks of vulcanized rubber. In this study, the devulcanization of sulfur-vulcanized natural rubber with a variety of diphenyldisulfides has been studied using 2,3-dimethyl-2-butene and squalene as model compounds, vulcanized by sulfur and 2-bisbenzothiazole-2,2’-disulfide. 2-aminodiphenyldisulfide; 4-amino-diphenyldisulfide; bis(2-benzamido-)diphenyldisulfide and 2,2’-bithiosalicylic acid were used as aromatic disulfides devulcanization agents. Thermal analysis was used to investigate interactions between various combinations of curatives in the vulcanization systems in the absence of model compounds. Thermogravimetric analysis was used to detect mass changes during vulcanization and whether the samples decompose/evaporate so as not to contaminate differential scanning calorimetry instrumentation. Differential scanning calorimetry was used to investigate reactions occurring between curatives. Comparison of reversing and non-reversing signals in modulated experiments are suggestive of reactions between devulcanization agents and sulfur, and accelerators Vulcanization of the model compounds were performed in 10m evacuated sealed glass ampoules placed in an oil bath at 160 °C and agitated for the duration of vulcanization. After 60 min the ampoules were removed and quenched. These were then devulcanized by exposure to a devulcanization agent in a sealed ampoule at 180 for 60 min. Crosslinked 2,3-dimethyl-2-butene species were isolated and analysed by reversed phase high performance liquid chromatography. Particular attention was paid to changes in the number of sulfur atoms in the crosslinks. Results indicate that of the devulcanization agents tested 4-amino-diphenyldisulfide was the most effective. No detrimental effect on devulcanization efficiency was caused by the substitution of a basic amino group with an acidic carboxylic acid group Gel permeation chromatography was performed on devulcanized squalene crosslinks using a tetrahydrofuran eluent. GPC investigations with squalene were less effective than HPLC experiments with 2,3-dimethyl-2-butene at evaluating the relative efficiency of individual devulcanization agents. Results were, however, consistent with 4-amino-diphenyldisulfide again being the most efficient devulcanization agent.
- Full Text:
- Date Issued: 2017
Phylogeny and phylogeography of dominant South African surf diatoms
- Authors: Du Preez, Debbie Patricia
- Date: 2017
- Subjects: Phylogeography -- South Africa , Diatoms -- South Africa Phylogeny -- Molecular aspects DNA -- Analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/29794 , vital:30778
- Description: Genetic studies of diatoms are lagging behind those on other organisms. The reasons for this are, among others, that many species are difficult to culture (some surf diatoms in particular), single cells contain only a small amount of DNA, and selection of single cells from environmental samples is difficult. Globally, there are only a few species of surf diatom: Anaulus australis Drebes et Schultz, Asterionellopsis glacialis (Castracane) Round, Asterionellopsis socialis (Lewin & Norris) Crawford & Gardner, Attheya armata (West) Crawford, Aulacodiscus petersii Ehrenberg, Aulacodiscus johnsonii Arnott, Aulacodiscus kittonii Arnott ex Ralfs and Aulacodiscus africanus Cottam. These species occur exclusively in the surf zone with the exception of A. glacialis, which is also found in coastal and oceanic waters. The overall aim of this project was to investigate the phylogeny or the phylogeography of the two dominant South African surf diatoms. In order to do this, it was necessary to develop methods for extracting DNA from environmental surf diatom patch samples. This method was then used in the investigation into the phylogeography of Anaulus australis along the South African coastal zone. Due to other recent work into diatom phylogeny and phylogeography there was also the opportunity to compare the genetics of the South African surf diatom Asterionellopsis found at Sundays River Beach to localities recently sampled and sequenced around the globe in order to identify the species found in South Africa. The direct method was successful for DNA extraction from Anaulus australis cells preserved using either isopropanol, ethanol or glutaraldehyde (provided the samples were not older than two years), but not formalin. Extraction of DNA from Asterionellopsis glacialis s.l. cells was successful with the direct method for ethanol-preserved samples, but the extraction from Attheya armata cells required some modifications be added to the method. Sequencing of the ITS region of Anaulus australis cells from along the southern coast of South Africa indicated connectivity between the various populations rather than the expected isolation of populations in the surf zones of the log-spiral bays. Comparison of the ITS and RbcL regions of the species of Asterionellopsis found at the Sundays River Beach indicated that it is Asterionellopsis lenisilicea which is a species only ii recorded from Canada to date and which has only recently been discovered and recognised as a new species within the genus. This genetic identification was supported by morphological measurements of frustules.
- Full Text:
- Date Issued: 2017
- Authors: Du Preez, Debbie Patricia
- Date: 2017
- Subjects: Phylogeography -- South Africa , Diatoms -- South Africa Phylogeny -- Molecular aspects DNA -- Analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/29794 , vital:30778
- Description: Genetic studies of diatoms are lagging behind those on other organisms. The reasons for this are, among others, that many species are difficult to culture (some surf diatoms in particular), single cells contain only a small amount of DNA, and selection of single cells from environmental samples is difficult. Globally, there are only a few species of surf diatom: Anaulus australis Drebes et Schultz, Asterionellopsis glacialis (Castracane) Round, Asterionellopsis socialis (Lewin & Norris) Crawford & Gardner, Attheya armata (West) Crawford, Aulacodiscus petersii Ehrenberg, Aulacodiscus johnsonii Arnott, Aulacodiscus kittonii Arnott ex Ralfs and Aulacodiscus africanus Cottam. These species occur exclusively in the surf zone with the exception of A. glacialis, which is also found in coastal and oceanic waters. The overall aim of this project was to investigate the phylogeny or the phylogeography of the two dominant South African surf diatoms. In order to do this, it was necessary to develop methods for extracting DNA from environmental surf diatom patch samples. This method was then used in the investigation into the phylogeography of Anaulus australis along the South African coastal zone. Due to other recent work into diatom phylogeny and phylogeography there was also the opportunity to compare the genetics of the South African surf diatom Asterionellopsis found at Sundays River Beach to localities recently sampled and sequenced around the globe in order to identify the species found in South Africa. The direct method was successful for DNA extraction from Anaulus australis cells preserved using either isopropanol, ethanol or glutaraldehyde (provided the samples were not older than two years), but not formalin. Extraction of DNA from Asterionellopsis glacialis s.l. cells was successful with the direct method for ethanol-preserved samples, but the extraction from Attheya armata cells required some modifications be added to the method. Sequencing of the ITS region of Anaulus australis cells from along the southern coast of South Africa indicated connectivity between the various populations rather than the expected isolation of populations in the surf zones of the log-spiral bays. Comparison of the ITS and RbcL regions of the species of Asterionellopsis found at the Sundays River Beach indicated that it is Asterionellopsis lenisilicea which is a species only ii recorded from Canada to date and which has only recently been discovered and recognised as a new species within the genus. This genetic identification was supported by morphological measurements of frustules.
- Full Text:
- Date Issued: 2017
Exploring feeding ecology and population growth rate responses of ungulates in Southern African arid biomes
- Authors: Vermeulen, Mika Margaret
- Date: 2017
- Subjects: Ungulates -- South Africa Arid regions -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/15237 , vital:28189
- Description: Limited resources, extreme temperatures and predators are some of the stresses that are faced by ungulates in arid biomes. Understanding how these stressors influence ungulate feeding ecology and population growth rates is important for managers, as these could influence the persistence of ungulates in protected areas. An understanding of these stressors is especially relevant given the significant population declines in ungulate species globally. The Nama Karoo biome and the arid Savanna, an arid form of the Savanna biome, are both arid, but have distinct rainfall seasonality and vegetation structure and represent unique characteristics that need to be properly considered in their own regard. The literature on African ungulate feeding ecology covers a range of species and biomes from southern and east Africa, however, very little is known about ungulate dietary preferences in the Nama Karoo. Unexplained population declines in springbok (Antidorcas marsupialis) and red hartebeest (Alcelaphus buselaphus caama) have occurred at local scales across the Nama Karoo and the arid Savanna, most notably springbok population declines at the Karoo National Park (Karoo NP). This study sought to improve the understanding of ungulate feeding ecology and population growth rate responses in two arid biomes of South Africa. To achieve this, ungulate dietary composition was characterised, in terms of the proportional seasonal contribution of C4 and C3 plant forms, of a range of ungulates in the Nama Karoo, at the Karoo NP and the arid Savanna, at the Tswalu Kalahari Reserve (Tswalu KR), using stable carbon isotope analysis. Fresh faecal samples of ungulate species were collected from both the biomes during the dry, early wet and late wet seasons. Species were categorised per biome into feeding guilds and the effects of season, biome and the interaction thereof on the diets of the ungulate species explored. Furthermore, the findings were interpreted against what is known about diets of the respective species elsewhere in southern and east Africa. Secondly, trends in ungulate population growth rates were assessed within the Karoo NP and the Tswalu KR over the past 12 and14 years respectively. Furthermore, the variables influencing ungulate population growth rates (and generality of trends), with emphasis on ungulate biomass and rainfall, were explored at biome and species level. Population size data were obtained from annual aerial censuses for the period 2002-2015 and used to calculate annual growth rates and biomass for each ungulate species. The contribution of C4 forage to the diets of ungulate species in the arid Savanna was generally higher than in the Nama Karoo,in line with greater relative abundance of C4 grasses in the former. During winter (dry season) C3 intake was higher in the Nama Karoo than in the arid Savanna, reflecting C3 plant growth (C3 grasses and shrubs) and rainfall during winter in the Nama Karoo. Mean population growth rates during the study period were negative in some of the threatened species considered, i.e. mountain reedbuck (Redunca fulvorufula fulvorufula), tsessebe (Damaliscus lunatus lunatus) and Hartmann’s mountain zebra (Equus zebra hartmannae). No evidence for negative density dependent regulation (~intra-/interspecific competition) of ungulate population growth rates was found, whereas bottom up (~rainfall) and positive density dependent (~biomass of the species under investigation) regulatory mechanisms were most influential. The rainfall and biomass variables influenced the population growth rates of smaller ungulate species more than those of larger bodied ungulate species. Knowledge of ungulate diets will enable managers of protected areas to better understand how climate change, and resultant changes in relative abundances of plant growth forms, will influence specific ungulate species. The finding that increased population biomass positively influenced certain ungulate species’ growth rates has potential implications for management intervention as ungulate biomass is a variable that can be manipulated in protected areas. The reinforcement of existing mountain reedbuck, springbok and red hartebeest populations, specifically, at the Karoo NP and the Tswalu KR may counter their current negative growth rates in these two protected areas. Finally, the influence of protected area size and fencing, on ungulate vulnerability to predators (~top down) and forage quality (~bottom up) mechanisms in arid biomes needs to be further explored.
- Full Text:
- Date Issued: 2017
- Authors: Vermeulen, Mika Margaret
- Date: 2017
- Subjects: Ungulates -- South Africa Arid regions -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/15237 , vital:28189
- Description: Limited resources, extreme temperatures and predators are some of the stresses that are faced by ungulates in arid biomes. Understanding how these stressors influence ungulate feeding ecology and population growth rates is important for managers, as these could influence the persistence of ungulates in protected areas. An understanding of these stressors is especially relevant given the significant population declines in ungulate species globally. The Nama Karoo biome and the arid Savanna, an arid form of the Savanna biome, are both arid, but have distinct rainfall seasonality and vegetation structure and represent unique characteristics that need to be properly considered in their own regard. The literature on African ungulate feeding ecology covers a range of species and biomes from southern and east Africa, however, very little is known about ungulate dietary preferences in the Nama Karoo. Unexplained population declines in springbok (Antidorcas marsupialis) and red hartebeest (Alcelaphus buselaphus caama) have occurred at local scales across the Nama Karoo and the arid Savanna, most notably springbok population declines at the Karoo National Park (Karoo NP). This study sought to improve the understanding of ungulate feeding ecology and population growth rate responses in two arid biomes of South Africa. To achieve this, ungulate dietary composition was characterised, in terms of the proportional seasonal contribution of C4 and C3 plant forms, of a range of ungulates in the Nama Karoo, at the Karoo NP and the arid Savanna, at the Tswalu Kalahari Reserve (Tswalu KR), using stable carbon isotope analysis. Fresh faecal samples of ungulate species were collected from both the biomes during the dry, early wet and late wet seasons. Species were categorised per biome into feeding guilds and the effects of season, biome and the interaction thereof on the diets of the ungulate species explored. Furthermore, the findings were interpreted against what is known about diets of the respective species elsewhere in southern and east Africa. Secondly, trends in ungulate population growth rates were assessed within the Karoo NP and the Tswalu KR over the past 12 and14 years respectively. Furthermore, the variables influencing ungulate population growth rates (and generality of trends), with emphasis on ungulate biomass and rainfall, were explored at biome and species level. Population size data were obtained from annual aerial censuses for the period 2002-2015 and used to calculate annual growth rates and biomass for each ungulate species. The contribution of C4 forage to the diets of ungulate species in the arid Savanna was generally higher than in the Nama Karoo,in line with greater relative abundance of C4 grasses in the former. During winter (dry season) C3 intake was higher in the Nama Karoo than in the arid Savanna, reflecting C3 plant growth (C3 grasses and shrubs) and rainfall during winter in the Nama Karoo. Mean population growth rates during the study period were negative in some of the threatened species considered, i.e. mountain reedbuck (Redunca fulvorufula fulvorufula), tsessebe (Damaliscus lunatus lunatus) and Hartmann’s mountain zebra (Equus zebra hartmannae). No evidence for negative density dependent regulation (~intra-/interspecific competition) of ungulate population growth rates was found, whereas bottom up (~rainfall) and positive density dependent (~biomass of the species under investigation) regulatory mechanisms were most influential. The rainfall and biomass variables influenced the population growth rates of smaller ungulate species more than those of larger bodied ungulate species. Knowledge of ungulate diets will enable managers of protected areas to better understand how climate change, and resultant changes in relative abundances of plant growth forms, will influence specific ungulate species. The finding that increased population biomass positively influenced certain ungulate species’ growth rates has potential implications for management intervention as ungulate biomass is a variable that can be manipulated in protected areas. The reinforcement of existing mountain reedbuck, springbok and red hartebeest populations, specifically, at the Karoo NP and the Tswalu KR may counter their current negative growth rates in these two protected areas. Finally, the influence of protected area size and fencing, on ungulate vulnerability to predators (~top down) and forage quality (~bottom up) mechanisms in arid biomes needs to be further explored.
- Full Text:
- Date Issued: 2017
Microstructure and properties of zirconium silicide surface layers on zirlo for improved nuclear fuel cladding
- Authors: Ngongo, Sinoyolo
- Date: 2017
- Subjects: Zirconium alloys Zirconium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/20098 , vital:29107
- Description: Zirconium alloys have important applications as nuclear reactor fuel cladding material. In this study the microstructure and properties of zirconium silicide synthesized by heating ZIRLO (which is an alloy of zirconium and niobium) in contact with silicon powder has been investigated. The silicide acts as a coating layer to protect the ZIRLO from oxidation which is associated with hydrogen pick-up. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the morphology and crystal structure of the silicides respectively. Heating of ZIRLO with silicon powder was carried out in a Webb 89 Vacuum Furnace for various temperatures (1000–1400 °C) and times (4–8 hours) in an argon atmosphere or under vacuum, which resulted in the diffusion of silicon into the ZIRLO and the formation of zirconium silicide layers. The sample heat treated for 8 hours at 1000 °C did not show any evidence of inter-diffusion between the ZIRLO and silicon, this suggests that a temperature of 1000 °C is not sufficient to facilitate the formation of a silicide layer. The formation of the silicide layer was however observed after heat treatments at 1200 °C and 1400 °C using SEM and TEM. The silicide formed at 1200 °C as a layer on the ZIRLO sample and voids were observed in this layer, most likely due to the Kirkendall effect which occurs in solid state diffusion. The results suggest that Zr has a larger flux than Si as the voids formed in the ZIRLO. The temperature of 1400 °C appears to exceed the ideal required for silicide formation on the surface of ZIRLO, since the silicon infiltrated very far into the ZIRLO and in fact reacted with the entire ZIRLO sample. Both these samples were heat treated for 8 hours in an argon atmosphere. Silicide layers without voids were obtained in the case where ZIRLO and Si were heat treated for 8 and 4 hours at 1200 °C in an argon atmosphere and under vacuum respectively. The average penetration rate, calculated from the aforementioned heat treatments, of Si into Zr was calculated to be 4.5 μm/hour. The diffusion coefficient of Si in Zr was also estimated and it differs by about a factor of 104 from the reported value Zr into Si diffusion coefficient.
- Full Text:
- Date Issued: 2017
- Authors: Ngongo, Sinoyolo
- Date: 2017
- Subjects: Zirconium alloys Zirconium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/20098 , vital:29107
- Description: Zirconium alloys have important applications as nuclear reactor fuel cladding material. In this study the microstructure and properties of zirconium silicide synthesized by heating ZIRLO (which is an alloy of zirconium and niobium) in contact with silicon powder has been investigated. The silicide acts as a coating layer to protect the ZIRLO from oxidation which is associated with hydrogen pick-up. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the morphology and crystal structure of the silicides respectively. Heating of ZIRLO with silicon powder was carried out in a Webb 89 Vacuum Furnace for various temperatures (1000–1400 °C) and times (4–8 hours) in an argon atmosphere or under vacuum, which resulted in the diffusion of silicon into the ZIRLO and the formation of zirconium silicide layers. The sample heat treated for 8 hours at 1000 °C did not show any evidence of inter-diffusion between the ZIRLO and silicon, this suggests that a temperature of 1000 °C is not sufficient to facilitate the formation of a silicide layer. The formation of the silicide layer was however observed after heat treatments at 1200 °C and 1400 °C using SEM and TEM. The silicide formed at 1200 °C as a layer on the ZIRLO sample and voids were observed in this layer, most likely due to the Kirkendall effect which occurs in solid state diffusion. The results suggest that Zr has a larger flux than Si as the voids formed in the ZIRLO. The temperature of 1400 °C appears to exceed the ideal required for silicide formation on the surface of ZIRLO, since the silicon infiltrated very far into the ZIRLO and in fact reacted with the entire ZIRLO sample. Both these samples were heat treated for 8 hours in an argon atmosphere. Silicide layers without voids were obtained in the case where ZIRLO and Si were heat treated for 8 and 4 hours at 1200 °C in an argon atmosphere and under vacuum respectively. The average penetration rate, calculated from the aforementioned heat treatments, of Si into Zr was calculated to be 4.5 μm/hour. The diffusion coefficient of Si in Zr was also estimated and it differs by about a factor of 104 from the reported value Zr into Si diffusion coefficient.
- Full Text:
- Date Issued: 2017
Microencapsulation of anti-tuberculosis drugs using sporopollenin
- Authors: Mhlana, Kanyisile
- Date: 2017
- Subjects: Mycobacterium tuberculosis -- South Africa -- Prevention Microencapsulation , Plant spores
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/13912 , vital:27357
- Description: In this thesis, we explore the benefits of microencapsulating isoniazid and pyrazinamide within sporopollenin exine capsules derived from Lycopodium clavatum. Sporopollenin is a natural biopolymer, which is extracted from the outer shell of pollen grains. These hollow microcapsules can encapsulate and release drug actives in a controlled manner and possess many other advantages such as homogeneity in morphology and size, resilience to both strong acids and bases, they have antioxidant properties as well as UV protection to protect the material inside the microcapsule. Compared to artificial microcapsules, sporopollenin’s muco-adhesion to intestinal tissues contributes greatly to the extended contact of the sporopollenin with the intestines leading to an increased efficiency of delivery of drugs. The hollow microcapsules can be easily filled with a solution of the active or active in a liquid form by simply mixing both together. The drug actives are released in the human body depending on pH factors. Active release can otherwise have controlled by adding a coating on the shell, or co-encapsulation with the active inside the shell so that high drug concentrations are delivered to the site of infection. Encapsulation of the drug active will possibly improve therapeutic abilities of the drugs; simplify the treatment of TB-HIV coinfections by eliminating troublesome drug-drug interactions and drastically reduce or eliminates side effects. The SECs were loaded using a passive filling method. The drug active (0.1 g) was dissolved in a solvent and mixed with the SECs (0.1 g) for 10 minutes. After mixing for 10 minutes, the solvent was removed by a rotary evaporator and dried to a constant mass. The surface of the sporopollenin exines were analysed on a FTIR to observe if there are any drug deposits on the surface of the SECs. The loading efficiency and drug release percentage was determined by using calibrations curves and analysed on a UV-vis spectrophotometer. Further work has been proposed in which to characterize the SECs further and producing coated tablets from loaded SECs.
- Full Text:
- Date Issued: 2017
- Authors: Mhlana, Kanyisile
- Date: 2017
- Subjects: Mycobacterium tuberculosis -- South Africa -- Prevention Microencapsulation , Plant spores
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/13912 , vital:27357
- Description: In this thesis, we explore the benefits of microencapsulating isoniazid and pyrazinamide within sporopollenin exine capsules derived from Lycopodium clavatum. Sporopollenin is a natural biopolymer, which is extracted from the outer shell of pollen grains. These hollow microcapsules can encapsulate and release drug actives in a controlled manner and possess many other advantages such as homogeneity in morphology and size, resilience to both strong acids and bases, they have antioxidant properties as well as UV protection to protect the material inside the microcapsule. Compared to artificial microcapsules, sporopollenin’s muco-adhesion to intestinal tissues contributes greatly to the extended contact of the sporopollenin with the intestines leading to an increased efficiency of delivery of drugs. The hollow microcapsules can be easily filled with a solution of the active or active in a liquid form by simply mixing both together. The drug actives are released in the human body depending on pH factors. Active release can otherwise have controlled by adding a coating on the shell, or co-encapsulation with the active inside the shell so that high drug concentrations are delivered to the site of infection. Encapsulation of the drug active will possibly improve therapeutic abilities of the drugs; simplify the treatment of TB-HIV coinfections by eliminating troublesome drug-drug interactions and drastically reduce or eliminates side effects. The SECs were loaded using a passive filling method. The drug active (0.1 g) was dissolved in a solvent and mixed with the SECs (0.1 g) for 10 minutes. After mixing for 10 minutes, the solvent was removed by a rotary evaporator and dried to a constant mass. The surface of the sporopollenin exines were analysed on a FTIR to observe if there are any drug deposits on the surface of the SECs. The loading efficiency and drug release percentage was determined by using calibrations curves and analysed on a UV-vis spectrophotometer. Further work has been proposed in which to characterize the SECs further and producing coated tablets from loaded SECs.
- Full Text:
- Date Issued: 2017
Benthic algal communities of shallow reefs in the Eastern Cape: availability of abalone habitat
- Authors: Witte, Andrew Dennis
- Date: 2017
- Subjects: Reef ecology -- South Africa -- Eastern Cape Abalone fisheries -- Habitat -- South Africa -- Eastern Cape , Algal communities -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12032 , vital:27021
- Description: Marine ranching has been identified as an alternative to traditional aquacultural rearing and growing organisms for consumption. In the Eastern Cape, abalone ranching is a new and experimental industry. The aims of the research were to: first develop a GIS model to assist management in site selection for abalone seeding; and secondly to develop and standardize the sampling methodology in order to ground truth the sites, and assist in the monitoring and habitat identification of abalone. The GIS model developed in Chapter 3 was created using an unsupervised classification and fuzzy logic approach. Both vector and raster datasets were utilized to represent 7 different layers. Predominantly satellite imagery was used to classify the different substrate groups according to pixel colour signatures. The basic process was to apply a fuzzy rule set (membership) to rasters which gave an output raster (Fuzzification). The membership output rasters were overlaid which creates a single model output. It was found that model accuracy increased significantly as more layers were overlaid, due to the high variability within each of the individual layers. Model ground-truthing showed a strong and significant correlation (r2 = 0.91; p < 0.001) between the model outputs and actual site suitability based on in situ evaluation. Chapter 4 describes the investigation towards the optimal sampling methods for abalone ranching habitat assessments. Both destructive sampling methods and imagery methods were considered as methods of data collection. The study also evaluated whether quadrat and transects were going to be suitable methods to assess sites, and what size or length respectively they should be to collect the appropriate data. Transect length showed great variation according to the factor assessed. A transect of 15 metres was found to be optimal. Abalone counts showed no significant (p = 0.1) change in the Coefficent of Variance (CV) for transect lengths greater than 15m, and had a mean of 0.2 abalone per metre. Quadrat size showed a significant difference in functional group richness between quadrat sizes of 0.0625m2, and 0.25m2 but no difference between 0.25m2 and 1m2 quadrats for both scape and photographic quadrats. It was also found that between 5 and 10 replicates (p = 0.08) represents the functional groups appropriately using quadrats and that a 0.25m2 quadrat is most suitable for sampling. Chapter 5 describes the benthic community structure of Cape Recife shallow water reefs. Using the standardized methodology previously mentioned, 45 sites were assessed to identify the community structure. These sites were grouped into 5 different groups influenced by depth and substrate, as well as functional group composition according to a Wards classification. The community structure showed that depth and substrate play a significant role (p < 0.05) in the community type. There is also a significant relationship (p < 0.05) between complexity, rugosity, abalone presence and substrate. During this study the basic protocols for site selection and benthic community monitoring have been developed to support the abalone ranching initiative in the Cape Recife area. It has also provided a baseline of the benthic community in the ranching concession area which will be used as a benchmark for future monitoring efforts. The site selection, sampling, and monitoring methods developed during the course of this work have now been rolled out as Standard Operating Procedures for the ranching programme in this area.
- Full Text:
- Date Issued: 2017
- Authors: Witte, Andrew Dennis
- Date: 2017
- Subjects: Reef ecology -- South Africa -- Eastern Cape Abalone fisheries -- Habitat -- South Africa -- Eastern Cape , Algal communities -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12032 , vital:27021
- Description: Marine ranching has been identified as an alternative to traditional aquacultural rearing and growing organisms for consumption. In the Eastern Cape, abalone ranching is a new and experimental industry. The aims of the research were to: first develop a GIS model to assist management in site selection for abalone seeding; and secondly to develop and standardize the sampling methodology in order to ground truth the sites, and assist in the monitoring and habitat identification of abalone. The GIS model developed in Chapter 3 was created using an unsupervised classification and fuzzy logic approach. Both vector and raster datasets were utilized to represent 7 different layers. Predominantly satellite imagery was used to classify the different substrate groups according to pixel colour signatures. The basic process was to apply a fuzzy rule set (membership) to rasters which gave an output raster (Fuzzification). The membership output rasters were overlaid which creates a single model output. It was found that model accuracy increased significantly as more layers were overlaid, due to the high variability within each of the individual layers. Model ground-truthing showed a strong and significant correlation (r2 = 0.91; p < 0.001) between the model outputs and actual site suitability based on in situ evaluation. Chapter 4 describes the investigation towards the optimal sampling methods for abalone ranching habitat assessments. Both destructive sampling methods and imagery methods were considered as methods of data collection. The study also evaluated whether quadrat and transects were going to be suitable methods to assess sites, and what size or length respectively they should be to collect the appropriate data. Transect length showed great variation according to the factor assessed. A transect of 15 metres was found to be optimal. Abalone counts showed no significant (p = 0.1) change in the Coefficent of Variance (CV) for transect lengths greater than 15m, and had a mean of 0.2 abalone per metre. Quadrat size showed a significant difference in functional group richness between quadrat sizes of 0.0625m2, and 0.25m2 but no difference between 0.25m2 and 1m2 quadrats for both scape and photographic quadrats. It was also found that between 5 and 10 replicates (p = 0.08) represents the functional groups appropriately using quadrats and that a 0.25m2 quadrat is most suitable for sampling. Chapter 5 describes the benthic community structure of Cape Recife shallow water reefs. Using the standardized methodology previously mentioned, 45 sites were assessed to identify the community structure. These sites were grouped into 5 different groups influenced by depth and substrate, as well as functional group composition according to a Wards classification. The community structure showed that depth and substrate play a significant role (p < 0.05) in the community type. There is also a significant relationship (p < 0.05) between complexity, rugosity, abalone presence and substrate. During this study the basic protocols for site selection and benthic community monitoring have been developed to support the abalone ranching initiative in the Cape Recife area. It has also provided a baseline of the benthic community in the ranching concession area which will be used as a benchmark for future monitoring efforts. The site selection, sampling, and monitoring methods developed during the course of this work have now been rolled out as Standard Operating Procedures for the ranching programme in this area.
- Full Text:
- Date Issued: 2017
Characterization of a glycated gelatin model to explore the therapeutic properties of macrofungi in diabetic wound healing: an in vitro study
- Authors: Pringle, Nadine Alex
- Date: 2017
- Subjects: Diabetes -- Animal models Chronic diseases -- Age factors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11992 , vital:27017
- Description: Diabetic wounds frequently undergo impaired and prolonged wound healing due to a multitude of factors including hypoxia, impaired angiogenesis, hyperglycaemia, formation of ROS and AGEs, and infection - all of which may lead to cellular dysfunction. To date, however, treatment options for individuals suffering from impaired diabetic wound healing are limited, non-specific, and generally unsuccessful. The search for new and effective treatment strategies is severely hampered by the availability of adequately characterized screening models which comprehensively mimic the complexity of the diabetic wound healing process. In order to explore natural products as potential therapeutics to treat diabetic wounds and to encourage more research on this topic, this study sought out to develop and characterize a more convenient and cost effective in vitro screening assay which mimics the effects of protein glycation on the healing process of diabetic wounds. As proof of principal, this model was subsequently used to screen the potential of five wild mushroom species (P. tinctorius, R. capensis, B. badius, P. ostreatus and G. lucidum) as suitable diabetic wound healing therapies. The glycated gelatin model developed during this study was found to suitably mimic the diabetic state as it successfully simulated the major cellular dysfunctions in macrophages (NO production, phagocytosis, macrophage polarization, NF-ĸB translocation and COX-2 expression) and fibroblasts (proliferation and migration) documented during diabetic wound healing. Together these findings provide confidence that the model may serve as a valuable tool to study the poorly understood mechanisms which characterize cellular dysfunction in response to AGE accumulation and also to aid the identification of novel therapeutic agents to treat this pathology. Screening a number of mushroom extracts revealed that the ethanol extracts of R. capensis and P. ostreatus had the greatest potential for attenuating chronic inflammation due to their ability to promote macrophage phagocytosis, increased M2 activation (R. capensis) and decreased M1 activation (P. ostreatus) as well as reduced COX-2 expression while the water extract of G. lucidum proved to be the most promising candidate for stimulating fibroplasia as it was the most successful at promoting both fibroblast proliferation and migration. Different mushroom species were thus shown to promote different stages of the wound healing process providing sufficient evidence to support further studies related to the use of macrofungi as therapeutic agents in the search for more cost-effective and efficient treatment strategies for impaired diabetic wound healing.
- Full Text:
- Date Issued: 2017
- Authors: Pringle, Nadine Alex
- Date: 2017
- Subjects: Diabetes -- Animal models Chronic diseases -- Age factors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11992 , vital:27017
- Description: Diabetic wounds frequently undergo impaired and prolonged wound healing due to a multitude of factors including hypoxia, impaired angiogenesis, hyperglycaemia, formation of ROS and AGEs, and infection - all of which may lead to cellular dysfunction. To date, however, treatment options for individuals suffering from impaired diabetic wound healing are limited, non-specific, and generally unsuccessful. The search for new and effective treatment strategies is severely hampered by the availability of adequately characterized screening models which comprehensively mimic the complexity of the diabetic wound healing process. In order to explore natural products as potential therapeutics to treat diabetic wounds and to encourage more research on this topic, this study sought out to develop and characterize a more convenient and cost effective in vitro screening assay which mimics the effects of protein glycation on the healing process of diabetic wounds. As proof of principal, this model was subsequently used to screen the potential of five wild mushroom species (P. tinctorius, R. capensis, B. badius, P. ostreatus and G. lucidum) as suitable diabetic wound healing therapies. The glycated gelatin model developed during this study was found to suitably mimic the diabetic state as it successfully simulated the major cellular dysfunctions in macrophages (NO production, phagocytosis, macrophage polarization, NF-ĸB translocation and COX-2 expression) and fibroblasts (proliferation and migration) documented during diabetic wound healing. Together these findings provide confidence that the model may serve as a valuable tool to study the poorly understood mechanisms which characterize cellular dysfunction in response to AGE accumulation and also to aid the identification of novel therapeutic agents to treat this pathology. Screening a number of mushroom extracts revealed that the ethanol extracts of R. capensis and P. ostreatus had the greatest potential for attenuating chronic inflammation due to their ability to promote macrophage phagocytosis, increased M2 activation (R. capensis) and decreased M1 activation (P. ostreatus) as well as reduced COX-2 expression while the water extract of G. lucidum proved to be the most promising candidate for stimulating fibroplasia as it was the most successful at promoting both fibroblast proliferation and migration. Different mushroom species were thus shown to promote different stages of the wound healing process providing sufficient evidence to support further studies related to the use of macrofungi as therapeutic agents in the search for more cost-effective and efficient treatment strategies for impaired diabetic wound healing.
- Full Text:
- Date Issued: 2017
The action of sutherlandia frutescens on macrophage differentiation & function
- Authors: Camille, Ned
- Date: 2017
- Subjects: Medicinal plants Macrophages
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22112 , vital:29841
- Description: Sutherlandia frutescens (S. frutescens) is a medicinal plant, indigenous to South Africa used to treat various conditions, including Type II Diabetes (T2D) and immune disorders. Many of these conditions involve the macrophage lineage in low grade chronic inflammation, characterized by elevated pro-inflammatory cytokines. The macrophage population can be divided into pro-inflammatory (M1) and anti-inflammatory (M2) sub-populations. S. frutescens is believed to possess the potential to regulate macrophage differentiation and metabolic immune diseases. This makes it important to investigate its molecular action to determine its potential ethnopharmacological use. The aims of this study were to explore the role of S. frutescens on M1/M2 macrophage function, using extracts prepared from a single plant source previously shown to target T2D, and to determine its potential mechanistic pathways using the murine macrophage-like RAW 264.7 cell line. The action of a hot aqueous and a 100% ethanolic extract of S. frutescens were tested in the RAW 264.7 cell line following Lipopolysaccharide (LPS) induction. The effect of these extracts on activation of a pro-inflammatory M1 phenotype and an anti-inflammatory M2 phenotype was investigated by flow cytometry using the CD markers CD86 (M1) and CD206 (M2). M1 macrophage pro-inflammatory responses were measured by production of nitric oxide (NO) using the Griess reagent and reactive oxygen species (ROS) production and cyclooxygenase 2 (COX-2) expression by flow cytometry. Cytokine production was quantified by ELISA assays. Toll-like receptor-4 (TLR4), inducible nitric oxide synthase (iNOS) (M1) and Heme-oxygenase 1 (HMOX-1) (M2) mRNA expression were quantified by quantitative reverse transcription polymerase chain reaction (RT-qPCR). Arginase-1 activity (M2) was measured by the urea assay. The effect of S. frutescens extracts on nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) and mitogen activated protein kinases (MAPK) signaling pathway were determined with flow cytometry and Image Express XLS microscopy. After 24 hour treatment, both the hot aqueous and ethanolic extracts of S. frutescens significantly inhibited all M1 functions, and altered the pattern of CD expression from M1 (CD86+) to M2 (CD206+) in RAW 264.7 cells following activation by LPS, with the ethanolic extract having the greatest activity. M1-type cytokines were downregulated, while the M2 cytokine profile remained unchanged. S. frutescens was shown to mediate its action through suppression of both NF-κB and MAPK pathways and not through HMOX-1, exerting most activity through decreased p38 MAPK phosphorylation. We show that S. frutescens aids in the potential reversal of imbalances in the macrophage M1 and M2 sub-populations, leading to amelioration of disease. We hypothesize that regulation occurs during the differentiation and activation processes, with reduction in inflammation and direction towards M2 anti-inflammatory activity. This could promote tissue remodeling and immune regulation and has potential to alleviate the pathogenesis of both T2D and immune diseases.
- Full Text:
- Date Issued: 2017
- Authors: Camille, Ned
- Date: 2017
- Subjects: Medicinal plants Macrophages
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22112 , vital:29841
- Description: Sutherlandia frutescens (S. frutescens) is a medicinal plant, indigenous to South Africa used to treat various conditions, including Type II Diabetes (T2D) and immune disorders. Many of these conditions involve the macrophage lineage in low grade chronic inflammation, characterized by elevated pro-inflammatory cytokines. The macrophage population can be divided into pro-inflammatory (M1) and anti-inflammatory (M2) sub-populations. S. frutescens is believed to possess the potential to regulate macrophage differentiation and metabolic immune diseases. This makes it important to investigate its molecular action to determine its potential ethnopharmacological use. The aims of this study were to explore the role of S. frutescens on M1/M2 macrophage function, using extracts prepared from a single plant source previously shown to target T2D, and to determine its potential mechanistic pathways using the murine macrophage-like RAW 264.7 cell line. The action of a hot aqueous and a 100% ethanolic extract of S. frutescens were tested in the RAW 264.7 cell line following Lipopolysaccharide (LPS) induction. The effect of these extracts on activation of a pro-inflammatory M1 phenotype and an anti-inflammatory M2 phenotype was investigated by flow cytometry using the CD markers CD86 (M1) and CD206 (M2). M1 macrophage pro-inflammatory responses were measured by production of nitric oxide (NO) using the Griess reagent and reactive oxygen species (ROS) production and cyclooxygenase 2 (COX-2) expression by flow cytometry. Cytokine production was quantified by ELISA assays. Toll-like receptor-4 (TLR4), inducible nitric oxide synthase (iNOS) (M1) and Heme-oxygenase 1 (HMOX-1) (M2) mRNA expression were quantified by quantitative reverse transcription polymerase chain reaction (RT-qPCR). Arginase-1 activity (M2) was measured by the urea assay. The effect of S. frutescens extracts on nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) and mitogen activated protein kinases (MAPK) signaling pathway were determined with flow cytometry and Image Express XLS microscopy. After 24 hour treatment, both the hot aqueous and ethanolic extracts of S. frutescens significantly inhibited all M1 functions, and altered the pattern of CD expression from M1 (CD86+) to M2 (CD206+) in RAW 264.7 cells following activation by LPS, with the ethanolic extract having the greatest activity. M1-type cytokines were downregulated, while the M2 cytokine profile remained unchanged. S. frutescens was shown to mediate its action through suppression of both NF-κB and MAPK pathways and not through HMOX-1, exerting most activity through decreased p38 MAPK phosphorylation. We show that S. frutescens aids in the potential reversal of imbalances in the macrophage M1 and M2 sub-populations, leading to amelioration of disease. We hypothesize that regulation occurs during the differentiation and activation processes, with reduction in inflammation and direction towards M2 anti-inflammatory activity. This could promote tissue remodeling and immune regulation and has potential to alleviate the pathogenesis of both T2D and immune diseases.
- Full Text:
- Date Issued: 2017
Characterisation of photovoltaic devices using large area light beam induced current measurements
- Okullo, Michael, Van Dyk, Ernes, Okullo, W
- Authors: Okullo, Michael , Van Dyk, Ernes , Okullo, W
- Date: 2017
- Subjects: Photovoltaic cells Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20526 , vital:29314
- Description: Photovoltaic (PV) modules are made by connecting PV cells in series in order to generate a reasonable voltage that can be used for any productive work. Inaccuracy in cell sorting during crystalline silicon module construction, or non-uniform deposition of PV material and laser scribing during thin _lm module construction, may introduce current mismatch in the module. Current mismatch is a consequence of connecting module cells which have non-identical electrical characteristics. When current mismatch occurs in a module, it is the cell generating the lowest current that determines the module output current and this leads to a decrease in the output power and lifespan of the module. Investigation of current uniformity and the different current reducing features in PV modules, which are potential sources of current mismatch, is therefore critical in optimising the performance of PV modules. In this study, a large area light beam induced current (LA-LBIC) measurement system was developed. This non-destructive technique was used to characterise crystalline silicon PV modules (mono-crystalline and multi-crystalline), thin _lm PV modules (amorphous silicon and copper indium diselenide) and a combined concentrator photovoltaic (CPV) module. A light source mounted onto a motorised x-y scanning stage was used to illuminate a PV module, or the Fresnel lens of a CPV module, point-by-point, while measuring the module output current. The measured current was mapped as a function of position and presented as an LBIC image. The point-illuminated circuit model of a PV module was designed and used to explain the variation in current between and within module cells in the LA-LBIC maps. Application of the model to crystalline silicon modules attributes the variation in photo-generated current between cells mainly to current mismatch between series connected cells. Current variation within cells is attributed to individual cell shunts. In the thin _lm modules, the model attributes the variation in photo-generated current mainly to differences in local cell shunts and series resistances originating from the scribing procedure during cell formation in the manufacturing process. In the PV modules studied, variation in photo-generated current was found to exist both between and within cells. The variation was more pronounced between cells than within cells. Module point I-V curves at different points of the module were measured in order to extract short circuit current, to quantify the variations between and within cells. A striation ring defect, causing a drop in short circuit current of 38%, was detected in the mono-crystalline module. Investigation of the striation ring defect indicated that the defect is active in the bulk (p-type) but inactive in the top (n-type) layer. Further characterisation of the defect revealed that a higher percentage loss in short circuit current occurs at lower light intensities. In the multi-crystalline silicon module, cracks were detected and found to electrically isolate the module cells into two parts, causing them to operate in parallel and consequently introducing current mismatch in the module. The I-V curve of the module at standard test condition (STC) revealed a step below the knee, which is a manifestation of current mismatch in the module. High currents, as a consequence of diffuse reflection, leading to multiple reflections by the top glass were also observed at localised points on the bus bar and cell separations. In the a-Si module, the variation in photo-current within some cells, was found to be substantial. In the copper indium diselenide (CIS) module, an electrical disconnection across the module cells was identified. A disconnection in the form of a triangular shape was also identified in this module, which completely disconnected the front contact of this area from the module. This unique disconnection feature caused current in the module to follow in a reverse direction when the light spot was incident within the boundary of the disconnection. Scans performed under different forward voltage biases were useful in identifying severely shunted module cells. A severely shunted cell was found to generate a higher photo-current than a good cell at the same forward bias voltage. This unique observation was explored further using point-illuminated module I-V measurements, and was found to be due to the crossing over of the I-V curves of the two cells. In order to explore the relationship between cell photo-current and cell shunt resistance, a method to determine the shunt resistances of the cells in an encapsulated module was devised. The method involves measuring the I-V curves of a fully illuminated module and a partially illuminated module when one of its cells is shaded and the I-V curves used to determine the short circuit current and the shunt resistance of the shaded cell. A strong correlation was found to exist between the short circuit current of the shaded cell and the cell shunt resistance, as well as between the short circuit current of the shaded cell and dark LBIC. The LA-LBIC technique was further applied to characterise a combine CPV module. Results showed that the Fresnel lens facets close to the centre generate a higher photo-current at the receiver than those towards the edges. The reduced photo-current towards the edges was attributed to losses due to di_raction, dielectric reflection and internal re_ection. About 65% of the area of the Fresnel lenses were found to be e_ective in light collection in terms of the photo-current generated at the receiver. Abrasions and scratches on the Fresnel lenses were identi_ed as some of the current limiting features in a CPV module. The LA-LBIC technique used in this study has demonstrated the potential to investigate current mismatch, current limiting and current enhancing features in PV modules. The capacity to further characterise current limiting features in order to investigate their effects on photo-current under different wavelengths and light intensities was also demonstrated. Extending the LA-LBIC technique to characterise a combined CPV module is a great achievement of this work.
- Full Text:
- Date Issued: 2017
- Authors: Okullo, Michael , Van Dyk, Ernes , Okullo, W
- Date: 2017
- Subjects: Photovoltaic cells Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20526 , vital:29314
- Description: Photovoltaic (PV) modules are made by connecting PV cells in series in order to generate a reasonable voltage that can be used for any productive work. Inaccuracy in cell sorting during crystalline silicon module construction, or non-uniform deposition of PV material and laser scribing during thin _lm module construction, may introduce current mismatch in the module. Current mismatch is a consequence of connecting module cells which have non-identical electrical characteristics. When current mismatch occurs in a module, it is the cell generating the lowest current that determines the module output current and this leads to a decrease in the output power and lifespan of the module. Investigation of current uniformity and the different current reducing features in PV modules, which are potential sources of current mismatch, is therefore critical in optimising the performance of PV modules. In this study, a large area light beam induced current (LA-LBIC) measurement system was developed. This non-destructive technique was used to characterise crystalline silicon PV modules (mono-crystalline and multi-crystalline), thin _lm PV modules (amorphous silicon and copper indium diselenide) and a combined concentrator photovoltaic (CPV) module. A light source mounted onto a motorised x-y scanning stage was used to illuminate a PV module, or the Fresnel lens of a CPV module, point-by-point, while measuring the module output current. The measured current was mapped as a function of position and presented as an LBIC image. The point-illuminated circuit model of a PV module was designed and used to explain the variation in current between and within module cells in the LA-LBIC maps. Application of the model to crystalline silicon modules attributes the variation in photo-generated current between cells mainly to current mismatch between series connected cells. Current variation within cells is attributed to individual cell shunts. In the thin _lm modules, the model attributes the variation in photo-generated current mainly to differences in local cell shunts and series resistances originating from the scribing procedure during cell formation in the manufacturing process. In the PV modules studied, variation in photo-generated current was found to exist both between and within cells. The variation was more pronounced between cells than within cells. Module point I-V curves at different points of the module were measured in order to extract short circuit current, to quantify the variations between and within cells. A striation ring defect, causing a drop in short circuit current of 38%, was detected in the mono-crystalline module. Investigation of the striation ring defect indicated that the defect is active in the bulk (p-type) but inactive in the top (n-type) layer. Further characterisation of the defect revealed that a higher percentage loss in short circuit current occurs at lower light intensities. In the multi-crystalline silicon module, cracks were detected and found to electrically isolate the module cells into two parts, causing them to operate in parallel and consequently introducing current mismatch in the module. The I-V curve of the module at standard test condition (STC) revealed a step below the knee, which is a manifestation of current mismatch in the module. High currents, as a consequence of diffuse reflection, leading to multiple reflections by the top glass were also observed at localised points on the bus bar and cell separations. In the a-Si module, the variation in photo-current within some cells, was found to be substantial. In the copper indium diselenide (CIS) module, an electrical disconnection across the module cells was identified. A disconnection in the form of a triangular shape was also identified in this module, which completely disconnected the front contact of this area from the module. This unique disconnection feature caused current in the module to follow in a reverse direction when the light spot was incident within the boundary of the disconnection. Scans performed under different forward voltage biases were useful in identifying severely shunted module cells. A severely shunted cell was found to generate a higher photo-current than a good cell at the same forward bias voltage. This unique observation was explored further using point-illuminated module I-V measurements, and was found to be due to the crossing over of the I-V curves of the two cells. In order to explore the relationship between cell photo-current and cell shunt resistance, a method to determine the shunt resistances of the cells in an encapsulated module was devised. The method involves measuring the I-V curves of a fully illuminated module and a partially illuminated module when one of its cells is shaded and the I-V curves used to determine the short circuit current and the shunt resistance of the shaded cell. A strong correlation was found to exist between the short circuit current of the shaded cell and the cell shunt resistance, as well as between the short circuit current of the shaded cell and dark LBIC. The LA-LBIC technique was further applied to characterise a combine CPV module. Results showed that the Fresnel lens facets close to the centre generate a higher photo-current at the receiver than those towards the edges. The reduced photo-current towards the edges was attributed to losses due to di_raction, dielectric reflection and internal re_ection. About 65% of the area of the Fresnel lenses were found to be e_ective in light collection in terms of the photo-current generated at the receiver. Abrasions and scratches on the Fresnel lenses were identi_ed as some of the current limiting features in a CPV module. The LA-LBIC technique used in this study has demonstrated the potential to investigate current mismatch, current limiting and current enhancing features in PV modules. The capacity to further characterise current limiting features in order to investigate their effects on photo-current under different wavelengths and light intensities was also demonstrated. Extending the LA-LBIC technique to characterise a combined CPV module is a great achievement of this work.
- Full Text:
- Date Issued: 2017