The process of thicket encroachment in semi-arid savanna: community patterns and biotic interactions
- Authors: Nell, Rhys
- Date: 2022-10-14
- Subjects: Scrub encroachment , Savanna ecology , Biotic interaction , Plant nutrients , Plant-water relationships
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/364966 , vital:65666
- Description: Bush encroachment in savannas is widespread in South Africa and is concerning, from both socio-economic and conservation viewpoints, as it affects ecosystem services, functioning and productivity. This phenomenon depends on multiple factors such as history, vegetation, management and environmental conditions, and their interplay. Encroachment into savannas has been relatively well-documented, however understanding of the different roles of tree-tree interactions between species that occur during this process is still limited. This includes the interactions causing spatial patterning, or how interactions and outcomes change over time in terms of encroachment succession from open savanna to closed-canopy thicket. The main objectives of this research are to document thicket establishment in a savanna ecosystem and consider the ecological roles of the key woody species and the abiotic properties of their micro-sites. Determining interactive effects of species co-occurrence is critical to understanding or predicting patterns and changes in biodiversity, nutrient distribution and available water resources. It is also imperative in determining correct and effective land management practices, particularly for reducing bush encroachment and its negative effect on rangelands. All data were collected on Endwell farm, located in the Smaldeel region of the Eastern Cape, South Africa. Endwell farm is a semi-arid savanna with a mean annual rainfall of 730 mm. First, I examine and describe the thicket encroachment process by exploring the associations between species and their size classes in the field. This was done by using plot-based belt transects and looking at changes in species size-class compositions from early to late successional stages. Association rules (market basket) analysis was used to identify the most common species size-class association patterns. The association between the savanna tree Vachellia karroo and the thicket pioneer Scutia myrtina was the most prevalent at all stages, with V. karroo being central to all associations in the first stage of encroachment; during later stages of encroachment, associations shift to incorporating other thicket pioneer species. The demography and clump formation of S. myrtina was strongly linked to associations with V. karroo to initiate bush clump formation. Results suggest that mature V. karroo facilitate the establishment and growth of S. myrtina. These two species were the focus of more detailed investigations to explore the nature and magnitude of their interspecific interactions. I then examined the effects of pairwise tree interactions between V. karroo and S. myrtina on soil and leaf nutrient content. I measureddifferences betweeninter-canopy and sub-canopy soil nutrient content, and the effect of associations on plant leaf nutrients, between pair-size combinations and individual controls. Results confirmed that pair-size tree interactions affected both soil nutrient and leaf nutrient content. All individuals increased soil K, N and organic C in the sub-canopy, while association with V. karrooincreased S. myrtinafoliar N, Pand K. In contrast, association with S. myrtinaloweredV. karroofoliar N, P and K. Small S. myrtina individuals werefound to benefit most from establishing and growing next to a large V. karroo individual, through mechanisms affecting soil and foliar nutrients. Scutia myrtina individuals establishing in association with smaller size classes of V. karroo showed no significant effects. I tested for positive and negative effects of pairwise tree interactions between Vachellia karroo and Scutia myrtina on available soil water and plant water potential (Ψ). This was done by looking at differences betweeninter-canopy and sub-canopy soil moisture and bulk density and associations on plant water stress (pre-dawn and mid-day leaf Ψ), between pair-size combinations and individual controls. I also selectively removed large V. karroo individuals from pairs to confirm the effects of competition andfacilitation. Similar to other studies, results confirmed positive and negative effects of pairwise tree interactions. Small S. myrtina individuals weremost facilitated by establishing and growing up next to a large V. karroo individual, through mechanisms affecting soil water content, bulk density and leaf Ψ. Scutia myrtina establishing in association with other size classes of V. karroo were much less facilitated, showing no significant effects. In contrast, large S. myrtina showed competitive interactions with V. karroo. , Thesis (MSc) -- Faculty of Science, Botany, 2022
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The effectiveness of bank debt financing on the growth of small and medium enterprises (SMEs) in Namibia
- Authors: Paulus, Panduleni Hambeleleni
- Date: 2023-10-13
- Subjects: Business enterprises Finance , Small business Namibia , Small and medium enterprises , Stakeholder management , Debt financing (Corporations)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/419176 , vital:71622
- Description: Globally, SMEs are valued for their contribution to economic growth and development as well as for driving employment. To succeed, small firms require support especially in terms of obtaining funding and financial services that can enable them to meet day to day operational needs. Commercial banks play an important role for the financing of SMEs as small firms generally depend on bank loans to obtain external finance. However, despite the support and contribution, very little attention is given to the actual forms of finance used by small and medium-sized enterprises, the available finance made by lending institutions or investors and the relation between the use of the said debt finance and enterprise performance. Furthermore, several research studies carried out focusing on the effect of debt financing on performance of firms are inconsistent. Thus, this study sought to determine the effectiveness of bank debt finance on the growth of SMEs in Namibia. To achieve the objective of the study, it was important to have it rooted in the pragmatism paradigm; followed by both the deductive and inductive approaches. Interviews were conducted with the six SME owners and structured questionnaires were completed by the seven staff of the selected bank. The study used thematic analysis to analyze primary data from interviews by following three steps namely: reducing the data referred to as coding, analyzing data by creating patterns, and generating themes and drawing conclusion. Data from self-administered questionnaires was populated and textually analyzed aided by tables. The main findings of the study were that: (1) debt financing contributed to the growth and performance of SMEs as all firms under the study who made use of debt had experienced growth in terms of generated profits and acquired assets, (2) during the assessment and approving process, the bank looked at various lending factors and that collateral was not considered as prime to accessing funding, (3) the SMEs were not sufficiently funded and that there was no appropriate funding option for SMEs, (4) in terms of relationships, there was a lack of engagement and support between the bank and the SMEs. The support received from the bank was only in terms of lending. , Thesis (MBA) -- Faculty of Commerce, Rhodes Business School, 2023
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Freshwater invasive alien crayfish species in South Africa: testing eDNA assessment and DNA barcoding
- Authors: Mdidimba, Nonkazimulo Dorothea
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424413 , vital:72151
- Description: The expansion of the wild populations of the two invasive alien crayfish species, i.e., Cherax quadricarinatus and Procambarus clarkii in South Africa is of high concern. Given this, innovative and improved monitoring methods are required to be explored in order to effectively detect and manage their spread. Environmental DNA (eDNA) has shown promising and reliable results to detect and monitor alien crayfish in freshwater systems even at low densities. This research study aimed to field-test the application of eDNA for detecting and monitoring invasive alien freshwater crayfish species (IAFCs) in South African freshwater systems (Chapter 2). Further, this study also aimed to confirm the true taxonomic identity of the IAFCs in South African freshwater systems by using DNA barcoding to avoid potential misidentifications with morphological identification alone (Chapter 3). Also, ectocommensal temnocephalans and leeches attached to the crayfishes were also identified with DNA barcoding. The mitochondrial COI gene fragment of the crayfishes and the ectocommensal temnocephalans and leeches was amplified, sequenced, and used for species identification. For eDNA monitoring of C. cainii, C. quadricarinatus and P. clarkii, water samples were collected from Eastern Cape, Free State and KwaZulu Natal sites that are known to house these species. The current study did not detect the eDNA of the wild populations of both C. quadricarinatus and P. clarkii. This failure was encountered despite employing several methods, such as, end-point polymerase chain reaction (PCR), quantitative PCR (qPCR) and next-generation sequencing (NGS). The eDNA assessment to detect IAFCs in the wild populations is discussed in detail, and corrective measures suggested (Chapter 2). However, only C. cainii was able to be detected by eDNA. Cherax cainii is housed/farmed in an aquaculture facility (Vaughn Bursey’s Stock Farm in Eastern Cape) with large number of individuals per pond. For this, NGS was able to detect C. cainii but the other two methods, end-point PCR and qPCR were not able to detect the species. Based on the results, refinement of eDNA monitoring methods for the South African freshwater systems is recommended. Evaluation of different DNA collection methods, preservation, DNA extraction kits and primer design to obtain effective eDNA detection is discussed as possible sources of error. Interestingly, the newly established population of P. clarkii in Mimosa Dam in Free State was infested with alien leeches, that were confirmed by DNA barcoding to be Helobdella europaea and Helobdella octatestica. Consequently, this study reports for the first time in South Africa the presence of this alien freshwater leeches. The presence of alien leeches and P. clarkii suggests a double invasion in Mimosa Dam, P. clarkii seems to continue expanding its range in the country. However, the long-established population of P. clarkii in Driehoek Farm in Mpumalanga, which has been in the country for over 30 years did not have any leech or temnocephalan infestation. This could suggest several interesting ecological phenomena, including environmental filtering over time of the co-invaders, differential source populations, and post-introduction adaptation. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
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