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Foraging behaviour and thermal physiology of Cape sugarbirds: sex-specific responses to temperature

  • Authors: Molepo, Mokgatla Jerry
  • Date: 2017
  • Subjects: Sexual dimorphism (Animals) , Sex differences Birds -- Behavior
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/19124 , vital:28775
  • Description: Body size (Mb) determines an animal’s energy and water demands for thermoregulation. Sexual dimorphism in Mb is common across many species, but its physiological consequences (e.g. energy and water demands) remain poorly understood. In this study, I determined if the sexually dimorphic Cape Sugarbird (Promerops cafer)–males are up to 15% larger than females, show sex-specific foraging patterns and physiological responses. To determine intraspecific variability behavioural in response to temperature, I compared flower visitation rates between male and female Cape Sugarbirds at different times of the day, and among days that varied in maximum air temperature. A total of 1207 males and 561 females were observed. Female Cape Sugarbirds visited flowers more often and continued to feed especially on hot days. Males generally dominated flower resources throughout the day, except on hot days. I also compared physiological responses in EWL, RMR and Tb between males and females at high air temperatures. There were no significant differences between the two sexes. Aggression which was overlooked appeared to have a high influence on foraging behaviour of Cape Sugarbirds. These results suggest that female Cape Sugarbirds will be more prone to energy and water stress during hot and dry summers in the Fynbos region because of resource dominance by male Cape Sugarbirds. Endemic birds, such as the Cape Sugarbird, warrant a conservation priority, especially since they are the dominant pollinator of the Protea plants in the Fynbos biome. The findings of this study will provide insights into population persistence of Cape Sugarbirds in response to predicted heat waves and rise in global temperatures.
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  • Date Issued: 2017

Foraging ecology of gentoo penguins pygoscelis papua at the Falkland Islands

  • Authors: Handley, Jonathan Murray
  • Date: 2017
  • Subjects: Gentoo penguin -- Food -- Falkland Islands Gentoo penguin -- Ecology
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/14113 , vital:27431
  • Description: Marine top predators often occupy broad geographical ranges that encompass varied habitats. Therefore, a pre-requisite towards conserving these animals is to determine the components of their realized niche, and investigate whether a species is a specialist or a generalist. For generalist species, it is also necessary to understand if local specialisation occurs. Uncovering these components can allow us to build models of a species realized niche that may then be used to infer habitat use in unsampled locations. However, fully understanding the components of a marine top predators realized niche is challenging owing to the limited opportunity for in situ observations. Overcoming these limitations is a key step in marine top predator research. It will enhance our understanding of trophic coupling in marine systems, and aid in the development of tools to better study these predators in their dynamic environment. Seabirds, penguins (Spheniscids) in particular, are a group of animals for which investigating their realized niche is of vital importance. This is because numerous species face growing uncertainty in the Anthropocene, and in a time of rapid environmental change there is furthermore a need to better understand the potential use of these birds as indicators of ecosystem health. The aim of this thesis, therefore, is to investigate the foraging ecology of gentoo penguins (Pygoscelis papua) at the Falkland Islands. At the Falkland Islands, limited historical information exists regarding this species foraging ecology, with most information coming from a single location at the Falklands. As the Falkland Islands have the world’s largest population of gentoo penguins, elucidating factors influencing this population will have global relevance. Furthermore, historical information indicated potential competition with fisheries, and with prospecting for hydrocarbons and an inshore fishery, there is a need to understand the distribution of these birds across the islands. Penguins are also well suited to carry biologging devices allowing for in situ observations of inter and intraspecific interactions, as well as habitat specific interactions. In this study, I sampled birds over three breeding seasons, from four breeding colonies - chosen for their varied surrounding at sea habitat - across the Falkland Islands. I investigated the diet with stomach content and stable isotope analysis, the at-sea distribution with GPS and time depth recorders, and how these birds behaved at sea using custom made animal-borne camera loggers. Furthermore, I developed a method to recognise prey encounter events from back mounted accelerometers, using a supervised machine learning approach. As part of the first species specific description of diet at this scale for the Falklands, I revealed six key prey items for the birds: rock cod (Patagonotothen spp.), lobster krill (Munida spp.), Falkland herring (Sprattus fuegensis), Patagonian squid (Doryteuthis gahi), juvenile fish (likely all nototheniids), and southern blue whiting (Micromesistius australis). The use of animal-borne camera loggers verified that not only do gentoo penguins consume a diverse array of prey items, but they adopted various methods to capture and pursue prey, with evidence of birds following optimal foraging theory. Prey composition varied significantly between study sites with the at-sea distribution and habitat use of penguins reflecting that of local prey. Birds from colonies close to gently sloping, shallow waters, foraged primarily in a benthic manner and had larger niche widths. However, those at a colony surrounded by steeply sloping, deeper waters, typically foraged in a pelagic manner. Contrasting diet patterns were also prevalent from stable isotope data, and the niche widths of birds relating to both stomach content and stable isotope data were larger at colonies where benthic foraging was prevalent. Therefore, it was clear that surrounding bathymetry played a key role in shaping this species’ foraging ecology, and that at the population level at the Falkland Islands birds are generalists. However, at individual colonies some specialisation occurs to take advantage of locally available prey. I developed habitat distribution models - via boosted regression trees – which transferred well in time but poorly across space. Reasons for poor model transfer might relate to the generalist foraging nature of these birds and the reduced availability of environmental predictors owing to the limited range of these birds. I furthermore developed a method to identify prey encounter events that can also, to a degree, distinguish between prey items. This method will be a promising approach to refine habitat distribution models in future. These habitat distribution models could potentially contribute to marine spatial planning at the Falkland Islands. Footage from animal-borne camera loggers clearly showed that prey behaviour can significantly influence trophic coupling in marine systems and should be accounted for in studies using marine top predators as samplers of mid to lower trophic level species. Ultimately, flexibility in foraging strategies and inter-colony variation will play a critical role when assessing factors such as interspecific competition or overlap with anthropogenic activities.
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  • Date Issued: 2017

Freshwater invertebrate assemblages of the Eastern Cape Karoo region (South Africa) earmarked for shale gas exploration

  • Authors: Mabidi, Annah
  • Date: 2017
  • Subjects: Invertebrates -- South Africa -- Karoo , Shale gas -- Conservation -- South Africa -- Karoo Freshwater animals -- South Africa -- Karoo Stream ecology -- South Africa -- Karoo
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/13713 , vital:27301
  • Description: The Eastern Cape Karoo region is semi-arid with highly variable rainfall. This variability in rainfall sustains a mosaic of surface freshwater bodies that range from permanently to temporarily inundated. These waterbodies provide habitats for diverse invertebrate assemblages. The imminent hydraulic fracturing for shale gas has a potential to modify the water regime, with particular risk of salinisation. Accumulation of salts in freshwater wetlands results in loss of biodiversity, as invertebrate species shift from salt intolerant to salt tolerant species. This study therefore aims to expand on existing knowledge and provide new information on the distribution, diversity and structure of macroinvertebrate assemblages associated with various freshwater bodies in the region prior to shale gas exploration. Limnological and ecological aspects of thirty-three waterbodies (rivers, dams and depression wetlands) were investigated between November 2014 and March 2016. An experimental study on the effects of salinity on hatching success of branchiopod resting eggs was also included in the research. Rivers were characterised by high conductivity and depression wetlands by high turbidity, while dams had relatively higher pH than the other two waterbody types. In terms of global phosphorus interpretation guidelines, the results indicate that freshwater systems in the study region are predominantly eutrophic, indicating that agricultural run-off, particularly from livestock dung (goats, cattle and sheep), is an important source of phosphorus in the freshwater systems studied. Our results revealed new distribution records for branchiopod crustaceans in the Eastern Cape region, including the first record of Laevicaudata. Results showed that the sampled variables were unable to explain the variation in physicochemistry and invertebrate assemblage of several sites. Waterbody type, whether a depression wetland or a river, was the only factor that consistently showed an effect on the composition of both physicochemical data and invertebrate data. Depression wetlands ranged from completely bare to being extensively covered by macrophytes. Therefore, the effect of macrophyte cover in structuring macroinvertebrate assemblages was the focus of further investigation. The results indicated that the macrophyte cover gradient had little influence on the structure of the invertebrate assemblages in the depression wetlands, while only the presence/absence of vegetation significantly influenced the structure of the invertebrate assemblages in these systems. Surface area, dissolved inorganic nitrogen and pelagic chlorophyll-a were the environmental variables that best explained the variation in the macroinvertebrate assemblages among the sites. However, the differences in macroinvertebrate richness, abundance and distribution patterns among sites were only weakly influenced by local and regional environmental factors. These findings suggest that invertebrate in temporary wetland systems are adapted to the highly variable nature of temporary habitats, thus the influence of local variables is negligible. Results of the experimental study, on the effect of salinity on hatching success of branchiopod resting eggs, revealed that hatchling abundance and diversity of large branchiopods was significantly reduced at salinities of 2.5 g L−1 and above. Salt-tolerant taxa such as Copepoda and Ostracoda were the only ones to emerge in the highest salinity of 10 g L−1. Thus, should the region continue to experience increasing aridity and possible shale gas development, which all aggravate the salinisation problem, severe loss of branchiopod diversity (Anostraca, Laevicaudata, Spinicaudata and Notostraca) is likely to occur. This may lead to considerable decline in invertebrate diversity in the region, with cascading effects on food webs and ecosystem functions. The findings of this study can potentially be used in comparative studies on wetland invertebrate ecology in other semi-arid regions and in the formulation of policy and strategies for biodiversity conservation.
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  • Date Issued: 2017

Gypsum deposits associated with the Whitehill Formation (Ecca Group) in the Steytlerville-Jansenville Area, Southern Karoo, South Africa

  • Authors: Almanza, Roberto Daniel
  • Date: 2017
  • Subjects: Gypsum -- South Africa Concretions -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/15292 , vital:28215
  • Description: The Steyterville-Jansenville gypsum field is one of South Africa’s smaller deposits, yet plays host to several gypsum mines, both past and present. This study aims to deconstruct the processes involved in the precipitation of various quantities and grades of gypsum in the lower Ecca Group of the Karoo Supergroup. The calcium and sulphate ions required to form the gypsum mineral (CaSO4•2H2O) are derived from the mid- to lower-shale of the Whitehill Formation, which is carbonate- and pyrite-rich. Gypsum formation is dependent on the availability of pyrite as opposed to calcite, which is in abundance throughout the 30m thick, Early Ufimian (late Permian) Whitehill Formation. Weathered shale, which has been folded and faulted, forms the host environment in which gypsum has precipitated. Folding of the shale occurs as a series of large- and medium-scale anticlines and synclines that strike east to west. These structures, which formed during the Cape Orogeny indicate that stresses were exerted from the south-southwest towards the north-northeast. Folded calcite veins surrounded by amorphous pyrite, observed in thin section suggest that pyrite and calcite were precipitated together prior to a deformation event. Oxidation of pyrite following these deformation events results in the concentration of sulphides within the hinge zones of the folds (weakest zone) and this is where the larger gypsum deposits are found at the surface. Carbonate concretions in the Whitehill Formation up to 5m in length and 3m in width are common in the study area, and suggest a relationship with the deposition of the shale whereby calcium-rich nuclei grew in a concentric fashion during a non-depositional hiatus period. This period is also associated with a higher concentration of pyrite and could explain the occurrence of concretions together with adjacent gypsum-rich shale. Pyrite framboids observed under the Scanning Electron Microscope (SEM) provide evidence to suggest concentric growth of initially deposited microcrystals including nucleation and growth of nodules and concretions observed within the Whitehill Formation. Prerequisites for gypsum formation also include restricted drainage such as a pan, a clay layer in the drainage area and an arid climate where evaporation exceeds precipitation. The preferred surface conditions for gypsum formation would be low-lying areas which are surrounded by gently-sloping topography promoting the concentration of aqueous solutions in a calcite- and pyrite-rich area. Groundwater solution would initially dissolve the calcite and clay minerals, and pyrite and the quartz minerals would remain in the host rock. Areas with greater calcite and clay pores would accommodate more groundwater and thus promote a greater surface area for chemical reactions. This enhances the potential for the oxidation of pyrite to form sulphate ions, which can later combine with calcium ions to precipitate gypsum crystals. Alternatively, the oxidation of pyrite, which produces acidity, dissolves the carbonate host and the calcium- and sulphate-rich solution then precipitates gypsum. The combination of the structural and geomorphological processes is key to the formation of economic gypsum deposits. The potential for extensive gypsum reserves within the Steytlerville-Jansenville field remains valid, provided the target is located over a predominantly weathered Whitehill Formation outcrop, preferably in an area which has undergone extensive deformation (such as a fold hinge zone), and is favourable for the concentration of ground and surface water within a low-lying area.
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  • Date Issued: 2017

Identification and classification of micro-estuaries using selected abiotic and biotic characteristics along the Eastern Cape coast, South Africa

  • Authors: Naidoo, Lyndle Sherae
  • Date: 2017
  • Subjects: Estuarine ecology -- South Africa -- Eastern Cape Estuaries -- South Africa -- Eastern Cape
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/11920 , vital:27007
  • Description: Many of the larger estuaries along the South African coastline are highly degraded due to human impacts, highlighting the need to conserve pristine systems. There are approximately 100 micro-estuaries along our coastline which have not yet been identified or classified and hence their ecological functioning is unknown. The aim of this study was to identify and classify micro-estuaries along the Eastern Cape coast. Specific objectives of the study were to: 1) map the distribution of estuarine habitats in a selection of micro-estuaries and assess changes over time; 2) measure the physico-chemical characteristics of the micro-estuaries in the field; 3) investigate the distribution of vegetation, identify macrophyte species and habitat integrity and classify the micro-estuaries sampled using abiotic and botanical characteristics. A total of 30 systems were identified of which 10 were selected for sampling which took place seasonally (2015-2016). A relationship between open water surface area and short term rainfall was only evident in Cunge, Sandy Bottom and Ichabana. In the field it was observed that after heavy rainfall, open water surface area increased and mouth breaching occurred. Salinity was the only water column characteristic that showed differences; salinity increased in response to over wash events. Sand was dominant in all systems and there were no differences in sediment characteristics. A total of 8 macroalgal species, 16 estuarine macrophyte species, six freshwater species and 72 riparian plant species were found. Seed bank reserves were low in all systems despite them being vegetated. Only abiotic characteristics were used for classification using Principle Components Analysis since there were no botanical differences between systems. Micro-estuaries were larger (> 0.03 ha), had a higher salinity (oligohaline, mesohaline and polyhaline conditions) and a constant water body. Micro-outlets were smaller (< 0.03 ha), had a lower salinity (oligohaline conditions were most common) and showed periods of drying. Five micro-estuaries (Shelbertsstroom, Kwesani, Cunge, Mtwendwe and Mtendwe) and five micro-outlets (Stromatolite, Sandy Bottom, Ichabana, Palm Tree and Black Rock) were classified. This study has shown that the micro-estuaries along the Eastern Cape coast are pristine (i.e. intact riparian zone and catchment), untouched and highly dynamic systems (i.e. great variation in water surface area and mouth condition) highlighting their need for protection.
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  • Date Issued: 2017

Impacts of African elephant feeding on white rhinoceros foraging opportunities

  • Authors: Prinsloo, Dominique
  • Date: 2017
  • Subjects: Herbivores -- Ecology -- South Africa , Grassland ecology -- South Africa Animal-plant relationships -- South Africa Ecology
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/13768 , vital:27306
  • Description: In this study, I investigated the interaction between two megaherbivores, the African elephant and white rhinoceros, that has the potential to impact grazing lawns of which white rhino are the creators and maintainers and elephants are potentially the modifiers. I hypothesized that as elephants browse, they discard a variety of coarse woody debris onto the ground; should this woody debris (of varying amounts and sizes) fall onto grazing lawns, white rhino either move them, consume grass around the woody debris or abandon the lawn entirely. If high levels of woody debris are deposited here, grazing by white rhino is likely to be prevented, at which time I predicted that mesoherbivores would have a competitive advantage in accessing forage that white rhino cannot. I examined the mechanistic links between different levels of elephant-deposited woody debris and grass response at a point scale and feeding patch spatial scale of grazing lawns in an African savanna. In addition, I assessed the response of mesoherbivores in terms of vigilance behaviour with increasing levels of predation risk posed by increasing levels of woody debris. I present the first evidence of an indirect effect of elephant on white rhino foraging behaviour. I demonstrate how increasing levels of woody debris lead to a decreasing probability of foraging by white rhino. I also demonstrate how the probability of foraging by mesoherbivores increases as the amount of forage increases. However, since this study took place during a severe drought where resources are extremely limited, I was unable to properly separate the effects of elephant-deposited woody debris from the severe lack of rainfall on grass response and subsequently herbivore foraging behaviour. Due possibly to the drought, mesoherbivores responded less or not at all to risk factors such as woody debris therefore woody debris was not a predictor of vigilance behaviour in my study. This study contributes to our understanding of how the impacts of elephants, as ecosystem engineers, have cascading effects on savanna ecosystems. My study showed that elephant impact mediates the foraging behaviour of white rhino during a drought. However, under average rainfall periods, my original hypothesized effect of the indirect impacts of elephants on white rhino foraging and grazing lawn dynamics could still hold. This key hypothesis that I was unable to test under ‘normal’ conditions due to the drought is still valid and functionally important for understanding the ecosystem processes driving grazing lawn formation, persistence and composition in African savannas where elephants and white rhinos coexist.
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  • Date Issued: 2017

Influence of sedimentological and hydrological processes on the distribution of the Spartina maritima salt marsh in the Keurbooms Estuary, Western Cape

  • Authors: Mfikili, Athi Nkosibonile
  • Date: 2017
  • Subjects: Salt marshes -- South Africa -- Western Cape Estuarine hydrology -- South Africa -- Western Cape
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/13004 , vital:27143
  • Description: Salt marshes are some of the most productive ecosystems in the world and have been the centre of attention over the past few decades, due to their decline as a result of global climate change and anthropogenic impacts. The growth of salt marshes is determined by substrate type, soil conductivity and elevation. The permanently open Keurbooms Estuary along the south-east coast of South Africa is subjected to occasional fluvial flooding and its intertidal area lacks well developed salt marshes, with Spartina maritima restricted to the lower reaches of the Bitou tributary and a few sections of the Keurbooms tributary. Presumeably because of fine sediment habitat in the confluence and lower Bitou tributary. The salinity of the estuarine water ranges between 0.1 – 26.9 and 3.2 – 35.3 in the Bitou and Keurbooms tributaries respectively. A typical salt wedge salinity pattern is common in the Keurbooms tributary where saline water often intrudes underneath the freshwater, especially during high river flows. The following hypotheses were developed and tested in this study: The limited spatial distribution of S. maritima in the Keurbooms Estuary is due to limited availability of fine sediment habitat; and the source of the fine sediment in the estuary is the Bitou tributary rather than the Keurbooms tributary or the sea. It was further postulated that after sediment characteristics, floods are the major hydrological driver determining the distribution of S. maritima in the Keurbooms Estuary. The results of the surveys of the estuarine channel bottom sediments showed that the Keurbooms tributary was mostly characterized by the sand-size sediment fraction derived from the feldspathic and sandstone with evidence of fine sediment fractions restricted to the upper reaches at the confluence with Whiskey Creek. The Bitou was almost always composed of coarse sized sediments in the upper reaches, fine sediment deposits in the middle and lower reaches and medium sorted sand with almost no clay or calcium carbonate in the estuarine component below the confluence of the tributaries. These findings were further supported by the surface sediment deposited within the S. maritima intertidal salt marsh, which showed finer sediment deposits in the Bitou marsh compared to the Keurbooms marsh surface. Similar results were also found in the sediment cores, with the Keurbooms marsh sediment becoming finer with increasing depth whereas fine sediments reduced with depth in the Bitou marsh. The results of the sediment mineralogy indicated that the increased concentrations of clay minerals in the S. maritima surface sediments are derived from the Bokkeveld shale, siltstone and clay slate exposed above the N2 Bridge in the Keurbooms Estuary. GIS mapping shows that S. maritima has been declining over the past two decades, with rapid decreases especially evident after big flooding events. The GIS mapping also indicates that the patches of the S. maritima in the Keurbooms tributary are more exposed to big floods than the Bitou marsh. Despite showing an overall decline, S. maritima area coverage remained more consistent in the lower reaches of the Bitou tributary than in the Keurbooms tributary. Despite the larger and more persistent area cover, the S. maritima plants were shorter and less dense than the plants growing in the sandy substrate. The black/grey colouration of soil with increasing depth in the Bitou tributary was an indication of the reduced state of the soil caused by prolonged waterlogged conditions. The roots of S. maritima in both tributaries were mostly restricted to the sub-surface substrate layer (i.e. 0 – 0.25 m), although the Bitou populations showed more vegetative propagation than the Keurbooms populations. This mechanism of reproduction was also demonstrated during the transplant experiment which showed a greater number of new stem production in the fine sediment substrates compared to the sandy silt substrates. Although accretion rates were not determined in this study, the short-term sediment deposition rates revealed that sedimentation is active in the marshes of the Keurbooms Estuary. Therefore, in spite of showing a decline in area cover, the production of viable seed and observed vegetative propagation suggest that the S. maritima is likely to colonize open stable intertidal mudflats / sandflats, thus maintaining its distribution as an intertidal species in the salt marshes of the Keurbooms Estuary.
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  • Date Issued: 2017

Integration of Eucalyptus coppice regeneration with mechanical harvesting in South Africa

  • Authors: Schwegman, Kylle , Ackerman, S A
  • Date: 2017
  • Subjects: Eucalyptus -- Regeneration Harvesting machinery
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/21131 , vital:29443
  • Description: In South Africa, ca. 530 000 ha of the plantation area is planted to Eucalyptus spp. which are native to Australia. Commercially grown hardwoods account for 40.5% of the total area planted to trees, yet contribute more than 70% of the timber to the pulpwood market. This is largely attributed to the superior quality of fibre and pulping properties associated with eucalypt plantations, increases in global short-fibre pulp demands. This as well as the ability to reduce the temporary unplanted period and associated re-establishment costs when choosing to regenerate a stand through coppice management. With the unlikelihood of additional eucalypts being introduced into South Africa, and a reduction in genetic gains from 3rd-4th generation tree breading programmes, most of the eucalypts currently planted will be managed for at least one coppice rotation before replanting with improved genetic material if available. This together with the increased use of mechanised silvicultural and harvesting operations, concerns have been raised as to whether the integration of Eucalyptus coppice regeneration and mechanical harvesting in South Africa is both possible and financially viable for the forest industry to practise. The need for integration becomes more important as often mechanised systems have smaller tolerance levels when compared to manual systems. The first trial was situated in Zululand and was implemented to determine the type and severity of stump damage, coppicing potential and coppice growth over the rotation, associated with four types of harvesting and extraction systems on coppice regeneration. Results obtained from these four treatments (harvesting systems that ranged from manual to fully mechanised cut-to-length systems), found that irrespective of the harvesting system used, more damage occurred to the top than bottom half of the stump, with a significant decrease in coppice regrowth with increasing stump damage. Most damage and least coppice regrowth occurred in the extraction rows where the damage recorded could be attributed to vehicle movement, tear-outs and/or log stripping. There was no significant difference between the harvesting systems in terms of stump mortality, final stem stocking and rotation-end volume. Although this trial indicates that the harvesting systems tested had no impact on tree production the severity of damage and/or difference may have been masked by the excellent coppice potential of the species used for this trial (E. grandis x E. urophylla). Based on the results obtained in the first trial, and using five existing data sets, each data set consisted of four treatment sub-sets (4m_8m_s; 2m_8m_s; 4m_8m_BOP; 2m_8m_Or) where possible to determine the cost benefits associated with each treatment at various levels of stocking over a full rotation period. BOP (best operating practice) and Or (original stocking) refers to treatments with two stems stump-1, and s (single stem) refers to one stem stump-1. Within each of the four treatment sub-sets, treatments with three levels of stump survival were sought (60%; 80%; 100%), in order to assess financial viability of harvesting different coppice regimes (one coppice stem and two coppiced stems stump-1) using a fully mechanised cut-to-length harvesting system was tested. No differences were found between one coppice stem and two coppiced stems stump-1 in terms of financial returns (internal rate of return). Of the four treatment sub-sets (4m_8m_s; 2m_8m_s; 4m_8m_BOP; 2m_8m_Or), treatments which had two coppice stems stump-1 lead to increased harvesting cost, while coppice stumps with one stem favours mechanised harvesting and reduced harvesting costs. The final trial, which was also implemented in Zululand, tested the timing of reduction of one coppice stem stump-1 at various stump and stem densities in order to develop an appropriate coppice regime that could favour fully mechanised CTL harvesting systems. Although significant differences were detected at 23 months between the additional control (current recommendation) and the various Reduction_ht (3.5 m, 4.5 m, and 6.5 m) treatments for Dbh, Ba, and Stocking. It is likely that these differences may become less with time due to the decrease in absolute and relative differences between the various treatments with time. This thesis indicates that it is possible to successfully integrate eucalypt coppice regeneration and fully mechanised CTL harvesting. As the results obtained showed that despite the harvesting-associated damage found, no significant difference occurred between the harvesting systems tested in terms of stump mortality, stem stocking (after the final reduction) and rotation-end volume. With regards to the financial implications (using internal rates of return - IRR) associated with harvesting coppice stands of one or two stems stump-1, no clear cost-benefits were found between either of these two treatment scenarios. As those factors that contribute to increased volumes per hectare (increased stem numbers and the retention of two stems stump-1), tend to become normalised across a treatment sub-set, this results in increased harvesting costs with a reduction in the IRR. Coppice management regimes need to be investigated that favour fully mechanised CTL harvesting systems (fewer stems to harvest, but with increased volumes per stem). This includes a reduction to one stem stump-1, as opposed to the current recommendations where some stumps have two stems, such as was tested in the final trial. Although initial results were promising, rotation-end data would be needed to determine any longer term impacts from carrying out an early thinning of coppice shoots to one stem stump-1. Future research needs to be carried out to: determine the influence of mechanised harvesting and extraction for difference species of eucalypts, especially for those that do not coppice as well as the species tested in these trials (Eucalyptus grandis x Eucalyptus urophylla), develop harvesting productivity and/or volume models for coppiced stands of one and two stems stump-1 for different Eucalyptus spp., determine financial returns using specifically designed coppice management regimes which optimise the integration of both mechanical harvesting and silvicultural perations.
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  • Date Issued: 2017

Maize stalk fibre reinforced natural rubber/tyre-tread reclaimed rubber composites

  • Authors: Mente, Pumza
  • Date: 2017
  • Subjects: Polymeric composites Rubber
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/19332 , vital:28852
  • Description: This research project focuses on the production of reclaimed rubber composites reinforced with natural fibres obtained from agricultural waste. The prepared natural fibre composites were characterized through evaluation of curing characteristics, tensile properties, thermal properties, dynamic mechanical properties and electron microscopy imaging. Untreated composites generally showed poor properties which were attributed to poor compatibility and fibre agglomeration. Various treatments were then employed in attempts to improve the composite properties. Fibre treatments used were water treatment and silane treatments using two different silane coupling agents. Torque, reaction rate and tensile modulus were observed to increase with addition of reclaimed rubber and natural fibres. Tensile strength and elongation at break increased with addition of natural rubber. An increase in thermal stability was observed with addition of reclaimed rubber. Dynamic mechanical analysis (DMA) results have shown that addition of reclaimed rubber resulted to an increase in glass transition temperature. Scanning electron microscopy (SEM) images of tensile fractured composites showed evidence of fibre pull-outs from the matrix. Removal of lignin from treated natural fibres was evident from thermogravimetric analysis (TGA) for all fibre treatments. There were no noticeable improvements in composites properties with use of fibre treatments and there were no statistical differences observed among the different fibre treatments. Generally, the composites prepared showed high stiffness and low tensile strength.
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  • Date Issued: 2017

Microencapsulation of anti-tuberculosis drugs using sporopollenin

  • Authors: Mhlana, Kanyisile
  • Date: 2017
  • Subjects: Mycobacterium tuberculosis -- South Africa -- Prevention Microencapsulation , Plant spores
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/13912 , vital:27357
  • Description: In this thesis, we explore the benefits of microencapsulating isoniazid and pyrazinamide within sporopollenin exine capsules derived from Lycopodium clavatum. Sporopollenin is a natural biopolymer, which is extracted from the outer shell of pollen grains. These hollow microcapsules can encapsulate and release drug actives in a controlled manner and possess many other advantages such as homogeneity in morphology and size, resilience to both strong acids and bases, they have antioxidant properties as well as UV protection to protect the material inside the microcapsule. Compared to artificial microcapsules, sporopollenin’s muco-adhesion to intestinal tissues contributes greatly to the extended contact of the sporopollenin with the intestines leading to an increased efficiency of delivery of drugs. The hollow microcapsules can be easily filled with a solution of the active or active in a liquid form by simply mixing both together. The drug actives are released in the human body depending on pH factors. Active release can otherwise have controlled by adding a coating on the shell, or co-encapsulation with the active inside the shell so that high drug concentrations are delivered to the site of infection. Encapsulation of the drug active will possibly improve therapeutic abilities of the drugs; simplify the treatment of TB-HIV coinfections by eliminating troublesome drug-drug interactions and drastically reduce or eliminates side effects. The SECs were loaded using a passive filling method. The drug active (0.1 g) was dissolved in a solvent and mixed with the SECs (0.1 g) for 10 minutes. After mixing for 10 minutes, the solvent was removed by a rotary evaporator and dried to a constant mass. The surface of the sporopollenin exines were analysed on a FTIR to observe if there are any drug deposits on the surface of the SECs. The loading efficiency and drug release percentage was determined by using calibrations curves and analysed on a UV-vis spectrophotometer. Further work has been proposed in which to characterize the SECs further and producing coated tablets from loaded SECs.
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  • Date Issued: 2017

Microstructure and properties of zirconium silicide surface layers on zirlo for improved nuclear fuel cladding

  • Authors: Ngongo, Sinoyolo
  • Date: 2017
  • Subjects: Zirconium alloys Zirconium
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/20098 , vital:29107
  • Description: Zirconium alloys have important applications as nuclear reactor fuel cladding material. In this study the microstructure and properties of zirconium silicide synthesized by heating ZIRLO (which is an alloy of zirconium and niobium) in contact with silicon powder has been investigated. The silicide acts as a coating layer to protect the ZIRLO from oxidation which is associated with hydrogen pick-up. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the morphology and crystal structure of the silicides respectively. Heating of ZIRLO with silicon powder was carried out in a Webb 89 Vacuum Furnace for various temperatures (1000–1400 °C) and times (4–8 hours) in an argon atmosphere or under vacuum, which resulted in the diffusion of silicon into the ZIRLO and the formation of zirconium silicide layers. The sample heat treated for 8 hours at 1000 °C did not show any evidence of inter-diffusion between the ZIRLO and silicon, this suggests that a temperature of 1000 °C is not sufficient to facilitate the formation of a silicide layer. The formation of the silicide layer was however observed after heat treatments at 1200 °C and 1400 °C using SEM and TEM. The silicide formed at 1200 °C as a layer on the ZIRLO sample and voids were observed in this layer, most likely due to the Kirkendall effect which occurs in solid state diffusion. The results suggest that Zr has a larger flux than Si as the voids formed in the ZIRLO. The temperature of 1400 °C appears to exceed the ideal required for silicide formation on the surface of ZIRLO, since the silicon infiltrated very far into the ZIRLO and in fact reacted with the entire ZIRLO sample. Both these samples were heat treated for 8 hours in an argon atmosphere. Silicide layers without voids were obtained in the case where ZIRLO and Si were heat treated for 8 and 4 hours at 1200 °C in an argon atmosphere and under vacuum respectively. The average penetration rate, calculated from the aforementioned heat treatments, of Si into Zr was calculated to be 4.5 μm/hour. The diffusion coefficient of Si in Zr was also estimated and it differs by about a factor of 104 from the reported value Zr into Si diffusion coefficient.
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  • Date Issued: 2017

Optical fibre measurement for clock tones in telescope networks

  • Authors: Dlamini, Phumla Patience
  • Date: 2017
  • Subjects: Fiber optics Very large array telescopes
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/22200 , vital:29872
  • Description: Astronomy dates back to the early man’s impression of the heavens with little information recorded including some drawings of comets, eclipse and supernovas[1]. Major progress has been made in the field of Astronomy since then. Scientific curiosity to probe the universe in attempt to answer questions such as the origin of the universe, the matter it is made of, the formation of stars, planets and galaxies, and tracking life in other solar systems has brought about the need for more advanced tools capable of detailed observations. In 1608 H. Lippershey developed the first refracting telescope[2], [3]. A year later Galileo used a similar telescope pointing skywards discovering mountains and craters on the earth’s moon, the moons of Jupiter and the phases of Venus. Over the years telescopes have been developed with advancements from the optical telescope towards much larger and more sensitive radio telescopes. The first radio signal from space was detected by Karl Jansky and ever since then astronomers have been using radio telescopes to explore the universe by detecting radio waves emitted by cosmic objects[4]. The ability of radio telescopes to detect weak signals is related to the signal capture surface. As the demand for sensitivity, transmission bandwidth and data rate increases, so does the need for telescopes with a large field of view and capability to observe different parts of the sky at once[5]. This is possible with radio telescope array, with the data from the antennas combined electronically to produce a high resolution image of the sky. The South African MeerKAT radio telescope is an array of 64 interlinked antennas each transmitting up to 160 Gbps of data to the central processing site over optical fibre which is ideal for carrying large volumes of data at high speeds. The MeerKAT telescope is a precursor to the Square kilometer Array which will have up to 50 times the sensitivity and 10000 times the survey speed than the best telescope[6].
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  • Date Issued: 2017

Optimal cycle dating of large financial time series

  • Authors: Kapp, Konrad Phillip
  • Date: 2017
  • Subjects: Computer algorithms
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/17767 , vital:28452
  • Description: The study of cycles in the context of economic time series has been active for many decades, if not centuries; however, it was only in recent decades that more formal approaches for identifying cycles have been developed. Litvine and Bismans (2015) proposed a new approach for dating cycles in financial time series, for purposes of optimising buysell strategies. In this approach, cycle dating is presented as an optimisation problem. They also introduced a method for optimising this problem, known as the hierarchical method (using full evaluation 2, or HR-FE2). However, this method may be impractical for large data sets as it may require unacceptably long computation time. In this study, new procedures that date cycles using the approach proposed by Litvine and Bismans (2015), were introduced, and were speciffically developed to be feasible for large time series data sets. These procedures are the stochastic generation and adaptation (SGA), buy-sell adapted Extrema importance identity sequence retrieval (BSA-EIISR) and buysell adapted bottom-up (BSA-BU) methods. An existing optimisation technique, known as particle swarm optimisation (PSO), was also employed. A statistical comparison was then made between these methods, including HR-FE2. This involved evaluating, on simulated data, the performance of the algorithms in terms of objective function value and computation time on different time series lengths, Hurst exponent, and number of buy-sell points. The SRace methodology (T. Zhang, Georgiopoulos, and Anagnostopoulos 2013) was then applied to these results in order to determine the most effcient methods. It was determined that, statistically, SGA, BSA-EIISR and BSA-BU are the most effcient methods. Number of buysell points was found to have the largest effect on relative performance of these methods. In some cases, the Hurst exponent also has a small effect on relative performance.
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  • Date Issued: 2017

Optimising syzygium cordatum dye extraction and subsequent cotton dyeing incorporating organic electrolytes

  • Authors: Gamedze, Nombuso Faith
  • Date: 2017
  • Subjects: Dyes and dyeing -- Cotton Syzygium cordatum
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/19509 , vital:28888
  • Description: The present investigation was carried out to optimize the extraction of natural dye from Syzygium cordatum,bark trees and then to evaluate its use in the dyeing of cotton fabric incorporating organic electrolyte. The bark was collected from recently fallen trees and twigs pruned from old trees, since they have greater dye content than the younger trees, dried for two weeks, crushed with a hammer and ground into powder. Grinding of bark was done to ensure a uniform particle size with a large surface area to facilitate quick extraction. The relevant conditions for natural dye extraction using a methanol/water mixture were optimized by Response Surface Methodology (RSM), with the help of Design Expert Version 7.0. The central composite design (CCD) was applied to design experiments for the evaluation of the interactive effects of the three most important operating extracting variables namely, temperature, time and liquor volume on 25g bark powder. This approach decreased the required number of experiments, and the following optimized extraction conditions were derived; temperature 700C, time 51minutes and material-to-liquor ratio 1:16. Dye used for subsequent dyeing was extracted using the optimized conditions. To determine the best conditions for dyeing cotton fabric with the dye extract, dyeing was carried out in a rotating canister machine, using two different organic electrolytes, namely trisodium nitrilo triacetate (trisodium NTA) and dimethylformamide, as mordants. The use of organic electrolytes, as mordants, was to ensure eco-friendliness of the dyeing, and with a maximum concentration of 3g/L being used to reduce the effluent load. Three different mordanting techniques, namely simultaneous, pre-mordanting and post-mordanting were investigated so as to establish which is best. The impact of the two organic electrolyte mordants on certain physical properties of the cotton fabric was also determined. The dyeing of cotton with theSyzygium cordatum bark dye extract, in conjuction with an organic electrolyte, generally showed good results, with trisodium NTA superior to dimethylformamide as a mordant. An increase in trisodium NTA mordant concentration increased dye exhaustion and a dye exhaustion of 23.7% being achieved with 3g/L pre-mordanting. This is still relatively low, however, and the use of an exhausting agent needs to be explored. The fabric dyed with a mordant, exhibited good wash, rub and perspiration fastness, with trisodium NTA superior to dimethylformamide. The use of trisodium NTA increased the strength of the dyed fabric whereas the use of dimethylformamide decreased it. In general, pre- and simultaneous mordants were better than post-mordanting. It has been shown that the dyeing of cotton, using Syzygium cordatum bark dye extract, in conjuction with an organic electrolyte, particulary trisodium NTA, has potential and can be recommended for craft applications. Optimised conditions for dye extraction and cotton dyeing have been derived and which can be recommended for use by crafters in Swaziland.
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  • Date Issued: 2017

Optimization of flexible spectrum in optical transport networks

  • Authors: Boiyo, Duncan Kiboi , Gamatham, Romeo
  • Date: 2017
  • Subjects: Digital communications Optical fiber communication , Optical communications Fiber optics
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/14609 , vital:27803
  • Description: The ever-increasing demand for broadband services by end-user devices utilising 3G/4G/LTE and the projected 5G in the last mile will require sustaining broadband supply from fibre-linked terminals. The eventual outcome of the high demand for broadband is strained optical and electronic devices. The backbone optical fibre transport systems and techniques such as dense wavelength division multiplexing (DWDM), higher modulation formats, coherent detection and signal amplification have increased both fibre capacity and spectrum efficiency. A major challenge to fibre capacity and spectrum efficiency is fibre-faults and optical impairments, network management, routing and wavelength assignment (RWA). In this study, DWDM and flexible spectrum techniques such as wavelength assignment and adjustment, wavelength conversion and switching, optical add and drop multiplexing (OADM) and bitrate variable transmission have been experimentally optimized in a laboratory testbed for short- and long-haul optical fibre networks. This work starts by experimentally optimising different transmitters, fibre-types and receivers suitable for implementing cost effective and energy efficient flexible spectrum networks. Vertical cavity surface-emitting lasers (VCSELs) and distributed feedback (DFB) lasers have been studied to provide up to 10 Gb/s per channel in 1310 nm and 1550 nm transmission windows. VCSELs provide wavelength assignment and adjustment. This work utilises the non-return-to-zero (NRZ) on-off keying (OOK) modulation technique and direct detection due to their cost and simplicity. By using positive intrinsic negative (PIN) photo-receivers with error-free BER sensitivity of -18±1 dBm at the acceptable 10-9-bit error rate (BER) threshold level, unamplified transmission distances between 6 km and 76 km have been demonstrated using G.652 and G.655 single mode fibres (SMFs). For the first time, an all optical VCSEL to VCSEL wavelength conversion, switching, transmission at the 1550 nm window and BER evaluation of a NRZ data signal is experimentally demonstrated. With VCSEL wavelength conversion and switching, wavelength adjustments to a spectrum width of 4.8 nm (600 GHz) can be achieved to provide alternative routes to signals when fibre-cuts and wavelength collision occurs therefore enhancing signal continuity. This work also demonstrates a technique of removing and adding a wavelength in a bundle of DWDM and flexible channels using an OADM. This has been implemented using a VCSEL and a fibre Bragg grating (FBG) providing a wavelength isolation ratio of 31.4 dB and ~0.3 𝑑𝐵 add/drop penalty of 8.5 Gb/s signal. As a result, an OADM improves spectrum efficiency by offering wavelength re-use. Optical impairments such as crosstalk, chromatic dispersion (CD) and effects of polarization mode dispersion (PMD) have been experimentally investigated and mitigated. This work showed that crosstalk penalty increased with fibre-length, bitrate, interfering signal power and reduced channel spacing and as a result, a crosstalk-penalty trade-off is required. Effects of CD on a transmitted 10 Gb/s signal were also investigated and its mitigation techniques used to increase the fibre-reach. This work uses the negative dispersion fibres to mitigate the accumulated dispersion over the distance of transmission. A 5 dB sensitivity improvement is reported for an unamplified 76 km using DFB transmitters and combination of NZDSF true-wave reduced slope (TW-RS) and submarine reduced slope (TW-SRS) with + and – dispersion coefficients respectively. We have also demonstrated up to 52 km 10 Gb/s per channel VCSEL-based transmission and reduced net dispersion. Experimental demonstration of forward Raman amplification has achieved a 4.7 dB on-off gain distributed over a 4.8 nm spectral width and a 1.7 dB improvement of receiver sensitivity in Raman-aided 10 Gb/s per wavelength VCSEL transmission. Finally, 4.25-10 Gb/s PON-based point to point (P2P) and point to multipoint (P2MP) broadcast transmission have been experimentally demonstrated. A 10 Gb/s with a 1:8 passive splitter incurred a 3.7 dB penalty for a 24.7 km fibre-link. In summary, this work has demonstrated cost effective and energy efficient potential flexible spectrum techniques for high speed signal transmission. With the optimized network parameters, flexible spectrum is therefore relevant in short-reach, metro-access and long-haul applications for national broadband networks and the Square Kilometre Array (SKA) fibre-based signal and data transmission.
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  • Date Issued: 2017

Phylogeny and phylogeography of dominant South African surf diatoms

  • Authors: Du Preez, Debbie Patricia
  • Date: 2017
  • Subjects: Phylogeography -- South Africa , Diatoms -- South Africa Phylogeny -- Molecular aspects DNA -- Analysis
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/29794 , vital:30778
  • Description: Genetic studies of diatoms are lagging behind those on other organisms. The reasons for this are, among others, that many species are difficult to culture (some surf diatoms in particular), single cells contain only a small amount of DNA, and selection of single cells from environmental samples is difficult. Globally, there are only a few species of surf diatom: Anaulus australis Drebes et Schultz, Asterionellopsis glacialis (Castracane) Round, Asterionellopsis socialis (Lewin & Norris) Crawford & Gardner, Attheya armata (West) Crawford, Aulacodiscus petersii Ehrenberg, Aulacodiscus johnsonii Arnott, Aulacodiscus kittonii Arnott ex Ralfs and Aulacodiscus africanus Cottam. These species occur exclusively in the surf zone with the exception of A. glacialis, which is also found in coastal and oceanic waters. The overall aim of this project was to investigate the phylogeny or the phylogeography of the two dominant South African surf diatoms. In order to do this, it was necessary to develop methods for extracting DNA from environmental surf diatom patch samples. This method was then used in the investigation into the phylogeography of Anaulus australis along the South African coastal zone. Due to other recent work into diatom phylogeny and phylogeography there was also the opportunity to compare the genetics of the South African surf diatom Asterionellopsis found at Sundays River Beach to localities recently sampled and sequenced around the globe in order to identify the species found in South Africa. The direct method was successful for DNA extraction from Anaulus australis cells preserved using either isopropanol, ethanol or glutaraldehyde (provided the samples were not older than two years), but not formalin. Extraction of DNA from Asterionellopsis glacialis s.l. cells was successful with the direct method for ethanol-preserved samples, but the extraction from Attheya armata cells required some modifications be added to the method. Sequencing of the ITS region of Anaulus australis cells from along the southern coast of South Africa indicated connectivity between the various populations rather than the expected isolation of populations in the surf zones of the log-spiral bays. Comparison of the ITS and RbcL regions of the species of Asterionellopsis found at the Sundays River Beach indicated that it is Asterionellopsis lenisilicea which is a species only ii recorded from Canada to date and which has only recently been discovered and recognised as a new species within the genus. This genetic identification was supported by morphological measurements of frustules.
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  • Date Issued: 2017

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.
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  • 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.
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  • Date Issued: 2017

Rhenium complexes of benzazole derivatives

  • Authors: Van Niekerk, Xandri
  • Date: 2017
  • Subjects: Rhenium Benzimidazoles
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/21252 , vital:29467
  • Description: A series of rhenium(I) complexes with monodentate benzazole ligands containing the fac-[Re(CO)3]+ was synthesized. The rhenium(I) compound [ReCl(Hmbt)2(CO)3] was prepared from the reaction of [Re(CO)5Cl] and 2-aminobenzothiazole (Hmbt) in toluene. The ligand coordinates in a monodentate manner via the thiazole nitrogen atom. A similar reaction between [Re(CO)5Cl] and N-(1,3-benzothiazol-2-yl)-2- chloroacetamide (Hbct) resulted in the formation of [ReCl(Hbct)(CO)3(NCMe)], where only one ligand binds per rhenium in a monodentate fashion. The reaction of ligands 2-mercaptobenzimidazole (Hmbi) (dibenzothiazol-2-yl)tetraazathiapentalene (Hdbt) with rhenium(I) gave [ReCl(Hmbi)2(CO)3] and [ReCl(Hdbt)2(CO)3] respectively. The study on the coordination behaviour between ethyl-(1H-benzimidazol-2-yl-sulfanyl) acetate (Hbsa) and [Re(CO)5Cl] surprisingly gave the dimeric species (μ-Cl)2[Re(Hbsa)(CO)3]2, where the two rhenium atoms are bridged by two chloro ligands. The coordination of Hbsa occurs through the imidazole nitrogen, leaving the ethoxy tail free on each Hbsa ligand. The coordination behaviour of benzimidazole and benzothiazole derivatives gave rhenium complexes in oxidation states I, III and V, where all the ligands coordinate as bidentate N,N-chelating ligands. The study on 2-(2-aminophenyl)-1-benzothiazole (Hapt) and 2-(2-aminophenyl)-1-benzimidazole (H2apz) with [ReVOCl3(PPh3)2] resulted in the formation of [ReVOCl2(apt)(OPPh3)] and [ReVCl2(apz)(PPh3)2](ReO4), respectively. 1,2-Bis(2-benzimidazole)-1,2-ethanediol (Hbed) and 2,6-bis(2- benzimidazol-2-yl)pyridine (H2bip) were studied towards rhenium(I) and rheniumV) respectively. The former gave a dimeric species (μ-bbi)[Re(CO)4]2 (H2bbi – bisbenzimidazole) by reaction with [Re(CO)5Cl], whereas H2bip produced the rhenium(III) cationic salt [ReCl3(H3bip)(PPh3)]Cl, where the ligand coordinates as a cationic H3bip+ with protonation of an uncoordinated imidazole nitrogen atom. The pyridine derivatives 2-hydrazino-pyridinyl-2-benzothiazole (Hhpt) and (E)-1-benzo[d]thiazol-2-yl)-2- (pyridin-2-ylmethylene)hydrazine (btp) were reacted with [Re(CO)5Cl]. The neutral complex [ReCl(Hhpt)(CO)3] was isolated upon reaction with Hhpt, where Hhpt coordinates as a neutral bidentate ligand. The reaction of [Re(CO)5Cl] with btp gave two different complexes when using different solvents. In methanol, [ReCl(btp)(CO)3] was isolated, whereas in toluene, the conjugate of btp (btp1) was formed which resulted in the formation of [ReCl(btp1)(CO)3]. The study on potentially bidentate thiourea derivatives containing a benzothiazole moiety towards [ReI(CO)3]+ and [ReVO]3+ cores gave rise to a wide variety of complexes. The reaction of [Re(CO)5Cl] with N-phenyl-N-(2-benzothiazole)thiourea (Hpbt) produced the rhenium(I) complex [Re(Hpbt)(pbt)(CO)3]. Hpbt coordinates both as a monodentate neutral ligand and as a bidentate monoanionic chelate. The study of the reaction between trans-[ReOCl3(PPh3)2] and Hpbt gave the rhenium(V) product [ReOCl2(pbt)(PPh3)], with pbt acting as a bidentate ligand. The reaction of 1-(1,3- benzothiazol-2-yl)-3-benzoylthiourea (Hbbt) with [Re(CO)5Cl] led to the isolation of [ReCl(Hbbt)(CO)3]. Similar reaction of Hbbt with trans-[ReOCl3(PPh3)2] gave the unique compound [ReOCl2(Hbnt)(PPh3)], where the ligand coordinates via the ketonic oxygen and a methine carbon. The complex [Re(Hmby)(mby)(CO)3] was isolated upon reacting [Re(CO)5Cl] with methylbenzothiazol-2-ylidenecarbamodithioate (Hmby), with Hmby coordinating as a monodentate neutral ligand and mby as a bidentate monoanionic chelate. The coordination behaviour of N-(benzothiazol-2-yl)-S,S’- dimethyldithiocarboimine (Hbdc) towards rhenium(I) led to the formation of [ReCl(Hbdc)(CO)3]. The reactivity of 1-(benzothiozol-2-yl)-3,3-dimethylthiourea (Hbdm), a derivative of Hmby, was studied with trans-[ReOCl3(PPh3)2] and trans- [ReO(OEt)I2(PPh3)2] producing the square pyramidal compound [ReOCl(bdm)2] and the salt [Re(bdm)2(MeCN)2]I3, respectively. Pyrazole derivatives containing a benzothiazole ring were studied towards rhenium in oxidation states +I and +V. The reaction between 2-(3,5-dimethylpyrazol-1-yl)benzothiazole (Hdmp) and [Re(CO)5Cl] gave the neutral rhenium complex [ReCl(Hdmp)(CO)3], whereas its reaction with [ReOCl3(PPh3)2] surprisingly results in the formation of a dimeric complex (μ-O)[ReOCl2(Hdmp)]2. The study on the reactivity of 1-(benzo[d]thiazol-2-yl)-4-methyl-1H-pyrrol-2-ol (Hbtm) with [Re(CO)5Cl] gave the unexpected trimer [Re(btm)(CO)3]3 containing the fac-[Re(CO)3]+ core. The ligand btm forms a bridge between each rhenium metal, serving as a bidentate ligand to one rhenium, and a monodentate ligand to another rhenium atom. The study on the coordination chemistry between trans-[ReOCl3(PPh3)2] and Hbtm gave two different complexes when using different solvents. In ethanol, [ReOCl(btm)(btm1)] formed, whereas [ReOCl(btm1)(btz)] (Hbtz = 1-(benzo[d]thiazol-2-yl)-4-(1-iminoethyl)-3- methyl-1H-pyrazol-5-ol) was isolated in acetonitrile. The reaction of cis-[ReO2I(PPh3)2] also gave two different products when using different solvents, where the respective solvents coordinate to the metal. The rhenium(V) compound [ReO(OMe)(btm)(btm1)] was formed in methanol, whereas [ReO(OEt)(btm)(btm1)] was formed in ethanol. The coordination chemistry of 2-(2-Benzothiazoleyl)-4,5,6,7-tetrahydro-2H-indazol-3-ol (Hbth) was studied towards [Re(CO)5Cl] and trans-[ReOCl3(PPh3)2]. The resulting complexes which formed are [ReCl(Hbth)(CO)3] and [ReOCl(bth)(bth1)] respectively. The reactivity of potentially tridentate Schiff base ligands towards rhenium(I) and (V) was studied. The rhenium(I) precursor [Re(CO)5Cl] was reacted with (E)-1- (benzo[d]thiazol-2-yl)-2-(phenol-2-ylmethylene)hydrazine (H3bph) to give [ReCl(CO)3(H3bph)], which contains the kinetically inert fac-[Re(CO)3]+ core coordinated to a neutral bidentate ligand. The reaction of [ReO2(py)4Cl] with H3bph gave the dimeric species (μ-O)[ReO(Hbph)(py)]2, where the ligand coordinates as a tridentate dianionic chelate. A similar complex was isolated with (E)-1- (benzo[d]thiazol-2-yl)-2-(2,4-dihydroxy-2-ylmethylene)hydrazine (H3bdh) to give (μ-O)[ReO(Hbdh)(py)]2. The reaction of trans-[ReOCl3(PPh3)2] with H3bph afforded [Re(abt)(imp)Cl2(PPh3)] (abt = 2-aminobenzothiazole, imp = 2-(iminomethyl)phenol), where the ligand broke up into two fragments, both of which coordinated without any modification. The dioxo rhenium precursor cis-[ReO2I(PPh3)2] gave [ReO(Hbdh)(imp)] upon reaction with H3bdh. Ligand imp coordinates as a bidentate monoanionic ligand via the imine nitrogen and deprotonated phenolic oxygen and ligand Hbdh coordinatesas a tridentate dianionic chelate.
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  • Date Issued: 2017

Scanning probe force microscopy of III-V semiconductor structures

  • Authors: Kameni Boumenou, Christian
  • Date: 2017
  • Subjects: Scanning probe microscopy -- South Africa Semiconductors -- Optical properties
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/13992 , vital:27380
  • Description: In this dissertation, cross-sectional potential imaging of GaAs-based homoepitaxial, heteroepitaxial and quantum well structures, all grown by atmospheric pressure Metal-organic Vapor Phase Epitaxy (MOVPE) is investigated. Kelvin probe force microscopy (KPFM), using amplitude modulation (AM) and frequency modulation (FM) modes in air and at room temperature, is used for the potential imaging. Studies performed on n-type GaAs homoepitaxial structures have shown two different potential profiles, related to the difference in electron density between the semi-insulating (SI) substrate and the epilayers. It is shown that the contact potential difference (CPD) between the tip and sample is higher on the semi-insulating substrate side than on the n-type epilayer side. This change in CPD across the interface has been explained by means of energy band diagrams indicating the relative Fermi level positions. In addition, it has also been found that the CPD across the interface increases with electron density. This result is in qualitative agreement with theory. In addition, as known from literature, even under ambient conditions FM mode KPFM provides better lateral resolution and more realistic CPD values than AM mode KPFM. Compared to the case of AM mode analysis, where the experimental CPD values were on average of the theoretical values, the CPD values from FM mode analysis are on average of the theoretical ones. Furthermore, by using FM mode, the transition across the interface is sharper and the surface potential flattens/saturates as expected when scanning sufficiently far away from the junction. The non-neutral space charge region of the sample with an electron density of for example, is as measured by FM-KPFM, whereas for AM-KPFM, the width is even more than and the potential profiles do not saturate. For the p-type GaAs homoepitaxial structures, FM mode measurements from a sample with a dopant density of are presented. As in the case of n-type GaAs,a similar potential profile showing two main domains has been obtained. However, unlike the case of type GaAs where the potential measured on the epilayer side is higher than that on the substrate side, the potential on the epilayer side of the junction is lower in this case due to the fact that the Fermi level of p-type GaAs is below that of the substrate.
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  • Date Issued: 2017
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