Incorporating prey demographics and predator social structure into prey selection and carrying capacity estimates for cheetah
- Authors: Clements, Hayley Susan
- Date: 2012
- Subjects: Carnivorous animals , Cheetah
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10754 , http://hdl.handle.net/10948/d1018606
- Description: There is a need for a refined understanding of large carnivore prey preference and carrying capacity (K). To date, K estimates for large carnivores have been developed from predictions of carnivore diet at a prey and predator species-level. These predictions therefore assume that all social classes within a carnivore species display similar prey preferences and that all demographic classes within a prey species are equally preferred or avoided. The objective of this study was to investigate the importance of including prey demographics and carnivore social class in carnivore diet descriptions and thereby K estimates, using cheetah Acinonyx jubatus as a study species. It was predicted that prey sex, prey age and cheetah social class influence cheetah prey preferences, when they influence the risk and ease of prey capture, and that their inclusion in a K model would improve its predictive strength. Based on an analysis of 1290 kills from South Africa, male coalition cheetah were found to prefer a broader weight range of prey than solitary cheetah. Prey demographics further influenced cheetah prey preference, when it corresponded to differences in prey size and the presence of horns. The current species-level K regression model for cheetah is based on preferred prey and thus omits highly abundant antelope that often comprise the majority of the diet, an artefact of the way in which preferences are calculated. A refinement of the species-level K regression model, to account for prey demographic- and cheetah social class-level differences in diet and the biomass of accessible prey (defined in this study as all non-avoided prey) instead of just preferred prey, doubled the predictive strength of the K model. Because group-hunting enabled predation on a broader weight range of prey, cheetah K was influenced by the ratio of male coalition cheetah to solitary cheetah in the population. The refined K regression model is derived from ecosystems supporting an intact carnivore guild. A mechanistic approach to estimating K, based on Caughley‟s (1977) maximum sustainable yield model, therefore better predicted cheetah K in systems devoid of lion Panthera leo and African wild dog Lycaon pictus, which were found to suppress cheetah density. This study improves our understanding of the relationships between prey demographics, cheetah social classes and intra-guild competition in determining cheetah prey preferences and K. This study therefore paves the way for similar work on other large carnivores.
- Full Text:
- Date Issued: 2012
Investigation of the performance of photovoltaic systems
- Authors: Alistoun, Warren James
- Date: 2012
- Subjects: Photovoltaic power systems -- South Africa , Photovoltaic power generation -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10517 , http://hdl.handle.net/10948/d1008396 , Photovoltaic power systems -- South Africa , Photovoltaic power generation -- South Africa
- Description: The main objective of this study was to investigate the performance of grid integrated PV systems. A data acquisition (DAQ) system was developed to monitor the performance of an existing grid integrated PV system with battery storage. This system is referred to as a grid assisted PV system. A data logger was used together with the inverters built in data logger to monitor environmental and electrical data on a grid tie PV system which was deployed during this study. To investigate the performance of these grid integrated PV systems PV and BOS device characterization was performed. This was achieved by using current voltage curve tracers and the DAQ system developed. Energy yield estimations were calculated referring to the literature review and a meteorological reference for comparison with measured energy yields from the grid tie PV system.
- Full Text:
- Date Issued: 2012
Macrophyte distribution and responses to drought in the St Lucia Estuary
- Authors: Nondoda, Sibulele Phefumlela
- Date: 2012
- Subjects: Estuaries -- South Africa -- Saint Lucia, Lake , Lakes -- South Africa -- Saint Lucia, Lake , Vegetation mapping -- South Africa -- Saint Lucia, Lake , Estuarine sediments -- South Africa -- Saint Lucia, Lake , Wetland mapping -- South Africa --Saint Lucia, Lake
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10632 , http://hdl.handle.net/10948/d1012330 , Estuaries -- South Africa -- Saint Lucia, Lake , Lakes -- South Africa -- Saint Lucia, Lake , Vegetation mapping -- South Africa -- Saint Lucia, Lake , Estuarine sediments -- South Africa -- Saint Lucia, Lake , Wetland mapping -- South Africa --Saint Lucia, Lake
- Description: This study investigated the response of the macrophytes in St Lucia Estuary, northern KwaZulu-Natal to drought. The present distribution of vegetation (2010 / 2011) was mapped and changes over time recorded from past aerial photographs. The changes in macrophyte cover in response to environmental factors (sediment and groundwater characteristics) was measured along four transects in 2010 and compared with results from previous years, in 2005 and 2006. In the current study, 1960 images were digitized to illustrate macrophyte distribution and cover of the Narrows, Makakatana and the Eastern Shores during a low rainfall period which started in 1958. The 2001 images were digitized to illustrate vegetation distribution and cover of the same area prior to the current drought which started in June/ July 2002. The 2008 images were digitized to illustrate vegetation distribution and cover of estuarine vegetation within the floodplain during the drought (after 6 years). The sites were visited in June 2011 for verification of the distribution and boundaries of each macrophyte habitat. The area covered by the water column varied over time. In 1960 during a low rainfall period the water was 32705 ha, 33320 ha in 2001 and reduced to 30443 ha in 2008. The area cover of inundated and dry reeds fluctuated with the water level. Under high water levels, low-lying areas such as Fanies Island and Selley‟s Lake were flooded and under low water levels, intertidal sand and mudflats were exposed and colonised by succulent salt marsh (Sarcocornia spp. and Salicornia meyeriana). Similar conditions were observed at Makakatana. Mangroves were observed from the mouth to the Forks. Avicennia marina was the dominant mangrove species and primary colonizer of dredge spoil. The area cover of mangroves in the vicinity of the mouth fluctuated as a result of fluctuating water levels, dredging operations, excavation of the Back Channel and Cyclone Gamede which killed intertidal vegetation. Between 2001 and 2008, mangrove expansion was faster in the Mfolozi Swamps area (± 1.4 ha yr -1) compared to the Narrows (± 0.4 ha yr -1). Long term monitoring transects were set up in 2005, at Makakatana, Charters Creek, Catalina Bay and at Listers Point to document changes in sediment conditions and vegetation cover. These were sampled in July 2005, October 2005, February 2006 and May 2010. Silt was the dominant particle size at Catalina Bay, Charters Creek and Makakatana. At Makakatana, average ground water salinity was 17.2 ± 6.6 ppt, 4.1± 4.9 ppt at Catalina Bay and 32.9 ± 19.3 ppt at Charters Creek. Drought resulted in the accumulation of salt on the surface sediment layer at Listers Point and Charters Creek due to low rainfall. Listers Point, the site with the lowest freshwater input and habitat diversity had the lowest macrophyte species richness with only three species. The dominant species at this site were Sporobolus virginicus and Chenopodium album L. which are highly salt tolerant species. Catalina Bay had the highest species richness (18 to 27); as a result of freshwater input via groundwater seepage from the sand dune aquifers on the Eastern Shores. Along the Eastern Shores, vegetation was dominated by species of Cyperaceae, Juncaceae and Juncaginaceae. Fluctuations in groundwater depth were observed at all sites, Listers Point groundwater depth in February 2006 was 80 cm and the ground water level was not reached during the May 2010 field trip. During the May 2010 field trip, the water column salinity of the St Lucia system was highly variable, Makakatana had the lowest water column salinity of 7.1 ppt, 42.1 ppt at Catalina Bay, 44 ppt at Charters Creek and Listers Point had the highest water column salinity of 95 ppt. An assessment of the changes in macrophyte cover along the transects showed that cover fluctuated in response to rainfall, water level and drought. At Listers Point, there was a continuous decline in the abundance of Sporobolus virginicus over time which was sparsely distributed in the first 40 m of the transect. Sarcocornia natalensis, a succulent and obligate halophyte, was recorded, in areas with high sediment conductivity. In May 2010, bare ground increased to an average percentage cover of 96.5% and was covered with dead organic matter and a salt crust at Listers Point. At Makakatana, there was a significant decrease in bare ground from July 2005 to May 2010 (H = 24.58, N = 197, p<0.001) as bare areas were colonized by salt marsh. Multivariate analysis showed that the abundance of Sporobolus virginicus was positively influenced by sediment moisture content and Paspalum vaginatum abundance was strongly influenced by the water column salinity. At Catalina Bay, low sediment conductivity at the groundwater seepage area resulted in terrestrial vegetation encroaching on estuarine vegetation. Sarcocornia natalensis became more abundant towards the water column. During the period of study, species richness at St Lucia ranged from 2 (Listers Point, May 2010) to 27 (Catalina Bay, February 2006). Salinity and water level fluctuation have a significant impact on the distribution of macrophytes at St Lucia during the drought. In saline areas salt marsh plants have colonized exposed shorelines and along the Eastern Shores groundwater seepage has increased macrophyte species richness. Low water levels have resulted in the exposure and desiccation of submerged macrophytes, which are replaced by macroalgae.
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- Date Issued: 2012
Microalgae and macrophytes as indicators of ecological health in the Great Brak Estuary
- Authors: Nunes, Monique
- Date: 2012
- Subjects: Microalge -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10629 , http://hdl.handle.net/10948/d1012097 , Microalge -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Description: The Great Brak temporarily open/closed estuary was subjected to a drought during the spring and summer of 2009/2010 resulting in the mouth remaining closed for a prolonged period. According to the Great Brak Estuary management programme, the mouth of the estuary had to be open for a total of 308 days during spring and summer of 2009/2010, respectively, but was closed for almost the entire two years (693 days). The aim of this study was to assess monthly changes in the abiotic characteristics (salinity, temperature, oxygen, pH and nutrients) and the biotic responses of phytoplankton and macroalgae; identify sources of nutrient input into the estuary and determine the response of the salt marsh to water level and salinity changes. The results indicated that physico-chemical parameters were similar to that previously recorded during the closed mouth condition. However mouth closure combined with elevated nutrient concentrations led to a shift from rooted submerged macrophytes to one where either microalgae or macroalgae were dominant. Soluble reactive phosphorus concentrations were significantly higher in bottom compared with surface waters. There was a significant negative correlation with SRP and dissolved oxygen for the sampling period indicating potential release of phosphorus from the sediment during closed mouth conditions. Microalgal biomass increased in response to remineralised nutrients and freshwater pulses. Flagellates were the dominant microalgal group (21718 ± 3336 cells m l-1, p < 0.05) because of their morphological ability to migrate vertically within the water column. The macroalgal cover was highest during the closed mouth state but only during winter (August 2010) when temperatures were below 20 oC. Five major point sources of nutrient input into the Great Brak Estuary were identified during rainfall periods. Point sources 4 and 5 in the upper reaches of the estuary had the highest DIN input whereas point source 3 in the middle reaches of the estuary had the highest DIP input. As a result of the drought and low water level, the salt marsh was never inundated for longer than 3 months. Die-back of Sarcocornia decumbens (r 2= -0.62, p < 0.05) was related to smothering by dead macroalgae whereas dieback of Sporobolus virginicus was related to decreasing nutrient (r2 = 0.59, p < 0.05) and salinity (r2 = 0.55, p < 0.05) levels. The physico-chemical characteristics alone did not convey the true health status of the Great Brak Estuary for the duration of the sampling (April 2010-April 2011). The study showed that microalgae and macroalgae are valuable indicators of the status of the estuary. Therefore it is suggested that bio-indicators are incorporated into the management/monitoring plan in order to assist in improving the health assessment of the Great Brak Estuary.
- Full Text:
- Date Issued: 2012
Microstructural and analytical characterization of plasma dissociated zircon
- Authors: Minnaar, Ettiénne Gerald
- Date: 2012
- Subjects: Zircon , Zirconium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10547 , http://hdl.handle.net/10948/d1015972
- Description: This dissertation focuses on the microstructural and analytical characterization of plasma dissociated zircon (PDZ) which was produced by the South African Nuclear Energy Corporation (NECSA). The techniques used in the analysis of the material include scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy and wavelength dispersive X-ray spectrometry (EDS and WDS), infrared spectroscopy, Raman spectroscopy and X-ray diffraction (XRD). The differences in morphology of the zirconia (ZrO2) crystals observed in the PDZ are related to the thermal history of the material. Large zirconia crystals grow in a spherulitic manner and have the monoclinic crystal structure. Some smaller crystals formed via a rapid cooling process appear to retain the tetragonal or cubic crystal structures rather than relaxing to the monoclinic structure, and this may be because such nanocrystals are stabilised by small surface area or constraints from surrounding materials. Impurity distribution analysis of the PDZ showed that majority of the impurities present in zircon segregates to the silica phase during the dissociation process. The infrared and Raman spectroscopy analysis of the PDZ material indicated that the zirconia is present in the monoclinic and tetragonal polymorphs. X-ray diffraction revealed the presence of monoclinic, tetragonal and cubic zirconia phases. Rietveld refinement of the XRD patterns revealed zirconia to be predominantly found in the monoclinic polymorph followed by the tetragonal and cubic polymorphs. A Fourier transform infrared (FTIR) spectrometer equipped with an attenuated total reflectance (ATR) cell proved to be a viable method for determining the percentage dissociated zircon in PDZ.
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- Date Issued: 2012
Morphological variation and species diversity of South African Estuarine macrophytes
- Authors: Veldkornet, Dimitri Allastair
- Date: 2012
- Subjects: Estuarine ecology -- South Africa , Aquatic plants -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10635 , http://hdl.handle.net/10948/d1013001
- Description: Studies on morphological variation are important as it can depict the relationship with environmental factors clearly and convey an understanding of the manner, mechanism and factors influencing plant adaptation and evolution. Although many studies have been conducted on South African salt marsh plant physiology and phytosociology there are at present very few morphological studies on estuarine plants. The aim of this study was to compare the morphological variation of estuarine macrophytes in three different estuary types in the warm temperate biogeographic zone of South Africa and to compare characters used in the taxonomic descriptions of species with those measured in the field. Permanently open estuaries investigated were Ngqusi (WC), Kowie (KW) and Swartkops (SW) estuaries. The Knysna Estuary (KN) was the estuarine bay investigated and the temporarily open/ closed estuaries (TOCEs) were the East Kleinemonde (EK) and Great Brak (GB) estuaries. Macrophytes were morphologically different across different estuary types. This suggests that there were different factors operating between these estuary types that would directly influence the morphology of species. The variation of plant height with different estuary types can be attributed to the fact that smaller salt marshes also have smaller habitat ranges compared to larger ones. The variation in morphological characteristics such as plant height can also be attributed to biogeographical range. Most morphological characteristics measured in the field fall within previously published ranges, and so these characters are useful in delimiting species. There were significant relationships between phenotypic variables and multivariate environmental variables. The most important of these variables were soil electrical conductivity, soil organic content and soil water content. Specifically, plant height increased with water content and decreased with salinity, flower stalk length had strong significant positive correlations with moisture content, organic content and pH while there were strong significant correlations with redox potential and electrical conductivity. Salt marshes are considered ideal for studying variation of species due to the explicit environmental gradients and plants occurring in salt marshes are halophytes that exhibit a range of morphological traits that allows for growth and reproduction under the stressful and extreme conditions. Considering recent climate change predictions and the consequent effects on South African estuaries this study provides significant information with regard to the response of species to a changing environment. The study was also aimed at updating the existing botanical database for South African estuaries in terms of species occurrence in South African estuaries, taxonomic name changes of existing species, new species, common names and habitats. Species diversity indices were also calculated for different estuaries, estuary types and biogeographic zones and diagnostic descriptions of the dominant salt marsh species were developed. The objective of this was that these data should provide baseline information for determining habitat richness and plant species diversity of South African estuaries which in turn should be used in determining priority estuaries for conservation and management. The identification key, developed using the DELTA software, would also aid researchers, managers and laymen in identifying salt marsh species. Results showed that the total number of macrophyte species, including intraspecific taxa and macroalgae, was 242 in 53 estuaries that were updated . There was an increase in the number of taxa recorded in the database primarily due to 1) research focus and full taxonomic surveys on larger estuaries and the big research projects has led to the identification of more species, 2) the addition of species that are not characteristically known as estuarine species, 3) the addition of 50 macroalgal taxa and 4) minor changes due to taxonomic revisions of species and the addition of newly described species. The Shannon diversity index showed that greater species diversity was found in the Berg (Groot) Estuary (4.220) and the Uilkraals Estuary (4.025). The cool temperate bioregion was the most diverse in the number of taxa (58) with the highest Shannon index (4.736). Permanently open estuaries were the most diverse in the number of unique taxa (56) with the highest Shannon index (4.867). Estuarine managers need to be aware of the species diversity in different estuarine types as well as the associated impacts on them. Conservation planning must therefore include species. Diagnostic features of INTKEY indicated that all 57 taxa were distinguishable from each other. Contrary to expectations plant height and not floral morphology was the best diagnostic characteristic. Ecological information such as the estuarine habitat, where different life forms occur, was important in delimiting species.
- Full Text:
- Date Issued: 2012
Motivation levels of tuberculosis healthcare staff at a district hospital in Kenya
- Authors: Busolo, Mellanda Isia
- Date: 2012
- Subjects: Health services administration , Employee motivation , Tuberculosis -- Prevention
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10135 , http://hdl.handle.net/10948/d1008292 , Health services administration , Employee motivation , Tuberculosis -- Prevention
- Description: Background: The success of tuberculosis (TB) treatment largely depends on healthcare team factors within a healthcare system, as healthcare workers play a vital role in fostering patient adherence to TB treatment. Strengthening motivation amongst Kenya’s TB healthcare workers should thus be reinforced in order to improve on clinical outcomes of TB treatment in Kenya. Objectives: To determine motivational needs of TB healthcare staff at a district hospital in Kenya and to provide recommendations on how to enhance their motivation. Design: TB healthcare workers including nurses, doctors, pharmacists and community healthcare workers were purposively sampled from a district hospital in Kenya. Their motivational levels were measured using a questionnaire adapted from Bennet and colleagues (2000). Key Findings: A high level of job satisfaction was present in more than 50 percent of the employees, although the ‘extrinsic job satisfaction’ sub-scale stood out as scoring relatively poorly in comparison to the other ‘job satisfaction’ sub-scales. Cognitive motivation yielded mixed results with 44 percent of respondents rating themselves as being satisfied, and 56 percent between neutral and very dissatisfied. The overall organisational commitment was positive, with the majority (60 percent) of respondents rating themselves as being committed to their organisation. The majority (96 percent) of workers rated their performance at work as very high. Conclusion: Improvement in staff motivation can be attributed to how well a hospital's management organises and runs its hospital. It was recommended that hospitals should provide an environment where motivational strategies are continuously implemented and where change is positively rewarded. This may, in turn, have a positive impact on TB treatment outcomes. The study may be of interest to key decision makers in Kenya’s healthcare system as well as TB programme managers, hospital managers and health managers in general. Further investigations are needed in order to determine whether Kenya’s public healthcare system has a staff retention strategy that is up to date with the motivational needs of Kenya’s health workforce.
- Full Text:
- Date Issued: 2012
On the design of concentrator photovoltaic modules
- Authors: Schultz, Ross Dane
- Date: 2012
- Subjects: Photovoltaic cells -- Design and construction , Photovoltaic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10546 , http://hdl.handle.net/10948/d1015766 , Photovoltaic cells -- Design and construction , Photovoltaic cells
- Description: High concentration photovoltaics (HCPV) promise a more efficient, higher power output than traditional photovoltaic modules. This is achieved by concentrating sunlight onto a small 1 cm2 triple junction (CTJ) InGaP/InGaAs/Ge cell by using precision optics. In order to achieve high performance, careful and informed design decisions must be made in the development of a HCPV module . This project investigated the design of a HCPV module and is divided into sections that concentrate on the optical design, thermal dissipation and electrical characterization of a concentration triple junction cell. The first HCPV module (Module I) design was based on the Sandia III Baseline Fresnel module which comprised of a Fresnel lens and truncated reflective secondary as the optical elements. The parameters of the CTJ cell in Module I increased with increased concentration. This included the short circuit current, open circuit voltage, power and efficiency. The best performance achieved was at 336 times operational concentration which produced 10.3 W per cell, a cell efficiency of 38.4 percent, and module efficiency of 24.2 percent Investigation of the optical subsystem revealed that the optics played a large role in the operation of the CTJ cell. Characterization of the optical elements showed a transmission loss of 15 percent of concentrated sunlight for the irradiance of which 66 percent of the loss occurred in wavelength region where the InGaP subcell is active. Characterization of the optical subsystem indicated regions of non-uniform irradiance and spectral intensity across the CTJ cell surface. The optical subsystem caused the InGaP subcell of the series monolithic connected CTJ cell to be current limiting. This was confirmed by the CTJ cell having the same short circuit current as the InGaP subcell. The performance of the CTJ cell decreased with an increase in operational temperature. A form of thermal dissipation was needed as 168 times more heat needs to be dissipated when compared to a flat plate photovoltaic module. The thermal dissipation was achieved by passive means with a heat sink which reduced the operational temperature of the CTJ cell from 50 oC to 21 oC above ambient. Cell damage was noted in Module I due to bubbles in the encapsulation epoxy bursting from a high, non-uniform intensity distribution. The development of the second module (Module II) employed a pre-monitoring criteria that characterized the CTJ cells and eliminated faulty cells from the system. These criteria included visual inspection of the cell, electroluminescence and one sun current-voltage (I-V) characteristic curves. Module II was designed as separate units which comprised of a Fresnel lens, refractive secondary, CTJ cell and heatsink. The optimal configuration between the two modules were compared. The CTJ cells in module II showed no form of degradation in the I-V characteristics and in the detected defects. The units under thermal and optical stress showed a progressive degradation. A feature in the I-V curve at V > Vmax was noted for the thermally stressed unit. This feature in the I-V curve may be attributed to the breakdown of the Ge subcell in the CTJ cell. Based on the results obtained from the two experimental HCPV modules, recommendations for an optimal HCPV module were made.
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- Date Issued: 2012
On the optical and electrical design of low concentrator photovoltaic modules
- Authors: Benecke, Mario Andrew
- Date: 2012
- Subjects: Photovoltaic cells -- Design and construction , Photovoltaic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10543 , http://hdl.handle.net/10948/d1013102
- Description: The increasing interest in non-fossil fuel based electricity generation has caused a prominent boost for the renewable energy sector, especially the field of Photovoltaics (PV) with one of the main reasons being the decrease in cost of PV electricity generation. However, over the last few years a saturation in the efficiency of solar cells have been reached leading into a renewed search for other means to further reduce the cost of electricity generation from photovoltaic sources. One of the technologies that has attracted a lot of attention is low concentration photovoltaics (LCPV). LCPV investigates an alternative strategy to replace costly semiconductor material with relatively cheap optical materials by developing a Low Concentration Photovoltaic (LCPV) module. A LCPV module is divided into three subsystems, namely, the optical, electrical and thermal subsystem. This study focussed on the design, construction and characterisation of an optical subsystem accompanied by a thorough investigation into the design of an electrical subsystem. A facetted parabolic concentrator using a vertical receiver was modelled and a first prototype was constructed having a geometric concentration factor of 6.00 X. Upon electrical characterisation of this first vertical receiver LCPV prototype a concentration of only 4.53 X (receiver 1) and 4.71 X (receiver 2) was obtained. The first vertical receiver LCPV prototype did not reach the expected concentration factor due to optical losses and misalignment of optical elements. The illumination profile obtained from the reflector element was investigated and an undesirable non-uniform illumination profile was discovered. A second vertical receiver LCPV prototype was constructed in an attempt to improve on the first prototype, this second vertical receiver prototype had a geometrical concentration factor of 5.80 X. The results indicated a much improved illumination profile, yet still containing a number of non-uniformities. The second vertical receiver LCPV module yielded an operational concentration factor of 5.34 X. From the preliminary results obtained it was discovered that under concentrated illumination there was a limitation on the maximum power that could be obtained from the receiver. Upon further investigation it was discovered that this limitation was due to the higher current levels under concentrated illumination accompanied by a high series resistance of the receiver. This lead to the construction of new PV receivers, where this limitation could be minimised. 3 cell, 4 cell, 6 cell and 8 cell string configurations were constructed and used for the electrical characterisation of the prototypes. Due to non-uniformity of the illumination profile obtained from the second LCPV prototype a third vertical receiver LCPV prototype was constructed. This vertical receiver design illustrated more uniformity in the obtained illumination distribution and had a geometrical concentration factor of 4.61 X, although under operation only 4.26 X could be obtained. It is important to note that the geometric concentration factor does not account for reflective losses of the reflective material. One of the main reasons for the difficulty in obtaining a uniform illumination profile with the vertical receiver design is that the facetted reflector element is far away from the PV receiver. This enhances the effect of the slightest misalignment of any of the optical elements. This large distance also increases the effect of lensing from each facet. These factors lead to the consideration of a second design, which would counteract these factors. A horizontal receiver LCPV module design implementing a facetted parabolic reflector was considered to counteract these effects. From a mathematical model a horizontal receiver LCPV prototype was constructed having a geometrical concentration factor 5.3 X. The optical characterisation of the illumination profile showed a much improved illumination profile, which was much more uniform than the previous illumination profiles obtained from the other LCPV prototypes. The uniformity of the illumination profile could be seen in results obtained from the electrical characterisation where the concentrator reached operational concentration factor of 5.01 X. The reliability of the third vertical receiver LCPV prototype and the horizontal receiver LCPV prototype as well as the receivers were investigated by placing each receiver under stressed operational conditions for 60 sun hours. I-V characteristics were obtained after every five sun hours to investigate any signs of degradation. After 60 sun hours none of the receiver displayed any signs of degradation or reduction in electrical performance.
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- Date Issued: 2012
On the thermal and electrical properties of low concentrator photovoltaic systems
- Authors: Gerber, Jacques Dewald
- Date: 2012
- Subjects: Photovoltaic power systems , Photovoltaic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10561 , http://hdl.handle.net/10948/d1021219
- Description: Low concentrator photovoltaic systems are capable of increasing the power produced by conventional silicon photovoltaic cells, thus effectively lowering the cost per kWh. However, power losses associated with resistance and temperature have limited the large scale implementation of this technology. In this study, the optical-,electrical- and thermal sub-systems of a low concentrator photovoltaic system are theoretically and experimentally evaluated with the aim of minimizing the power losses associated with series resistance and temperature. A 7-facet reflector system, with an effective concentration ratio of 4.7, is used to focus irradiance along a string of series connected poly-crystalline photovoltaic cells. I-V characteristics of 4-, 6- and 8-cell photovoltaic receivers are measured under 1-sun and 4.83-sun conditions. Under concentration, the 8-cell photovoltaic receiver produced 23 percent more power than the 4-cell photovoltaic receiver, which suggests that the effect of series resistance can be minimized if smaller, lower current photovoltaic cells are used. A thermal model, which may be used to predict operating temperatures of a low concentrator photovoltaic system, is experimentally evaluated within a thermally insulated enclosure. The temperatures predicted by the thermal model are generally within 5 percent of the experimental temperatures. The high operating temperatures associated with the low concentrator photovoltaic system are significantly reduced by the addition of aluminium heat sink. In addition, the results of a thermal stress test indicated that these high operating temperatures do not degrade the photovoltaic cells used in this study. The results of this study suggest that the power output of low concentrator photovoltaic systems can be maximized by decreasing the size of the photovoltaic cells and including an appropriate heat sink to aid convective cooling.
- Full Text:
- Date Issued: 2012
Phenotypic plasticity of metabolic rate in an afrotropical bird species (Euplectes orix) across a temperature gradient
- Authors: Van de Ven, Tanja Maria Francisca Nicole
- Date: 2012
- Subjects: Phenotypic plasticity , Evolutionary genetics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10718 , http://hdl.handle.net/10948/d1012659 , Phenotypic plasticity , Evolutionary genetics
- Description: Avian species are known to have the capacity to respond to environmental changes through physiological adjustments. The process whereby organisms adjust their phenotype without genetic change is termed phenotypic plasticity and it is mostly observed to be a phenotypic improvement to ecological challenges. Metabolic rate (MR), which is the rate of energy expenditure in a species, is a highly flexible physiological parameter which results in a great diversity of avian standardised metabolic rates. Like birds from high latitudes, Afrotropical bird species are expected to have the capacity to adjust their energy expenditure to match the availability of resources. Previous studies on the flexibility of physiological parameters in birds have focused on the magnitude of change of physiological adjustments and the cues inducing these changes. Comparative research has furthermore investigated metabolic rates across aridity, altitude, latitude and temperature gradients. Recently, a clear dichotomy has become evident with elevated metabolic rates observed in high latitude birds in winter and a down-regulation of metabolic rates observed in birds exposed to low latitude mild winters. In this study, the shape of the reaction norm, the magnitude, the reversibility, the direction and the rate of change of two physiological parameters, basal metabolic rate (BMR) and summit metabolic rate (Msum), were investigated in a coastal and an inland population of Southern Red Bishops (Euplectes orix) through seasonal acclimatisation and laboratory acclimation. Summer and winter basal metabolic rates as well as body mass, were highly flexible traits in free-ranging coastal and inland Red Bishops. Birds acclimatised to a mild coastal climate in winter exhibited reduced basal and summit metabolic rates, whereas birds originating from a more variable inland climate increased basal metabolic rate in winter, but did not show increases of Msum in winter. Red Bishops responded to short term thermal acclimation under laboratory conditions by gradually changing body mass. Acclimation periods of 21 days revealed a negative relationship between body mass and acclimation air temperature. Peak responses of basal metabolic rate to ambient temperature change were observed in both coastal and inland birds between two and eight days after the change in acclimation air temperature. The influences of seasonal acclimatisation on energy expenditure differed between coastal and inland birds, however, during laboratory acclimation individuals from the two populations showed no difference in response. Within the individuals of the coastal and inland Southern Red Bishops, phenotypic flexibility is observed in body mass, basal metabolic rate and summit metabolic rate as a response to environmental changes. This flexibility is thought to increase thermoregulatory capacities of the Southern Red Bishop in different habitats and climates.
- Full Text:
- Date Issued: 2012
Physico-chemical and microalgal characteristics of the Goukamma Estuary
- Authors: Kaselowski, Tanja
- Date: 2012
- Subjects: Estuarine ecology , Estuaries -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10623 , http://hdl.handle.net/10948/d1011130 , Estuarine ecology , Estuaries -- South Africa
- Description: Estuaries are intrinsically complex and dynamic ecosystems that display marked spatial and temporal variability. Because estuaries are situated at the receiving end of catchment activities, they are at particular risk of alterations to their natural complexity. The overarching objective of this study was to gain an overview of the abiotic conditions and biotic response of the Goukamma Estuary, a small temporarily open/closed estuary (TOCE) which is situated in a relatively undisturbed catchment in the Southern Cape. Physico-chemical properties drive estuarine ecology, and together with biological indicators, are commonly assessed to determine the present status of an estuary. During the study, physico-chemical parameters reflected great spatial and temporal variability in response to the mouth state over a 13 month period. Parameters ranged within expected limits, as proposed by the conceptual model for water quality of TOCE’s (Snow and Taljaard 2007). Of particular importance was the prominent occurrence of salinity stratification and hypoxic conditions (dissolved oxygen [DO] < 3 mg l-1) during both open and closed mouth states. Data indicated that in the wide and shallow lower reaches, weak stratification gradients were present and oxygenated conditions (DO > 6 mg l-1) were maintained throughout the water column mainly by wind and tidal action. However, stratification increased towards the deeper, channel-like middle and upper reaches of the estuary, followed by a significant reduction in bottom DO concentrations and development of hypoxia and anoxia. Bottom water hypoxia commonly occurs in microtidal estuaries due to the limited influence of mixing forces, mainly by wind and tidal action. The Goukamma Estuary is a channel-like microtidal estuary where stratification effectively limited oxygenation of the bottom water which resulted in frequent occurrence of bottom water hypoxia. During June 2010 when the highest local rainfall (75 mm) was recorded for the region, salinity and DO data showed that this amount of rainfall was insignificant as it did not replenish the water column of oxygen. Only the surface 0.5 m layer was fresh and oxygenated while below this, the water column was completely hypoxic. In an unimpacted state, the Goukamma Estuary is a blackwater system and is expected to be nutrient poor; however, farming activities in the catchment have resulted in elevated nutrient concentrations. This study showed that significantly higher nutrient concentrations were measured in the middle and upper reaches of the estuary, adjacent to cattle farms situated in the floodplain of these reaches. Nutrient concentrations represented mesotrophic (dissolved inorganic nitrogen [DIN] > 500 μg l-1) to eutrophic conditions (dissolved inorganic phosphorus [DIP] > 25 μg l-1). Nutrient input stimulated phytoplankton to attain a significantly high biomass, ranging between 0.3 – 112 μg l-1 (~ 7.7 ± 1.3 μg l-1; n = 128) and 0.8 – 289 μg l-1 (~ 21.1 ± 4.4 μg l-1; n = 80) during the open and closed states, respectively. High organic loads are associated with high oxygen demands which consequently result in hypoxia following decomposition. Exacerbated by natural salinity stratification which effectively limits oxygenation of the water column, unnaturally high nutrient concentrations and coinciding organic loads place the estuary at particular risk of degradation. This study captured key patterns and processes by quantifying salinity, oxygen and nutrient concentrations in addition to biological indicators (phytoplankton biomass and community composition). Considering possible budget constraints, it is recommended that monthly salinity and oxygen concentrations should be monitored as well as seasonal nutrient concentrations. It is also recommended that riparian buffer zones should be established in the middle and upper reaches of the estuary, as these vegetation buffers have been well documented to contribute to nutrient attenuation and improved water quality from agricultural run-off.
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- Date Issued: 2012
Phytoplankton associated with mesoscale eddies in the Mozambique Channel
- Authors: O'Reilly, Bevan James
- Date: 2012
- Subjects: Mozambique Channel. , Phytoplankton
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10622 , http://hdl.handle.net/10948/d1010967 , Mozambique Channel. , Phytoplankton
- Description: The study undertaken was an attempt to provide information on the effect that oceanographic features common in the Mozambique Channel have on primary production. Oligotrophic conditions dominated the Mozambique Channel at the time of sampling and the introduction of nutrients into the euphotic zone by upwelling processes were identified as cyclonic eddies. Differences in physico-chemical variables between surface and F-max across all sites proved to be stronger than the physico-chemical variables between 4 grouped oceanographic features. This was revealed by stronger variations in phytoplankton community structure and chlorophyll a concentration between surface and F-max compared to oceanographic features sampled. One of the hypotheses presented for the study was that diatoms would dominate phytoplankton communities within a cyclonic eddy. This was not the case as the coccolithophorid, Emiliania huxleyi Lohmann (Hay and Mohler 1967) dominated F-max and surface water in the cyclonic eddies and most other sites. Phytoplankton community structure did not differ significantly between the oceanographic features sampled which contradicted another one of hypotheses presented in the study. Chlorophyll a concentration in surface water of the cyclonic eddies was significantly higher than in surface waters within the anti-cyclonic eddy. F-max was not significantly different in phytoplankton biomass between these two system types. The cyclonic eddies and anti-cyclone had similar phytoplankton diversity which did not verify the hypothesis that there would be less phytoplankton species diversity within cyclonic eddies compared to the anti-cyclonic eddy. Phytoplankton community structure differed between F-max (depth at which maximum chlorophyll a is found) and the surface. This phytoplankton community difference was linked to differences in physico-chemical variables between the two depths. The diatoms Thalassionema nitzschioides, Pseudo-nitzschia sp.A, Pseudo-nitzschia sp.B, Thalassiosira sp.C, Thalassiosira sp.E, Bacteriastrum furcatum, Guinardia cylindrus, Nitzschia closterium, Hemiaulus hauckii, and Nitzschia braarudii revealed the only discernible ecological similarity amongst phytoplankton species across all sites and depths. This is important as it revealed that these species were regularly found occupying similar depths and potentially similar physico-chemical ranges in the water column which suggest these diatom species responded to a dominant source of variation. Distribution patterns of species and of ecologically defined groups support the hypothesis that diatom species and assemblages are good indicators of the changing character of an upwelling system. These statements lead to the assumption that the diatom grouping found in this study indicates areas of upwelling where water temperatures are reduced and nutrients are more readily available. One must keep in mind that ordination techniques are only descriptive and no significance is tested. The coccolithophorid D. anthos and the dinoflagellate Phalacroma spp. were noted as being most dissimilar to all other phytoplankton species with regards to their position in the water column and their response to physico-chemical variables. Finally, the dominance of E. huxleyi in the Mozambique Channel during November/December of 2009 reveals the potential vulnerability of phytoplankton in the channel to ocean acidification.
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- Date Issued: 2012
Population dynamics of the white shark, Carcharodon carcharias, at Mossel Bay, South Africa
- Authors: Ryklief, Rabiah
- Date: 2012
- Subjects: White shark -- South Africa -- Mossel Bay , Sharks -- South Africa -- Mossel Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10717 , http://hdl.handle.net/10948/d1012077 , White shark -- South Africa -- Mossel Bay , Sharks -- South Africa -- Mossel Bay
- Description: Mossel Bay is internationally recognised as one of the centres of abundance of white sharks in South Africa. During 2008 – 2010 there were four sites within the bay i.e. Seal Island, Hartenbos, Kleinbrak and Grootbrak, which were sampled to gain insight into the population dynamics of this species. Currently, life history information on white sharks in this area is limited. This study used a combination of mark-recapture using photographic identification techniques and sight per unit effort methods. Inter-annual, seasonal and spatial patterns in abundance are assessed. The effects of environmental parameters on abundance are also investigated. Photographic identification techniques were employed to identify unique individuals within the sampled population. This modified mark-recapture approach is therefore non-invasive and cost-effective. Open population POPAN parameterization was used to analyse the data in software program MARK. The total population was estimated at 389 sharks (351 – 428; 95 percent CI). Over the three year period, a marginal (yet non-significant) decline in numbers was observed, in terms of both monthly and seasonal population estimates. Sightings per unit effort data were collected during sampling trips. The relative abundance and body size composition of white sharks demonstrated significant spatial and seasonal variation. The highest and lowest relative abundance was observed at Seal Island and Hartenbos, respectively, and is likely attributed to prey availability. Although white sharks were present year-round in Mossel Bay, the highest relative abundance occurred during summer and the lowest relative abundance occurred during spring. White sharks were grouped into three main size classes based on estimated total length (TL): Young of the year (YOY) (125 – 174cm), juvenile (175 – 324cm) and adult (325 – 524cm). YOY white sharks were most prevalent at Grootbrak, with juvenile and adult individuals concentrating at Seal Island. Although most size classes were present throughout the year, seasonal differences were observed. YOY individuals were most abundant in the autumn months, juvenile size-classes appeared to concentrate in the study area during winter, and the adult individuals were most abundant in the spring months. Overall, there was a high concentration of white sharks ranging in size between 175 – 324cm TL, and it was thus hypothesised that Mossel Bay represents an interim nursery or grow out area for white sharks in South Africa. Data collected from 2008 and 2009 was used to investigate the relationship between specific environmental parameters, i.e. sea surface temperature and vertical water clarity, in relation to the relative abundance of white sharks. Sea surface temperature and vertical water clarity observed in this study ranged from 9.3 - 22.7°C and 0 – 10m, respectively. Sea surface temperature did not have a significant influence on the relative abundance of white sharks and this may be attributed to the thermoregulatory capacity of the species. Vertical water clarity, however, did significantly influence the relative abundance. Furthermore, the combined effect of site and season significantly influenced the relative abundance of white sharks and is probably linked to the distribution and abundance of inshore prey resources.
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- Date Issued: 2012
Population dynamics of the Zuurberg Cycad and the predicted impact of climate change
- Authors: Singh, Karishma
- Date: 2012
- Subjects: Cycads -- South Africa -- Eastern Cape , Encephalartos -- South Africa -- Eastern Cape , Climate change -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10633 , http://hdl.handle.net/10948/d1012857
- Description: Cycads first appeared about 300 million years ago and historical data indicates that they survived fluctuations of global temperature and carbon dioxide concentrations and reached peak abundance during periods where temperature and carbon dioxide concentrations were much higher than the present conditions as well as the predicted increased levels. With Africa being one of the most vulnerable regions to climate change and in the absence of an evaluation of predicted impacts of climate change on cycads, this study aims to contribute to our understanding of responses of Encephalartos longifolius to increased temperature. Encephalartos longifolius (Jacq.) Lehm is an Eastern Cape endemic and like most cycads has been around for millions of years with very little change to its basic structure. Photosynthetic rates showed E.longifolius seedlings have C3 photosynthesis and even under stress they do not switch over to CAM photosynthesis. The photosynthetic rates of seedlings showed a typical C3 -plant type response under elevated carbon dioxide levels. Increased temperatures could be detrimental to the species but coupled with elevated carbon dioxide levels the growth of Encephalartos longifolius are postulated to outweigh the negative impacts of increased temperatures. Whilst climatic conditions in the Eastern Cape might not impact the abundance of Encephalartos longifolius, the species however is declining rapidly to the present near-threatened status. Demographic studies revealed a high percentage of juvenile numbers in the wild; however juvenile plants are impacted on by animals thereby jeopardizing their survival. Adult plants are heavily impacted on by animals; this reduces the probability of new offspring being produced. Cycads are also very slow - growing which is the primary cause of their ruin in the wild. Encephalartos longifolius grows at just over approximately 1 cm per year with growth being more rapid in the juvenile plants. Once juvenile plants reach approximately 60 cm they stop growing in diameter but only get taller. Seed germination is also a very slow process with an optimum temperature of 28°C and a growth medium of at least 50 percent moisture. Regardless of the Eastern Cape predicted to become the hottest province in South Africa as a result of climate change, cycads will be able to adapt to the changing environment and conservation plans should focus on animal and human impacts that are the major force causing decreasing abundance of Encephalartos longifolius in the wild.
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- Date Issued: 2012
Post occupancy evaluation of an office building : the case of country club estate, Johannesburg
- Authors: Matshili, Humbulani Emmanuel
- Date: 2012
- Subjects: Architectural design -- Evaluation , Offices -- Design , Office buildings -- South Africa -- Johannesburg -- Evaluation , Real property -- South Africa -- Johannesburg
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9703 , http://hdl.handle.net/10948/d1018554
- Description: Most organisations nowadays want to build offices that are cost effective, but at the same time they forget to consider the impact of IEQ on the occupants’ wellbeing and performance. These offices are equipped with air-conditioners, which may impact negatively on performances if not monitored, controlled and maintained. An occupant’s performance may be accelerated or reduced, based on the effectiveness of IEQ in the office buildings. It is imperative that the employer or management create a work environment that is conducive to the occupants’ needs, so that the occupants may be able to improve their work performance that often yields increased productivity. The main aim of the study was to investigate the efficiency of a building’s Indoor Environmental Quality (IEQ) and how it affects workers with regard to productivity. The objectives of the study were: to determine the level of satisfaction of the occupants in terms of the IEQ, evaluate the effects that the current IEQ of the building has on the productivity of the occupants, and proffer solutions to identified problems so that the building performance can be improved, and similar future buildings can be improved upon in terms of IEQ. Post Occupancy Evaluation (POE) was utilised to conduct the evaluation. This will help stakeholders and managements to ensure that past mistakes committed are not repeated in the future buildings. POE analyses IEQ related to Indoor Air Quality (IEQ), thermal comfort, occupant’s satisfaction and occupant performance and productivity. There is a correlation between different indoor parameters of the occupants’ satisfaction, health and productivity at the workplace. For these correlations to complement each other successfully, IEQ factors must be conducive to human wellbeing. Workplace environments are perceived as unsafe and unhygienic. This situation is caused by poor planning of workstations, low indoor air quality, inappropriate lighting in the office, lack of ventilation and insufficient safety measures. In particular, findings of this study demonstrate the low level of occupants’ satisfaction with regard to office buildings in the Country Club Estate, Johannesburg. The results from this study show that POE is perceived to be completely new to occupants of the Country Club Estate. Management or stakeholders have a huge task ahead to address the benefits of implementing POE and to face the consequences if POE is not implemented.
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- Date Issued: 2012
Propagation and stress physiology of selected Subtropical Thicket species : towards increasing biodiversity at rehabilitation sites
- Authors: Louw, Merika
- Date: 2012
- Subjects: Biodiversity conservation , Plant physiology , Stress (Physiology) , Plant propagation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10758 , http://hdl.handle.net/10948/d1021115
- Description: Sundays Thicket and Spekboomveld vegetation in the Eastern Cape have experienced intensive and extensive degradation due to over-browsing by domestic stock. The Subtropical Thicket Restoration Project aims to take advantage of the high carbon sequestration potential of Portulacaria afra (Spekboom) and other Thicket species, to rehabilitate degraded Thicket by restoring biodiversity and ecosystem services, create job opportunities and socio-economic upliftment in local communities, and promote the trade of carbon credits generated by planting and „farming‟ with Spekboom truncheons, rather than domestic stock. Plant material (seeds and length of stem) was sourced from the farm Krompoort, outside Uitenhage in the Eastern Cape. The effectiveness of four different rooting media i.e. plain pool filter sand and 1:1 mixtures of pool filter sand with perlite, potting soil and Thicket soil, on the rooting of ten Thicket species, were tested. Species with the greatest percentage strike and mean root length on stem cuttings were succulent species, Crassula ovata (84 percent strike) and Portulacaria afra (97 percent), as was expected. The application of rooting hormone Seradix© No. 3 did not significantly promote cutting strike or increase mean root length in C. ovata and P. afra. Woody canopy shrub species with the greatest cutting strike and mean root length, overall, were Rhigozum obovatum (24 percent), Lycium cinereum and L. oxycarpum (21 percent), and Searsia longispina (19 percent). These species, as well as Grewia robusta (4 percent), are considered „easy-to-root‟ species, or of sufficient functional value in terms of their spinescence, flower and fruit production, and soil-binding capabilities. Very low percentage strike (<1 percent) and mean root length were achieved in Azima tetracantha, Carissa bispinosa and Gymnosporia polyacantha subsp. polyacantha. These species are considered unsuitable for propagation for rehabilitation purposes. Crassula ovata, L. cinereum, L. oxycarpum, P. afra and S. longispina cuttings produced longer roots when planted in Thicket soil, the same having been found in R. obovatum cuttings planted in perlite. Thicket soil was, therefore, best at promoting cutting strike and root growth in „easy-to-root‟ species. Plain pool filter sand was the only medium in which A. tetracantha, C. bispinosa and G. robusta, cuttings rooted, and perlite the only medium in which G. polyacantha subsp. polyacantha cuttings rooted. Potting soil did not promote significant cutting strike or root growth in any of the species tested. Physiological variables i.e. photosynthetic efficiency (chlorophyll a fluorescence, Fv/Fm) and stomatal conductance (mmol H2O m-2 s-1) were measured for ten Thicket species, including Portulacaria afra. Control plants were watered well once a week, and treatment plants were dried out for 30 days, rewatered on the 30th day and their recovery from drought stress monitored for a further 17 days. Species that responded poorly to drought stress were Gymnosporia buxifolia and Putterlickia pyracantha. In addition to Portulacaria afra, species that showed the fastest recovery and resprout after rewatering, were: Crassula ovata, Ehretia rigida, Grewia robusta, Lycium ferocissimum, Rhigozum obovatum and Searsia longispina. These species produced the smallest decline in volumetric moisture content of soil, and had the lowest decline in photosynthetic efficiency and stomatal conductance during simulated drought. Unlike C. ovata and P. afra, which are CAM or C3-CAM switching species, mortality of transplants will most likely be high, if not total, during transplantation, as this study was done at lower light and temperature, and higher humidity levels than experienced at rehabilitation sites. This study has shown that the reintroduction of propagated woody canopy shrubs and trees into degraded Thicket sites does not appear to be a practical or economical method of actively restoring biodiversity to rehabilitation sites. As woody climax species have been shown to return to sites planted with Spekboom truncheons through „natural regeneration‟ within approximately 50 years, future research efforts should focus on optimising restoration site selection and planting techniques in order to maximize carbon sequestration potential of planted truncheons, which will, in the long term, result in an environment that can support regeneration of the biodiversity to something resembling intact Thicket.
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- Date Issued: 2012
Quantitative evaluation of starch determination in feed samples using Near Infra-red Reflectance
- Authors: Mapekula, Nwabisa Nolwazi
- Date: 2012
- Subjects: Near infrared spectroscopy , Animal feeding , Feeds -- Enzyme content
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10421 , http://hdl.handle.net/10948/d1015617
- Description: In an attempt to reduce the costs and turn around times experienced with outsourcing starch analysis in finished feed products, the company decided to invest in a NIR instrument to carry out such analyses in house. The particular instrument purchased by the company comes with a build in calibration for specific finished feed products and the main objective of this investigation was to evaluate whether the instrumentation and build in calibration gives reliable analyses of a finished poultry feed. The results obtained showed that : - The NIR results obtained have a positive bias compared to the theoretical (formulation specified value) and also to the value obtained by enzymatic starch analysis. - Despite the positive bias, the starch values were well within the allowable limits - Repeatability measurements on the data generated by two different analysts showed that while the percentage relative standard deviations obtained (< 1.0 percent) were well within the company specifications of percentage RSD < 5.0 percent, the inter sample repeatability showed small, but significant variation. - The results for intermediate precision showed that there is no statistically significant difference between the results obtained by two different analysts, nor was there any difference in the results of the same samples analysed at different time periods. - Reproducibility could not be evaluated due to the lack of another instrument within the company that were similarly set up as the instrument used for the investigation. This investigation has shown that, given the restrictions enforced by the build incalibration of the NIR instrument, the use of NIR for the analyses of the finished feed product is valid, but will require that careful attention be paid to data collection procedures.
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- Date Issued: 2012
Recolonisation of the Robberg Peninsula by the Cape Fur Seal Arctocephalus pusillus pusillus and its prey preferences
- Authors: Huisamen, Johan
- Date: 2012
- Subjects: South African fur seal -- South Africa -- Plettenberg Bay , South African fur seal -- Food -- South Africa -- Plettenberg Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10745 , http://hdl.handle.net/10948/d1006438 , South African fur seal -- South Africa -- Plettenberg Bay , South African fur seal -- Food -- South Africa -- Plettenberg Bay
- Description: The Cape fur seal Arctocephalus pusillus pusillus colony at the Robberg Peninsula, Plettenberg Bay, on the south-east coast of South Africa, was driven to extirpation by indiscriminate harvesting by the late 1800s and seals only began to recolonise this site in the 1990s. This study describes the recolonisation process from 2000 to 2009, exploring within- and between-year variation in the number of seals using the site. Numbers increased over the study period from less than 300 animals to over 3 100. Year and month were important in explaining variability in seal counts, whereas sea condition, time of day and lunar phase had minimal explanatory power. Within-year variation in seal counts decreased during the study period, which may indicate an increasing proportion of resident (as opposed to transient) seals in the colony. However, the colony is currently still in a transition phase with a low ratio of breeding to non-breeding animals and low numbers of pups born on the colony (currently still < 100 per year). The influx of seals to the Robberg area may be associated with an increase in prey availability in the area. The relative protection afforded by the Nature Reserve status of the Robberg Peninsula and the existence of a Marine Protected Area adjacent to it are likely to contribute to the growth of this colony. However, human interference associated with fishing and/or ecotourism on the Peninsula may prevent the colony from developing into a breeding colony. Faecal (scat) sampling was employed to study the diet of this increasing seal population at Robberg. Species composition and size of prey were determined, temporal variation in the diet was explored, and the potential for competition between seals and the fisheries around Plettenberg Bay was investigated. Of the 445 scats collected, 90 % contained hard prey remains. These comprised of 3 127 identified otoliths representing 15 teleost prey species, 25 cephalopod beaks representing three 6 species and three feathers representing two bird species. The seals' most important prey species in terms of numerical abundance and frequency of occurrence in the diet were anchovy, sardine, horse mackerel, sand tongue-fish and shallow-water hake (in decreasing order of importance). The proportion of anchovy in the diet increased during the study period, while sardine decreased. Sardine was the only species that increased significantly in the diet during the upwelling season. Little evidence was found of direct competition between seals and linefisheries in Plettenberg Bay, both in terms of prey species composition and quantities consumed. Scat sampling in seals holds promise as a method to track long-term changes in prey species availability. The conservation and management of this colony are discussed in light of the research findings.
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- Date Issued: 2012
Seasonal changes in the heat production of an African small mammal, Rhabdomys pumilio
- Authors: Welman, Shaun
- Date: 2012
- Subjects: Mice -- Physiology Body temperature -- Regulation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21417 , vital:29514
- Description: Endothermy refers to the ability of an individual to produce heat from internal sources, and allows animals to maintain a body temperature that is higher than their external environment. Although much is known about the benefits of endothermy, its origin is highly debated. Nonetheless, due to environmental variation, endotherms have to regulate their heat production (thermogenesis) in order to remain normothermic. An endotherms regulatory response seems to be body size dependent. Keeping warm during cold periods is energetically expensive, and for small mammals this is exacerbated by their high rate of heat loss due to high surface area to volume ratios. To compensate for the heat lost, small non-hibernating mammals must increase their level of thermogenesis. Much of our current understanding of thermogenic responses of small mammals is derived from laboratory acclimated animals, and studies on naturally acclimatized animals are uncommon. In addition, most studies on thermogenesis tend to focus on one level of animal organisation, such as subcellular, tissue or in-vivo, but seldom integrate these data. The aim of this study was to measure year-round variation in thermogenesis across all levels of organisation, using naturally acclimatized Rhabdomys pumilio individuals from the Nelson Mandela Metropolitan University, Port Elizabeth. It was predicted that the level of thermogenesis would be significantly higher during winter relative to other seasons in order to cope with the low ambient temperatures (Tas) experienced during this season. Open flow respirometry was used to measure the animal's oxygen consumption, as a proxy for metabolism; the by product of which is heat production. The animal's basal metabolic rate (BMR), nonshivering thermogenesis (NST) capacity and summit metabolic rate (MSUM) were measured. A Western blot analysis was used to determine the expression of uncoupling protein 1 (UCP 1) in the animals' brown adipose tissue (BAT), as well as determine its relative concentration. The cytochrome c oxidase (COX) activity of the animals' visceral organs and BAT was measured, as an indicator of the tissues' metabolic activity. COX activity was determined as the difference in the tissues' oxygen consumption before and after the addition of horse cytochrome c.
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- Date Issued: 2012