Initiating biological control for Nymphaea mexicana zuccarini (Nymphaeaceae) in South Africa
- Authors: Reid, Megan
- Date: 2020
- Subjects: Nymphaea mexicana zuccarini -- Biological control -- South Africa , Nymphaeaceae -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144510 , vital:38352
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an aquatic plant originating from south-eastern USA that is becoming increasingly invasive in South Africa as other invasive aquatic plants are being managed successfully through biological control. Mechanical and chemical control of aquatic weeds is expensive, damaging to the environment, and only effective in the short term, so biological control is more desirable as a management strategy for N. mexicana. The biological control of invasive alien plants requires that agents are host specific so that non-target risks are mitigated. For success to be achieved, it is important to ensure that the genetic structure of invasive populations is clarified so that agents can be collected from populations in the native range that match genetically to populations in the invasive range. This is especially important in cases where the morphology of invasive alien plants does not reflect genetic differences between populations. A previous study of the genetic structure of the invasive populations of N. mexicana in South Africa suggests the presence of hybrid forms of the plant in South Africa, with only one of these populations matching with samples from the native range. However, the study only used samples from two sites in the native range using amplified fragment length polymorphisms (AFLPs), so it was necessary to conduct further genetic analyses using samples from more sites in the native range. Hence, the first aim of this study was to develop a better understanding of the genetic structure of N. mexicana populations in the native and invaded range. Genetic samples were collected from sites in the native range during field surveys for potential biological control agents, and inter-simple sequence repeats (ISSRs) were used to compare the genetic structure of invasive and native populations of N. mexicana in South Africa. The results from these analyses suggest that seven of the 14 investigated invasive populations of N. mexicana in South Africa are genetically similar to populations in the native range, while the remaining seven populations are likely to be hybrid forms of the plant. This knowledge will be useful to target populations for biological control and highlights the need for further genetic analyses to determine the parentage of these hybrids so that biological control efforts are more likely to be successful. The initiation of a biological control programme requires that a series of steps are taken in order to maximise the likelihood that this form of intervention will be successful. The first few steps include: identification of the target weed and its genetic structure; exploration in the native range for potential biological control agents; and prioritisation of these agents based on factors such as climatic and genetic compatibility, feeding damage, abundance, and likely host range. Hence, the second aim of this study was to conduct surveys for potential biological control agents in the native range of N. mexicana, and to prioritise these agents. Field surveys were conducted between August and October in 2018 at 17 sites in Florida, Louisiana, and Texas, USA. Sites were selected based on climatic similarity of native sites compared to invasive sites by use of MaxEnt modelling. Native N. mexicana plants were searched for natural enemies, and these were prioritised based on feeding damage, abundance, incidence, and observations of field host range. Two species were prioritised: Bagous americanus LeConte (Coleoptera: Curculionidae) and Megamelus toddi Beamer (Hemiptera: Delphacidae). These species will be imported into quarantine facilities at Rhodes University for host specificity tests to be conducted. Understanding the factors that contribute to the successful establishment of biological control agents is important to improve the efficiency and reduce the costs incurred during the initiation of biological control programmes. Acquiring knowledge of the factors that predict the efficacy of biological control agents is similarly important, and these factors are discussed in the last chapter of this study. The challenges of the biological control of hybrids are also considered, and recommendations are made for the control of N. mexicana and other plants in South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Reid, Megan
- Date: 2020
- Subjects: Nymphaea mexicana zuccarini -- Biological control -- South Africa , Nymphaeaceae -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144510 , vital:38352
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an aquatic plant originating from south-eastern USA that is becoming increasingly invasive in South Africa as other invasive aquatic plants are being managed successfully through biological control. Mechanical and chemical control of aquatic weeds is expensive, damaging to the environment, and only effective in the short term, so biological control is more desirable as a management strategy for N. mexicana. The biological control of invasive alien plants requires that agents are host specific so that non-target risks are mitigated. For success to be achieved, it is important to ensure that the genetic structure of invasive populations is clarified so that agents can be collected from populations in the native range that match genetically to populations in the invasive range. This is especially important in cases where the morphology of invasive alien plants does not reflect genetic differences between populations. A previous study of the genetic structure of the invasive populations of N. mexicana in South Africa suggests the presence of hybrid forms of the plant in South Africa, with only one of these populations matching with samples from the native range. However, the study only used samples from two sites in the native range using amplified fragment length polymorphisms (AFLPs), so it was necessary to conduct further genetic analyses using samples from more sites in the native range. Hence, the first aim of this study was to develop a better understanding of the genetic structure of N. mexicana populations in the native and invaded range. Genetic samples were collected from sites in the native range during field surveys for potential biological control agents, and inter-simple sequence repeats (ISSRs) were used to compare the genetic structure of invasive and native populations of N. mexicana in South Africa. The results from these analyses suggest that seven of the 14 investigated invasive populations of N. mexicana in South Africa are genetically similar to populations in the native range, while the remaining seven populations are likely to be hybrid forms of the plant. This knowledge will be useful to target populations for biological control and highlights the need for further genetic analyses to determine the parentage of these hybrids so that biological control efforts are more likely to be successful. The initiation of a biological control programme requires that a series of steps are taken in order to maximise the likelihood that this form of intervention will be successful. The first few steps include: identification of the target weed and its genetic structure; exploration in the native range for potential biological control agents; and prioritisation of these agents based on factors such as climatic and genetic compatibility, feeding damage, abundance, and likely host range. Hence, the second aim of this study was to conduct surveys for potential biological control agents in the native range of N. mexicana, and to prioritise these agents. Field surveys were conducted between August and October in 2018 at 17 sites in Florida, Louisiana, and Texas, USA. Sites were selected based on climatic similarity of native sites compared to invasive sites by use of MaxEnt modelling. Native N. mexicana plants were searched for natural enemies, and these were prioritised based on feeding damage, abundance, incidence, and observations of field host range. Two species were prioritised: Bagous americanus LeConte (Coleoptera: Curculionidae) and Megamelus toddi Beamer (Hemiptera: Delphacidae). These species will be imported into quarantine facilities at Rhodes University for host specificity tests to be conducted. Understanding the factors that contribute to the successful establishment of biological control agents is important to improve the efficiency and reduce the costs incurred during the initiation of biological control programmes. Acquiring knowledge of the factors that predict the efficacy of biological control agents is similarly important, and these factors are discussed in the last chapter of this study. The challenges of the biological control of hybrids are also considered, and recommendations are made for the control of N. mexicana and other plants in South Africa.
- Full Text:
- Date Issued: 2020
The effect of top dressing treatments on stolon weaning and keeping quality on two potato cultivars in the Gamtoos river valley
- Authors: Murray, Roger Benjamin
- Date: 2020
- Subjects: Plants -- Effect of nitrates on
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/48522 , vital:40884
- Description: Potatoes are an important crop in the Eastern Cape, and in South Africa as a whole, as a nutritious staple food. For consumers, they provide a quality, relatively low-priced form of carbohydrate and, for farmers, they are a valuable cash crop. The nutritional requirements of Solanum tuberosum L., in particular its nitrogen (N) needs, during cultivation is an aspect warranting further research. The Eastern Cape is a prime potato-producing region and, as such, is an appropriate and logical choice in terms of a suitable location for the required study. Improper farming practices with regards to improper fertilizer application techniques can adversely affect yields, and excessive application of fertilizer is fundamentally economically unsound, adverse towards the environment and potentially detrimental to the crop. It is therefore imperative that nutrients – and nitrogen in particular – are available to the crop in the correct quantities at the correct time. The objective of this dissertation was to accurately identify the nitrogen fertilizer needs of potatoes – with specific emphasis on whether or not nitrogen affects stolon growth and development. The potato cultivar used in the research trial was Mondial, which is a cultivar well-established in the region. Nitrogen applications needed to be closely monitored with regards to the total seasonal amount of nitrogen applied, the timing of applications and the amount applied at each application. Meaningful data accumulated from this study will help farmers in the area to accurately assess the efficiency of their farming operations. Excessive or insufficient plant nutrition affects tuber bulking and quality. The objective was to accurately identify this “sweet spot” (i.e. the optimal measure and timing) with regards to fertilization, especially nitrogen, while also taking into account various other factors that affect healthy tuber development and stolon formation. The untested assertion that prompted this study was that too much nitrogen adversely affects the number of stolons – and therefore, the number of tubers, since tubers grow from the stolons. It is generally accepted that too little N will adversely affect yields and yield potential will not be achieved, and that too much N will adversely affect yields, incur unnecessary costs and potentially degrade the environment. Optimum nitrogen application quantities were therefore identified, along with points at which deviations from optimum yields occurred. There were 8 distinct treatment combinations – namely: a rate of 150kg/ha, 250kg/ha, 350kg/ha and 450kg/ha – of nitrogen (N) throughout the growing season, administered at 2 different timings (hereafter referred to as the Application Timings). The applications of nitrogen were administered as follows: Application Timing 1 (50% N at planting : 25% N as Topdressing 1 : 25% N as Topdressing 2) and Application Timing 2 (75% N at planting : 12.5% N as Topdressing 1 : 12.5% N as Topdressing 2). The findings suggest that while nitrogen played a role in increasing yield, there was no conclusive evidence to suggest that stolons were weaned by excessive amounts of nitrogen throughout the growing season. The results obtained from statistical analysis showed that, between Application Timing 1 (50%:25%:25%) and Application Timing 2 (75%:12.5%:12.5%), neither split application timing was superior to the other in terms of tuber yield or effect on the average number of stolons when data from all three plantings were combined. In some instances, high stolon numbers were observed in the high N application plots. The highest stolon count in a single data collection in Planting 1 was in the 450kg/ha App. 1 plots in the 3rd data collection. The highest stolon count in a single data collection in Planting 2 was in the 250kg/ha App. 2 plots in the 2nd data collection. The highest stolon count in a single data collection was in the 350kg/ha App. 2 plots in the 3rd data collection. The conjecture that excessive nitrogen causes stolon weaning in potatoes was not supported by the findings of the experiments conducted in the three trial plantings which constituted this research study.
- Full Text:
- Date Issued: 2020
- Authors: Murray, Roger Benjamin
- Date: 2020
- Subjects: Plants -- Effect of nitrates on
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/48522 , vital:40884
- Description: Potatoes are an important crop in the Eastern Cape, and in South Africa as a whole, as a nutritious staple food. For consumers, they provide a quality, relatively low-priced form of carbohydrate and, for farmers, they are a valuable cash crop. The nutritional requirements of Solanum tuberosum L., in particular its nitrogen (N) needs, during cultivation is an aspect warranting further research. The Eastern Cape is a prime potato-producing region and, as such, is an appropriate and logical choice in terms of a suitable location for the required study. Improper farming practices with regards to improper fertilizer application techniques can adversely affect yields, and excessive application of fertilizer is fundamentally economically unsound, adverse towards the environment and potentially detrimental to the crop. It is therefore imperative that nutrients – and nitrogen in particular – are available to the crop in the correct quantities at the correct time. The objective of this dissertation was to accurately identify the nitrogen fertilizer needs of potatoes – with specific emphasis on whether or not nitrogen affects stolon growth and development. The potato cultivar used in the research trial was Mondial, which is a cultivar well-established in the region. Nitrogen applications needed to be closely monitored with regards to the total seasonal amount of nitrogen applied, the timing of applications and the amount applied at each application. Meaningful data accumulated from this study will help farmers in the area to accurately assess the efficiency of their farming operations. Excessive or insufficient plant nutrition affects tuber bulking and quality. The objective was to accurately identify this “sweet spot” (i.e. the optimal measure and timing) with regards to fertilization, especially nitrogen, while also taking into account various other factors that affect healthy tuber development and stolon formation. The untested assertion that prompted this study was that too much nitrogen adversely affects the number of stolons – and therefore, the number of tubers, since tubers grow from the stolons. It is generally accepted that too little N will adversely affect yields and yield potential will not be achieved, and that too much N will adversely affect yields, incur unnecessary costs and potentially degrade the environment. Optimum nitrogen application quantities were therefore identified, along with points at which deviations from optimum yields occurred. There were 8 distinct treatment combinations – namely: a rate of 150kg/ha, 250kg/ha, 350kg/ha and 450kg/ha – of nitrogen (N) throughout the growing season, administered at 2 different timings (hereafter referred to as the Application Timings). The applications of nitrogen were administered as follows: Application Timing 1 (50% N at planting : 25% N as Topdressing 1 : 25% N as Topdressing 2) and Application Timing 2 (75% N at planting : 12.5% N as Topdressing 1 : 12.5% N as Topdressing 2). The findings suggest that while nitrogen played a role in increasing yield, there was no conclusive evidence to suggest that stolons were weaned by excessive amounts of nitrogen throughout the growing season. The results obtained from statistical analysis showed that, between Application Timing 1 (50%:25%:25%) and Application Timing 2 (75%:12.5%:12.5%), neither split application timing was superior to the other in terms of tuber yield or effect on the average number of stolons when data from all three plantings were combined. In some instances, high stolon numbers were observed in the high N application plots. The highest stolon count in a single data collection in Planting 1 was in the 450kg/ha App. 1 plots in the 3rd data collection. The highest stolon count in a single data collection in Planting 2 was in the 250kg/ha App. 2 plots in the 2nd data collection. The highest stolon count in a single data collection was in the 350kg/ha App. 2 plots in the 3rd data collection. The conjecture that excessive nitrogen causes stolon weaning in potatoes was not supported by the findings of the experiments conducted in the three trial plantings which constituted this research study.
- Full Text:
- Date Issued: 2020
Beef quality, oxidative stability and fatty acid composition of Nguni heifers fed diets with incremental levels of Opuntia ficus-indica (cactus) cladodes
- Authors: Mkhosi, Silungile
- Date: 2020
- Subjects: Meat -- Quality
- Language: English
- Type: Thesis , Masters , MSc (Animal Science )
- Identifier: http://hdl.handle.net/10353/18732 , vital:42728
- Description: The objective of the study was to determine meat quality, fatty acid (FA) composition and shelf-life stability of longissimus muscle of Nguni heifers fed incremental levels of Opuntia ficus-indica (cactus) cladodes. A total of 32 heifers aged 36 months were allocated randomly to four dietary treatments: 10% cactus, 20% cactus, commercial and control diets for 90 days. The longissimus thoracis et lumborum (LTL) samples were taken from each carcass for the determination of meat quality, retail shelf-life stability and FA composition. Diet had no effect (P > 0.05) on pH and drip display, however, there was an increase in drip display with ageing time (P ≤ 0.05). Meat colour attributes (L* a* b* and C*) were influenced by diet, with 20% cactus diet having lower L* values compared to other diets (P ≤ 0.05). During a 14-day retail display, a diet day interaction was observed for hue angle with the cactus diets having the lowest values at day 14 of display compared to the other diets (P ≤ 0.05). Differences in meat from heifers fed different diets were observed with 20% cactus accounting for significantly (P ≤ 0.05) higher levels of deoxymyoglobin and the lowest levels of oxymyoglobin. Thawing loss and Warner Bratzler shear force decreased (P ≤ 0.05) with ageing period. Meat from heifers fed cactus diets had lower (P ≤ 0.05) proportions of oleic acid (C18:1n9c) and total MUFA, higher (P ≤ 0.05) proportions of total SFA, C15:1, C17:1, linoleic acid (C18:2n6c) and total PUFA. The control diet produced meat with the highest thiobarbituric acid reactive substances (TBARS) values compared to other diets (P ≤ 0.05) and with ageing TBARS values increased (P ≤ 0.05). Diet showed an effect (P ≤ 0.05) on sensory attributes such as overall tenderness and mouth feel with cactus diets accounting for lower scores. However, juiciness, overall tenderness, grassy and animal like attributes increased with ageing (P ≤ 0.05). Inclusion of cactus in the diet did not produce any adverse effects on meat quality, fatty acid composition, lipid oxidation and sensory quality. Therefore, it can be concluded that inclusion of cactus in Nguni heifer finisher diets up to 20% can improve meat quality.
- Full Text:
- Date Issued: 2020
- Authors: Mkhosi, Silungile
- Date: 2020
- Subjects: Meat -- Quality
- Language: English
- Type: Thesis , Masters , MSc (Animal Science )
- Identifier: http://hdl.handle.net/10353/18732 , vital:42728
- Description: The objective of the study was to determine meat quality, fatty acid (FA) composition and shelf-life stability of longissimus muscle of Nguni heifers fed incremental levels of Opuntia ficus-indica (cactus) cladodes. A total of 32 heifers aged 36 months were allocated randomly to four dietary treatments: 10% cactus, 20% cactus, commercial and control diets for 90 days. The longissimus thoracis et lumborum (LTL) samples were taken from each carcass for the determination of meat quality, retail shelf-life stability and FA composition. Diet had no effect (P > 0.05) on pH and drip display, however, there was an increase in drip display with ageing time (P ≤ 0.05). Meat colour attributes (L* a* b* and C*) were influenced by diet, with 20% cactus diet having lower L* values compared to other diets (P ≤ 0.05). During a 14-day retail display, a diet day interaction was observed for hue angle with the cactus diets having the lowest values at day 14 of display compared to the other diets (P ≤ 0.05). Differences in meat from heifers fed different diets were observed with 20% cactus accounting for significantly (P ≤ 0.05) higher levels of deoxymyoglobin and the lowest levels of oxymyoglobin. Thawing loss and Warner Bratzler shear force decreased (P ≤ 0.05) with ageing period. Meat from heifers fed cactus diets had lower (P ≤ 0.05) proportions of oleic acid (C18:1n9c) and total MUFA, higher (P ≤ 0.05) proportions of total SFA, C15:1, C17:1, linoleic acid (C18:2n6c) and total PUFA. The control diet produced meat with the highest thiobarbituric acid reactive substances (TBARS) values compared to other diets (P ≤ 0.05) and with ageing TBARS values increased (P ≤ 0.05). Diet showed an effect (P ≤ 0.05) on sensory attributes such as overall tenderness and mouth feel with cactus diets accounting for lower scores. However, juiciness, overall tenderness, grassy and animal like attributes increased with ageing (P ≤ 0.05). Inclusion of cactus in the diet did not produce any adverse effects on meat quality, fatty acid composition, lipid oxidation and sensory quality. Therefore, it can be concluded that inclusion of cactus in Nguni heifer finisher diets up to 20% can improve meat quality.
- Full Text:
- Date Issued: 2020
Synthesis and characterization of MXS (M = Mo & V) and carbon supported MXS nanocomposites as Pt-free counter electrodes for electrode for DSSC application
- Authors: Bede, Asanda
- Date: 2020
- Subjects: Voltammetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/18599 , vital:42612
- Description: It has been reported that the morphology, crystalline phase composition and electrochemical properties of counter electrode materials such MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials was of considerable importance because it governs the efficiency of many photon assisted chemical and physical reactions in dye sensitized solar cells (DSSCs). The efficiency of DSSCs with composite counter electrode materials is reliant on the stability of the photochemistry reactions which can be optimized by appropriate doping levels of the composite materials. Moreover, the microstructure such as surface area, distribution of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials, and the stability of the electrostatic bonds between the MxS (Mo, V) with the carbon support also play a significant role in the performance of the DSSCs. This work evaluates the effect of different mole ratios of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials on the morphological, structural and electrochemical properties of the composite materials. MoS2 nanoflakes nanostructures have been synthesized by hydrothermal technique using sodium orthovanadate (Na2MoO4) as precursor. In this work Carbon supported MoS2 NFs have been prepared by physically/chemically mixing different mole ratios of MoS2 NFs with multi-walled carbon nanotubes (MWCNTs) and polyvinylidene in N-methyl-2-pyrrolidinone. The morphological, structural and electrochemical properties of the composite counter electrode materials have been investigated using SEM, XRD FTIR, TEM, RS and CV. SEM analysis has revealed the presence of large MoS2 nanoflakes (NFs) as synthesized. SEM analysis has also revealed significant change in the surface morphology of carbon supported MoS2 composite nanostructures with the change in the mole ratio of the MoS2 NFs and carbon support multi-walled carbon nanotubes. Structural analysis through HRTEM analysis revealed a d-spacing of 0.65 nm with a corresponding (002) lattice plane belonging to a trigonal crystalline phase of MoS2. Also, HRTEM analysis has revealed d-spacing of 0.291 nm corresponding to 002 plane of MWCNTs. Raman spectroscopy has revealed Characteristic Raman vibration frequencies and symmetries at 264.6 cm-1(Eg), 354.2 cm-1 (Ag ) belonging trigonal phase of MoS2 (1T-MoS2). FTIR analysis has revealed a narrow peak at 457.6 cm-1 due Mo-S vibration bond. This observation confirms the success of synthesis of MoS2 nanostructures. Cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS) measurements have revealed that the ratio 6:3:1 have shown to be optimum ratio due to its large reduction rate compared to pristine MoS2 NFs and other carbon supported MoS2 NFs. Calculated Rreduction for the carbon supported MoS2 NFs is the order 3:6:1>1:8:1>6:3:1>8:1:1 indicating the trend of ratio 3:6:1 appeared to have higher reduction rate than the rest of the material and it had far less ΔEpp than the rest of other ratios. All CV curves for both pristine MoS2 NFs and carbon supported MoS2 NFs confirmed a distinct Faradic characteristic. The VS2 nanosheets (NSs) and carbon supported VS2 NSs were also effectively synthesized via hydrothermal method. The SEM micrographs for VS2 NSs and carbon supported VS2 NSs samples reveals level increased. Furthermore, SEM-EDX analysis have confirmed the presence of V and S as well as C and O on carbon supported VS2 nanocomposites, and it clearly shown a gradually blending as the ratios increases. The structural studies through XRD analysis have revealed peaks at 2θ angles of 15.4◦, 28.2◦, 34.2◦, 36.2◦, 43.3◦,48.3◦, 54.4◦, 57.7◦ and 66.2◦ which correspond to the lattice planes (001), (002), (100), (011), (102), (003), (110), (103) and (201) belonging to hexagonal VS2 (H-VS2) crystalline phase as per JCPDS card 36-1139. The HRTEM have revealed that the VS2 NSs have an edge to edge length of ~ 0.294 – 1.248 µm. Also, HRTEM micrographs of VS2 NSs have revealed interplanar d spacing of 0.571 nm belonging to the (001) lattice plane of hexagonal VS2 (H-VS2) structure. FTIR analysis have shown a peak at 558 cm-1 attributed to V-S which is evident that sulfur has bonded with the metal (V) and is in agreement with EDS. CV, CD and EIS measurements have shown that the ratio 1:8:1 is more superior to VS2 NSs and other carbon supported VS2 NSs. Based on Rreduction for the carbon supported nanosheets VS2 nanosheets are ordered as 1:8:1>3:6:1>6:3:1>8:1:1. Carbon supported VS2 NSs of the mole ratio 1:8:1 showed a small resistance of 0.32 Ω. This is further evidence that the carbon supported VS2 NSs of the mole ratio 1:8:1 in addition to revealing excellent catalytic behaviour is also more chemically stable and has good conductivity properties._________
- Full Text:
- Date Issued: 2020
- Authors: Bede, Asanda
- Date: 2020
- Subjects: Voltammetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/18599 , vital:42612
- Description: It has been reported that the morphology, crystalline phase composition and electrochemical properties of counter electrode materials such MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials was of considerable importance because it governs the efficiency of many photon assisted chemical and physical reactions in dye sensitized solar cells (DSSCs). The efficiency of DSSCs with composite counter electrode materials is reliant on the stability of the photochemistry reactions which can be optimized by appropriate doping levels of the composite materials. Moreover, the microstructure such as surface area, distribution of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials, and the stability of the electrostatic bonds between the MxS (Mo, V) with the carbon support also play a significant role in the performance of the DSSCs. This work evaluates the effect of different mole ratios of the MxS (Mo, V) and carbon supported MxS (Mo, V) composite nanomaterials on the morphological, structural and electrochemical properties of the composite materials. MoS2 nanoflakes nanostructures have been synthesized by hydrothermal technique using sodium orthovanadate (Na2MoO4) as precursor. In this work Carbon supported MoS2 NFs have been prepared by physically/chemically mixing different mole ratios of MoS2 NFs with multi-walled carbon nanotubes (MWCNTs) and polyvinylidene in N-methyl-2-pyrrolidinone. The morphological, structural and electrochemical properties of the composite counter electrode materials have been investigated using SEM, XRD FTIR, TEM, RS and CV. SEM analysis has revealed the presence of large MoS2 nanoflakes (NFs) as synthesized. SEM analysis has also revealed significant change in the surface morphology of carbon supported MoS2 composite nanostructures with the change in the mole ratio of the MoS2 NFs and carbon support multi-walled carbon nanotubes. Structural analysis through HRTEM analysis revealed a d-spacing of 0.65 nm with a corresponding (002) lattice plane belonging to a trigonal crystalline phase of MoS2. Also, HRTEM analysis has revealed d-spacing of 0.291 nm corresponding to 002 plane of MWCNTs. Raman spectroscopy has revealed Characteristic Raman vibration frequencies and symmetries at 264.6 cm-1(Eg), 354.2 cm-1 (Ag ) belonging trigonal phase of MoS2 (1T-MoS2). FTIR analysis has revealed a narrow peak at 457.6 cm-1 due Mo-S vibration bond. This observation confirms the success of synthesis of MoS2 nanostructures. Cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS) measurements have revealed that the ratio 6:3:1 have shown to be optimum ratio due to its large reduction rate compared to pristine MoS2 NFs and other carbon supported MoS2 NFs. Calculated Rreduction for the carbon supported MoS2 NFs is the order 3:6:1>1:8:1>6:3:1>8:1:1 indicating the trend of ratio 3:6:1 appeared to have higher reduction rate than the rest of the material and it had far less ΔEpp than the rest of other ratios. All CV curves for both pristine MoS2 NFs and carbon supported MoS2 NFs confirmed a distinct Faradic characteristic. The VS2 nanosheets (NSs) and carbon supported VS2 NSs were also effectively synthesized via hydrothermal method. The SEM micrographs for VS2 NSs and carbon supported VS2 NSs samples reveals level increased. Furthermore, SEM-EDX analysis have confirmed the presence of V and S as well as C and O on carbon supported VS2 nanocomposites, and it clearly shown a gradually blending as the ratios increases. The structural studies through XRD analysis have revealed peaks at 2θ angles of 15.4◦, 28.2◦, 34.2◦, 36.2◦, 43.3◦,48.3◦, 54.4◦, 57.7◦ and 66.2◦ which correspond to the lattice planes (001), (002), (100), (011), (102), (003), (110), (103) and (201) belonging to hexagonal VS2 (H-VS2) crystalline phase as per JCPDS card 36-1139. The HRTEM have revealed that the VS2 NSs have an edge to edge length of ~ 0.294 – 1.248 µm. Also, HRTEM micrographs of VS2 NSs have revealed interplanar d spacing of 0.571 nm belonging to the (001) lattice plane of hexagonal VS2 (H-VS2) structure. FTIR analysis have shown a peak at 558 cm-1 attributed to V-S which is evident that sulfur has bonded with the metal (V) and is in agreement with EDS. CV, CD and EIS measurements have shown that the ratio 1:8:1 is more superior to VS2 NSs and other carbon supported VS2 NSs. Based on Rreduction for the carbon supported nanosheets VS2 nanosheets are ordered as 1:8:1>3:6:1>6:3:1>8:1:1. Carbon supported VS2 NSs of the mole ratio 1:8:1 showed a small resistance of 0.32 Ω. This is further evidence that the carbon supported VS2 NSs of the mole ratio 1:8:1 in addition to revealing excellent catalytic behaviour is also more chemically stable and has good conductivity properties._________
- Full Text:
- Date Issued: 2020
The role of custodial grandparents in psychosocial well-being of adolescents from single parents in Buffalo City Municipality of Eastern Cape, South Africa
- Authors: Adenike,Folorunsho Fausat
- Date: 2020
- Subjects: Grandparents as parents Grandparent and child Grandparenting
- Language: English
- Type: Thesis , Doctoral , PhD(Social Work)
- Identifier: http://hdl.handle.net/10353/17943 , vital:41994
- Description: It has been a historical norm in African societies for children to leave in the homes of caregivers. Among these caregivers are the grandparents, who are from time immemorial, being a pillar of support to their children in caring for their grandchildren. Against this background, the study assesses custodial the role of grandparents in the psychosocial well-being of adolescent children from single parents' homes in Buffalo City Metropolitan Municipality, Eastern Cape Province, South Africa. The study was guided theoretically by Role and Ryff's psychosocial well-being theories. Four sets of participants totaling 323 gathered using a mixed-method approach comprised of 150 adolescents and 136 custodial grandparents through questionnaires, 30 single parents, through in-depth interviews, and seven social workers through focus group discussions. The study utilized a multi-stage sampling technique to select adolescents and their grandparents, a purposive sampling technique for single parents, and a convenient sampling technique for social workers. The quantitative data were analyzed using descriptive statistics and Pearson's Correlation Coefficient, while the qualitative data were categorized manually into themes and subthemes. Findings indicated a correlation between the attainment of the adolescent children's psychosocial well-being and the effectiveness of the custodial grandparents' role. More also, the challenges encountered by custodial grandparents do affect the attainment of the psychosocial well-being of adolescent children. Furthermore, finding from the study revealed that non-governmental organizations in the municipality were not rendering social support for the custodial grandparents. Finally, the child-support grant received by poor grandparents is grossly inadequate to meet up with the astronomical needs of the adolescent children. The study concluded that custodial grandparents' social support is an effective mechanism in meeting adolescent children's psychosocial well-being. Several recommendations were made from the conclusions to various stakeholders and proposed a responsive conceptual grand-parenting model to cater for effective parenting.
- Full Text:
- Date Issued: 2020
- Authors: Adenike,Folorunsho Fausat
- Date: 2020
- Subjects: Grandparents as parents Grandparent and child Grandparenting
- Language: English
- Type: Thesis , Doctoral , PhD(Social Work)
- Identifier: http://hdl.handle.net/10353/17943 , vital:41994
- Description: It has been a historical norm in African societies for children to leave in the homes of caregivers. Among these caregivers are the grandparents, who are from time immemorial, being a pillar of support to their children in caring for their grandchildren. Against this background, the study assesses custodial the role of grandparents in the psychosocial well-being of adolescent children from single parents' homes in Buffalo City Metropolitan Municipality, Eastern Cape Province, South Africa. The study was guided theoretically by Role and Ryff's psychosocial well-being theories. Four sets of participants totaling 323 gathered using a mixed-method approach comprised of 150 adolescents and 136 custodial grandparents through questionnaires, 30 single parents, through in-depth interviews, and seven social workers through focus group discussions. The study utilized a multi-stage sampling technique to select adolescents and their grandparents, a purposive sampling technique for single parents, and a convenient sampling technique for social workers. The quantitative data were analyzed using descriptive statistics and Pearson's Correlation Coefficient, while the qualitative data were categorized manually into themes and subthemes. Findings indicated a correlation between the attainment of the adolescent children's psychosocial well-being and the effectiveness of the custodial grandparents' role. More also, the challenges encountered by custodial grandparents do affect the attainment of the psychosocial well-being of adolescent children. Furthermore, finding from the study revealed that non-governmental organizations in the municipality were not rendering social support for the custodial grandparents. Finally, the child-support grant received by poor grandparents is grossly inadequate to meet up with the astronomical needs of the adolescent children. The study concluded that custodial grandparents' social support is an effective mechanism in meeting adolescent children's psychosocial well-being. Several recommendations were made from the conclusions to various stakeholders and proposed a responsive conceptual grand-parenting model to cater for effective parenting.
- Full Text:
- Date Issued: 2020
PKS 2250−351: A Giant Radio Galaxy in Abell 3936
- Seymour, N, Huynh, M, Shabala, S S, Rogers, J, Davies, L J M, Turner, R J, O'Brien, A, Ishwara-Chandra, C H, Thorne, J E, Galvin, T J, Jarrett, T, Anderbach, H, Anderson, A, Bunton, J, Chow, K, Collier, J D, Driver, S, Filipovic, M D, Gurkan, G, Hopkins, A M, Kapinska, A D, Leahy, D A, Marvil, J, Manojlovic, P, Norris, R P, Phillips, C, Robotham, A, Rudnick, L, Singh, V, White, S V
- Authors: Seymour, N , Huynh, M , Shabala, S S , Rogers, J , Davies, L J M , Turner, R J , O'Brien, A , Ishwara-Chandra, C H , Thorne, J E , Galvin, T J , Jarrett, T , Anderbach, H , Anderson, A , Bunton, J , Chow, K , Collier, J D , Driver, S , Filipovic, M D , Gurkan, G , Hopkins, A M , Kapinska, A D , Leahy, D A , Marvil, J , Manojlovic, P , Norris, R P , Phillips, C , Robotham, A , Rudnick, L , Singh, V , White, S V
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150320 , vital:38967 , https://doi.org/10.1017/pasa.2019.49
- Description: We present a detailed analysis of the radio galaxy PKS , a giant of 1.2 Mpc projected size, its host galaxy, and its environment. We use radio data from the Murchison Widefield Array, the upgraded Giant Metre-wavelength Radio Telescope, the Australian Square Kilometre Array Pathfinder, and the Australia Telescope Compact Array to model the jet power and age. Optical and IR data come from the Galaxy And Mass Assembly (GAMA) survey and provide information on the host galaxy and environment.
- Full Text:
- Date Issued: 2020
- Authors: Seymour, N , Huynh, M , Shabala, S S , Rogers, J , Davies, L J M , Turner, R J , O'Brien, A , Ishwara-Chandra, C H , Thorne, J E , Galvin, T J , Jarrett, T , Anderbach, H , Anderson, A , Bunton, J , Chow, K , Collier, J D , Driver, S , Filipovic, M D , Gurkan, G , Hopkins, A M , Kapinska, A D , Leahy, D A , Marvil, J , Manojlovic, P , Norris, R P , Phillips, C , Robotham, A , Rudnick, L , Singh, V , White, S V
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150320 , vital:38967 , https://doi.org/10.1017/pasa.2019.49
- Description: We present a detailed analysis of the radio galaxy PKS , a giant of 1.2 Mpc projected size, its host galaxy, and its environment. We use radio data from the Murchison Widefield Array, the upgraded Giant Metre-wavelength Radio Telescope, the Australian Square Kilometre Array Pathfinder, and the Australia Telescope Compact Array to model the jet power and age. Optical and IR data come from the Galaxy And Mass Assembly (GAMA) survey and provide information on the host galaxy and environment.
- Full Text:
- Date Issued: 2020
From housing to sustainable human settlements : a case study of Buffalo City Metropolitan Municipality
- Authors: Mofokeng, Mosa
- Date: 2020
- Subjects: Human settlements -- South Africa -- Buffalo City Housing policy -- South Africa -- Buffalo City
- Language: English
- Type: Thesis , Masters , MSBE
- Identifier: http://hdl.handle.net/10948/49518 , vital:41731
- Description: This study aimed to evaluate whether there has been any shift from housing to sustainable human settlements in the Buffalo City Metropolitan Municipality (BCMM). The objective of the study was to establish the perceived value of inclusive development by relevant stakeholders in the transformation of housing to integrated and sustainable human settlements; assess the effectiveness of available systems in transforming housing to integrated and sustainable human settlements and to establish the level of effectiveness of the current human settlements development model in transforming housing to integrated and sustainable human settlement outcomes. Following a case study approach, the study employed a combination of qualitative and quantitative approaches which is also known as the mixed-method research design. Purposive sampling technique was used to arrive at a sample of 16 relevant officials, whereas the snow-ball convenience sampling technique was used to select a sample of 12 housing beneficiaries in Ndevana, Potsdam and Mzamomhle housing developments. A survey questionnaire was used to elicit data from the officials In-depth interviews were used to gather data from BCMM officials and Focus Group Discussions were used to extract data from twelve housing beneficiaries from (four from Ndevana, four from Potsdam and four from Mzamomhle) housing projects in the BCMM. The findings from this study show that although several people have been provided with houses in Ndevana, Mzamomhle and Potsdam, the settlements lack the requisite economic and social infrastructure that creates integrated and liveable settlements. Furthermore, the type, quality, and layout of houses delivered by the government falls short of the concept of sustainable development. The available systems for transforming housing to integrated sustainable human settlements have been rendered ineffective by the shortage of proper land for land-use planning and spatial development, lack of organizational capacity, lack of accountability, unaffordability of sustainable housing by the poor and insufficiency of the current housing quantum subsidy to deliver sustainable human settlements. The study further established that the integrated sustainable human settlements programs do not incorporate the community needs which have greatly affected sustainable housing delivery in BCMM. The placement of the poor households in the urban peripheries is phenomenal and hence unemployment, poverty and civil unrest have taken a toll in Ndevana, Potsdam, and Mzamomhle. The study recommends a capacity building and competency-based model to BCMM and Eastern Cape Department of Human Settlements, Integration of Government departments and Stakeholder Engagement, the establishment of monitoring and evaluation systems, alignment of provincial and local government budget cycles.
- Full Text:
- Date Issued: 2020
- Authors: Mofokeng, Mosa
- Date: 2020
- Subjects: Human settlements -- South Africa -- Buffalo City Housing policy -- South Africa -- Buffalo City
- Language: English
- Type: Thesis , Masters , MSBE
- Identifier: http://hdl.handle.net/10948/49518 , vital:41731
- Description: This study aimed to evaluate whether there has been any shift from housing to sustainable human settlements in the Buffalo City Metropolitan Municipality (BCMM). The objective of the study was to establish the perceived value of inclusive development by relevant stakeholders in the transformation of housing to integrated and sustainable human settlements; assess the effectiveness of available systems in transforming housing to integrated and sustainable human settlements and to establish the level of effectiveness of the current human settlements development model in transforming housing to integrated and sustainable human settlement outcomes. Following a case study approach, the study employed a combination of qualitative and quantitative approaches which is also known as the mixed-method research design. Purposive sampling technique was used to arrive at a sample of 16 relevant officials, whereas the snow-ball convenience sampling technique was used to select a sample of 12 housing beneficiaries in Ndevana, Potsdam and Mzamomhle housing developments. A survey questionnaire was used to elicit data from the officials In-depth interviews were used to gather data from BCMM officials and Focus Group Discussions were used to extract data from twelve housing beneficiaries from (four from Ndevana, four from Potsdam and four from Mzamomhle) housing projects in the BCMM. The findings from this study show that although several people have been provided with houses in Ndevana, Mzamomhle and Potsdam, the settlements lack the requisite economic and social infrastructure that creates integrated and liveable settlements. Furthermore, the type, quality, and layout of houses delivered by the government falls short of the concept of sustainable development. The available systems for transforming housing to integrated sustainable human settlements have been rendered ineffective by the shortage of proper land for land-use planning and spatial development, lack of organizational capacity, lack of accountability, unaffordability of sustainable housing by the poor and insufficiency of the current housing quantum subsidy to deliver sustainable human settlements. The study further established that the integrated sustainable human settlements programs do not incorporate the community needs which have greatly affected sustainable housing delivery in BCMM. The placement of the poor households in the urban peripheries is phenomenal and hence unemployment, poverty and civil unrest have taken a toll in Ndevana, Potsdam, and Mzamomhle. The study recommends a capacity building and competency-based model to BCMM and Eastern Cape Department of Human Settlements, Integration of Government departments and Stakeholder Engagement, the establishment of monitoring and evaluation systems, alignment of provincial and local government budget cycles.
- Full Text:
- Date Issued: 2020
A comparative mineralogical and geochemical study of manganese deposits in the Postmasburg Manganese Field, South Africa
- Authors: Thokoa, Mamello
- Date: 2020
- Subjects: Manganese ores -- South Africa -- Postmasburg , Geology -- South Africa -- Postmasburg
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167609 , vital:41496
- Description: The Postmasburg Manganese Field (PMF), located in the Northern Cape Province of South Africa, is host to some of the largest deposits of iron and manganese metal in the world. These deposits are restricted to a geographical area known as the Maremane Dome, an anticlinal structure defined by folded dolostones of the Campbellrand Subgroup and overlying ironformations of the Asbestos Hills Subgroup of the Neoarchaean-Palaeproterozoic Transvaal Supergroup. Manganese ores associated with the Maremane Dome have been divided into two major classes in the literature: the Wolhaarkop breccia-hosted massive ores of the Eastern Belt, as well as the shale-associated ores of the Western Belt. The Eastern Belt ores have been classed as siliceous in nature, while the Western Belt deposits are reported to be typically ferruginous. These divisions were made based on their varying bulk chemical and mineralogical compositions in conjunction with their different stratigraphic sub-settings. Presently, both deposit types are explained as variants of supergene mineralisation that would have formed through a combination of intense ancient lateritic weathering in the presence of oxygen, extreme residual enrichments in Mn (and Fe), and accumulations in karstic depressions at the expense of underlying manganiferous dolostones. This study revisits these deposits and their origins by sampling representative end-member examples of both Eastern Belt and Western Belt manganese ores in both drillcore (localities Khumani, McCarthy and Leeuwfontein), and outcrop sections (locality Bishop). In an attempt to provide new insights into the processes responsible for the genesis of these deposits, the possibility of hydrothermal influences and associated metasomatic replacement processes is explored in this thesis. This was achieved using standard petrographic and mineralogical techniques (transmitted and reflected light microscopy, XRD , SEM-EDS and EMPA), coupled with bulk-rock geochemical analysis of the same samples using a combination of XRF and LAICP- MS analyses. Combination of field observations, petrographic and mineralogical results, and geochemical data allowed for the re-assessment of the different ore types encountered in the field. Comparative considerations made between the bulk geochemistry of the different end-member ore types revealed no clear-cut compositional distinctions and therefore do not support existing classifications between siliceous (Eastern Belt) and ferruginous (Western Belt) ores. This is supported by trace and REE element data as well, when normalised against average shale. The geochemistry reflects the bulk mineralogy of the ores which is broadly comparable, whereby braunite and hematite appear to be dominant co-existing minerals in both Eastern Belt (Khumani) and Western Belt (Bishop) ore. In the case of the McCarthy locality, manganese ore is cryptomelane-rich and appears to have involved recent supergene overprint over Eastern Belt type ore, whereas the Leeuwfontein ores are far more ferruginous than at any other locality studied and therefore represent a more complex, hybrid type of oxide-rich Mn mineralisation (mainly bixbyitic) within massive hematite iron ore. In terms of gangue mineralogy, the ores share some close similarities through the omnipresence of barite, and the abundance of alkalirich silicate minerals. Eastern Belt ores contain abundant albite and serandite whereas the main alkali-rich phase in Western Belt ores is the mineral ephesite. In both cases, Na contents are therefore high at several wt% levels registered in selected samples. The afore-mentioned alkali enrichments have been variously reported for both these deposit types. The occurrence of high alkalis cannot be explained through classic residual or aqueous supergene systems of ore formation, as proposed in prevailing genetic models in the literature. Together with the detection of halogens such as F and Br through SEM-EDS analyses of ore from both belts, the alkali enrichments suggest possible hydrothermal processes of ore formation involving circulation of metalliferous sodic brines. Selected textural evidence from samples from both ore belts lends support to fluid-related models and allow the proposal for a common hydrothermal-replacement model to have been responsible for ore formation across the broader Maremane Dome region.
- Full Text:
- Date Issued: 2020
- Authors: Thokoa, Mamello
- Date: 2020
- Subjects: Manganese ores -- South Africa -- Postmasburg , Geology -- South Africa -- Postmasburg
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167609 , vital:41496
- Description: The Postmasburg Manganese Field (PMF), located in the Northern Cape Province of South Africa, is host to some of the largest deposits of iron and manganese metal in the world. These deposits are restricted to a geographical area known as the Maremane Dome, an anticlinal structure defined by folded dolostones of the Campbellrand Subgroup and overlying ironformations of the Asbestos Hills Subgroup of the Neoarchaean-Palaeproterozoic Transvaal Supergroup. Manganese ores associated with the Maremane Dome have been divided into two major classes in the literature: the Wolhaarkop breccia-hosted massive ores of the Eastern Belt, as well as the shale-associated ores of the Western Belt. The Eastern Belt ores have been classed as siliceous in nature, while the Western Belt deposits are reported to be typically ferruginous. These divisions were made based on their varying bulk chemical and mineralogical compositions in conjunction with their different stratigraphic sub-settings. Presently, both deposit types are explained as variants of supergene mineralisation that would have formed through a combination of intense ancient lateritic weathering in the presence of oxygen, extreme residual enrichments in Mn (and Fe), and accumulations in karstic depressions at the expense of underlying manganiferous dolostones. This study revisits these deposits and their origins by sampling representative end-member examples of both Eastern Belt and Western Belt manganese ores in both drillcore (localities Khumani, McCarthy and Leeuwfontein), and outcrop sections (locality Bishop). In an attempt to provide new insights into the processes responsible for the genesis of these deposits, the possibility of hydrothermal influences and associated metasomatic replacement processes is explored in this thesis. This was achieved using standard petrographic and mineralogical techniques (transmitted and reflected light microscopy, XRD , SEM-EDS and EMPA), coupled with bulk-rock geochemical analysis of the same samples using a combination of XRF and LAICP- MS analyses. Combination of field observations, petrographic and mineralogical results, and geochemical data allowed for the re-assessment of the different ore types encountered in the field. Comparative considerations made between the bulk geochemistry of the different end-member ore types revealed no clear-cut compositional distinctions and therefore do not support existing classifications between siliceous (Eastern Belt) and ferruginous (Western Belt) ores. This is supported by trace and REE element data as well, when normalised against average shale. The geochemistry reflects the bulk mineralogy of the ores which is broadly comparable, whereby braunite and hematite appear to be dominant co-existing minerals in both Eastern Belt (Khumani) and Western Belt (Bishop) ore. In the case of the McCarthy locality, manganese ore is cryptomelane-rich and appears to have involved recent supergene overprint over Eastern Belt type ore, whereas the Leeuwfontein ores are far more ferruginous than at any other locality studied and therefore represent a more complex, hybrid type of oxide-rich Mn mineralisation (mainly bixbyitic) within massive hematite iron ore. In terms of gangue mineralogy, the ores share some close similarities through the omnipresence of barite, and the abundance of alkalirich silicate minerals. Eastern Belt ores contain abundant albite and serandite whereas the main alkali-rich phase in Western Belt ores is the mineral ephesite. In both cases, Na contents are therefore high at several wt% levels registered in selected samples. The afore-mentioned alkali enrichments have been variously reported for both these deposit types. The occurrence of high alkalis cannot be explained through classic residual or aqueous supergene systems of ore formation, as proposed in prevailing genetic models in the literature. Together with the detection of halogens such as F and Br through SEM-EDS analyses of ore from both belts, the alkali enrichments suggest possible hydrothermal processes of ore formation involving circulation of metalliferous sodic brines. Selected textural evidence from samples from both ore belts lends support to fluid-related models and allow the proposal for a common hydrothermal-replacement model to have been responsible for ore formation across the broader Maremane Dome region.
- Full Text:
- Date Issued: 2020
The role of microhabitats within mangroves: an invertebrate and fish larval perspective
- Authors: Vorsatz, Lyle Dennis
- Date: 2020
- Subjects: Mangrove ecology -- South Africa , Mangrove forests -- South Africa , Niche (Ecology) , Rhizophora mucronata , Acanthaceae , Rhizophoraceae , Fishes -- Larvae -- South Africa , Aquatic ecology -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167644 , vital:41499
- Description: Microhabitats provided through structural complexity are central for the diversity, productivity, connectivity and niche differentiation within and among ecosystems. Mangrove forests afford juvenile fish and invertebrates with nursery and recruitment habitats, facilitated by the fine scale configuration of their specialised root systems. Although the importance of mangroves for resident and transient juveniles is well recognised, the roles that mangrove microhabitats play for larvae is not yet comprehensively understood. This study aimed to determine how microhabitats with varying degrees of complexity influence the composition, abundance and distribution of larval communities that inhabit mangrove forests and the physiological responses of larvae to acute temperature variations in relation to ontogenetic stage and microenvironment exposure. Two relatively pristine study sites were selected to represent a warm temperate and subtropical mangrove system in the Eastern Cape and KwaZulu-Natal on the east coast of South Africa, respectively. The differences in complexity among the root systems of Rhizophora mucronata, Avicennia marina and Bruguiera gymnorhiza were assessed using 3D scanning and the computed 3D models were then analysed using four complexity metrics. Results indicated that A. marina is the most complex in terms of surface-volume ratio, R. mucronata has the most interstitial space among its roots and B. gymnorhiza and R. mucronata differ in their fractal dimensions. Larvae collected in each microhabitat at each site using light traps showed that, despite temperature and salinity homogeneity across microenvironments, spatio-temporal differences occurred in both fish and invertebrate assemblages. This trend suggests that microhabitat structural complexity exerts an influence on larval community composition by acting as a microscape of available habitat, which ensures ecological linkages within and among the mangrove forest and adjacent ecosystems. In addition, the oxygen consumption rates of mangrove-associated brachyuran larvae varied according to mangrove microhabitat, whereby larvae collected at less complex environments had the highest metabolic rates at increased temperatures. Moreover, ontogenetic shifts in physiology were prevalent as older brachyuran larvae were more eurythermal than earlier stages, suggesting that thermally stressful events will have a greater impact on recently spawned larvae. Overall, the interstitial spaces within individual root systems are the most important complexity measure, as utilisation of these mangrove microhabitats is scale-dependent, and larvae will most likely occupy spaces inaccessible to large predators. Likewise, microscale variation in the environmental conditions and ontogenetic stage of brachyuran larvae within the mangrove microscape, can amplify the physiological responses to rapid temperature variations. Results suggest that early stage larvae are the most vulnerable to mass-mortality, and if thermally stressful events increase in frequency, duration and magnitude, the larval supply for the successful recruitment into adult populations could be under threat. Through linking how mangrove microhabitat complexity influences larvae in terms of community metrics and physiology, this study paves the way for further advancement of our understanding of how microscale processes emerge into meso- and macroscale patterns and influence the stability and functioning of highly productive ecosystems.
- Full Text:
- Date Issued: 2020
- Authors: Vorsatz, Lyle Dennis
- Date: 2020
- Subjects: Mangrove ecology -- South Africa , Mangrove forests -- South Africa , Niche (Ecology) , Rhizophora mucronata , Acanthaceae , Rhizophoraceae , Fishes -- Larvae -- South Africa , Aquatic ecology -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167644 , vital:41499
- Description: Microhabitats provided through structural complexity are central for the diversity, productivity, connectivity and niche differentiation within and among ecosystems. Mangrove forests afford juvenile fish and invertebrates with nursery and recruitment habitats, facilitated by the fine scale configuration of their specialised root systems. Although the importance of mangroves for resident and transient juveniles is well recognised, the roles that mangrove microhabitats play for larvae is not yet comprehensively understood. This study aimed to determine how microhabitats with varying degrees of complexity influence the composition, abundance and distribution of larval communities that inhabit mangrove forests and the physiological responses of larvae to acute temperature variations in relation to ontogenetic stage and microenvironment exposure. Two relatively pristine study sites were selected to represent a warm temperate and subtropical mangrove system in the Eastern Cape and KwaZulu-Natal on the east coast of South Africa, respectively. The differences in complexity among the root systems of Rhizophora mucronata, Avicennia marina and Bruguiera gymnorhiza were assessed using 3D scanning and the computed 3D models were then analysed using four complexity metrics. Results indicated that A. marina is the most complex in terms of surface-volume ratio, R. mucronata has the most interstitial space among its roots and B. gymnorhiza and R. mucronata differ in their fractal dimensions. Larvae collected in each microhabitat at each site using light traps showed that, despite temperature and salinity homogeneity across microenvironments, spatio-temporal differences occurred in both fish and invertebrate assemblages. This trend suggests that microhabitat structural complexity exerts an influence on larval community composition by acting as a microscape of available habitat, which ensures ecological linkages within and among the mangrove forest and adjacent ecosystems. In addition, the oxygen consumption rates of mangrove-associated brachyuran larvae varied according to mangrove microhabitat, whereby larvae collected at less complex environments had the highest metabolic rates at increased temperatures. Moreover, ontogenetic shifts in physiology were prevalent as older brachyuran larvae were more eurythermal than earlier stages, suggesting that thermally stressful events will have a greater impact on recently spawned larvae. Overall, the interstitial spaces within individual root systems are the most important complexity measure, as utilisation of these mangrove microhabitats is scale-dependent, and larvae will most likely occupy spaces inaccessible to large predators. Likewise, microscale variation in the environmental conditions and ontogenetic stage of brachyuran larvae within the mangrove microscape, can amplify the physiological responses to rapid temperature variations. Results suggest that early stage larvae are the most vulnerable to mass-mortality, and if thermally stressful events increase in frequency, duration and magnitude, the larval supply for the successful recruitment into adult populations could be under threat. Through linking how mangrove microhabitat complexity influences larvae in terms of community metrics and physiology, this study paves the way for further advancement of our understanding of how microscale processes emerge into meso- and macroscale patterns and influence the stability and functioning of highly productive ecosystems.
- Full Text:
- Date Issued: 2020
Exploring the privacy calculus on social networking services from a South African perspective
- Authors: Mathew, Boney George
- Date: 2020
- Subjects: Data encryption (Computer science) , Public key cryptography Online social networks -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MIT
- Identifier: http://hdl.handle.net/10948/46163 , vital:39510
- Description: Social Network Services (SNSs) have revolutionized the way we communicate, interact and present ourselves before others. The business model of SNS’S like Facebook is primarily based on SNS’S user self-disclosure of personal information. It is argued that the SNS’S user conducts a cost-benefit analysis before deciding to self-disclose their personal information, and this user behaviour forms the basis of the Privacy Calculus Theory. Enjoyment, Self-Presentation and Relationship Maintenance is considered as the benefits and the Privacy Concerns of the users is considered as the costs of disclosing personal information.As national or regional culture could influence SNS’S user self-disclosure behaviour, it would be advantageous for multinational SNS’S’s like Facebook to understand the perceptions of SNS’S user’s from different nationalities. Currently, no studies have been conducted amongst the South African (SA) SNSs’ users’ self-disclosure behaviour. This research is aimed at understanding the South African SNSs’ users’ perceptions regarding their perceived costs, benefits and selfdisclosure using the Privacy Calculus theory. This study is a replication of a similar study undertaken amongst the United States of America (US) and German SNS’S users. To remain competitive in the market and to sustain the viability of their business model, SNS like Facebook will have to encourage user self-disclosure. Studies have proven that national cultures play an important role on the nature and extent of user disclosure (Krasnova & Veltri, 2010; Lewis, Kaufman, & Christakis, 2008). However, no similar research has been undertaken in South Africa, and currently we do not understand South African SNS users’ self-disclosure behaviour in terms of the privacy calculus theory. The primary objective of this study is to understand the perceptions of South African SNS’S users regarding the perceived benefits, costs, moderating factors and self-disclosure, using the Privacy Calculus Theory. To achieve this objective, we initially undertook a detailed literature review to understand the concept of information privacy, privacy calculus, information privacy policy and legal framework, SNS’S and self-disclosure and the various factors affecting self-disclosure. We then proceeded to validate the theoretical framework by collecting data from two South African universities, namely the Nelson Mandela University (NMU) and Walter Sisulu University (WSU (NMD Campus – Former University of Transkei)), by adopting the same methodology and instrument used in the original study (and the isiXhosa translation). The theoretical framework used for this study is based on the Privacy Calculus theory, which argues that users conduct a cost-benefit calculus before deciding to self-disclose their personal information. This analysis is further influenced by other moderating factors like trust, control and awareness. All these factors have been incorporated into the theoretical framework and the instrument, adapted from the original research was used to collect data from the participants. The data from 239 respondents, who finally qualified for analysis was collated and proceeded with the analysis of that data. The data was analysed in four stages using established statistical tests. The first three phases were used to determine the actual value placed by the users on selfdisclosure, its determinants and moderating factors, and the last phase concentrated on how each of the constructs included in the theoretical framework influenced the other constructs. The results obtained from the analysis provided valuable insights into the self-disclosure behaviour of South African SNS’S users. Entertainment was the primary benefit the students derived from using SNS like Facebook, followed by relationship maintenance and those who enjoyed the platform more tended to Self-Disclose more. Those who tended to derive more benefits from the platform were found to trust the platform and the other users of the network. The theoretical framework was validated and it was determined that privacy paradox exists within the South African SNS’S user community, meaning that even with high privacy concerns, these SNS users are willing to self-disclose their personal information.
- Full Text:
- Date Issued: 2020
- Authors: Mathew, Boney George
- Date: 2020
- Subjects: Data encryption (Computer science) , Public key cryptography Online social networks -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MIT
- Identifier: http://hdl.handle.net/10948/46163 , vital:39510
- Description: Social Network Services (SNSs) have revolutionized the way we communicate, interact and present ourselves before others. The business model of SNS’S like Facebook is primarily based on SNS’S user self-disclosure of personal information. It is argued that the SNS’S user conducts a cost-benefit analysis before deciding to self-disclose their personal information, and this user behaviour forms the basis of the Privacy Calculus Theory. Enjoyment, Self-Presentation and Relationship Maintenance is considered as the benefits and the Privacy Concerns of the users is considered as the costs of disclosing personal information.As national or regional culture could influence SNS’S user self-disclosure behaviour, it would be advantageous for multinational SNS’S’s like Facebook to understand the perceptions of SNS’S user’s from different nationalities. Currently, no studies have been conducted amongst the South African (SA) SNSs’ users’ self-disclosure behaviour. This research is aimed at understanding the South African SNSs’ users’ perceptions regarding their perceived costs, benefits and selfdisclosure using the Privacy Calculus theory. This study is a replication of a similar study undertaken amongst the United States of America (US) and German SNS’S users. To remain competitive in the market and to sustain the viability of their business model, SNS like Facebook will have to encourage user self-disclosure. Studies have proven that national cultures play an important role on the nature and extent of user disclosure (Krasnova & Veltri, 2010; Lewis, Kaufman, & Christakis, 2008). However, no similar research has been undertaken in South Africa, and currently we do not understand South African SNS users’ self-disclosure behaviour in terms of the privacy calculus theory. The primary objective of this study is to understand the perceptions of South African SNS’S users regarding the perceived benefits, costs, moderating factors and self-disclosure, using the Privacy Calculus Theory. To achieve this objective, we initially undertook a detailed literature review to understand the concept of information privacy, privacy calculus, information privacy policy and legal framework, SNS’S and self-disclosure and the various factors affecting self-disclosure. We then proceeded to validate the theoretical framework by collecting data from two South African universities, namely the Nelson Mandela University (NMU) and Walter Sisulu University (WSU (NMD Campus – Former University of Transkei)), by adopting the same methodology and instrument used in the original study (and the isiXhosa translation). The theoretical framework used for this study is based on the Privacy Calculus theory, which argues that users conduct a cost-benefit calculus before deciding to self-disclose their personal information. This analysis is further influenced by other moderating factors like trust, control and awareness. All these factors have been incorporated into the theoretical framework and the instrument, adapted from the original research was used to collect data from the participants. The data from 239 respondents, who finally qualified for analysis was collated and proceeded with the analysis of that data. The data was analysed in four stages using established statistical tests. The first three phases were used to determine the actual value placed by the users on selfdisclosure, its determinants and moderating factors, and the last phase concentrated on how each of the constructs included in the theoretical framework influenced the other constructs. The results obtained from the analysis provided valuable insights into the self-disclosure behaviour of South African SNS’S users. Entertainment was the primary benefit the students derived from using SNS like Facebook, followed by relationship maintenance and those who enjoyed the platform more tended to Self-Disclose more. Those who tended to derive more benefits from the platform were found to trust the platform and the other users of the network. The theoretical framework was validated and it was determined that privacy paradox exists within the South African SNS’S user community, meaning that even with high privacy concerns, these SNS users are willing to self-disclose their personal information.
- Full Text:
- Date Issued: 2020
Ecological assessment of a temperate river system using biomonitoring techniques: a case study of the Bloukrans River system, South Africa
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Date Issued: 2020
Understanding climate change and rural livelihoods in Zimbabwe: adaptation by communal farmers in Ngundu, Chivi District
- Authors: Nciizah, Elinah
- Date: 2020
- Subjects: Agriculture -- Zimbabwe , Agriculture -- Climatic factors -- Chivi District (Zimbabwe) , Chivi District (Zimbabwe) -- Rural conditions
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/118765 , vital:34666
- Description: Climate change and variability is a global phenomenon which has deeply localised patterns, dynamics and effects. Amongst those people who are particularly vulnerable to climate change effects are small-scale farmers who are dependent in large part on rain-fed agriculture in pursuing their livelihoods. This is true of small-scale farmers in contemporary Zimbabwe and, more specifically, farmers in communal areas. At the same time, at international and national levels, there are attempts currently to minimise the effects of, and to adapt to, climate change. However, adaptation measures also exist at local levels amongst small-scale farmers, such as communal farmers in Zimbabwe. In this context, as its main objective, this thesis examines climate change and small-scale farmer livelihood adaptation to climate change with specific reference to communal farmers in Chivi District in Zimbabwe and, in particular, in Ward 25 which is popularly known as Ngundu. In pursuing this main objective, a number of subsidiary objectives are addressed, including a focus on the established livelihoods of Ngundu farmers, the perceptions and concerns of Ngundu farmers about climate change, the coping and adaptation measures of Ngundu farmers, and the enablements and constraints which affect attempts by Ngundu farmers to adopt such measures. The fieldwork for the thesis involved a diverse array of research methods, such as a questionnaire survey, life-history interviews, key informant interviews, focus group discussions and transect walks. In terms of theoretical framing, the thesis makes use of both middle-level theory (the Sustainable Livelihoods Framework) and macro-theory in the form of the sociological work of Margaret Archer. Combined, these two theories allow for a focus on both structure and agency when seeking to understand livelihood adaptations to climate change by communal farmers in Ngundu. The thesis concludes that there are massive constraints inhibiting adaptation measures by Ngundu farmers, but that this should not distract from the deep, often historically-embedded, concerns of Ngundu farmers about climate change and the multiple ways in which they express agency in and through adaptation and coping activities. It also highlights the need for more specifically sociological investigations of climate change and small-scale farmer adaptation, as well as the need for localised studies which are able to identify and analyse the specificities of adaptation.
- Full Text:
- Date Issued: 2020
- Authors: Nciizah, Elinah
- Date: 2020
- Subjects: Agriculture -- Zimbabwe , Agriculture -- Climatic factors -- Chivi District (Zimbabwe) , Chivi District (Zimbabwe) -- Rural conditions
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/118765 , vital:34666
- Description: Climate change and variability is a global phenomenon which has deeply localised patterns, dynamics and effects. Amongst those people who are particularly vulnerable to climate change effects are small-scale farmers who are dependent in large part on rain-fed agriculture in pursuing their livelihoods. This is true of small-scale farmers in contemporary Zimbabwe and, more specifically, farmers in communal areas. At the same time, at international and national levels, there are attempts currently to minimise the effects of, and to adapt to, climate change. However, adaptation measures also exist at local levels amongst small-scale farmers, such as communal farmers in Zimbabwe. In this context, as its main objective, this thesis examines climate change and small-scale farmer livelihood adaptation to climate change with specific reference to communal farmers in Chivi District in Zimbabwe and, in particular, in Ward 25 which is popularly known as Ngundu. In pursuing this main objective, a number of subsidiary objectives are addressed, including a focus on the established livelihoods of Ngundu farmers, the perceptions and concerns of Ngundu farmers about climate change, the coping and adaptation measures of Ngundu farmers, and the enablements and constraints which affect attempts by Ngundu farmers to adopt such measures. The fieldwork for the thesis involved a diverse array of research methods, such as a questionnaire survey, life-history interviews, key informant interviews, focus group discussions and transect walks. In terms of theoretical framing, the thesis makes use of both middle-level theory (the Sustainable Livelihoods Framework) and macro-theory in the form of the sociological work of Margaret Archer. Combined, these two theories allow for a focus on both structure and agency when seeking to understand livelihood adaptations to climate change by communal farmers in Ngundu. The thesis concludes that there are massive constraints inhibiting adaptation measures by Ngundu farmers, but that this should not distract from the deep, often historically-embedded, concerns of Ngundu farmers about climate change and the multiple ways in which they express agency in and through adaptation and coping activities. It also highlights the need for more specifically sociological investigations of climate change and small-scale farmer adaptation, as well as the need for localised studies which are able to identify and analyse the specificities of adaptation.
- Full Text:
- Date Issued: 2020
Effects of economic growth on greenhouse emissions
- Mkunyana, Asebenzile Priscilla
- Authors: Mkunyana, Asebenzile Priscilla
- Date: 2020
- Subjects: Greenhouse gases -- Environmental aspects -- Africa , Climate change mitigation
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: http://hdl.handle.net/10948/50404 , vital:42162
- Description: This study employs the panel cointegration and Pooled Mean Group technique to examine the effects of economic growth on greenhouse emissions using the panel data from the period of 1970 to 2014 for five Southern African Development Community group of countries. The increase in the combustion of burning fossil fuels has become the global threat in environmental quality. The Environmental Kuznets Curve hypothesis postulates that at the primary stages of industrial economies there is more extracting of natural resources and more agricultural activities taking place as a result the waste generation and resource depletion accelerate. However, as the economic development improves more, the curve reaches a threshold where it starts to decline due to the increase in economic growth and the change to information-based industries. Based on the empirical evidence, the variables of this study were found to be stationary at first difference and integrated of I(0) and I(1) using Im, Pesaran & Shin W-stat, Fisher ADF, and Levin, Lin & Chu panel unit root test. The existing long-run relationship between the variables were found in both the Pedroni and Kao cointegration test and were significant at 5% in finding the relationship between the variables. The Pooled Mean Group demonstrated mixed results in the study’s regressions, monotonic relationship was found between carbon dioxide and economic growth. The strong existence relationship between economic growth and energy consumption was found to be significant at the 1% level. These results are in line with the EKC hypothesis, which assumes that as the income level increases the society will start to be environmentally friendly and the technology advancement will decrease the emission of pollutants. In addition, in finding the causal relationship between variables, the researcher used the Granger causality test, with the results from this test revealing a unidirectional and bidirectional relationship between all the chosen variables. These results are important for policy makers.
- Full Text:
- Date Issued: 2020
- Authors: Mkunyana, Asebenzile Priscilla
- Date: 2020
- Subjects: Greenhouse gases -- Environmental aspects -- Africa , Climate change mitigation
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: http://hdl.handle.net/10948/50404 , vital:42162
- Description: This study employs the panel cointegration and Pooled Mean Group technique to examine the effects of economic growth on greenhouse emissions using the panel data from the period of 1970 to 2014 for five Southern African Development Community group of countries. The increase in the combustion of burning fossil fuels has become the global threat in environmental quality. The Environmental Kuznets Curve hypothesis postulates that at the primary stages of industrial economies there is more extracting of natural resources and more agricultural activities taking place as a result the waste generation and resource depletion accelerate. However, as the economic development improves more, the curve reaches a threshold where it starts to decline due to the increase in economic growth and the change to information-based industries. Based on the empirical evidence, the variables of this study were found to be stationary at first difference and integrated of I(0) and I(1) using Im, Pesaran & Shin W-stat, Fisher ADF, and Levin, Lin & Chu panel unit root test. The existing long-run relationship between the variables were found in both the Pedroni and Kao cointegration test and were significant at 5% in finding the relationship between the variables. The Pooled Mean Group demonstrated mixed results in the study’s regressions, monotonic relationship was found between carbon dioxide and economic growth. The strong existence relationship between economic growth and energy consumption was found to be significant at the 1% level. These results are in line with the EKC hypothesis, which assumes that as the income level increases the society will start to be environmentally friendly and the technology advancement will decrease the emission of pollutants. In addition, in finding the causal relationship between variables, the researcher used the Granger causality test, with the results from this test revealing a unidirectional and bidirectional relationship between all the chosen variables. These results are important for policy makers.
- Full Text:
- Date Issued: 2020
The relationship between employee wellness and work engagement in a non-governmental organisation
- Authors: Coopasamy, Kubashinie
- Date: 2020
- Subjects: Employee health promotion
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/47685 , vital:40323
- Description: Employee wellness and work engagement have a positive influence on organisational behaviour. The main aim of the research study was to understand whether a relationship existed between employee wellness and work engagement in a Non-Governmental organisation (NGO). The research used a cross-sectional design and a composite questionnaire to measure employee wellness and work engagement. This was a paper and pen-based questionnaire which was distributed to 160 employees. Of the 160 questionnaires distributed only 155 participants responded. These participants are employed at NGO’s based in Port Elizabeth, Johannesburg and East London. An exploratory factor analysis determined a new more reliable factor structure for PWS. Employee wellness lost items and became a three-factor structure. The results showed that the new EFA model was best suited for the present study. Work Engagement remained a three-factor structure. T-tests and ANOVAs revealed significant differences between the constructs and the demographic groups. Correlations showed the main findings of the study to be a relationship between employee wellness and work engagement in a non-governmental organisation.
- Full Text:
- Date Issued: 2020
- Authors: Coopasamy, Kubashinie
- Date: 2020
- Subjects: Employee health promotion
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/47685 , vital:40323
- Description: Employee wellness and work engagement have a positive influence on organisational behaviour. The main aim of the research study was to understand whether a relationship existed between employee wellness and work engagement in a Non-Governmental organisation (NGO). The research used a cross-sectional design and a composite questionnaire to measure employee wellness and work engagement. This was a paper and pen-based questionnaire which was distributed to 160 employees. Of the 160 questionnaires distributed only 155 participants responded. These participants are employed at NGO’s based in Port Elizabeth, Johannesburg and East London. An exploratory factor analysis determined a new more reliable factor structure for PWS. Employee wellness lost items and became a three-factor structure. The results showed that the new EFA model was best suited for the present study. Work Engagement remained a three-factor structure. T-tests and ANOVAs revealed significant differences between the constructs and the demographic groups. Correlations showed the main findings of the study to be a relationship between employee wellness and work engagement in a non-governmental organisation.
- Full Text:
- Date Issued: 2020
Towards the synthesis of trimethoprim using continuous flow Chemistry
- Authors: Ngwenya, Sandiso
- Date: 2020
- Subjects: Trimethoprim
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47475 , vital:39994
- Description: The continuous flow synthesis of trimethoprim, an antibiotic, was investigated in this study from simple commercially available reagents, such as aniline and dimethylamine. The first step of the synthesis involves a highly exothermic Michael reaction, between acrylonitrile and dimethylamine; process intensification through miniaturization provides a safe and efficient method of synthesis through the use of microreactors. This is afforded by their large surface area-to-volume ratio; one of the many characteristics of continuous flow synthesis that allows for rapid heat dissipation allowing for exothermic reaction to be conducted safely at ambient or higher temperatures. This study was optimized on a Chemtrix Labtrix® Start unit using a Chemtrix reactor achieving a conversion of 99% in 12 sec residence time at 25oC. Subsequently the base catalyzed condensation of the intermediate with 3,4,5- trimethoxybenzaldehyde was investigated using Little Things Factory reactors (Channel diameter: 1.0mm). Maximum conversion (100%) was obtained at 80oC in 20 mins. Due to the poor cyclisation observed with this intermediate, according to literature findings, the 3-dimethylamino group was substituted for aniline. The optimisation for this acid catalysed substitution reaction was performed on a homemade PTFE tubing reactor (Diameter: 0.5mm) and it was found that at 120oC in 10 mins residence time a conversion of 97% was obtained. From the results obtained, an investigation into an integrated process for the condensation and substitution reaction was done using the Little Things Factory system (Channel Diameter: 1.0mm) coupled with a homemade PTFE coil reactor (Diameter: 0.5mm). This process, under optimum conditions of temperature 80oC and residence time of 30 mins, attained a conversion of 76%.
- Full Text:
- Date Issued: 2020
- Authors: Ngwenya, Sandiso
- Date: 2020
- Subjects: Trimethoprim
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47475 , vital:39994
- Description: The continuous flow synthesis of trimethoprim, an antibiotic, was investigated in this study from simple commercially available reagents, such as aniline and dimethylamine. The first step of the synthesis involves a highly exothermic Michael reaction, between acrylonitrile and dimethylamine; process intensification through miniaturization provides a safe and efficient method of synthesis through the use of microreactors. This is afforded by their large surface area-to-volume ratio; one of the many characteristics of continuous flow synthesis that allows for rapid heat dissipation allowing for exothermic reaction to be conducted safely at ambient or higher temperatures. This study was optimized on a Chemtrix Labtrix® Start unit using a Chemtrix reactor achieving a conversion of 99% in 12 sec residence time at 25oC. Subsequently the base catalyzed condensation of the intermediate with 3,4,5- trimethoxybenzaldehyde was investigated using Little Things Factory reactors (Channel diameter: 1.0mm). Maximum conversion (100%) was obtained at 80oC in 20 mins. Due to the poor cyclisation observed with this intermediate, according to literature findings, the 3-dimethylamino group was substituted for aniline. The optimisation for this acid catalysed substitution reaction was performed on a homemade PTFE tubing reactor (Diameter: 0.5mm) and it was found that at 120oC in 10 mins residence time a conversion of 97% was obtained. From the results obtained, an investigation into an integrated process for the condensation and substitution reaction was done using the Little Things Factory system (Channel Diameter: 1.0mm) coupled with a homemade PTFE coil reactor (Diameter: 0.5mm). This process, under optimum conditions of temperature 80oC and residence time of 30 mins, attained a conversion of 76%.
- Full Text:
- Date Issued: 2020
Cross-sectional study of prevalence and determinants of uncontrolled hypertension among South African adult residents of Mkhondo municipality
- Masilela, Charity, Pearce, Brendon, Ongole, Joven Jebio, Adeniyi, Oladele Vincent, Benjeddou, Mongi
- Authors: Masilela, Charity , Pearce, Brendon , Ongole, Joven Jebio , Adeniyi, Oladele Vincent , Benjeddou, Mongi
- Date: 2020
- Subjects: Blood pressure control , Dyslipidaemia , Uncontrolled hypertension
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/11260/4481 , vital:44124 , https://doi.org/10.1186/s12889-020-09174-7
- Description: Achieving the blood pressure treatment target in individuals with hypertension is a serious global health challenge. Furthermore, the actual burden of uncontrolled hypertension is poorly understood, especially in the developing countries. Therefore, this study comprehensively examined the prevalence and factors associated with uncontrolled hypertension in individuals receiving care at the primary healthcare facilities in the rural areas of Mkhondo Municipality in the Mpumalanga Province, South Africa. Methods: In this cross-sectional study, 329 individuals attending care for hypertension were recruited from January 2019 to June 2019 at three primary healthcare centres, namely, Piet Retief hospital, Mkhondo town clinic and Thandukukhanya community health centre. Uncontrolled hypertension was defined as systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg in accordance with the South African Hypertension Society guideline (2014). Multiple logistic regression (Forward LR method) analysis was used to identify the significant determinants of uncontrolled hypertension. Results: The majority of the participants were 55 years old and above (69.0%), Zulus (81.2%), non-smokers (84.19%) and had been diagnosed with hypertension for more than a year prior to the study (72.64%). The overall prevalence of uncontrolled hypertension was 56.83% (n = 187) with no significant difference between sexes, 57.38% male versus 56.88% female, respectively. In the multiple logistic regression model analysis after adjusting for confounding variables, obesity (AOR = 2.90; 95% CI 1.66–5.05), physical activity (AOR = 4.79; 95% CI 2.15–10.65) and HDL-C (AOR = 5.66; 95% CI 3.33–9.60) were the significant and independent determinants of uncontrolled hypertension in the cohort. Conclusion: The high prevalence of uncontrolled hypertension in the study setting can be largely attributed to obesity, physical activity and dyslipidaemia. Treatment will require the collaborative efforts of individuals, clinicians and health authorities. All these determinants should be addressed decisively so as to achieve the treatment blood pressure targets in the study population.
- Full Text:
- Date Issued: 2020
- Authors: Masilela, Charity , Pearce, Brendon , Ongole, Joven Jebio , Adeniyi, Oladele Vincent , Benjeddou, Mongi
- Date: 2020
- Subjects: Blood pressure control , Dyslipidaemia , Uncontrolled hypertension
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/11260/4481 , vital:44124 , https://doi.org/10.1186/s12889-020-09174-7
- Description: Achieving the blood pressure treatment target in individuals with hypertension is a serious global health challenge. Furthermore, the actual burden of uncontrolled hypertension is poorly understood, especially in the developing countries. Therefore, this study comprehensively examined the prevalence and factors associated with uncontrolled hypertension in individuals receiving care at the primary healthcare facilities in the rural areas of Mkhondo Municipality in the Mpumalanga Province, South Africa. Methods: In this cross-sectional study, 329 individuals attending care for hypertension were recruited from January 2019 to June 2019 at three primary healthcare centres, namely, Piet Retief hospital, Mkhondo town clinic and Thandukukhanya community health centre. Uncontrolled hypertension was defined as systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg in accordance with the South African Hypertension Society guideline (2014). Multiple logistic regression (Forward LR method) analysis was used to identify the significant determinants of uncontrolled hypertension. Results: The majority of the participants were 55 years old and above (69.0%), Zulus (81.2%), non-smokers (84.19%) and had been diagnosed with hypertension for more than a year prior to the study (72.64%). The overall prevalence of uncontrolled hypertension was 56.83% (n = 187) with no significant difference between sexes, 57.38% male versus 56.88% female, respectively. In the multiple logistic regression model analysis after adjusting for confounding variables, obesity (AOR = 2.90; 95% CI 1.66–5.05), physical activity (AOR = 4.79; 95% CI 2.15–10.65) and HDL-C (AOR = 5.66; 95% CI 3.33–9.60) were the significant and independent determinants of uncontrolled hypertension in the cohort. Conclusion: The high prevalence of uncontrolled hypertension in the study setting can be largely attributed to obesity, physical activity and dyslipidaemia. Treatment will require the collaborative efforts of individuals, clinicians and health authorities. All these determinants should be addressed decisively so as to achieve the treatment blood pressure targets in the study population.
- Full Text:
- Date Issued: 2020
Privacy risk and the use of Facebook Apps: a gender-focused vulnerability assessment
- van der Schyff, Karl, Flowerday, Stephen, Furnell, Steven
- Authors: van der Schyff, Karl , Flowerday, Stephen , Furnell, Steven
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149054 , vital:38800 , https://doi.org/10.1016/j.cose.2020.101866
- Description: The surveillance and subsequent privacy risks (i.e., misuse of personal information) of Facebook App data constitute a persistent problem that affects millions of users. However, despite Facebook App research on specifics such as privacy concerns, value of information, and demographics, none of them has conducted vulnerability assessments on the use of Facebook Apps as influenced by specific factors such as age, gender, and information privacy attitudes. As such, the purpose of this study was to predict the extent to which these factors influence an individual's intention to continue using Facebook Apps as part of a gender-focused vulnerability assessment. We evaluate two hypotheses by way of ordinal logistic regression using data gathered from 621 respondents. The results are indicative of the following: First, females are particularly vulnerable to privacy risks as a function of continued use of Facebook Apps. More specifically, those risks related to Facebook's access to personal information. Second, results indicate that a user's age is nonsignificant in relation to the continued use of Facebook Apps. We conclude with several theoretical and practice-oriented information privacy recommendations.
- Full Text:
- Date Issued: 2020
- Authors: van der Schyff, Karl , Flowerday, Stephen , Furnell, Steven
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149054 , vital:38800 , https://doi.org/10.1016/j.cose.2020.101866
- Description: The surveillance and subsequent privacy risks (i.e., misuse of personal information) of Facebook App data constitute a persistent problem that affects millions of users. However, despite Facebook App research on specifics such as privacy concerns, value of information, and demographics, none of them has conducted vulnerability assessments on the use of Facebook Apps as influenced by specific factors such as age, gender, and information privacy attitudes. As such, the purpose of this study was to predict the extent to which these factors influence an individual's intention to continue using Facebook Apps as part of a gender-focused vulnerability assessment. We evaluate two hypotheses by way of ordinal logistic regression using data gathered from 621 respondents. The results are indicative of the following: First, females are particularly vulnerable to privacy risks as a function of continued use of Facebook Apps. More specifically, those risks related to Facebook's access to personal information. Second, results indicate that a user's age is nonsignificant in relation to the continued use of Facebook Apps. We conclude with several theoretical and practice-oriented information privacy recommendations.
- Full Text:
- Date Issued: 2020
Enabling violence: the ethics of writing and reading rape in South Africa
- Authors: Lloyd Dylan Reumen
- Date: 2020
- Subjects: Rape -- South Africa , Rape -- Fiction , Rape in literature , Rape in literature -- South Africa , Psychic trauma in literature , Post-traumatic stress disorder in literature , Dystopias in literature , Coetzee, J. M., 1940- Disgrace , South African fiction (English) -- History and criticism
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/166173 , vital:41335
- Description: This thesis is concerned with describing the stakes of reading, writing and criticising fictional depictions of rape in a country plagued by high levels of sexual violence. I consider the capacity of rape representations to cause harm to women and rape survivors, and worsen the various injuries suffered by survivors as a direct or indirect consequence of rape. The possibility of such harm prompts me to examine the role and responsibilities of readers and critics in facilitating or preventing such harm. I further discuss the potential strategies of harm prevention that readers of novelistic portrayals of rape might adopt as well as the positive outcomes that such reading strategies make possible, and which might balance out the risks that accompany them. My description of the potential harm of rape representations combines postmodern critical feminist analysis with Miranda Fricker’s work on epistemic justice and Judith Herman’s work on trauma in order to illustrate the way that these representations shape our conception of rape in a manner that affects everything from how it is enacted to our treatment of survivors to the possibility of their recovery from posttraumatic stress disorder. In order to situate my analysis in the context of South African literature and to explore the notion of responsibility in relation to the writing of scenes of rape, I utilise a close reading of J.M. Coetzee’s Disgrace. Furthermore, I discuss the utility and limits of the critical feminist strategy of using a normative critical approach to rape representations in order to prevent harm. Ultimately, I argue that the use of such a strategy, along with the development of a purpose-honed adaptive critical style, is essential to the fulfilment of our responsibilities as readers and to the prevention of further suffering.
- Full Text:
- Date Issued: 2020
- Authors: Lloyd Dylan Reumen
- Date: 2020
- Subjects: Rape -- South Africa , Rape -- Fiction , Rape in literature , Rape in literature -- South Africa , Psychic trauma in literature , Post-traumatic stress disorder in literature , Dystopias in literature , Coetzee, J. M., 1940- Disgrace , South African fiction (English) -- History and criticism
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/166173 , vital:41335
- Description: This thesis is concerned with describing the stakes of reading, writing and criticising fictional depictions of rape in a country plagued by high levels of sexual violence. I consider the capacity of rape representations to cause harm to women and rape survivors, and worsen the various injuries suffered by survivors as a direct or indirect consequence of rape. The possibility of such harm prompts me to examine the role and responsibilities of readers and critics in facilitating or preventing such harm. I further discuss the potential strategies of harm prevention that readers of novelistic portrayals of rape might adopt as well as the positive outcomes that such reading strategies make possible, and which might balance out the risks that accompany them. My description of the potential harm of rape representations combines postmodern critical feminist analysis with Miranda Fricker’s work on epistemic justice and Judith Herman’s work on trauma in order to illustrate the way that these representations shape our conception of rape in a manner that affects everything from how it is enacted to our treatment of survivors to the possibility of their recovery from posttraumatic stress disorder. In order to situate my analysis in the context of South African literature and to explore the notion of responsibility in relation to the writing of scenes of rape, I utilise a close reading of J.M. Coetzee’s Disgrace. Furthermore, I discuss the utility and limits of the critical feminist strategy of using a normative critical approach to rape representations in order to prevent harm. Ultimately, I argue that the use of such a strategy, along with the development of a purpose-honed adaptive critical style, is essential to the fulfilment of our responsibilities as readers and to the prevention of further suffering.
- Full Text:
- Date Issued: 2020
Understanding biotic interactions in invaded pond communities in the Sundays River irrigation network, South Africa
- Authors: Mofu, Lubabalo
- Date: 2020
- Subjects: Mozambique tilapia -- South Africa -- Sundays River (Eastern Cape) , Western mosquitofish -- South Africa -- Sundays River (Eastern Cape) , Gobiidae -- South Africa -- Sundays River (Eastern Cape) , Clupeidae -- South Africa -- Sundays River (Eastern Cape) , Reservoirs -- South Africa -- Sundays River (Eastern Cape) , Zooplankton -- South Africa -- Sundays River (Eastern Cape) , Freshwater ecology -- South Africa -- Sundays River (Eastern Cape) , Biotic communities -- South Africa -- Sundays River (Eastern Cape) , Fishes -- Effect of temperature on -- South Africa -- Sundays River (Eastern Cape) , Stable isotopes , Relative Impact Potential
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167089 , vital:41436
- Description: The Sundays River valley irrigation ponds provide a unique opportunity to investigate biotic interactions within a biological invasions context, as they contain both native and non-native fish species. This study focusses on two native species (Glossogobius callidus and Gilchristella aestuaria) and two non-native species (Oreochromis mossambicus and Gambusia affinis). The ecology of the ponds was driven by physico-chemical variables, mainly temperature, but the interactions between fishes were a complex interplay between temperature, pond community ecology and food web structure. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Chlorophyll-a, temperature, G. callidus and G. affinis were the drivers of the seasonal changes in macroinvertebrate composition. Stable isotope analysis identified substantial ontogenetic dietary shifts in all species, corresponding to changes in body size. Stable isotope analysis revealed that the niche space occupied by G. affinis was broad and overlapped with that of the other three focal species. Stable isotope metrics showed that G. affinis and O. mossambicus utilised a wide range of resources compared to G. callidus and G. aestuaria. Stomach content analysis showed that G. callidus, O. mossambicus and G. affinis fed predominantly on benthic resources, while G. aestuaria fed mainly plankton resources. Functional response experiments revealed that G. callidus and G. affinis both displayed Type II functional responses. In single fish trials, G. affinis had significantly higher functional responses than G. callidus. In heterospecific G. callidus-G. affinis combinations the functional response of G. callidus was reduced by the presence of G. affinis, whereas, this combination greatly enhanced G. affinis functional response magnitudes. The functional response of G. callidus, O. mossambicus and G. affinis under two temperature treatments along with fish abundance data was used to determine temporal differences in the ecological impacts of each fish species between seasons. The relative impact potential of O. mossambicus was consistently higher than that of G. callidus and G. affinis. This study demonstrates how seasonal temperature fluctuations affect the relative impact capacities of introduced species. Overall, this thesis showed that high temperature along with life-history traits contributes to the biotic interactions between native and non-native species in novel environments.
- Full Text:
- Date Issued: 2020
- Authors: Mofu, Lubabalo
- Date: 2020
- Subjects: Mozambique tilapia -- South Africa -- Sundays River (Eastern Cape) , Western mosquitofish -- South Africa -- Sundays River (Eastern Cape) , Gobiidae -- South Africa -- Sundays River (Eastern Cape) , Clupeidae -- South Africa -- Sundays River (Eastern Cape) , Reservoirs -- South Africa -- Sundays River (Eastern Cape) , Zooplankton -- South Africa -- Sundays River (Eastern Cape) , Freshwater ecology -- South Africa -- Sundays River (Eastern Cape) , Biotic communities -- South Africa -- Sundays River (Eastern Cape) , Fishes -- Effect of temperature on -- South Africa -- Sundays River (Eastern Cape) , Stable isotopes , Relative Impact Potential
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167089 , vital:41436
- Description: The Sundays River valley irrigation ponds provide a unique opportunity to investigate biotic interactions within a biological invasions context, as they contain both native and non-native fish species. This study focusses on two native species (Glossogobius callidus and Gilchristella aestuaria) and two non-native species (Oreochromis mossambicus and Gambusia affinis). The ecology of the ponds was driven by physico-chemical variables, mainly temperature, but the interactions between fishes were a complex interplay between temperature, pond community ecology and food web structure. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Chlorophyll-a, temperature, G. callidus and G. affinis were the drivers of the seasonal changes in macroinvertebrate composition. Stable isotope analysis identified substantial ontogenetic dietary shifts in all species, corresponding to changes in body size. Stable isotope analysis revealed that the niche space occupied by G. affinis was broad and overlapped with that of the other three focal species. Stable isotope metrics showed that G. affinis and O. mossambicus utilised a wide range of resources compared to G. callidus and G. aestuaria. Stomach content analysis showed that G. callidus, O. mossambicus and G. affinis fed predominantly on benthic resources, while G. aestuaria fed mainly plankton resources. Functional response experiments revealed that G. callidus and G. affinis both displayed Type II functional responses. In single fish trials, G. affinis had significantly higher functional responses than G. callidus. In heterospecific G. callidus-G. affinis combinations the functional response of G. callidus was reduced by the presence of G. affinis, whereas, this combination greatly enhanced G. affinis functional response magnitudes. The functional response of G. callidus, O. mossambicus and G. affinis under two temperature treatments along with fish abundance data was used to determine temporal differences in the ecological impacts of each fish species between seasons. The relative impact potential of O. mossambicus was consistently higher than that of G. callidus and G. affinis. This study demonstrates how seasonal temperature fluctuations affect the relative impact capacities of introduced species. Overall, this thesis showed that high temperature along with life-history traits contributes to the biotic interactions between native and non-native species in novel environments.
- Full Text:
- Date Issued: 2020
Conclusion: The diversity of contemporary African foreign policy: Selecting Signifiers to explain Agency
- Authors: Bischoff, Paul, 1954-
- Date: 2020
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/161681 , vital:40654 , ISBN 9780367348281 , https://www.routledge.com/African-Foreign-Policies-Selecting-Signifiers-to-Explain-Agency/Bischoff/p/book/9780367348281
- Description: This book explores, at a time when several powers have become serious players on the continent, aspects of African agency, past and present, by African writers on foreign policy, representative of geography, language and state size.
- Full Text:
- Date Issued: 2020
- Authors: Bischoff, Paul, 1954-
- Date: 2020
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/161681 , vital:40654 , ISBN 9780367348281 , https://www.routledge.com/African-Foreign-Policies-Selecting-Signifiers-to-Explain-Agency/Bischoff/p/book/9780367348281
- Description: This book explores, at a time when several powers have become serious players on the continent, aspects of African agency, past and present, by African writers on foreign policy, representative of geography, language and state size.
- Full Text:
- Date Issued: 2020