Population status and habitat use of Indian Ocean humpback dolphins (sousa plumbea) along the south coast of South Africa
- Authors: Conry, Danielle Shanè
- Date: 2017
- Subjects: Sousa -- Population viability analysis -- South Africa Sousa -- Habitat -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/15556 , vital:28269
- Description: Long-lived, top-level predators, such as some marine mammals, serve as important indicators of ecosystem health. Assessing the abundance and habitat use of such marine top predators is essential for the formulation of effective conservation and management actions. There is considerable concern over the viability of small humpback dolphin opulations across a global scale and a number of studies have raised concerns over their vulnerability to extinction. In light of the recent uplisting of Indian Ocean humpback dolphins (Sousa plumbea) to ‘Endangered’ on the South African Red Data list, there is an urgent need for a greater understanding of the abundance and spatial distribution of this species along the South African coastline. Using small vessels as survey platforms between March 2014 and June 2015, this study attempted to determine the abundance, spatial distribution and habitat preferences of Indian Ocean humpback dolphins along 150 km of South Africa’s south coast. A further aim was to assess the utilisation of the current Marine Protected Area network by humpback dolphins along this coastline relative to areas outside of formal protection. Mark-recapture methods applied to photo-identification data produced abundance estimates of 84 individuals (95% CI: 72-115) within the study area for both open and closed models. An average group size of 3.94 individuals (range 1-12; SD = ± 2.82) was observed during the study, indicating a decrease in average group size of ~45 % from a previous assessment in 2002/03. Such a decline in group size could potentially be a result of a change in social structure in response to reduced prey availability. Spatial analyses of humpback dolphin geographic positions, using a kernel density estimator (KDE) and effort-weighted density grid analyses, indicate that the species is unevenly distributed over the coastal zone within the area. Sightings occurred at the highest densities within Buffels Bay and along Goukamma MPA, followed by Plettenberg Bay, Nature’s Valley, and around the Bloukrans, Elandsbos and Groot River East mouths. Habitat preference was assessed using a standard classification-based method and the results indicate a strong preference, in particular, for Dissipative Intermediate Sandy Coast habitat, followed by Very Exposed Rocky Coast, Intermediate Sandy Coast, Estuarine Shore, Mixed Shore and Inshore Reef habitats. Areas of high humpback dolphin densities appear to be associated with these habitat types, especially with Dissipative-Intermediate Sandy Coast habitat. Humpback dolphins were sighted at relatively low densities along stretches of coastline consisting predominately of Exposed Rocky Shore habitat. Long expanses of this habitat type may limit humpback dolphin movements along the coast. The observed patterns in distribution and habitat preferences may be linked to the availability of prey and/or the avoidance of predators. Average sightings per kilometer travelled (SPUE) indicate that the utilisation of the Robberg and Tsitsikamma MPAs by humpback dolphins was low, most likely due to the low availability of sandy coastline in these areas. In contrast, the utilisation of the Goukamma MPA, which is characterised by a high availability of Dissipative-Intermediate Sandy Coast, was very high. The low population numbers and declines in average group size of Indian Ocean humpback dolphins within the study area warrant concern and call for effective conservation and management measures. In light of ever-increasing levels of anthropogenic threats to coastal areas, future research and long-term monitoring of the population is essential to broaden our knowledge of the species and to detect population trends.
- Full Text:
- Date Issued: 2017
- Authors: Conry, Danielle Shanè
- Date: 2017
- Subjects: Sousa -- Population viability analysis -- South Africa Sousa -- Habitat -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/15556 , vital:28269
- Description: Long-lived, top-level predators, such as some marine mammals, serve as important indicators of ecosystem health. Assessing the abundance and habitat use of such marine top predators is essential for the formulation of effective conservation and management actions. There is considerable concern over the viability of small humpback dolphin opulations across a global scale and a number of studies have raised concerns over their vulnerability to extinction. In light of the recent uplisting of Indian Ocean humpback dolphins (Sousa plumbea) to ‘Endangered’ on the South African Red Data list, there is an urgent need for a greater understanding of the abundance and spatial distribution of this species along the South African coastline. Using small vessels as survey platforms between March 2014 and June 2015, this study attempted to determine the abundance, spatial distribution and habitat preferences of Indian Ocean humpback dolphins along 150 km of South Africa’s south coast. A further aim was to assess the utilisation of the current Marine Protected Area network by humpback dolphins along this coastline relative to areas outside of formal protection. Mark-recapture methods applied to photo-identification data produced abundance estimates of 84 individuals (95% CI: 72-115) within the study area for both open and closed models. An average group size of 3.94 individuals (range 1-12; SD = ± 2.82) was observed during the study, indicating a decrease in average group size of ~45 % from a previous assessment in 2002/03. Such a decline in group size could potentially be a result of a change in social structure in response to reduced prey availability. Spatial analyses of humpback dolphin geographic positions, using a kernel density estimator (KDE) and effort-weighted density grid analyses, indicate that the species is unevenly distributed over the coastal zone within the area. Sightings occurred at the highest densities within Buffels Bay and along Goukamma MPA, followed by Plettenberg Bay, Nature’s Valley, and around the Bloukrans, Elandsbos and Groot River East mouths. Habitat preference was assessed using a standard classification-based method and the results indicate a strong preference, in particular, for Dissipative Intermediate Sandy Coast habitat, followed by Very Exposed Rocky Coast, Intermediate Sandy Coast, Estuarine Shore, Mixed Shore and Inshore Reef habitats. Areas of high humpback dolphin densities appear to be associated with these habitat types, especially with Dissipative-Intermediate Sandy Coast habitat. Humpback dolphins were sighted at relatively low densities along stretches of coastline consisting predominately of Exposed Rocky Shore habitat. Long expanses of this habitat type may limit humpback dolphin movements along the coast. The observed patterns in distribution and habitat preferences may be linked to the availability of prey and/or the avoidance of predators. Average sightings per kilometer travelled (SPUE) indicate that the utilisation of the Robberg and Tsitsikamma MPAs by humpback dolphins was low, most likely due to the low availability of sandy coastline in these areas. In contrast, the utilisation of the Goukamma MPA, which is characterised by a high availability of Dissipative-Intermediate Sandy Coast, was very high. The low population numbers and declines in average group size of Indian Ocean humpback dolphins within the study area warrant concern and call for effective conservation and management measures. In light of ever-increasing levels of anthropogenic threats to coastal areas, future research and long-term monitoring of the population is essential to broaden our knowledge of the species and to detect population trends.
- Full Text:
- Date Issued: 2017
A comparison of the comfort properties, measured with a sweating manikin (WalterTM), of clothing containing different fibres
- Authors: Britz, Lizaan
- Date: 2017
- Subjects: Textile chemistry Cotton fabrics , Cotton textiles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14752 , vital:27842
- Description: The main objective of the present study was to determine the relative role and importance of worsted suiting fabric fibre blend vis-à-vis fabric structural parameters, on the comfort related properties of 12 clothing ensembles, each comprising a different man’s suit, but the same wool/nylon underwear and cotton shirt. To achieve the objective, the comfort related properties, namely thermal resistance (Rt) and water vapour resistance (Ret) and water vapour permeability index (Im), of the clothing ensembles, as determined by means of WalterTM, a thermal sweating fabric manikin, were subjected to multi-linear and multi-quadratic analysis, as dependent variables, with the various suiting fabric parameters, namely weight, thickness, density, porosity, air permeability and wool content, as independent variables. It was found that the multi-quadratic regression analysis was able to best explain the observed differences in the clothing ensemble comfort related properties, in terms of the differences in suiting fabric properties. The regression analyses were used to isolate and quantify the effects of the various fabric and fibre content variables on the above mentioned comfort related properties of the various clothing ensembles. This study indicated that the suiting fabric structural properties (notably air permeability), had a more significant influence than either fibre blend or suiting fabric, as measured on WalterTM, a thermal sweating fabric manikin.
- Full Text:
- Date Issued: 2017
- Authors: Britz, Lizaan
- Date: 2017
- Subjects: Textile chemistry Cotton fabrics , Cotton textiles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14752 , vital:27842
- Description: The main objective of the present study was to determine the relative role and importance of worsted suiting fabric fibre blend vis-à-vis fabric structural parameters, on the comfort related properties of 12 clothing ensembles, each comprising a different man’s suit, but the same wool/nylon underwear and cotton shirt. To achieve the objective, the comfort related properties, namely thermal resistance (Rt) and water vapour resistance (Ret) and water vapour permeability index (Im), of the clothing ensembles, as determined by means of WalterTM, a thermal sweating fabric manikin, were subjected to multi-linear and multi-quadratic analysis, as dependent variables, with the various suiting fabric parameters, namely weight, thickness, density, porosity, air permeability and wool content, as independent variables. It was found that the multi-quadratic regression analysis was able to best explain the observed differences in the clothing ensemble comfort related properties, in terms of the differences in suiting fabric properties. The regression analyses were used to isolate and quantify the effects of the various fabric and fibre content variables on the above mentioned comfort related properties of the various clothing ensembles. This study indicated that the suiting fabric structural properties (notably air permeability), had a more significant influence than either fibre blend or suiting fabric, as measured on WalterTM, a thermal sweating fabric manikin.
- Full Text:
- Date Issued: 2017
Differential regulation of wheat (Triticum aestivum) callose synthases during Russian wheat aphid (diuraphis noxia)infestation
- Authors: Ngwenya, Nompilo
- Date: 2017
- Subjects: Russian wheat aphid Wheat -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/8100 , vital:31522
- Description: Plant production serves as the primary food source for all living beings and is continuously being affected by many biotic and abiotic factors. Wheat, one of the most consumed cereal crops in the world and the second most cultivated crop after maize in South Africa, is continuously being affected by Russian wheat aphid (RWA) since 1978. To counteract the effect of this aphid, the first resistant wheat cultivar was developed in 1984 in South Africa containing the Dn1 resistance gene. However, the mechanism of action of the resistance is still not fully understood to date. The feeding of the RWA on the wheat induces callose deposition especially in susceptible wheat cultivars, linking the β-1.3-polysaccharide (callose) to the resistance mechanism. Callose is synthesized by callose synthases, also known as glucan synthase-like genes (GSL). Not much is known about the mechanism of action of callose synthases or how they are regulated in response to the RWA. Bioinformatics tools, such as those available at NCBI, were used to identify the wheat callose synthases genes. The proteins encoded by the identified wheat callose synthases genes, were then analyzed for conserved domain motifs using the MEME suite and InterproScan, sequence similarities using ClustaL Omega and transmembrane domains using HMMTOP and ProtCamp. These were then compared with those of the already characterized Arabidopsis callose synthase proteins in an attempt to identify the wheat callose synthase(s) that responds to aphid feeding. Further bioinformatics studies were carried out to identify the presence of biotic stress associated cis-acting regulatory elements found in the 1.5 kbp upstream region of the start codon of the Arabidopsis callose synthase genes. Eight partial wheat callose synthase sequences were identified and two of these (TaGSL2 and TaGSL22) showed high similarities to the AtGSL5, which is up-regulated in response to aphid feeding in Arabidopsis. Six of the wheat callose synthase genes were mediated to code for the functional callose synthases proteins: TaGSL3, 8, 12, 19, 22 and 23, and analyzed for conserved protein motifs. Based on the sequence similarities and conserved protein domains, TaGSL2 and TaGSL22 were found to be the most similar to AtGSL5 and most likely to respond to RWA infestation. Cis-acting regulatory element analyses confirmed the possibility of TaGSL22 being responsible for callose deposition in wheat as biotic stress associated cis-acting regulatory elements, Box W1, TC- rich element and W- box were all found in the 1.5 kbp upstream of the TaGSL22 coding region. Callose was quantified in both susceptible and resistant wheat cultivars using the aniline blue fluorescence method. When infested with RWA-SA1, the susceptible wheat cultivar (Tugela) deposited significantly higher amounts of callose, compared to the resistant wheat cultivar (Tugela DN), which deposited little, to no callose with respect to the control samples. Transcription analysis, of the TaGSL2 and TaGSL22 in RWA-SA2 infested Tugela and Tugela DN wheat cultivars, was performed using real time polymerase chain reaction (qPCR). Both TaGSL2 and TaGSL22 genes were up-regulated in Tugela and Tugela DN wheat cultivars in response to RWA-SA2 infestation, with TaGSL22 being more expressed than TaGSL2 in both cultivars, indicating that RWA-SA2 is able to overcome the resistance of Tugela DN and cause callose deposition. However, significantly higher expression of both genes was still observed in the susceptible, Tugela wheat cultivar. This study therefore confirms that callose deposition is associated with RWA-SA1 feeding, only in the susceptible wheat cultivar, Tugela and not the resistant cultivar, Tugela DN. However, during RWA-SA2 feeding, two of the eight identified callose synthases in wheat, are up-regulated in response to RWA-SA2 feeding, in both the resistant and susceptible wheat cultivars with higher levels observed in the susceptible wheat cultivar when compared to the resistant wheat cultivar. TaGSL2 and TaGSL22 are therefore implicated in the callose deposition observed in the susceptible and resistant wheat cultivars, after RWA-SA2 infestation. Further studies are required to confirm the differential regulation of the two wheat callose synthases proteins during RWA infestation and their possible role in the resistance mechanism of the resistant wheat cultivar, Tugela DN.
- Full Text:
- Date Issued: 2017
- Authors: Ngwenya, Nompilo
- Date: 2017
- Subjects: Russian wheat aphid Wheat -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/8100 , vital:31522
- Description: Plant production serves as the primary food source for all living beings and is continuously being affected by many biotic and abiotic factors. Wheat, one of the most consumed cereal crops in the world and the second most cultivated crop after maize in South Africa, is continuously being affected by Russian wheat aphid (RWA) since 1978. To counteract the effect of this aphid, the first resistant wheat cultivar was developed in 1984 in South Africa containing the Dn1 resistance gene. However, the mechanism of action of the resistance is still not fully understood to date. The feeding of the RWA on the wheat induces callose deposition especially in susceptible wheat cultivars, linking the β-1.3-polysaccharide (callose) to the resistance mechanism. Callose is synthesized by callose synthases, also known as glucan synthase-like genes (GSL). Not much is known about the mechanism of action of callose synthases or how they are regulated in response to the RWA. Bioinformatics tools, such as those available at NCBI, were used to identify the wheat callose synthases genes. The proteins encoded by the identified wheat callose synthases genes, were then analyzed for conserved domain motifs using the MEME suite and InterproScan, sequence similarities using ClustaL Omega and transmembrane domains using HMMTOP and ProtCamp. These were then compared with those of the already characterized Arabidopsis callose synthase proteins in an attempt to identify the wheat callose synthase(s) that responds to aphid feeding. Further bioinformatics studies were carried out to identify the presence of biotic stress associated cis-acting regulatory elements found in the 1.5 kbp upstream region of the start codon of the Arabidopsis callose synthase genes. Eight partial wheat callose synthase sequences were identified and two of these (TaGSL2 and TaGSL22) showed high similarities to the AtGSL5, which is up-regulated in response to aphid feeding in Arabidopsis. Six of the wheat callose synthase genes were mediated to code for the functional callose synthases proteins: TaGSL3, 8, 12, 19, 22 and 23, and analyzed for conserved protein motifs. Based on the sequence similarities and conserved protein domains, TaGSL2 and TaGSL22 were found to be the most similar to AtGSL5 and most likely to respond to RWA infestation. Cis-acting regulatory element analyses confirmed the possibility of TaGSL22 being responsible for callose deposition in wheat as biotic stress associated cis-acting regulatory elements, Box W1, TC- rich element and W- box were all found in the 1.5 kbp upstream of the TaGSL22 coding region. Callose was quantified in both susceptible and resistant wheat cultivars using the aniline blue fluorescence method. When infested with RWA-SA1, the susceptible wheat cultivar (Tugela) deposited significantly higher amounts of callose, compared to the resistant wheat cultivar (Tugela DN), which deposited little, to no callose with respect to the control samples. Transcription analysis, of the TaGSL2 and TaGSL22 in RWA-SA2 infested Tugela and Tugela DN wheat cultivars, was performed using real time polymerase chain reaction (qPCR). Both TaGSL2 and TaGSL22 genes were up-regulated in Tugela and Tugela DN wheat cultivars in response to RWA-SA2 infestation, with TaGSL22 being more expressed than TaGSL2 in both cultivars, indicating that RWA-SA2 is able to overcome the resistance of Tugela DN and cause callose deposition. However, significantly higher expression of both genes was still observed in the susceptible, Tugela wheat cultivar. This study therefore confirms that callose deposition is associated with RWA-SA1 feeding, only in the susceptible wheat cultivar, Tugela and not the resistant cultivar, Tugela DN. However, during RWA-SA2 feeding, two of the eight identified callose synthases in wheat, are up-regulated in response to RWA-SA2 feeding, in both the resistant and susceptible wheat cultivars with higher levels observed in the susceptible wheat cultivar when compared to the resistant wheat cultivar. TaGSL2 and TaGSL22 are therefore implicated in the callose deposition observed in the susceptible and resistant wheat cultivars, after RWA-SA2 infestation. Further studies are required to confirm the differential regulation of the two wheat callose synthases proteins during RWA infestation and their possible role in the resistance mechanism of the resistant wheat cultivar, Tugela DN.
- Full Text:
- Date Issued: 2017
Development and validation of DNA barcoding for biodiversity assessment and conservation of red algae in the Algoa Bay region
- Authors: Mshiywa, Faith Masilive
- Date: 2017
- Subjects: Red algae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/9011 , vital:34182
- Description: DNA barcoding is a molecular technique that uses a short DNA sequence for species identification. It harnesses global community efforts to establish large-scale public reference libraries to allow species identification. Red algae are a complex group of species and are difficult to identify on morphological grounds only. Red algae have the highest production of halogenated compounds, and are used in the medical and pharmaceutical industries. This study therefore aimed at developing DNA barcodes, universal primers and a Kenton-on-Sea red algae species list, which will aid as a baseline for red algae biodiversity and conservation research. A potential DNA barcode region was designed from the rbcL gene, because rbcL is easy to amplify, easy to sequence and it can differentiate organisms to species level. Primers were designed from multiple red algae rbcL sequences and they were evaluated using bioinformatics tools. Red algae from the Algoa Bay region were screened with these primers and a 77% PCR amplification success was obtained. The PCR products were sequenced and 96% of the amplicons were successfully sequenced and resulted in a barcode sequence length above 700bp, which could be used to identify red algae species. Twenty-six (26) red algae species from Kenton-on-Sea, near Algoa Bay, were successfully identified using the Barcode sequence amplified from a primer set developed from the rbcL gene and were uploaded on the BOLD database for public access. This barcode is, therefore, suitable for use by the South African National Biodiversity Institute or other marine researchers, to identify South African red algae species and ensure the maintenance of their biodiversity and conservation.
- Full Text:
- Date Issued: 2017
- Authors: Mshiywa, Faith Masilive
- Date: 2017
- Subjects: Red algae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/9011 , vital:34182
- Description: DNA barcoding is a molecular technique that uses a short DNA sequence for species identification. It harnesses global community efforts to establish large-scale public reference libraries to allow species identification. Red algae are a complex group of species and are difficult to identify on morphological grounds only. Red algae have the highest production of halogenated compounds, and are used in the medical and pharmaceutical industries. This study therefore aimed at developing DNA barcodes, universal primers and a Kenton-on-Sea red algae species list, which will aid as a baseline for red algae biodiversity and conservation research. A potential DNA barcode region was designed from the rbcL gene, because rbcL is easy to amplify, easy to sequence and it can differentiate organisms to species level. Primers were designed from multiple red algae rbcL sequences and they were evaluated using bioinformatics tools. Red algae from the Algoa Bay region were screened with these primers and a 77% PCR amplification success was obtained. The PCR products were sequenced and 96% of the amplicons were successfully sequenced and resulted in a barcode sequence length above 700bp, which could be used to identify red algae species. Twenty-six (26) red algae species from Kenton-on-Sea, near Algoa Bay, were successfully identified using the Barcode sequence amplified from a primer set developed from the rbcL gene and were uploaded on the BOLD database for public access. This barcode is, therefore, suitable for use by the South African National Biodiversity Institute or other marine researchers, to identify South African red algae species and ensure the maintenance of their biodiversity and conservation.
- Full Text:
- Date Issued: 2017
Synthesis and evaluation of arylpyrrole-chalcone hybrids as antiplasmodial and antitrypanosomal agents
- Authors: Zulu, Ayanda Ignatia
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/65268 , vital:28716
- Description: Expected release date-May 2019
- Full Text:
- Date Issued: 2017
- Authors: Zulu, Ayanda Ignatia
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/65268 , vital:28716
- Description: Expected release date-May 2019
- Full Text:
- Date Issued: 2017
Release success of captive bred Cape Vultures (Gyps coprotheres) in the Magaliesberg Mountains, South Africa
- Authors: Hirschauer, Maggie
- Date: 2017
- Subjects: Vultures -- South Africa -- Magaliesburg , Vultures -- South Africa -- Behavior
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4743 , vital:20720
- Description: The Cape Vulture, Gyps coprotheres, is currently classified as ‘endangered’. Endemic to southern Africa, its population has declined continuously over the past 40 years. The species is facing multiple anthropogenic threats. Notably, birds frequently collide with power lines and some cannot be released after treatment. This has led to the establishment of a captive breeding population with the hope that captive bred young can supplement wild populations and re-establish a now- abandoned breeding colony in the Magaliesberg Mountains, South Africa. This study aimed to follow the breeding behaviours of the captive colony and assess the appropriateness of chick rearing conditions. The study also aimed to monitor the behaviour, physical condition and dispersal of ten captive bred vultures after release in relation to their age. Behavioural observations of captive adult breeding and parental behaviours were conducted to establish whether chicks developed under comparable conditions to wild chicks. A high percentage of total colony copulation attempts (22 %) were extra-pair copulations. Four paired males formed ephemeral extra-pair relationships, two of which were homosexual. Chicks fledged earlier than wild chicks, on average at 128 days old. Wild and captive bred birds were observed at carcasses to compare competitive and feeding behaviours. Older birds, both wild and captive, fed the most efficiently. Preliminary evidence suggests females are more dominant and have higher display rates than males. Captive bred juvenile and four year old birds’ competitive and feeding behaviours (interaction rate, feeding rate, display rate, dominance, aggressiveness, and feeding efficiency) were the closest to, but still generally below, average values for same-aged wild birds. An index of body condition, body mass, and the prevalence of fault bars on the rectrices were used to assess their physical condition. After eight months, none of the ten birds had moved more than 8 km from the release site, nor had they foraged away from the vulture restaurant on site. Although altitude records of > 3100 m were recorded, their flight skills seemed inadequate. Future management considerations include the initiation of a pre-release exercise regime, the establishment of an acclimatization enclosure removed from the breeding site, and a varied or reduced post-release feeding schedule. Fledglings should be relocated and housed at the release enclosure until they are four years old.
- Full Text:
- Date Issued: 2017
- Authors: Hirschauer, Maggie
- Date: 2017
- Subjects: Vultures -- South Africa -- Magaliesburg , Vultures -- South Africa -- Behavior
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4743 , vital:20720
- Description: The Cape Vulture, Gyps coprotheres, is currently classified as ‘endangered’. Endemic to southern Africa, its population has declined continuously over the past 40 years. The species is facing multiple anthropogenic threats. Notably, birds frequently collide with power lines and some cannot be released after treatment. This has led to the establishment of a captive breeding population with the hope that captive bred young can supplement wild populations and re-establish a now- abandoned breeding colony in the Magaliesberg Mountains, South Africa. This study aimed to follow the breeding behaviours of the captive colony and assess the appropriateness of chick rearing conditions. The study also aimed to monitor the behaviour, physical condition and dispersal of ten captive bred vultures after release in relation to their age. Behavioural observations of captive adult breeding and parental behaviours were conducted to establish whether chicks developed under comparable conditions to wild chicks. A high percentage of total colony copulation attempts (22 %) were extra-pair copulations. Four paired males formed ephemeral extra-pair relationships, two of which were homosexual. Chicks fledged earlier than wild chicks, on average at 128 days old. Wild and captive bred birds were observed at carcasses to compare competitive and feeding behaviours. Older birds, both wild and captive, fed the most efficiently. Preliminary evidence suggests females are more dominant and have higher display rates than males. Captive bred juvenile and four year old birds’ competitive and feeding behaviours (interaction rate, feeding rate, display rate, dominance, aggressiveness, and feeding efficiency) were the closest to, but still generally below, average values for same-aged wild birds. An index of body condition, body mass, and the prevalence of fault bars on the rectrices were used to assess their physical condition. After eight months, none of the ten birds had moved more than 8 km from the release site, nor had they foraged away from the vulture restaurant on site. Although altitude records of > 3100 m were recorded, their flight skills seemed inadequate. Future management considerations include the initiation of a pre-release exercise regime, the establishment of an acclimatization enclosure removed from the breeding site, and a varied or reduced post-release feeding schedule. Fledglings should be relocated and housed at the release enclosure until they are four years old.
- Full Text:
- Date Issued: 2017
Use of fungicides for the management of Uromycladium acaciae in Acacia mearnsii plantations, South Africa
- Authors: Payn, Richard Guy
- Date: 2017
- Subjects: Fungicides -- South Africa Acacia mearnsii -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/20500 , vital:29299
- Description: South Africa has ca. 110 000 ha planted to Acacia mearnsii with 85% of the revenue from the species obtained from the timber, and 15% from the bark. Since its detection in 2013, wattle rust (recently identified as Uromycladium acaciae) has spread throughout the black wattle plantation area in KwaZulu-Natal, and from 2015 it was recorded in southern Mpumalanga. The pathogen affects trees of all age classes, causing a reduction in growth, as well as mortality with severe infection. Research has been initiated to determine a number of strategies for the management of the pathogen. These strategies include understanding wattle rust biology and epidemiology, planting tolerant or resistant black wattle, the testing and use of fungicide for management, and remote sensing and process based modelling to assess black wattle loss and high risk areas. These, with the outcomes from this research, will be combined into an overall Integrated Pest Management plan. Of the various strategies, the management of wattle rust with the use of fungicides is important, not only as it will have the potential to reduce the negative impacts of wattle rust, but it will also provide an interim solution until the other research areas provide alternative solutions. To address the current lack of fungicides available (and knowledge around their application) for the management of wattle rust, a series of trials were implemented to screen fungicides for their potential use, extend periods between the re-application of fungicide (if possible), the linking of symptoms to Disease Expression to aid with the timing of application, and the cost:benefits associated with fungicide use. Prior to the initiation of research into managing wattle rust, no fungicides were registered in South Africa for the control of wattle rust. In October / November 2014, three A. mearnsii trials were initiated in the KwaZulu-Natal Midlands and SE Mpumulanga where fungicides were tested at varying rates for the control of wattle rust. Wattle rust had a significant and negative impact on tree growth, irrespective of site and/or previous infection. All fungicides tested and at all the rates applied, proved effective for control. For the most effective control of wattle rust, fungicides should be applied as a preventative, rather than corrective measure. In October 2015 a trial was initiated in southern KwaZulu-Natal to determine the effectiveness of varied application schedules and adjuvants of fungicides for the management of wattle rust. Two trials had initially been initiated but one had to be abandoned due to browsing damage. Wattle rust had a significant impact upon Groundline Diameter and Biomass Index but not Height. All of the adjuvants used and application schedules were effective in managing wattle rust. The most effective fungicide application used will therefore be based upon cost and in a manner that will reduce the likelihood of acquired resistance developing in wattle rust populations. The timing of fungicide application is necessary for optimal use of these fungicides. Fungicide applications could potentially be linked to the emergence of different wattle rust symptoms to optimize fungicide use. Wattle rust symptoms were analysed from the untreated control plots of two trials, one in the KwaZulu-Natal midlands and one in southern KwaZulu-Natal, to determine whether wattle rust Disease expression could be linked to black wattle tree growth. Regression trees were used for the analysis, as linear and multiple regression techniques would be unsuitable for the data. Regression trees were overfitted and attempts at testing the robustness of the model by cross-validation were unsuccessful. No individual symptom emerged as a significant predictor of tree growth, indicating that fungicide application should take place with the onset of any of the wattle rust symptoms tested. The results from six trials testing the use of fungicides for managing wattle rust were compared to assess costs associated with fungicide use. Relative growth for Biomass Index was compared to untreated controls to obtain comparisons within and between sites. Costs versus benefit were compared using a two-way table to determine the most optimum treatment. The largest portion of treatment costs was attributed to the cost of fungicide. No single treatment was found to be optimal for the recommended rate of application. The use of adjuvants increased the cost of treatment, without additional benefit in growth. Control of wattle rust is beneficial, although costly if over-applied. Rotation-end data is required to determine whether fungicide use is economical for managing wattle rust over an extended period of time. As a limited number of fungicides, from a limited number of fungicide groups were screened, the screening of additional fungicides from different fungicide groups will provide an additional selection of fungicides. If these are used in combination or alternation, the likelihood of acquired resistance developing among wattle rust populations will be reduced. Linking fungicide applications with wattle rust epidemiological and climatic data will aid in optimal use of fungicides, by timing applications to coincide with epidemiological and climatic cues. Rotation end research comparing final yield on fungicide treated versus untreated black wattle is needed to fully understand the economics of fungicide use. This will also aid in the understanding of the impact of wattle rust on tree age.
- Full Text:
- Date Issued: 2017
- Authors: Payn, Richard Guy
- Date: 2017
- Subjects: Fungicides -- South Africa Acacia mearnsii -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/20500 , vital:29299
- Description: South Africa has ca. 110 000 ha planted to Acacia mearnsii with 85% of the revenue from the species obtained from the timber, and 15% from the bark. Since its detection in 2013, wattle rust (recently identified as Uromycladium acaciae) has spread throughout the black wattle plantation area in KwaZulu-Natal, and from 2015 it was recorded in southern Mpumalanga. The pathogen affects trees of all age classes, causing a reduction in growth, as well as mortality with severe infection. Research has been initiated to determine a number of strategies for the management of the pathogen. These strategies include understanding wattle rust biology and epidemiology, planting tolerant or resistant black wattle, the testing and use of fungicide for management, and remote sensing and process based modelling to assess black wattle loss and high risk areas. These, with the outcomes from this research, will be combined into an overall Integrated Pest Management plan. Of the various strategies, the management of wattle rust with the use of fungicides is important, not only as it will have the potential to reduce the negative impacts of wattle rust, but it will also provide an interim solution until the other research areas provide alternative solutions. To address the current lack of fungicides available (and knowledge around their application) for the management of wattle rust, a series of trials were implemented to screen fungicides for their potential use, extend periods between the re-application of fungicide (if possible), the linking of symptoms to Disease Expression to aid with the timing of application, and the cost:benefits associated with fungicide use. Prior to the initiation of research into managing wattle rust, no fungicides were registered in South Africa for the control of wattle rust. In October / November 2014, three A. mearnsii trials were initiated in the KwaZulu-Natal Midlands and SE Mpumulanga where fungicides were tested at varying rates for the control of wattle rust. Wattle rust had a significant and negative impact on tree growth, irrespective of site and/or previous infection. All fungicides tested and at all the rates applied, proved effective for control. For the most effective control of wattle rust, fungicides should be applied as a preventative, rather than corrective measure. In October 2015 a trial was initiated in southern KwaZulu-Natal to determine the effectiveness of varied application schedules and adjuvants of fungicides for the management of wattle rust. Two trials had initially been initiated but one had to be abandoned due to browsing damage. Wattle rust had a significant impact upon Groundline Diameter and Biomass Index but not Height. All of the adjuvants used and application schedules were effective in managing wattle rust. The most effective fungicide application used will therefore be based upon cost and in a manner that will reduce the likelihood of acquired resistance developing in wattle rust populations. The timing of fungicide application is necessary for optimal use of these fungicides. Fungicide applications could potentially be linked to the emergence of different wattle rust symptoms to optimize fungicide use. Wattle rust symptoms were analysed from the untreated control plots of two trials, one in the KwaZulu-Natal midlands and one in southern KwaZulu-Natal, to determine whether wattle rust Disease expression could be linked to black wattle tree growth. Regression trees were used for the analysis, as linear and multiple regression techniques would be unsuitable for the data. Regression trees were overfitted and attempts at testing the robustness of the model by cross-validation were unsuccessful. No individual symptom emerged as a significant predictor of tree growth, indicating that fungicide application should take place with the onset of any of the wattle rust symptoms tested. The results from six trials testing the use of fungicides for managing wattle rust were compared to assess costs associated with fungicide use. Relative growth for Biomass Index was compared to untreated controls to obtain comparisons within and between sites. Costs versus benefit were compared using a two-way table to determine the most optimum treatment. The largest portion of treatment costs was attributed to the cost of fungicide. No single treatment was found to be optimal for the recommended rate of application. The use of adjuvants increased the cost of treatment, without additional benefit in growth. Control of wattle rust is beneficial, although costly if over-applied. Rotation-end data is required to determine whether fungicide use is economical for managing wattle rust over an extended period of time. As a limited number of fungicides, from a limited number of fungicide groups were screened, the screening of additional fungicides from different fungicide groups will provide an additional selection of fungicides. If these are used in combination or alternation, the likelihood of acquired resistance developing among wattle rust populations will be reduced. Linking fungicide applications with wattle rust epidemiological and climatic data will aid in optimal use of fungicides, by timing applications to coincide with epidemiological and climatic cues. Rotation end research comparing final yield on fungicide treated versus untreated black wattle is needed to fully understand the economics of fungicide use. This will also aid in the understanding of the impact of wattle rust on tree age.
- Full Text:
- Date Issued: 2017
Characterization of the distribution of platinum group elements in sulphide ores within the Merensky Reef at Modikwa and Two Rivers Platinum Mines, Eastern Bushveld Complex, South Africa
- Authors: Zilibokwe, Nosibulelo Julie
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7938 , vital:21326
- Description: The distribution of the platinum group element (PGE), in the Merensky Reef was characterized by, first determining the occurrence of the platinum group minerals (PGM), then by establishing the PGE concentration in the base metal sulphides (BMS) associated with the PGE mineralization in the Merensky Reef from selected borehole intersections, at the Two Rivers (TRP) and Modikwa Platinum Mines in the Eastern Bushveld Complex. A mineral liberation analyser (MLA) was then used to identify the PGM phases; their silicate and base metal associations; and their grain size distribution. Electron microprobe quantitative analysis and mapping were then used to determine the compositional variation of the PGM and the PGE elemental distribution in the BMS, respectively. The study showed that the BMS including pyrrhotite, pentlandite, and chalcopyrite were the principal sulphides, where pyrrhotite was most prominent with minor quantities of pyrite. Orthopyroxene, clinopyroxene and plagioclase were the most abundant primary silicate minerals identified, while secondary silicates identified included talc, serpentine and amphibole. Platinum group minerals showed three distinct groups with respect to the mineralogical association with the PGE; (i) BMS association; (ii) chromite association; and (iii) silicate association. Of the BMS, chalcopyrite showed the most dominant association with the PGMs. All samples from both mines exhibited a wide range of PGMs, including maslovite, braggite, cooperate, laurite and PGE alloys such as ferroplatinum as well as other unidentified platinum and palladium sulphides, arsenides and bismuthides, while gold was present as electrum. The PGMs ranged in size from less than a micron to about 125 microns with an average of 20 microns. The close association of PGM with BMS along the margins of sulphides indicates that the PGMs were derived from the sulphide melt. PGE distribution in the sulphides at Modikwa showed pentlandite contained the highest concentrations of palladium (up to 379 ppm) and chalcopyrite hosting the highest rhodium concentrations (up to 793 ppm). Samples from Two Rivers revealed pentlandite as the principal host to both palladium and rhodium, with concentrations reaching up to 695 and 930 ppm, respectively. Magnetite at both Modikwa and Two Rivers showed significant rhodium content, reaching up to 982 and 930 ppm, respectively. The pyrrhotite compared to other sulphides contained all the elements found in the platinum group (PPGE), namely, platinum, palladium and rhodium, with all the platinum identified found in the pyrrhotite. The concentrations for the iridium group (IPGE) namely, iridium, osmium, and ruthenium were below the detection limit. The PGE mineralization in the stratigraphy varied within each mine. The mineralization revealed top loading in the central sector (Modikwa) and bottom loading in the southern sector (Two Rivers). The sequence of the Merensky Reef at the two sectors of the Eastern Bushveld Complex showed a remarkable similarity in their mineralogy suggesting that these two sectors were formed from the same liquid or formed simultaneously within a single magma chamber; however the PGE distribution within the stratigraphy may have been controlled by the presence of cumulate sulphides.
- Full Text:
- Date Issued: 2017
- Authors: Zilibokwe, Nosibulelo Julie
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7938 , vital:21326
- Description: The distribution of the platinum group element (PGE), in the Merensky Reef was characterized by, first determining the occurrence of the platinum group minerals (PGM), then by establishing the PGE concentration in the base metal sulphides (BMS) associated with the PGE mineralization in the Merensky Reef from selected borehole intersections, at the Two Rivers (TRP) and Modikwa Platinum Mines in the Eastern Bushveld Complex. A mineral liberation analyser (MLA) was then used to identify the PGM phases; their silicate and base metal associations; and their grain size distribution. Electron microprobe quantitative analysis and mapping were then used to determine the compositional variation of the PGM and the PGE elemental distribution in the BMS, respectively. The study showed that the BMS including pyrrhotite, pentlandite, and chalcopyrite were the principal sulphides, where pyrrhotite was most prominent with minor quantities of pyrite. Orthopyroxene, clinopyroxene and plagioclase were the most abundant primary silicate minerals identified, while secondary silicates identified included talc, serpentine and amphibole. Platinum group minerals showed three distinct groups with respect to the mineralogical association with the PGE; (i) BMS association; (ii) chromite association; and (iii) silicate association. Of the BMS, chalcopyrite showed the most dominant association with the PGMs. All samples from both mines exhibited a wide range of PGMs, including maslovite, braggite, cooperate, laurite and PGE alloys such as ferroplatinum as well as other unidentified platinum and palladium sulphides, arsenides and bismuthides, while gold was present as electrum. The PGMs ranged in size from less than a micron to about 125 microns with an average of 20 microns. The close association of PGM with BMS along the margins of sulphides indicates that the PGMs were derived from the sulphide melt. PGE distribution in the sulphides at Modikwa showed pentlandite contained the highest concentrations of palladium (up to 379 ppm) and chalcopyrite hosting the highest rhodium concentrations (up to 793 ppm). Samples from Two Rivers revealed pentlandite as the principal host to both palladium and rhodium, with concentrations reaching up to 695 and 930 ppm, respectively. Magnetite at both Modikwa and Two Rivers showed significant rhodium content, reaching up to 982 and 930 ppm, respectively. The pyrrhotite compared to other sulphides contained all the elements found in the platinum group (PPGE), namely, platinum, palladium and rhodium, with all the platinum identified found in the pyrrhotite. The concentrations for the iridium group (IPGE) namely, iridium, osmium, and ruthenium were below the detection limit. The PGE mineralization in the stratigraphy varied within each mine. The mineralization revealed top loading in the central sector (Modikwa) and bottom loading in the southern sector (Two Rivers). The sequence of the Merensky Reef at the two sectors of the Eastern Bushveld Complex showed a remarkable similarity in their mineralogy suggesting that these two sectors were formed from the same liquid or formed simultaneously within a single magma chamber; however the PGE distribution within the stratigraphy may have been controlled by the presence of cumulate sulphides.
- Full Text:
- Date Issued: 2017
Statistical methods for the detection of non-technical losses: a case study for the Nelson Mandela Bay Municipality
- Authors: Pazi, Sisa
- Date: 2017
- Subjects: Nonparametric statistics Mathematical statistics , Statistics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/19706 , vital:28939
- Description: Electricity is one of the most stolen commodities in the world. Electricity theft can be defined as the criminal act of stealing electrical power. Several types of electricity theft exist, including illegal connections and bypassing and tampering with energy meters. The negative financial impacts, due to lost revenue, of electricity theft are far reaching and affect both developing and developed countries. . Here in South Africa, Eskom loses over R2 Billion annually due to electricity theft. Data mining and nonparametric statistical methods have been used to detect fraudulent usage of electricity by assessing abnormalities and abrupt changes in kilowatt hour (kWh) consumption patterns. Identifying effective measures to detect fraudulent electricity usage is an active area of research in the electrical domain. In this study, Support Vector Machines (SVM), Naïve Bayes (NB) and k-Nearest Neighbour (KNN) algorithms were used to design and propose an electricity fraud detection model. Using the Nelson Mandela Bay Municipality as a case study, three classifiers were built with SVM, NB and KNN algorithms. The performance of these classifiers were evaluated and compared.
- Full Text:
- Date Issued: 2017
- Authors: Pazi, Sisa
- Date: 2017
- Subjects: Nonparametric statistics Mathematical statistics , Statistics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/19706 , vital:28939
- Description: Electricity is one of the most stolen commodities in the world. Electricity theft can be defined as the criminal act of stealing electrical power. Several types of electricity theft exist, including illegal connections and bypassing and tampering with energy meters. The negative financial impacts, due to lost revenue, of electricity theft are far reaching and affect both developing and developed countries. . Here in South Africa, Eskom loses over R2 Billion annually due to electricity theft. Data mining and nonparametric statistical methods have been used to detect fraudulent usage of electricity by assessing abnormalities and abrupt changes in kilowatt hour (kWh) consumption patterns. Identifying effective measures to detect fraudulent electricity usage is an active area of research in the electrical domain. In this study, Support Vector Machines (SVM), Naïve Bayes (NB) and k-Nearest Neighbour (KNN) algorithms were used to design and propose an electricity fraud detection model. Using the Nelson Mandela Bay Municipality as a case study, three classifiers were built with SVM, NB and KNN algorithms. The performance of these classifiers were evaluated and compared.
- Full Text:
- Date Issued: 2017
Quality management systems – a fundamental business imperative for construction companies: a case study of Bay West city mall
- Mthi, Vuyolwethu Feza Philisa
- Authors: Mthi, Vuyolwethu Feza Philisa
- Date: 2017
- Subjects: Construction projects -- Management Construction industry -- Management , Total quality management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/45908 , vital:39319
- Description: The quality of construction projects in South Africa has long been below par which is evident in the reports of poor project performance, poorly implemented construction processes, or even worse projects delivered at an unexpected cost to the client. Private and public sector clients are dissatisfied with the quality of work produced by contractors whilst the rectification of substandard construction work on many of the low-cost housing projects throughout South Africa has left the state with a bill of around R50 billion. As a result this research suggests that company’s implement quality management systems as a means to differentiate and elevate themselves above current industry performance. The research inquiry was conducted through the use of a case study (Bay West City Mall). Data was collected primarily through participant observation and survey questionnaires with the various participants on the Bay West City Mall project. The collected data were extracted, errors eliminated/accounted for, coded and entered onto an excel spreadsheet for easy reference and analysis. For the interpretation of the data the researcher used the bivariate tabulation method where categorical data is measured using ordinal and nominal scales. The study concluded that the employment of quality management systems should no longer be seen as optional but as fundamental to the continual improvement of construction companies, those organizations that fully institutionalise the principles of quality management will have a strong chance of improving their project performance, reducing project costs, getting repeat business and increasing profits on projects. It is the recommendation of this study that more research be conducted into how quality management, in the construction industry, can assist in alleviating other problems that plague the South African construction industry such as poor performance relating to health & safety, cost, time, low profit margins and poor cultural practices.
- Full Text:
- Date Issued: 2017
- Authors: Mthi, Vuyolwethu Feza Philisa
- Date: 2017
- Subjects: Construction projects -- Management Construction industry -- Management , Total quality management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/45908 , vital:39319
- Description: The quality of construction projects in South Africa has long been below par which is evident in the reports of poor project performance, poorly implemented construction processes, or even worse projects delivered at an unexpected cost to the client. Private and public sector clients are dissatisfied with the quality of work produced by contractors whilst the rectification of substandard construction work on many of the low-cost housing projects throughout South Africa has left the state with a bill of around R50 billion. As a result this research suggests that company’s implement quality management systems as a means to differentiate and elevate themselves above current industry performance. The research inquiry was conducted through the use of a case study (Bay West City Mall). Data was collected primarily through participant observation and survey questionnaires with the various participants on the Bay West City Mall project. The collected data were extracted, errors eliminated/accounted for, coded and entered onto an excel spreadsheet for easy reference and analysis. For the interpretation of the data the researcher used the bivariate tabulation method where categorical data is measured using ordinal and nominal scales. The study concluded that the employment of quality management systems should no longer be seen as optional but as fundamental to the continual improvement of construction companies, those organizations that fully institutionalise the principles of quality management will have a strong chance of improving their project performance, reducing project costs, getting repeat business and increasing profits on projects. It is the recommendation of this study that more research be conducted into how quality management, in the construction industry, can assist in alleviating other problems that plague the South African construction industry such as poor performance relating to health & safety, cost, time, low profit margins and poor cultural practices.
- Full Text:
- Date Issued: 2017
Characterisation of antibacterial compounds produced by Pseudomonas spp. isolated from Hogsback wetlands, Eastern Cape, South Africa
- Authors: Obi, Akudo Odochi
- Date: 2017
- Subjects: Bacteriology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/15688 , vital:40507
- Description: With microbial pathogens developing resistance against currently existing antimicrobials, there is an earnest need to discover and develop new therapeutic compounds with unique and/or precise modes of action. Natural products have provided the inspiration for most of the active ingredients in medicines and thus are regarded as a potential screening resource lead for discovery of new drugs. Pseudomonads are ubiquitous, Gram-negative, motile bacteria that flourish and inhabit a diversity of environments. Literature has vastly revealed that some members of the genus Pseudomonas are capable of producing a plethora of biologically active metabolites and thus are regarded as “attractive” bacteria for testing as potential sources for new therapeutic compounds. In this regard, this study was undertaken with an aim to isolate and characterize antibacterial compounds produced by Pseudomonas species isolated from aquatic milieu of the Hogsback wetlands, Eastern Cape, South Africa. A total of 12 water samples were aseptically collected from Hogsback wetlands. To ascertain antimicrobial potential of the isolates, 9 test bacterial (sensitive) strains, namely Escherichia coli ATCC 3695, Vibrio fluvialis, Salmonella typhimurium, Salmonella enteritidis, Pseudomonas aeruginosa ATCC 27853, Escherichia coli (2), Listeria ivanovii, Listeria monocytogenes and Enterococcus faecalis ATCC 19433 were used for antimicrobial screening. A total of 500 presumptive Pseudomonas spp. were isolated and screened for the production of antibacterial compound through the Agar-well diffusion method. About 8percent of the presumptive Pseudomonas spp. produced compound with activity against the test bacteria and based on the levels of activity shown, three isolates coded as A53, Y55 and Y138 were selected and identified by 16S rDNA sequence analysis and The Basic Local Alignment Search Tool analysis revealed that the three isolates (A53, Y55 and Y138) belonged to the Pseudomonas genus. Using MEGA6 software, a molecular phylogenetic tree was constructed by Maximum Likelihood Method. The phylogenetic analysis by this method showed that all three isolate codes (A53, Y55 and Y138) formed the same clade with Pseudomonas viridiflava strain P3 (Accession number: AY972186) and Pseudomonas plecoglossicida strain P9 (Accession number: AY972231) at a high bootstrap value of 100percent. Isolate code A53 and Y55 also grouped together at a bootstrap value of 96percent. Factors affecting antibacterial compound production by the three isolates were elucidated. The effect of pH on the three isolates revealed that isolate code A53 and Y55 could produce antibacterial compounds over all pH ranges (pH 4-9), however, antibacterial production was produced optimally at acidic conditions (pH 4) and a less acidic-neutral condition (pH 6) respectively. Isolate Y138 showed optimal production at pH 5. The effect of temperature on all three isolates was studied at different temperatures ranging between 25°C-40°C. Study on effect of temperature variations on antibacterial production revealed that all three isolates are capable of growing and producing antibacterial compounds over all the different temperature ranges, however, maximum/optimum production was observed at temperature of 30°C. In order to establish the role of plasmids in antibacterial production, two curing agents; Sodium dodecyl sulfate (SDS) and Ethidium bromide under different sub-lethal concentrations (1 mg/ml -11mg/ml and 2.5 μg/ml- 125 μg/ml respectively) were used to cure the selected isolates. Plasmid DNA samples of A53, Y55 and Y138, were separated by electrophoresis on a 0.7percent (w/v) agarose. Agarose gel electrophoresis revealed that not all the concentrations used were effective in curing the plasmid. A Quick Load 1 kb Extend DNA ladder marker was used for determining the size of the plasmids. Isolate code A53 and Y138 had a plasmid size of 48.5 kb while isolate Y55 had a plasmid size of approximately 20 kb. Antibacterial activity by agar-well diffusion method after the curing process revealed that antibacterial production was not lost or prevented, but rather increased. Thus, it is suggested that the genes responsible for antibiotic production in this study were chromosomal-encoded and not plasmid-encoded. This study revealed that Hogsback wetlands may represent a previously unexplored environment/source of discovering novel and potent antibacterial compounds.
- Full Text:
- Date Issued: 2017
- Authors: Obi, Akudo Odochi
- Date: 2017
- Subjects: Bacteriology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/15688 , vital:40507
- Description: With microbial pathogens developing resistance against currently existing antimicrobials, there is an earnest need to discover and develop new therapeutic compounds with unique and/or precise modes of action. Natural products have provided the inspiration for most of the active ingredients in medicines and thus are regarded as a potential screening resource lead for discovery of new drugs. Pseudomonads are ubiquitous, Gram-negative, motile bacteria that flourish and inhabit a diversity of environments. Literature has vastly revealed that some members of the genus Pseudomonas are capable of producing a plethora of biologically active metabolites and thus are regarded as “attractive” bacteria for testing as potential sources for new therapeutic compounds. In this regard, this study was undertaken with an aim to isolate and characterize antibacterial compounds produced by Pseudomonas species isolated from aquatic milieu of the Hogsback wetlands, Eastern Cape, South Africa. A total of 12 water samples were aseptically collected from Hogsback wetlands. To ascertain antimicrobial potential of the isolates, 9 test bacterial (sensitive) strains, namely Escherichia coli ATCC 3695, Vibrio fluvialis, Salmonella typhimurium, Salmonella enteritidis, Pseudomonas aeruginosa ATCC 27853, Escherichia coli (2), Listeria ivanovii, Listeria monocytogenes and Enterococcus faecalis ATCC 19433 were used for antimicrobial screening. A total of 500 presumptive Pseudomonas spp. were isolated and screened for the production of antibacterial compound through the Agar-well diffusion method. About 8percent of the presumptive Pseudomonas spp. produced compound with activity against the test bacteria and based on the levels of activity shown, three isolates coded as A53, Y55 and Y138 were selected and identified by 16S rDNA sequence analysis and The Basic Local Alignment Search Tool analysis revealed that the three isolates (A53, Y55 and Y138) belonged to the Pseudomonas genus. Using MEGA6 software, a molecular phylogenetic tree was constructed by Maximum Likelihood Method. The phylogenetic analysis by this method showed that all three isolate codes (A53, Y55 and Y138) formed the same clade with Pseudomonas viridiflava strain P3 (Accession number: AY972186) and Pseudomonas plecoglossicida strain P9 (Accession number: AY972231) at a high bootstrap value of 100percent. Isolate code A53 and Y55 also grouped together at a bootstrap value of 96percent. Factors affecting antibacterial compound production by the three isolates were elucidated. The effect of pH on the three isolates revealed that isolate code A53 and Y55 could produce antibacterial compounds over all pH ranges (pH 4-9), however, antibacterial production was produced optimally at acidic conditions (pH 4) and a less acidic-neutral condition (pH 6) respectively. Isolate Y138 showed optimal production at pH 5. The effect of temperature on all three isolates was studied at different temperatures ranging between 25°C-40°C. Study on effect of temperature variations on antibacterial production revealed that all three isolates are capable of growing and producing antibacterial compounds over all the different temperature ranges, however, maximum/optimum production was observed at temperature of 30°C. In order to establish the role of plasmids in antibacterial production, two curing agents; Sodium dodecyl sulfate (SDS) and Ethidium bromide under different sub-lethal concentrations (1 mg/ml -11mg/ml and 2.5 μg/ml- 125 μg/ml respectively) were used to cure the selected isolates. Plasmid DNA samples of A53, Y55 and Y138, were separated by electrophoresis on a 0.7percent (w/v) agarose. Agarose gel electrophoresis revealed that not all the concentrations used were effective in curing the plasmid. A Quick Load 1 kb Extend DNA ladder marker was used for determining the size of the plasmids. Isolate code A53 and Y138 had a plasmid size of 48.5 kb while isolate Y55 had a plasmid size of approximately 20 kb. Antibacterial activity by agar-well diffusion method after the curing process revealed that antibacterial production was not lost or prevented, but rather increased. Thus, it is suggested that the genes responsible for antibiotic production in this study were chromosomal-encoded and not plasmid-encoded. This study revealed that Hogsback wetlands may represent a previously unexplored environment/source of discovering novel and potent antibacterial compounds.
- Full Text:
- Date Issued: 2017
Resource partitioning in the world’s largest gannetry
- Authors: Botha, Jonathan Aubrey
- Date: 2017
- Subjects: Gannets -- South Africa Birds of prey -- Behavior -- South Africa , Birds -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14707 , vital:27828
- Description: Understanding strategies of resource partitioning within populations is a fundamental aspect of the study of ecology, and one which has been well documented across various taxa. In seabirds, sex-specific differences in foraging behaviour are often thought to reflect strategies of resource partitioning to avoid intra-specific competition. At present Bird Island in Algoa Bay hosts the world’s largest breeding population of gannets, with recent population estimates numbering well over 90 000 breeding pairs. Given the large size of this colony, intense levels of intra-specific competition are expected during the breeding season, particularly in years of poor feeding conditions. In addition, continuous foraging around the breeding colony may lead to the local depletion of prey as the season progresses, calling for flexibility in the foraging behaviour and diet of breeding individuals. Therefore, the aim of this dissertation was to investigate resource partitioning in Cape gannets breeding at Bird Island through strategies of sex-specific foraging and intra-seasonal variability in foraging behaviour and diet. To achieve this, the spatial and temporal aspects of Cape gannet foraging behaviour were assessed during the early stages of chick rearing, over two consecutive breeding seasons (2011/12, 2012/13) using GPS tracking and VHF monitoring. In addition, intra-seasonal variability in foraging behaviour and diet were investigated, taking into account the influence of sex and chick age, to provide a comprehensive assessment of foraging behaviour throughout the chick rearing period. GPS tracking data for 79 birds revealed limited evidence for sex-specific differences over spatial dimensions. An extension in the foraging range of females during a year of lower prey availability (2012/13) was, however, evident. This suggests a possible sex-specific response to prey limitation, likely reflecting resource partitioning strategies or differences in nutritional requirements. VHF data for 95 additional birds revealed a clear pattern in temporal foraging behaviour. In general, females were more likely to be on a foraging trip during the early and mid-day hours, with the probability of males being on a foraging trip increasing towards the late afternoon. Continuous tracking of individuals throughout the 2015/16 breeding season further revealed little evidence for sex-specific differences in spatial distribution and forging effort during both the guard and post-guard stages of chick rearing. A clear increase in foraging range was evident during the early stages of chick rearing as the season progressed. However, birds attending chicks older than 50 days showed an unexpected contraction in foraging range, which appeared to coincide with a dietary shift. During the early stages of breeding the diet was comprised almost exclusively of anchovy, the proportion of which decreased progressively in the diet throughout the breeding season. This was mirrored by a substantial increase in the proportion of saury in the diet. These results suggest that Cape gannets increase their foraging range in response to local prey depletion as the breeding season progresses. However, when alternative prey becomes available they may shift their diet, allowing them to access prey closer to the breeding colony. Overall, this dissertation provides insight into sex-specific behaviour in a monomorphic seabird, suggesting a marginal degree of spatial segregation. The results provide the first support for sex-related temporal foraging segregation in gannets. Such separation could potentially be driven by resource partitioning, but could also relate to differential nutritional requirements. In addition, this study also provided the first comprehensive assessment of foraging behaviour throughout the guard and post guard stages of chick rearing in gannets. These results suggest that a combination of foraging and dietary flexibility may allow Cape gannets to buffer the effects of prey depletion during the breeding season. In conclusion, resource partitioning through sex-specific foraging appears to be limited in the Cape gannet population at Bird Island. Segregation via alternative pathways may however be possible and as such, future studies should consider the influence of individual level segregation and habitat specialization.
- Full Text:
- Date Issued: 2017
- Authors: Botha, Jonathan Aubrey
- Date: 2017
- Subjects: Gannets -- South Africa Birds of prey -- Behavior -- South Africa , Birds -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14707 , vital:27828
- Description: Understanding strategies of resource partitioning within populations is a fundamental aspect of the study of ecology, and one which has been well documented across various taxa. In seabirds, sex-specific differences in foraging behaviour are often thought to reflect strategies of resource partitioning to avoid intra-specific competition. At present Bird Island in Algoa Bay hosts the world’s largest breeding population of gannets, with recent population estimates numbering well over 90 000 breeding pairs. Given the large size of this colony, intense levels of intra-specific competition are expected during the breeding season, particularly in years of poor feeding conditions. In addition, continuous foraging around the breeding colony may lead to the local depletion of prey as the season progresses, calling for flexibility in the foraging behaviour and diet of breeding individuals. Therefore, the aim of this dissertation was to investigate resource partitioning in Cape gannets breeding at Bird Island through strategies of sex-specific foraging and intra-seasonal variability in foraging behaviour and diet. To achieve this, the spatial and temporal aspects of Cape gannet foraging behaviour were assessed during the early stages of chick rearing, over two consecutive breeding seasons (2011/12, 2012/13) using GPS tracking and VHF monitoring. In addition, intra-seasonal variability in foraging behaviour and diet were investigated, taking into account the influence of sex and chick age, to provide a comprehensive assessment of foraging behaviour throughout the chick rearing period. GPS tracking data for 79 birds revealed limited evidence for sex-specific differences over spatial dimensions. An extension in the foraging range of females during a year of lower prey availability (2012/13) was, however, evident. This suggests a possible sex-specific response to prey limitation, likely reflecting resource partitioning strategies or differences in nutritional requirements. VHF data for 95 additional birds revealed a clear pattern in temporal foraging behaviour. In general, females were more likely to be on a foraging trip during the early and mid-day hours, with the probability of males being on a foraging trip increasing towards the late afternoon. Continuous tracking of individuals throughout the 2015/16 breeding season further revealed little evidence for sex-specific differences in spatial distribution and forging effort during both the guard and post-guard stages of chick rearing. A clear increase in foraging range was evident during the early stages of chick rearing as the season progressed. However, birds attending chicks older than 50 days showed an unexpected contraction in foraging range, which appeared to coincide with a dietary shift. During the early stages of breeding the diet was comprised almost exclusively of anchovy, the proportion of which decreased progressively in the diet throughout the breeding season. This was mirrored by a substantial increase in the proportion of saury in the diet. These results suggest that Cape gannets increase their foraging range in response to local prey depletion as the breeding season progresses. However, when alternative prey becomes available they may shift their diet, allowing them to access prey closer to the breeding colony. Overall, this dissertation provides insight into sex-specific behaviour in a monomorphic seabird, suggesting a marginal degree of spatial segregation. The results provide the first support for sex-related temporal foraging segregation in gannets. Such separation could potentially be driven by resource partitioning, but could also relate to differential nutritional requirements. In addition, this study also provided the first comprehensive assessment of foraging behaviour throughout the guard and post guard stages of chick rearing in gannets. These results suggest that a combination of foraging and dietary flexibility may allow Cape gannets to buffer the effects of prey depletion during the breeding season. In conclusion, resource partitioning through sex-specific foraging appears to be limited in the Cape gannet population at Bird Island. Segregation via alternative pathways may however be possible and as such, future studies should consider the influence of individual level segregation and habitat specialization.
- Full Text:
- Date Issued: 2017
The pest status and integrated management programme of carob moth, Ectomyelois ceratoniae Zeller, attacking citrus in South Africa
- Authors: Thackeray, Sean Robin
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7758 , vital:21293
- Description: The carob moth, Ectomyelois ceratoniae Zeller, is a pest of agricultural commodities and stored products around the world. Carob moth is known to infest citrus in the Mediterranean region and in southern Africa. In grapefruit cultivars, carob moth infestations are associated with high levels of mealybug. However, although this relationship has been observed in other citrus types such as Navel oranges, this has never been quantified. A recent survey of infested fruit from various production areas in South Africa indicated that the pest status of carob moth on Navel oranges may have been underestimated. As a result of the incidental pest status of carob moth on citrus in South Africa in the past, a species specific integrated pest management (IPM) programme does not exist. Therefore, the overriding aim of this theses was to evaluate the pest status of carob moth in citrus and establish a species specific IPM programme by determine the autecology of carob moth in citrus. Reliable methods for monitoring carob moth in citrus orchards both for producers and for research purposes were developed. A user-friendly monitoring method for determining weekly carob moth infestation through dropped fruit was suitable for producers. A timed scouting method was also developed; although the accuracy of this method varied with the experience of the scout. The pest status of carob moth was highest in the Loskop Valley, Nelspruit and the Vaalharts production areas and economic injury to growers ranged from R512.35 to R3 719.80 per hectare as a direct result of infestation. No infestation was recorded in the Sundays River Valley and Citrusdal production areas over both the 2014-15 and 201516 growing seasons. A laboratory study showed the survival of carob moth larvae infesting citrus is less than 10% in the absence of mealybug. However, this increases to almost 40% in the presence of mealybug residues and sooty mould. There was a significant relationship between carob infestation at harvest and mealybug infestation in the middle months of the growing season. The relationship between carob moth and mealybug indicates that current production guidelines for the management of mealybug in citrus may need to be amended. Consequently, it is proposed that an orchard with a history of carob moth infestation and a high mealybug infestation in the previous season should be subjected to an early season preventative application of a registered control product. Also, if mealybug infestation in December is higher than a 5% of fruit per tree, then a corrective application of a registered product is recommended. The application of 2,4-D at petal drop reduced the size of the navel-end opening, decreasing the proportion of mealybug found in the navel-end, subsequently reducing carob moth infestation, resulting in a direct benefit for producers. Products registered for the control of false codling moth (FCM), Thaumatotibia leucotreta Meyrick, were effective in reducing carob moth infestation. In a spray trial conducted over two seasons, Delegate® and Runner® reduced infestation significantly in the 2014-15 season (over 80%), while only Delegate® was effective in the 2015-16 season (over 80%). If a late season corrective chemical application is targeted at both FCM and carob moth, this application should take place between 6-7 weeks prior to harvest. The mating disruption product, SPLAT® EC, reduced carob moth infestation by 70% compared to the untreated control. A laboratory culture was established and head-capsule size categories were determined for all five carob moth instars. A parasitoid survey indicated that parasitism of carob moth larvae is generally less than 5% in citrus orchards and a new species of Braconidae was described as Phanterotoma carobivora van Achterberg and Thackeray. Carob moth fifth instar were found to be the most cold-tolerant larval stage, and were shown to be more cold susceptible than the most cold-tolerant FCM instars at -0.55ºC for eighteen days. This cold treatment resulted in a mortality of 94.6% fifth instar carob moth compared to a combined fourth and fifth instar mortality of 87.8% for FCM after eighteen days. These results indicate that post-harvest cold treatments targeting FCM will be as, if not more, effective against carob moth, suggesting that current phytosanitary legislation for carob moth should be amended to incorporate this study’s findings.
- Full Text:
- Date Issued: 2017
- Authors: Thackeray, Sean Robin
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7758 , vital:21293
- Description: The carob moth, Ectomyelois ceratoniae Zeller, is a pest of agricultural commodities and stored products around the world. Carob moth is known to infest citrus in the Mediterranean region and in southern Africa. In grapefruit cultivars, carob moth infestations are associated with high levels of mealybug. However, although this relationship has been observed in other citrus types such as Navel oranges, this has never been quantified. A recent survey of infested fruit from various production areas in South Africa indicated that the pest status of carob moth on Navel oranges may have been underestimated. As a result of the incidental pest status of carob moth on citrus in South Africa in the past, a species specific integrated pest management (IPM) programme does not exist. Therefore, the overriding aim of this theses was to evaluate the pest status of carob moth in citrus and establish a species specific IPM programme by determine the autecology of carob moth in citrus. Reliable methods for monitoring carob moth in citrus orchards both for producers and for research purposes were developed. A user-friendly monitoring method for determining weekly carob moth infestation through dropped fruit was suitable for producers. A timed scouting method was also developed; although the accuracy of this method varied with the experience of the scout. The pest status of carob moth was highest in the Loskop Valley, Nelspruit and the Vaalharts production areas and economic injury to growers ranged from R512.35 to R3 719.80 per hectare as a direct result of infestation. No infestation was recorded in the Sundays River Valley and Citrusdal production areas over both the 2014-15 and 201516 growing seasons. A laboratory study showed the survival of carob moth larvae infesting citrus is less than 10% in the absence of mealybug. However, this increases to almost 40% in the presence of mealybug residues and sooty mould. There was a significant relationship between carob infestation at harvest and mealybug infestation in the middle months of the growing season. The relationship between carob moth and mealybug indicates that current production guidelines for the management of mealybug in citrus may need to be amended. Consequently, it is proposed that an orchard with a history of carob moth infestation and a high mealybug infestation in the previous season should be subjected to an early season preventative application of a registered control product. Also, if mealybug infestation in December is higher than a 5% of fruit per tree, then a corrective application of a registered product is recommended. The application of 2,4-D at petal drop reduced the size of the navel-end opening, decreasing the proportion of mealybug found in the navel-end, subsequently reducing carob moth infestation, resulting in a direct benefit for producers. Products registered for the control of false codling moth (FCM), Thaumatotibia leucotreta Meyrick, were effective in reducing carob moth infestation. In a spray trial conducted over two seasons, Delegate® and Runner® reduced infestation significantly in the 2014-15 season (over 80%), while only Delegate® was effective in the 2015-16 season (over 80%). If a late season corrective chemical application is targeted at both FCM and carob moth, this application should take place between 6-7 weeks prior to harvest. The mating disruption product, SPLAT® EC, reduced carob moth infestation by 70% compared to the untreated control. A laboratory culture was established and head-capsule size categories were determined for all five carob moth instars. A parasitoid survey indicated that parasitism of carob moth larvae is generally less than 5% in citrus orchards and a new species of Braconidae was described as Phanterotoma carobivora van Achterberg and Thackeray. Carob moth fifth instar were found to be the most cold-tolerant larval stage, and were shown to be more cold susceptible than the most cold-tolerant FCM instars at -0.55ºC for eighteen days. This cold treatment resulted in a mortality of 94.6% fifth instar carob moth compared to a combined fourth and fifth instar mortality of 87.8% for FCM after eighteen days. These results indicate that post-harvest cold treatments targeting FCM will be as, if not more, effective against carob moth, suggesting that current phytosanitary legislation for carob moth should be amended to incorporate this study’s findings.
- Full Text:
- Date Issued: 2017
Post-release evaluation and thermal physiology of the Pereskia stem-wilter, Catorhintha schaffneri (Coreidae), a new biological control agent for Pereskia aculeata (Cactaceae)
- Authors: Muskett, Phillippa Claire
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/36094 , vital:24477
- Description: Catorhintha schaffneri Brailovsky and Garcia (Hemiptera: Coreidae) is a biological control agent that was recently accepted for release in South Africa to control Pereskia aculeata Miller (Cactaceae), an invasive creeping cactus. The aim of this thesis was to conduct post-release research to ensure that C. schaffneri is utilised to its full potential. To achieve this aim, and focus release efforts, the thermal physiology of C. schaffneri was investigated to predict where in South Africa the agent is most likely to establish. These predictions were then tested by releasing the agent at field sites with a wide variety of climatic conditions and evaluating establishment success. When invasive plants invade a wide distribution, made up of areas with different climatic conditions, biological control agents may not establish or be effective throughout the invaded distribution. According to the thermal physiology of C. schaffneri, it is most likely to establish and become effective in the subtropical region of South Africa, along the coast of KwaZulu- Natal. Cold winters, or generally low year-round temperatures, may limit establishment in the more temperate areas of South Africa in the Eastern and Western Cape as well as inland in the Highveld region. These predictions can be used to focus release efforts to climatically suitable regions and stop releases in areas where C. schaffneri cannot survive. Predictions based on thermal physiology may not account for all of the variables which affect establishment. To account for other variables, the establishment of C. schaffneri was tested using closely monitored field release studies. During these studies the effect of other variables such as; microclimate temperature, humidity, precipitation, plant quality and release strategy were considered. Low humidity, precipitation and plant quality appear to affect the establishment of C. schaffneri in the subtropical areas of South Africa. The experiment was conducted during a period of drought, and this may have resulted in lower establishment rates. The most successful release strategy for C. schaffneri was the use of multiple, small releases rather than single releases of the same number of individuals. The field based study was therefore able to improve the biological control of P. aculeata by increasing the chance that each release of C. schaffneri results in establishment. The post-release studies presented in this thesis will increase the impact of C. schaffneri by focussing release efforts to climatically suitable sites, releasing at appropriate times of year and releasing the agent in a manner that increases establishment success. Post-release studies, such as those presented here, can make biological control programmes more efficient and effective.
- Full Text:
- Date Issued: 2017
- Authors: Muskett, Phillippa Claire
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/36094 , vital:24477
- Description: Catorhintha schaffneri Brailovsky and Garcia (Hemiptera: Coreidae) is a biological control agent that was recently accepted for release in South Africa to control Pereskia aculeata Miller (Cactaceae), an invasive creeping cactus. The aim of this thesis was to conduct post-release research to ensure that C. schaffneri is utilised to its full potential. To achieve this aim, and focus release efforts, the thermal physiology of C. schaffneri was investigated to predict where in South Africa the agent is most likely to establish. These predictions were then tested by releasing the agent at field sites with a wide variety of climatic conditions and evaluating establishment success. When invasive plants invade a wide distribution, made up of areas with different climatic conditions, biological control agents may not establish or be effective throughout the invaded distribution. According to the thermal physiology of C. schaffneri, it is most likely to establish and become effective in the subtropical region of South Africa, along the coast of KwaZulu- Natal. Cold winters, or generally low year-round temperatures, may limit establishment in the more temperate areas of South Africa in the Eastern and Western Cape as well as inland in the Highveld region. These predictions can be used to focus release efforts to climatically suitable regions and stop releases in areas where C. schaffneri cannot survive. Predictions based on thermal physiology may not account for all of the variables which affect establishment. To account for other variables, the establishment of C. schaffneri was tested using closely monitored field release studies. During these studies the effect of other variables such as; microclimate temperature, humidity, precipitation, plant quality and release strategy were considered. Low humidity, precipitation and plant quality appear to affect the establishment of C. schaffneri in the subtropical areas of South Africa. The experiment was conducted during a period of drought, and this may have resulted in lower establishment rates. The most successful release strategy for C. schaffneri was the use of multiple, small releases rather than single releases of the same number of individuals. The field based study was therefore able to improve the biological control of P. aculeata by increasing the chance that each release of C. schaffneri results in establishment. The post-release studies presented in this thesis will increase the impact of C. schaffneri by focussing release efforts to climatically suitable sites, releasing at appropriate times of year and releasing the agent in a manner that increases establishment success. Post-release studies, such as those presented here, can make biological control programmes more efficient and effective.
- Full Text:
- Date Issued: 2017
A smart home environment to support safety and risk monitoring for the elderly living independently
- Authors: Chiridza, Tongai
- Date: 2017
- Subjects: Multisensor data fusion , Raspberry Pi (Computer) -- Programming Adaptive computing systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14851 , vital:27880
- Description: The elderly prefer to live independently despite vulnerability to age-related challenges. Constant monitoring is required in cases where the elderly are living alone. The home environment can be a dangerous environment for the elderly living independently due to adverse events that can occur at any time. The potential risks for the elderly living independently can be categorised as injury in the home, home environmental risks and inactivity due to unconsciousness. The main research objective was to develop a Smart Home Environment (SHE) that can support risk and safety monitoring for the elderly living independently. An unobtrusive and low cost SHE solution that uses a Raspberry Pi 3 model B, a Microsoft Kinect Sensor and an Aeotec 4-in-1 Multisensor was implemented. The Aeotec Multisensor was used to measure temperature, motion, lighting, and humidity in the home. Data from the multisensor was collected using OpenHAB as the Smart Home Operating System. The information was processed using the Raspberry Pi 3 and push notifications were sent when risk situations were detected. An experimental evaluation was conducted to determine the accuracy with which the prototype SHE detected abnormal events. Evaluation scripts were each evaluated five times. The results show that the prototype has an average accuracy, sensitivity and specificity of 94%, 96.92% and 88.93% respectively. The sensitivity shows that the chance of the prototype missing a risk situation is 3.08%, and the specificity shows that the chance of incorrectly classifying a non-risk situation is 11.07%. The prototype does not require any interaction on the part of the elderly. Relatives and caregivers can remotely monitor the elderly person living independently via the mobile application or a web portal. The total cost of the equipment used was below R3000.
- Full Text:
- Date Issued: 2017
- Authors: Chiridza, Tongai
- Date: 2017
- Subjects: Multisensor data fusion , Raspberry Pi (Computer) -- Programming Adaptive computing systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14851 , vital:27880
- Description: The elderly prefer to live independently despite vulnerability to age-related challenges. Constant monitoring is required in cases where the elderly are living alone. The home environment can be a dangerous environment for the elderly living independently due to adverse events that can occur at any time. The potential risks for the elderly living independently can be categorised as injury in the home, home environmental risks and inactivity due to unconsciousness. The main research objective was to develop a Smart Home Environment (SHE) that can support risk and safety monitoring for the elderly living independently. An unobtrusive and low cost SHE solution that uses a Raspberry Pi 3 model B, a Microsoft Kinect Sensor and an Aeotec 4-in-1 Multisensor was implemented. The Aeotec Multisensor was used to measure temperature, motion, lighting, and humidity in the home. Data from the multisensor was collected using OpenHAB as the Smart Home Operating System. The information was processed using the Raspberry Pi 3 and push notifications were sent when risk situations were detected. An experimental evaluation was conducted to determine the accuracy with which the prototype SHE detected abnormal events. Evaluation scripts were each evaluated five times. The results show that the prototype has an average accuracy, sensitivity and specificity of 94%, 96.92% and 88.93% respectively. The sensitivity shows that the chance of the prototype missing a risk situation is 3.08%, and the specificity shows that the chance of incorrectly classifying a non-risk situation is 11.07%. The prototype does not require any interaction on the part of the elderly. Relatives and caregivers can remotely monitor the elderly person living independently via the mobile application or a web portal. The total cost of the equipment used was below R3000.
- Full Text:
- Date Issued: 2017
Assessing the potential impact of climate change in the south-eastern Great Escarpment, Southern Africa
- Authors: Bentley, Luke Kinross
- Date: 2017
- Subjects: Mountain plants -- Climatic factors -- Drakensberg Mountains , Mountain biodiversity -- Drakensberg Mountains , Climatic changes -- Drakensberg Mountains , Rain and rainfall -- Drakensberg Mountains , Plant diversity -- Climatic factors -- Drakensberg Mountains
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4657 , vital:20709
- Description: Rapid, anthropogenic climate change is a contemporary phenomenon which is threatening natural ecosystems. Mountains are globally important, housing high levels of plant and animal biodiversity, as well as being important suppliers of water with 50% of mountainous regions being essential for the provision of water to downstream inhabitants. Owing to their importance, an assessment of the historical, current and potential impacts of climate change on the south-eastern Great Escarpment encompassing South Africa and Lesotho is necessary and is the primary aim of this thesis. In order to assess the historical and current impacts of climate change, historical rainfall records were collected from 78 sites throughout the Eastern Cape. These records were used to determine rainfall trends and trends in the frequency of daily extreme events. Climate change projections predict increasing trends in summer and annual rainfall, and a marginal increase to a slightly decreasing trend in winter rainfall, depending on if statistically downscaled or dynamically downscaled projections are examined. Extreme events are also predicted to increase in frequency. Results showed trends which generally agree with the predictions, except for extreme events for which there was insufficient data to support the projections. This has implications for farmers in the area and validates the downscaled Regional Climate Models (RCMs) to be used for the predictive analysis determining the potential future impacts of climate change on plant species' distributions in the south-eastern Great Escarpment. In order to assess montane plant species to future climate predictions, occurrence records of 46 species were correlated to rainfall and temperature predictor variables and predictions for species richness and beta diversity were made for current and future climates. This predictive analysis used and compared two correlative species distribution modelling methods - one method used one correlating algorithm in a nuanced manner and the other method used five correlating algorithms in an ensemble. A trend of range restriction to higher elevations for the 46 species analysed was as expected from a warming climate. The nuanced, single algorithm modelling method produced less conservative models. The predicted trend of an elevational increase in montane vegetation in this region points to Lesotho and the Drakensberg highlands as being an important refugium for montane plant taxa of the southeastern Great Escarpment. The Maloti Drakensberg Transfrontier Conservation Area hence needs to be expanded and its mandate properly enforced to protect this region adequately.
- Full Text:
- Date Issued: 2017
- Authors: Bentley, Luke Kinross
- Date: 2017
- Subjects: Mountain plants -- Climatic factors -- Drakensberg Mountains , Mountain biodiversity -- Drakensberg Mountains , Climatic changes -- Drakensberg Mountains , Rain and rainfall -- Drakensberg Mountains , Plant diversity -- Climatic factors -- Drakensberg Mountains
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4657 , vital:20709
- Description: Rapid, anthropogenic climate change is a contemporary phenomenon which is threatening natural ecosystems. Mountains are globally important, housing high levels of plant and animal biodiversity, as well as being important suppliers of water with 50% of mountainous regions being essential for the provision of water to downstream inhabitants. Owing to their importance, an assessment of the historical, current and potential impacts of climate change on the south-eastern Great Escarpment encompassing South Africa and Lesotho is necessary and is the primary aim of this thesis. In order to assess the historical and current impacts of climate change, historical rainfall records were collected from 78 sites throughout the Eastern Cape. These records were used to determine rainfall trends and trends in the frequency of daily extreme events. Climate change projections predict increasing trends in summer and annual rainfall, and a marginal increase to a slightly decreasing trend in winter rainfall, depending on if statistically downscaled or dynamically downscaled projections are examined. Extreme events are also predicted to increase in frequency. Results showed trends which generally agree with the predictions, except for extreme events for which there was insufficient data to support the projections. This has implications for farmers in the area and validates the downscaled Regional Climate Models (RCMs) to be used for the predictive analysis determining the potential future impacts of climate change on plant species' distributions in the south-eastern Great Escarpment. In order to assess montane plant species to future climate predictions, occurrence records of 46 species were correlated to rainfall and temperature predictor variables and predictions for species richness and beta diversity were made for current and future climates. This predictive analysis used and compared two correlative species distribution modelling methods - one method used one correlating algorithm in a nuanced manner and the other method used five correlating algorithms in an ensemble. A trend of range restriction to higher elevations for the 46 species analysed was as expected from a warming climate. The nuanced, single algorithm modelling method produced less conservative models. The predicted trend of an elevational increase in montane vegetation in this region points to Lesotho and the Drakensberg highlands as being an important refugium for montane plant taxa of the southeastern Great Escarpment. The Maloti Drakensberg Transfrontier Conservation Area hence needs to be expanded and its mandate properly enforced to protect this region adequately.
- Full Text:
- Date Issued: 2017
Urban resilience determinants with specific reference to the Buffalo City Metropolitan Municipality, East London
- Authors: Ntakana, Khululekani
- Date: 2017
- Subjects: City planning -- South Africa -- East London Sustainable development -- South Africa -- East London , Regional planning -- South Africa -- East London Infrastructure (Economics) -- South Africa -- East London -- Planning
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/19495 , vital:28886
- Description: The year 1994 marked the dawn of the new democratic South Africa, bringing its own set of challenges to the country. Currently urban areas cover only one and a half percent of South Africa’s surface area. However, sixty one percent of South Africans live in urban areas. Furthermore, the average growth rate for urban areas has been consistently higher than the population growth rate during the period from 1998 to 2008. This resulted in larger towns and cities, growing at the expense of rural areas, with metropolitan areas experiencing the highest influx, followed by secondary cities. However, urban areas consume more water, food, energy, and durable goods, and have an impact far beyond the urban boundaries. This directly relates to urban decline. The rapid influx of people into urban areas that are already overcrowded with large service delivery backlogs, has led to the formation of informal settlements in exposed locations. Many of the informal dwellings in South Africa are subjected to environmental factors. The absence of basic services in overcrowded areas is linked to negative health outcomes and enhanced environmental degradation. This study is a critical review of a phenomenon named urban resilience. The report seeks to highlight the current status in cities and the transformation that cities need to undergo to enable them to become the cities of tomorrow. Indeed, “sustainable future cities and human settlements begin today”. The paper raises arguments on urban resilience by different theorists, philosophers, academics and scholars. The study proceeds to unpack the urban resilience determinants. Furthermore, the challenges cites will experience in responding to rapid urbanisation and their denial attitude to informal settlement and environmental degradation, which include how cities respond to climate change, are under investigation . The purpose of the study is to share the theoretical framework relative to the urban resilience determinants, with the intention to solicit criticism on gaps and blind spots. This is done with specific reference to Buffalo City Municipality. This study aims to contribute to the goals of municipalities by improving understanding of the drivers of urban resilience. This will, in turn, enable a city system to withstand and recover quickly from multiple and diverse shocks and stresses, and improve its performance over time. However, this study was conducted within a qualitative paradigm. The study followed a non-probability sampling technique. Categories of data sources were identified based on their probability to hold information that is crucial to the study. For each category, this study followed a 50 + 1 rule for sampling size when the population of the data sources were identified and access gained. he statistical software (SPSS) supported by a qualified statistician was used to analyse data qualitatively in attempt to answer the research question.
- Full Text:
- Date Issued: 2017
- Authors: Ntakana, Khululekani
- Date: 2017
- Subjects: City planning -- South Africa -- East London Sustainable development -- South Africa -- East London , Regional planning -- South Africa -- East London Infrastructure (Economics) -- South Africa -- East London -- Planning
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/19495 , vital:28886
- Description: The year 1994 marked the dawn of the new democratic South Africa, bringing its own set of challenges to the country. Currently urban areas cover only one and a half percent of South Africa’s surface area. However, sixty one percent of South Africans live in urban areas. Furthermore, the average growth rate for urban areas has been consistently higher than the population growth rate during the period from 1998 to 2008. This resulted in larger towns and cities, growing at the expense of rural areas, with metropolitan areas experiencing the highest influx, followed by secondary cities. However, urban areas consume more water, food, energy, and durable goods, and have an impact far beyond the urban boundaries. This directly relates to urban decline. The rapid influx of people into urban areas that are already overcrowded with large service delivery backlogs, has led to the formation of informal settlements in exposed locations. Many of the informal dwellings in South Africa are subjected to environmental factors. The absence of basic services in overcrowded areas is linked to negative health outcomes and enhanced environmental degradation. This study is a critical review of a phenomenon named urban resilience. The report seeks to highlight the current status in cities and the transformation that cities need to undergo to enable them to become the cities of tomorrow. Indeed, “sustainable future cities and human settlements begin today”. The paper raises arguments on urban resilience by different theorists, philosophers, academics and scholars. The study proceeds to unpack the urban resilience determinants. Furthermore, the challenges cites will experience in responding to rapid urbanisation and their denial attitude to informal settlement and environmental degradation, which include how cities respond to climate change, are under investigation . The purpose of the study is to share the theoretical framework relative to the urban resilience determinants, with the intention to solicit criticism on gaps and blind spots. This is done with specific reference to Buffalo City Municipality. This study aims to contribute to the goals of municipalities by improving understanding of the drivers of urban resilience. This will, in turn, enable a city system to withstand and recover quickly from multiple and diverse shocks and stresses, and improve its performance over time. However, this study was conducted within a qualitative paradigm. The study followed a non-probability sampling technique. Categories of data sources were identified based on their probability to hold information that is crucial to the study. For each category, this study followed a 50 + 1 rule for sampling size when the population of the data sources were identified and access gained. he statistical software (SPSS) supported by a qualified statistician was used to analyse data qualitatively in attempt to answer the research question.
- Full Text:
- Date Issued: 2017
Synthesis, characterisation and evaluation of novel ferrocene-thiazole derivatives as antiplasmodial agents
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96068 , vital:31232
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
- Date Issued: 2017
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96068 , vital:31232
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
- Date Issued: 2017
Interactions between two biological control agents released on Pereskia aculeata Miller (Cactaceae), in South Africa
- Authors: Mnqeta, Zezethu
- Date: 2017
- Subjects: Pereskia aculeata -- Biological control , Cactus -- Biological control -- South Africa , Alien plants -- Biological control -- South Africa , Flea beetles -- South Africa , Coreidae -- South Africa , Insects as biological pest control agents -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7949 , vital:21327
- Description: Pereskia aculeata Miller (Cactaceae) is an alien invasive plant introduced into South Africa from Brazil, which has negative impacts on native biodiversity in South Africa. Phenrica guerini Bechyne (Chrysomelidae) and Catorhintha schaffneri Brailovsky & Garcia (Coreidae) are two biological control agents released against P. aculeata in South Africa. Phenrica guerini was first released against P. aculeata, in 1991, followed by C. schaffneri in 2014. The overall aim of this study was to improve the biological control programme against P. aculeata in order to decrease its density to a level where it does not threaten the native biodiversity of South Africa. The first part of this study evaluated the efficacy of P. guerini on P. aculeata at Port Alfred (Eastern Cape) to better understand the role of P. guerini in the biological control of P. aculeata. An insecticide exclusion experiment was conducted over 100 days. Plots with P. guerini had a mean of 187 (SE ± 62) fewer leaves/m2 than plots without P. guerini. The agent reduced percentage cover in plots with P. guerini, with a mean of 19.42% (SE ± 3.15) lower cover than plots without P. guerini. Although P. guerini had an impact on P. aculeata at Port Alfred previous studies have indicated that a reduction to below 50% cover is required for native biodiversity to recover and the agent only reduced cover to 62% at Port Alfred. Phenrica guerini has therefore not reduced percentage cover sufficiently to completely control the weed. The data collected from Port Alfred was compared to the performance of the agent nationwide. Although P. guerini was found at far more sites than previously recorded, there were very few sites with comparable levels of damage to Port Alfred. This evidence suggests that P. guerini is not sufficiently damaging to reduce P. aculeata to acceptable levels and other biological control agents should be considered.Interactions between two biological control agents can have complex and unexpected impacts for a biological control programme. The second part of this study was to investigate interactions between C. schaffneri and P. guerini under laboratory conditions to test whether the two agents, individually or jointly, enhanced or reduced their impact on P. aculeata. Potted P. aculeata plants were exposed to one of four treatments: control (no agents), P. guerini only, C. schaffneri only and both species in combination. Four stocking densities, ranging from 2 to 12 insects per plant were used. Catorhintha schaffneri alone at high densities was more damaging than all other treatments with a significantly greater reduction in the mean number of leaves, 11.7 (SE ± 1.29), and shoot lengths, 2.17cm (SE ± O. 75). Even at lower density treatments, the combination of the two agents was not significantly more damaging than C. schaffneri alone and C. schaffneri was always more damaging than P. guerini alone. Mortality of P. guerini was significantly higher than C. schaffneri at the highest stocking density when in combination. Phenrica guerini contributes towards the biological control of P. aculeata at some sites in South Africa but not enough to completely control the weed. The antagonistic interaction between P. guerini and C. schaffneri suggests that these agents should not be released together because this would impact negatively on the overall biocontrol programme against P. aculeata. Catorhintha schaffneri should be released at sites were P. guerini is not present and evaluations of the success of this agent in the field should be conducted. Extrapolation of laboratory-based studies into the field is often challenging so mass-rearing of P. guerini should continue until there is convincing proof that C. schaffneri alone is more effective than P. guerini in the field.
- Full Text:
- Date Issued: 2017
- Authors: Mnqeta, Zezethu
- Date: 2017
- Subjects: Pereskia aculeata -- Biological control , Cactus -- Biological control -- South Africa , Alien plants -- Biological control -- South Africa , Flea beetles -- South Africa , Coreidae -- South Africa , Insects as biological pest control agents -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7949 , vital:21327
- Description: Pereskia aculeata Miller (Cactaceae) is an alien invasive plant introduced into South Africa from Brazil, which has negative impacts on native biodiversity in South Africa. Phenrica guerini Bechyne (Chrysomelidae) and Catorhintha schaffneri Brailovsky & Garcia (Coreidae) are two biological control agents released against P. aculeata in South Africa. Phenrica guerini was first released against P. aculeata, in 1991, followed by C. schaffneri in 2014. The overall aim of this study was to improve the biological control programme against P. aculeata in order to decrease its density to a level where it does not threaten the native biodiversity of South Africa. The first part of this study evaluated the efficacy of P. guerini on P. aculeata at Port Alfred (Eastern Cape) to better understand the role of P. guerini in the biological control of P. aculeata. An insecticide exclusion experiment was conducted over 100 days. Plots with P. guerini had a mean of 187 (SE ± 62) fewer leaves/m2 than plots without P. guerini. The agent reduced percentage cover in plots with P. guerini, with a mean of 19.42% (SE ± 3.15) lower cover than plots without P. guerini. Although P. guerini had an impact on P. aculeata at Port Alfred previous studies have indicated that a reduction to below 50% cover is required for native biodiversity to recover and the agent only reduced cover to 62% at Port Alfred. Phenrica guerini has therefore not reduced percentage cover sufficiently to completely control the weed. The data collected from Port Alfred was compared to the performance of the agent nationwide. Although P. guerini was found at far more sites than previously recorded, there were very few sites with comparable levels of damage to Port Alfred. This evidence suggests that P. guerini is not sufficiently damaging to reduce P. aculeata to acceptable levels and other biological control agents should be considered.Interactions between two biological control agents can have complex and unexpected impacts for a biological control programme. The second part of this study was to investigate interactions between C. schaffneri and P. guerini under laboratory conditions to test whether the two agents, individually or jointly, enhanced or reduced their impact on P. aculeata. Potted P. aculeata plants were exposed to one of four treatments: control (no agents), P. guerini only, C. schaffneri only and both species in combination. Four stocking densities, ranging from 2 to 12 insects per plant were used. Catorhintha schaffneri alone at high densities was more damaging than all other treatments with a significantly greater reduction in the mean number of leaves, 11.7 (SE ± 1.29), and shoot lengths, 2.17cm (SE ± O. 75). Even at lower density treatments, the combination of the two agents was not significantly more damaging than C. schaffneri alone and C. schaffneri was always more damaging than P. guerini alone. Mortality of P. guerini was significantly higher than C. schaffneri at the highest stocking density when in combination. Phenrica guerini contributes towards the biological control of P. aculeata at some sites in South Africa but not enough to completely control the weed. The antagonistic interaction between P. guerini and C. schaffneri suggests that these agents should not be released together because this would impact negatively on the overall biocontrol programme against P. aculeata. Catorhintha schaffneri should be released at sites were P. guerini is not present and evaluations of the success of this agent in the field should be conducted. Extrapolation of laboratory-based studies into the field is often challenging so mass-rearing of P. guerini should continue until there is convincing proof that C. schaffneri alone is more effective than P. guerini in the field.
- Full Text:
- Date Issued: 2017
Calibration and imaging with variable radio sources
- Authors: Mbou Sob, Ulrich Armel
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/37977 , vital:24721
- Description: Calibration of radio interferometric data is one of the most important steps that are required to produce high dynamic range radio maps with high fidelity. However, naive calibration (inaccurate knowledge of the sky and instruments) leads to the formation of calibration artefacts: the generation of spurious sources and the deformations in the structure of extended sources. A particular class of calibration artefacts, called ghost sources, which results from calibration with incomplete sky models has been extensively studied by Grobler et al. (2014, 2016) and Wijnholds et al. (2016). They developed a framework which can be used to predict the fluxes and positions of ghost sources. This work uses the approach initiated by these authors to study the calibration artefacts and ghost sources that are produced when variable sources are not considered in sky models during calibration. This work investigates both long-term and short-term variability and uses the root mean square (rms) and power spectrum as metrics to evaluate the “quality” of the residual visibilities obtained through calibration. We show that the overestimation and underestimation of source flux density during calibration produces similar but symmetrically opposite results. We show that calibration artefacts from sky model errors are not normally distributed. This prevents them from being removed by employing advanced techniques, such as stacking. The power spectrums measured from the residuals with a variable source was significantly higher than those from residuals without a variable source. This implies advanced calibration techniques and sky model completeness will be required for studies such as probing the Epoch of Reoinization, where we seek to detect faint signals below thermal noise.
- Full Text:
- Date Issued: 2017
- Authors: Mbou Sob, Ulrich Armel
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/37977 , vital:24721
- Description: Calibration of radio interferometric data is one of the most important steps that are required to produce high dynamic range radio maps with high fidelity. However, naive calibration (inaccurate knowledge of the sky and instruments) leads to the formation of calibration artefacts: the generation of spurious sources and the deformations in the structure of extended sources. A particular class of calibration artefacts, called ghost sources, which results from calibration with incomplete sky models has been extensively studied by Grobler et al. (2014, 2016) and Wijnholds et al. (2016). They developed a framework which can be used to predict the fluxes and positions of ghost sources. This work uses the approach initiated by these authors to study the calibration artefacts and ghost sources that are produced when variable sources are not considered in sky models during calibration. This work investigates both long-term and short-term variability and uses the root mean square (rms) and power spectrum as metrics to evaluate the “quality” of the residual visibilities obtained through calibration. We show that the overestimation and underestimation of source flux density during calibration produces similar but symmetrically opposite results. We show that calibration artefacts from sky model errors are not normally distributed. This prevents them from being removed by employing advanced techniques, such as stacking. The power spectrums measured from the residuals with a variable source was significantly higher than those from residuals without a variable source. This implies advanced calibration techniques and sky model completeness will be required for studies such as probing the Epoch of Reoinization, where we seek to detect faint signals below thermal noise.
- Full Text:
- Date Issued: 2017