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Foraging ecology of gentoo penguins (Pygoscelis papua) at the Falkland Islands
No full textMarine 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.National Research Foundation (South Africa
Predicting the effect of biofilm growth on the pressure drop over a biofilter
No full textHydrogen sulphide is a poisonous gas produced by several industries. It is therefore crucial
to investigate and mathematically model the environmentally friendly biofiltration process,
which has the ability to remove poisonous gasses, such as hydrogen sulphide, from an air
stream. In this study two approaches are used for modelling biofilm growth in three
different biofilters, i.e. an empirical and analytical approach. In the empirical modelling
approach, the pressure drop prediction of the Modified-Macdonald equation, the existing
granular rectangular Representative Unit Cell (RUC) model and the model of Comiti and
Renaud are used to determine the changes in biofilm affected porosity, specific surface area,
tortuosity and biofilm thickness. The results are obtained by using Excel R
Solver, which is
based on an optimization method. Thereafter a sensitivity analysis is performed in order
to analyze the effect of the sphericity. The analytical modelling approach involves only the
RUC model. The first step is to predict the biofilm thickness. Thereafter, two methods
are suggested for predicting the biofilm affected specific surface area. The first method is
based on an approach suggested in the literature. In the second method, the RUC model
is used to express the pressure drop in terms of the biofilm affected specific surface area,
which yields the adapted RUC model. The biofilm affected specific surface area values are
then obtained by making use of experimental pressure drop data and superficial velocity
values. After incorporating both the analytically and empirically determined sphericity
values into the adapted RUC model, the pressure drop results show the significant effect
that the sphericity value has on the model predictions. Finally, a sensitivity analysis is
performed on the input parameters to the model.National Research Foundatio
Rethinking refuges: Implications of climate change for dam busting
No full textClimate change is projected to alter river discharge in every populated basin in the world. In some parts of the world, dam removal now outpaces their construction and the diminishing cost efficiency of dams in drying regions is likely to further increase the rate of removals. However, the potential influence of climate change on the impact of dam removals has received almost no consideration. Most dams have major biological and ecological impacts and their removal would greatly benefit riverine ecosystems. However, using model regions in the Southern Hemisphere, we highlight that artificial lentic habitats created by dams can act as refuges for increasingly imperiled freshwater fishes, and dams may also prevent the upstream spread of invasive alien species in rivers. We argue that, in these and other regions where the major impact of climate change will be to reduce streamflow and aquatic refuge availability, a shifting balance between the negative and positive environmental impacts of dams requires policy makers to include climate change predictions in prioritisation processes for dam removal
Influence of the substrate gas-inlet gap on the growth rate, morphology, and microstructure of zirconium carbide films grown by chemical vapour deposition
No full textThe influence of the gap between the gas inlet and the substrate in an in-house developed thermal chemical vapour deposition (CVD) reactor, on the growth rate, surface morphology, phase composition and microstructure of deposited ZrC films was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ZrC films were grown on high density graphite substrates at different substrate-inlet gaps, viz. 70 mm, 90 mm, 120 mm, 145 mm and 170 mm, at substrate temperatures of 1200 °C and 1400 °C. The growth rate of ZrC films prepared at 1400 °C was observed to be higher than at 1200 °C., and was found to decrease with increase in substrate-inlet gap at both temperatures. The boundary layer thickness increased with an increase in substrate-inlet gap. The diffusion coefficients of the reactants were found to be 0.176 cm2/s and 0.200 cm2/s for the ZrC films deposited at 1200 °C and 1400 °C respectively. A model illustrating the diffusion of source materials through the boundary layer to the reacting surface was also given. The XRD results of ZrC films showed that at both 1200 °C and 1400 °C the (111) plane was the less preferred orientation, while (200) and (220) were the preferred planes. The degree of preferred orientation of ZrC films was found to decrease with increasing substrate-inlet gap. SEM results indicated that as the substrate-inlet gap increased from 70 mm to 170 mm for 1400 °C, the films became more uniform with increased particle agglomeration. The cauliflower-like clusters of particles grew larger in size and covered the whole surface. By contrast, at 1200 °C the surface crystallites had complex facets that decreased in size as the substrate-inlet gap increased from 70 mm to 170 mmNational Research Foundation (South Africa
Concentrating solar power in South Africa - a comparison between parabolic trough and power tower technologies with molten salt as heat transfer fluid
No full textThe most common type of concentrating solar power (CSP) plant in operation today
is the parabolic trough plant. In recent years molten salt power tower plants have
demonstrated the benefit of using molten salt as heat transfer fluid and a storage
medium. New research has shown that molten salt can be used in parabolic trough
technology in a similar manner. This thesis documents an investigation into both
technologies in order to compare them on a qualitative and quantitative basis.
South Africa has become a hotspot for the development of CSP thanks to the
abundant solar resource and the implementation of the Renewable Energy
Independent Power Producer Procurement Program (REIPPPP) in the country.
South Africa therefore provides a realistic backdrop for the comparison of the two
CSP technologies.
Parabolic trough and a power tower simulation models are constructed for the
comparison of the two technologies. Meteorological data for six selected sites in
South Africa are used to simulate the performance of both of the technologies, while
operating under a flat feed in tariff and a two-tiered feed in tariff.
Results of plant simulations show that molten salt can be used effectively as heat
transfer fluid in parabolic trough technology. Parabolic troughs are shown to have
higher annual optical efficiency compared to power towers. The main drawback of
the parabolic trough technology is the thermal losses experienced in the field during
overnight recirculation of the hot molten salt.
Parabolic trough solar fields show a large seasonal variation in efficiency while
power tower plants are shown to benefit from relatively consistent solar field
efficiency throughout the year. The seasonal variation in solar field efficiency results
in substantially higher thermal energy being available in the summer than in the
winter, thereby resulting in storages being filled and the subsequent dumping of
solar energy in parabolic trough plants.
A simple cost model is built to compare the financial performance of the two
technologies and allow for the optimization of the plants according to levelized cost
of electricity (LCOE). At a site near Springbok in the Northern Cape Province
optimization of both plant types resulted in an estimated LCOE of 0.127 USD/kWhe
and 0.129 USD/kWhe for parabolic trough and power tower plants respectively.
This study demonstrates that both parabolic trough and power tower plants require
careful consideration when selecting the most appropriate CSP technology for a
given location. Depending on the available solar resource and the tariff structure
under implementation, this thesis finds that both parabolic trough and power tower
plants can offer competitive CSP solutions with their own set of strengths and
weaknesses.National Research Foundatio
The development of simplistic and cost-effective methods for the evaluation of tray and packed column efficiencies
No full textNational Research Foundatio
Bioprospecting for novel biosurfactants and biosurfactant producing bacteria in wastewater
No full textNational Research Foundatio
The biochemical study of the R- and S-enantiomers of 2-(4-acetoxyphenyl)-2-chloro-Nmethylethylammonium chloride (Compound A)
No full textNational Research Foundatio
Interactive effect of busseola fusca and fusarium verticilloides on ear rot and fumonisin production in maize
No full textMaize is a crop of great economic importance in southern Africa, and is widely consumed as
a staple food and animal feed. Production of maize, however, is hampered by pathogens and
pests such as Fusarium verticillioides and the African stem borer Busseola fusca, respectively.
Fusarium verticillioides infection results in Fusarium ear rot (FER) and contamination of maize
kernels with fumonisin mycotoxins, while B. fusca, causes significant damage to maize tissues
during larval feeding. Despite attempts to control F. verticillioides, fungal infection and
fumonisin production remains a threat to maize production due to a lack of resistant maize
cultivars and the inability to target the pathogen with fungicides and biocontrol products.
Planting Bt maize hybrids have become an important mechanism for the management of stem
borers of maize. However, the recent discovery of B. fusca resistance to Bt maize with a single
crystal protein MON810 gene, indicates that care should be taken not to solely rely on this
technology for the management of B. fusca.
The interactive effect of B. fusca and F. verticillioides on FER and fumonisin production
in maize was investigated in this study. Maize ears were inoculated with F. verticillioides alone,
with both F. verticillioides and B. fusca, and with B. fusca alone. Fusarium verticillioides isolate
MRC826 was inoculated by injecting a spore suspension of the fungus into the silk channel of
each primary ear at the blister stage. For B. fusca infestation, aliquots of 10-15 neonate larvae
were deposited into the whorl of each plant at the 12-13th leaf stage before tasselling using a
mechanical applicator. Maize ears were also mechanically wounded at the blister stage with
a cork borer (different sizes and number of wounds) to mimic hail damage, and half of the
wounds infected with F. verticillioides. Results from this study indicated that the impact of B.
fusca infestation on FER varied seasonally, possibly due to its sporadic damage to maize
ears. Busseola fusca, however, did not result in a significant increase in fumonisin production.
The severity of wounding of maize ears was an important contributor to FER development and
fumonisin production.
The effect of host plant genetic modification and pesticide application on FER and
fumonisin production in maize was investigated by studying the response of a Bt hybrid and
its non-Bt isohybrid to F. verticillioides infection and B. fusca infestation; and by treating plants
with Beta-cyfluthrin (non-systemic) and Benfuracarb (systemic) insecticides. The field trials
were conducted over three seasons using a randomised complete block design with six
replicates per treatment. Uninoculated, uninfested and undamaged control treatments were
included. All ears were harvested at physiological maturity and FER, total fumonisin
concentration, stem borer cumulative tunnel length (B. fusca damage) and target DNA of
fumonisin-producing Fusarium spp. were quantified. Busseola fusca infestation had no effect on fungal colonisation and fumonisin production in maize. Bt and non-Bt kernels were equally
contaminated with fungal DNA, but FER and fumonisin production were reduced in the Bt
hybrid under natural farming conditions. Despite the evidence found in this study and others
that Bt maize indirectly reduces FER and fumonisin production, this was also inconsistent over
seasons. Benfuracarb controlled stem borers, and therewith indirectly reduced FER and
fumonisin production. FER development and fumonisin production by F. verticillioides varied
over seasons, indicating the importance of environmental conditions on FER and fumonisin
production.
A survey was also conducted at two sites in the North West province and one site in the
Free State province of South Africa to analyse mycoflora in B. fusca frass. The exposure of B.
fusca larvae to F. verticillioides in stem borer frass was also evaluated in both greenhouse
and field trials. Maize whorls were inoculated with a spore suspension of F. verticillioides
MRC826 4 weeks after plant emergence and infested with aliquots of 5-10 neonate B. fusca
larvae 2 days later. The control treatment consisted of B. fusca infestation only. Several fungal
species were associated with stem borer frass, including Acremonium zeae, Aspergillus
flavus, A. niger, F. chlamydosporum, F. incarnatum-equiseti species complex, F. oxysporum,
F. subglutinans, F. verticillioides, Mucor circinelloides, Rhizopus oryzae and Talaromyces
flavus. The occurrence of A. niger in the frass suggests that further studies need to be
conducted to determine the effect of A. niger infection on fumonisin production in maize in
South Africa. DNA quantity of fumonisin-producing Fusarium spp. was significantly more in
frass collected from greenhouse plants inoculated with F. verticillioides and infested with B.
fusca larvae than in frass collected from the uninoculated and infested control, whilst the field
trial showed no significant differences in quantity of target DNA in frass from inoculated and
uninoculated plants infested with B. fusca larvae. This indicates that plants in the field were
naturally infected with F. verticillioides.
This study showed that Bt maize had no effect on infection of maize ears by fumonisinproducing
Fusarium spp. and the subsequent production of fumonisin in F. verticillioidesinoculated
maize ears, indicating that the effect of Bt maize on fumonisin production in maize
ears is indirectly associated with its control of severe stem borer damage. Busseola fusca
frass was a reservoir of different fungal species; some pathogenic to maize, and others
antagonistic to maize pathogens. Moreover, B. fusca infestation of maize stems was
associated with higher levels of fumonisin-producing Fusarium spp. in larval frass when F.
verticillioides was present on the plant. Multiple large wounds created by cork borers resulted
in significantly more FER symptoms and fumonisin production, irrespective of artificial F.
verticillioides inoculation of maize ears whereas B. fusca infestation resulted in a significant
increase in FER in only one of the three seasons, moreover, it had no effect on fumonisin
production in all three seasons. This indicates that severe wounds that opens up husk coverage and exposes maize kernels; caused by factors such as insects, hail and bird
damage, and damage by implements; are important entry points for F. verticillioides that may
lead to the transition from symptomless infection to necrotrophic pathogenicity resulting in
FER and concomitant fumonisin production in maize kernels. However, climatic conditions are
also important in FER and fumonisin production in maize. Moreover, Acremonium zeae
endophytes occurring in frass can be used for the biological control of F. verticillioides resulting
in the management of FER and subsequent fumonisin production.National Research Foundatio
A model to address factors that could influence the information security behaviour of computing graduates
No full textThe fact that information is ubiquitous throughout most modern organisations cannot be denied. Information is not merely used as an enabler in modern organisations today, but is also used to gain a competitive advantage over competitors. Thus, information has become one of the most important business assets. It is, therefore, imperative that organisations protect information assets as they would protect other business assets. This is typically achieved through implementing various security measures.Technological and procedural security measures are largely dependent on humans. However, the incorrect behaviour of humans poses a significant threat to the protection of these information assets. Thus, it is vital to understand how human behaviour may impact the protection of information assets. While the focus of much literature is on organisations, the focus of this research is on higher education institutions and the factors of information security, with a specific focus on influencing the information security behaviour of computing graduates. Typically, computing graduates would be employed in organisations in various careers such as software developers, network administrators, database administrators and information systems analysts. Employment in these careers means that they would be closely interacting with information assets and information systems. A real problem, as identified by this research, is that currently, many higher education institutions are not consciously doing enough to positively influence the information security behaviour of their computing graduates. This research presents a model to address various factors that could influence the information security behaviour of computing graduates. The aim of this model is to assist computing educators in influencing computing graduates to adopt more secure behaviour, such as security assurance behaviour. A literature review was conducted to identify the research problem. A number of theories such as the Theory of Planned Behaviour, Protection Motivation Theory and Social Cognitive Theory were identified as being relevant for this research as they provided a theoretical foundation for factors that could influence the information security behaviour of computing graduates. Additionally, a survey was conducted to gather the opinions and perceptions of computing educators relating to information security education in higher education institutions. Results indicated that information security is not pervasively integrated within the higher education institutions surveyed. Furthermore, results revealed that most computing students were perceived to not be behaving in a secure manner with regard to information security. This could negatively influence their information security behaviour as computing graduates employed within organisations. Computing educators therefore require assistance in influencing the information security behaviour of these computing students. The proposed model to provide this assistance was developed through argumentation and modelling.National Research Foundatio