3. Electronic Theses and Dissertations (ETDs) - All submissions

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Functional ecology of afrotropical freshwaters in the Republic of Congo, west-central Africa
(2024) Walsh, Gina
Characterising functional freshwater biodiversity patterns and understanding community determinants can aid in predicting changes and prioritising specific conservation management actions. Afrotropical freshwater systems support diverse ecological communities, including many taxonomically undescribed species, yet few studies have been undertaken in this region and they remain poorly understood. Additionally, an overwhelming amount of research on north temperate streams has given rise to widely used lotic conceptual models which are superimposed over freshwaters globally, though the theory governing the structure of Afrotropical lotic communities remains largely unexplored. In this thesis I explored different aspects of the biodiversity, trophic ecology and functional diversity of an Afrotropical system in the Republic of Congo (west Central Africa) through a series of field studies. I formally describe two new to science fish species collected in the region, and use fish functional traitbased approaches to explore the functional diversity of fish assemblages and test selected expectations of riverine conceptual models in this regional setting. Following, I used carbon and nitrogen stable isotopes (δ13C, δ15N) from samples collected along a continuum of a coastal river in the Republic of the Congo to show temporal and spatial patterns of trophic diversity and basal carbon resource use. In addition to uncovering new fish diversity, I established that whilst tenets of certain conceptual models such as the River Continuum Concept and the River Habitat Template were supported by fish trait-environment relationships, unique patterns of functional diversity also exist which are scale dependent and result in different functional strategies driving communities between upper and lower positions in the basin. At sub-basin scale, headwater zones harbour substantial functional diversity in relation to upstream catchment size, and results suggest that historical forest refugia may play a role in the high functional richness at high elevations of the region. Isotopic analysis revealed that river order and season are important drivers in consumer trophic strategies along a river continuum in the wet Afrotropics, and that riparian forest sources are key basal carbon resources supporting consumers. Isotopic work reiterated that headwaters are distinctive in terms of trophic and functional diversity. I discovered potential evidence for methanogenic pathways in lateral swamp forests that may subsidize instream food webs. The outcomes of this work demonstrate that existing river conceptual models only partially explain patterns of richness and functional diversity of river systems in this region, and highlights the importance of understanding mechanisms structuring regional functional diversity (e.g. nestedness and turnover) in efforts to conserve freshwater systems. It also emphasizes the need for swamp forest- and riparian specific policies in central Africa to be incorporated into freshwater conservation plans and strategies for forested regions of the Afrotropics.
Habitat selection by a threatened lizard, the sungazer (Smaug giganteus): implications for conservation
(2024) Stanton-Jones, Wade
Climate change and habitat transformation are some of the primary threats that reptiles face as a consequence of persisting in their selected habitats. Some species, such as habitat specialists, may be particularly vulnerable to these threats given their restricted geographic ranges, strict habitat requirements, and limited dispersal abilities. Knowledge of the factors that drive habitat and microhabitat selection by a species, the impact that habitat transformation may have on that species, and how the species is expected to respond to climate change is necessary for informing conservation management strategies. Smaug giganteus (the sungazer) is a threatened (Vulnerable), habitat specialist lizard that is endemic to the Highveld grasslands of South Africa. Unfortunately, suitable habitat exists in a landscape where anthropogenic activities (e.g., agriculture and mining) are prevalent, and a major threat that sungazers face is habitat transformation and fragmentation. Sungazers are unique within their family (Cordylidae) in that they rely on self-constructed burrows in specific microhabitats within the grassland matrix as long-term, often permanent, shelter and refuge sites. Because of this, aspects of their life history, and the current threats that they face, sungazers may be particularly vulnerable to the combined effects of climate change and habitat transformation. The primary aim of this thesis was to assess the consequences of habitat selection and use by sungazers by investigating the potential impact of climate change on habitat suitability for the species, the fine-scale impacts of habitat transformation, and to identify the microhabitat requirements by sungazers such that recommendations for future conservation management of the species could be made. The potential impact of climate change on habitat suitability for sungazers was assessed by projecting their current ecological niche envelope into the future, under different climate change scenarios. The models predicted that sungazers may experience minor range contractions under the moderate case scenario, but vulnerability to climate change increased under the worst-case scenario. At the broadscale level, the models predicted that sungazers would shift their geographic range to the southwest. However, given the species life history traits, limited dispersal capacity, and the fragmented habitat in which subpopulations exist, climate tracking is unlikely, and sungazers may be more vulnerable to the effects of climate change than predicted by niche models. An assessment of the demographics and dynamics of four sungazer subpopulations existing at sites with different habitat conditions revealed that the impact of habitat transformation on sungazers may be more devasting than what was previously reported. In this study, the sungazer subpopulations existing in habitats transformed by mining activities, and severe overgrazing have declined by more than 50% over a 16-year period. This assessment at the subpopulation level (colony level) suggests that the current size of the sungazer population is probably an overestimate. A comparison between the microhabitat characteristics surrounding sungazer burrows and random sites in the landscape revealed that sungazers use microhabitats comprised of low vegetation cover and short grasses in which to construct their burrows. Burrow construction in these microhabitats generally occurs on northerly facing slopes. When constructing their burrows, sungazers tend to orientate burrow entrances in the same direction as the aspect of the slope but northerly directions are preferred. This thesis provides the first insights into the potential effects that climate change may have on sungazers in the future and highlights the severity of impact that habitat transformation has on sungazers at fine spatial scales. The findings not only justify the importance of conservation management for sungazers but provide critical information to assist with future conservation protocols.
Human-wildlife conflict regarding shark nets in Richards Bay, South Africa: seeking solutions
(2024) Atkins, Shanan
In the mid-1900s, shark bites in KwaZulu-Natal, South Africa, impacted bathers and tourism, and the authorities set gillnets to reduce shark numbers. This quintessential human-wildlife conflict was exacerbated by incidental catches of non-target species (bycatch). Sharks are now threatened globally, yet KwaZulu-Natal continues to use lethal bather protection gear (nets and baited hooks) to reduce shark populations. I aimed to map KwaZulu-Natal’s bather-shark conflict, engage stakeholders and work with them in a productive, learning space that bridges research and implementation to improve the conservation status of sharks without compromising bathers. To map the human-wildlife conflict - identify and characterise the social and ecological elements of the system and their interactions - I used various philosophical perspectives and a multifaceted approach. First, I reviewed the ecological impact of KwaZulu-Natal’s lethal gear and found that 88% of the catches were not the three target shark species, many were threatened species and 73% of the animals died. Second, I modelled the numbers of sharks, bycatch and bathers at a high-catch beach to predict temporal overlap between them. The findings yielded trade-offs to consider when striving for a positive impact on biodiversity without impacting the risk to bathers. Third, I characterised the social dimensions of the conflict using interviews, questionnaires and the literature, focussing on stakeholders whose work intersects with the bather-shark conflict. There were multiple stakeholders, varying in influence over decisions and interest in the bather protection programme, but communication flows were limited. Publications about the social and policy context describe the complexity of the conflict but studies of the economic impact are lacking. Fourth, I used a qualitative, constructionist approach to understand these stakeholders’ perspectives of changing the lethal gear. Narratives of the obstacles were mostly centred around governance issues whereas opportunities were about technology, research and education. Finally, I used transdisciplinary learning to engage these stakeholders, leveraged their knowledge of different parts of the bather-shark conflict system and together, we designed a preliminary strategy to support the Sharks Board in moving away from lethal methods. My findings have illuminated multiple perspectives of the bather-shark conflict and exposed the stakeholders to these varied perspectives, improving our shared understanding. This should aid change agents in planning to implement change that would allow both humans and sharks to swim safely in KwaZulu-Natal.
Implementing resource efficient and cleaner production as a tool to reduce carbon tax in the manufacturing industries
(2022) Mashau, Phathutshedzo Ndifelani Maggie
The carbon tax came into effect in South Africa in June 2019 to reduce greenhouse gas emissions (GHGs). With its first phase focusing on scope one carbon emissions, facilities that combust 10 megawatts or more became liable for a carbon tax. Among these are large emitting industries like manufacturing plants. This has placed a greater burden on industries under the current economic status, worsened by the COVID-19 pandemic. In addition to paying for the scope one tax liabilities, companies must report verified carbon emission and energy consumption patterns (energy plans), which require resources. Implementing resource-efficient and cleaner production (RECP) methodologies in industries have been the mandate of the National Cleaner Production Centre South Africa (NCPCSA), the programme of the national government, to reduce the environmental footprint and improve industry competitiveness. As a result, many industries in South Africa are focused on reducing their resource consumption and environmental footprint by improving efficiencies in production processes. This research evaluated the benefit of the implementation of RECP as a tool to reduce carbon tax in manufacturing industries. Quantitative methods were applied in the data collection and analysis of three manufacturing plants that embarked on RECP implementation. Semistructured interviews were also conducted with expert consultants and company managers who were part of the team for the RECP implementation facilitated by the NCPCSA. Quantitative data were collected during the RECP assessment and the case study phase of RECP implementation. Regression analyses were applied to determine the energy baseline for each plant for further evaluation of the RECP implementation results. The quantitative results of the RECP implementation have shown a reduction in energy consumption, equivalent carbon emissions, and associated costs including equivalent carbon tax savings in all three plants. The interview responses have shown that the perception of RECP expert consultants and company managers support that implementation of the RECP methodologies in industries provides the basis for measurement and verification of energy consumption and equivalent greenhouse gas emissions for reporting purposes as per legislative requirements. They also agreed that RECP is beneficial in reducing energy consumption, greenhouse gas emissions, and associated costs (resource costs and carbon tax). These reductions in GHG emissions and costs can reduce the manufacturing plants’ carbon tax liabilities if the reduced carbon emissions fall under scope one in the current phase of carbon tax implementation (June 2019- December 2022). Nevertheless, the resulting reduction in energy consumption and equivalent carbon emissions were sufficient to draw some conclusions and recommendations.
Maintaining plant diversity of a species-rich montane grassland system in the face of global change
(2022) Gordijn, Paul Jan
The rich grassland-plant diversity of the Drakensberg mountain region, which has persisted under heterogeneous fire and herbivory regimes, and significant fluctuations in climate, has come to face its most formidable threat—land transformation, which involves habitat destruction and land use intensification. Over the last ca. 200 years, human settlement in the northern Drakensberg study area, the Mdedelelo-Cathkin landscape in South Africa, has markedly increased, but the influence of human pressure on plant diversity has been largely unexplored, leaving an uncertain future for this biodiversity. This thesis aimed to reduce uncertainty around the influence of socio-ecological systems, represented by communal, private and protected land tenure systems, on grassland habitat and associated plant diversity. Analysis of changes in land use and land cover and field-based sampling of plant diversity revealed a conservation conundrum. Although grassland-plant diversity was maintained at higher levels on private systems, these systems were especially vulnerable to transformation. And while communal systems were less vulnerable to transformation, they were associated with heavy-continuous grazing that transformed grasslands into a novel state depauperate of plant diversity. Protected systems were, however, largely successful in maintaining primary grasslands, and their plant diversity. On these systems, where fire is the principal disturbance agent, the previously unexplored, multidecadal influence of heterogeneous fire regimes, was explored. A novel characterisation of heterogeneity in fire-return intervals and season of burning identified a threat of increasing fire regime homogeneity. The influence of socio-ecological systems, and their particular fire and herbivory disturbance regimes were framed by a construct termed, “socio-ecological disturbance regimes” (S-EDRs), which successfully reflected the interconnected nature of human society, disturbance regimes, and plant diversity. The transformation of a quarter of the landscape’s primary grassland over the 71-year period of assessment should draw urgent attention from conservationists and society. The S-EDR framework highlighted the critical responsibility society has in maintaining plant diversity. For the conservation of grassland-plant diversity a cross-societal approach is necessary, valuable plant diversity was found across the socio-ecological systems evaluated. Moreover, protecting Drakensberg-grassland ecosystems and their plant diversity will contribute to the global effort to mitigate the looming influence of climate change.
Natural Sciences teachers' views on Indigenous Knowledge and How to use it in teaching and learning in South African Classrooms
(2022) Raphothe, Paseka Nimrod
South Africa underwent much curricular change during Apartheid and post-Apartheid. The quality of education provided for black people was the worst during Apartheid; the education they received catered only for menial labour. However, the need to provide quality education to all strata of society took precedence when South Africa became a democratic state in 1994. Moreover, the need to respect different worldviews and knowledge systems from different societies came into focus at this time. Thus, post-Apartheid, revisions to the curriculum led to the current Curriculum and Assessment Policy Statement (CAPS), which mandates that teachers include Indigenous Knowledge (IK) in their teaching and learning of Science. Investigations are required to understand the level of guidance teachers receive on integrating IK into their teaching. The following documents were analysed for this study to examine the guidance provided to teachers CAPS, Annual Teaching Plan (ATP), and the Pacesetter. Three teachers were surveyed to explore their views as well. The focus in this study was grades 8 and 9 Natural Sciences teachers. The study aimed to explore ways in which teachers could integrate IK in their teaching and learning of science to make science more accessible to their learners. The research took a qualitative case study approach and used theoretical frameworks as the lens. Aikenhead and Jegede’s border crossing, Vygotsky's Social constructivism, specifically the More Knowledgeable Other (MKO) and Zone of Proximal Development (ZPD), and Piaget's Cognitive constructivism (a process of accommodation and assimilation). Data was collected using questionnaires and followed up with semi-structured interviews. Thematic content analysis was used to analyse data and develop themes that helped answer the research questions. Findings in this study indicated some misalignment between the different curriculum documents used by teachers with regards to IK. However, the study indicated 3 that teachers are integrating IK into their teaching, as mandated by the CAPS. Some teachers use their experiences learned in the communities they grew up in and integrated that knowledge in their teaching and learner discussion in a Science classroom. This study documents examples used by teachers in their integration of IK into their classroom practice and, therefore, can provide a resource for teacher development in this area. Moreover, documentation of these practical examples of IK integration into classroom practice can be helpful to teachers who seek to facilitate the students’ access to science concepts taught in Natural Sciences.
Quantifying drought strategies in C4 perennial Southern African grasses
(2024) Marutha, Tebogo Rector
Plants have a range of strategies for surviving drought associated with the morphological and physiological traits that govern water use and loss. Most research has been done on woody species and whether the research applies in C4 grasses whose above-ground biomass cures annually over a dry season is not clear. In this study I described and quantified drought strategies and recovery patterns of thirteen perennial C4 grass species found in savanna and grassland ecosystems in South Africa. An experiment was undertaken where the grasses were grown and then exposed to a drought for three months, after which they were watered for one week to simulate a post drought recovery. I monitored stomatal conductance, leaf water potential, osmotic adjustment, leaf senescence and post-drought resprouting to assess whether plants with restricted water availability retained varying proportions of live leaf material or whether a wasteful water strategy during drought was associated with increased leaf death and post-drought recovery. Based on the measurements of the thirteen species, a broad range of strategies emerged related to the trade-offs between being efficient or safe, whereby some grasses control water loss by closing stomata and sacrificing photosynthesis while others continue to lose water while they photosynthesise. Additionally, osmotic adjustment demonstrated in species such Digitaria eriantha and Panicum maximum demonstrated an alternative drought strategy that is not currently recognised in the literature. Grasses with low stomatal control cured faster than those with a high stomatal control, which might have implications for flammability and leaf phenology in seasonal ecosystems with annual drought.
Quantitative determination of BTEX in groundwater using dispersive liquid-liquid microextraction technique and GC-FID.
(2022) Gwanyuki, Doreen C.
“Dispersive liquid-liquid microextraction (DLLME) method was developed and validated for the extraction and analysis of aromatic hydrocarbons BTEX (benzene, toluene, ethylbenzene, xylene) in water samples. DLLME is a miniaturized version of liquid-liquid extraction (LLE) is a fast, efficient, and inexpensive microextraction method for pre-concentrating and extracting hydrocarbons.” “In this study the DLLME technique was used for the determination of BTEX in water samples. BTEX normally exists in trace amounts in environmental samples thus sample preparation plays a vital role. Sample preparation played a significant role in extracting the analytes, preconcentration of the sample and removal of interferences. This is important because GC-FID is a highly sensitive method and uses small volumes in the analysis. Sample preparation techniques such as liquid-liquid extraction are tedious, time-consuming, and insensitive, to counter these disadvantages and using large sample amounts of highly toxic hydrocarbons microextraction methods known as DLLME was used.” The importance of sample preparation is frequently ignored but it is a significant step in the analytical method because accuracy and precision depend largely on this step. Data obtained from this study compared with other microextraction methods from literature show that the extraction method demonstrated good precision, linearity, detection limit and enrichment factor for the extraction of the analysis. Extraction parameters such as the type of extracting solvent, extracting solvent volume, type of dispersion solvent, and the volume of the dispersion volume were optimized. Under optimum conditions, the detection limits for DLLME ranged from 1.8 to 2.6 μg. L−1 , repeatability from 2 to 4% and the extraction efficiency ranged from 60.1 to 95%. The applicability of the DLLME method was studied by gas chromatography with flame ionization detection system. The results demonstrated that the environmental water samples contained trace quantities of BTEX compounds, 2.7, 1.9, 0.3 and 0.4 μg. L−1 , respectively.”
Range size and dispersal of grasses (Poaceae) in Africa
(2024) Mashau, Aluoneswi Caroline
Geographic range size is the outcome of both evolutionary and ecological processes. Therefore both historical contingencies, and the ecological characteristics (traits) of particular species, interact to result in observed distribution patterns. These distribution patterns are also changing – expanding as species invade into new ecosystems, and shrinking as species are filtered from ecosystems due to climate change or changing land management. Understanding current distributions and range sizes is therefore important for helping explain biogeographic patterns and processes, for informing conservation action, the management of invasive plants, and interventions to adapt to climate change. The grass family (Poaceae) covers approximately 31– 43% of the land surface globally, and started to spread during the Miocene period (approximately 8–20 Million years ago) to achieve its current dominance. This would have occurred through rapid range expansion as well as speciation and has resulted in some species with almost cosmopolitan (global) distributions, as well as rare grass species found in only a few localities. This study aims to understand the drivers of range size and dispersal traits of grasses in Africa with the purpose of quantifying differences between clades and functional types, and determine the floral traits that likely influence dispersal modes. In Chapter 1 I compiled general introduction of the whole thesis including background, rationale, aims and objectives. In Chapter 2 I aimed to understand the geographical distribution of grasses in sub-Saharan Africa with reference to key plant traits thought to affect range size in this family (Poaceae). Specifically, to test hypotheses on the importance of plant height and lifespan in determining range size and invasion potential in the context of their evolutionary history. The range sizes of 757 grass species native to southern Africa were estimated for the sub-Saharan African region from geo-referenced herbarium records using the alpha hull function. Phylogenetic generalised least squares models and linear mixed effects models were fitted to test whether grass range size was related to plant height and lifespan. Tribe-level relationships between range size and plant height were assessed with linear models. For species introduced to other continents, generalised linear mixed effects models were fitted to test whether invasiveness was related to native range size, plant height and lifespan. Differences in native range size 4 among species in four invasion-related categories were assessed with linear mixed effects models. Geographic range sizes were larger for taller grass species and for species with shorter lifespans. The relationship between plant height and range size varies widely among tribes, with some environmentally-restricted tribes not showing significant responses to plant height. Grasses with larger native range sizes and shorter lifespans are more likely to become invasive after being introduced to other continents. Grass species introduced to other continents have larger native range sizes than those that have not, and native range size increases along the introducednaturalised-invasive continuum. The increased dispersal opportunities of annual-biannual grasses appears to have a greater positive effect on range size than do the longer generation times of perennial grasses. Grass height has and continues to be an important driver of grass biogeography, with implications for understanding the spread of certain grass tribes over the Miocene. Factors that promote large native range sizes are also likely to increase the probability of a species becoming invasive. Grass floral structures vary greatly but we have very little understanding of their functional significance. Due to the varied dispersal mechanisms shown by grasses, certain syndromes of floral traits would likely be associated with particular strategies for dispersal, and consequently, different environments. In particular, effective seed maturation and dispersal in fire-prone tall grasslands would require different floral trait syndromes than in short, frequently grazed ecosystems. In Chapter 3 I quantified floral traits of nearly 200 Poaceae species from savanna and grassland ecosystems in southern Africa and explored how their floral structures co-vary and correlate with other functional characteristics such as grass height. Using field information on the dominance disturbance regime of 163 of these grass species it was tested whether certain floral traits are more associated with fire vs grazing. Non-metric multi-dimensional scaling (NMDS) was used to illustrate how floral traits covaried among grass species, and to group them into syndromes based on these traits. Analysis of variance (ANOVA) was used to test whether certain floral trait syndromes were more associated with fire vs grazing. I identified four clear floral trait syndromes separated largely by awn length and the presence of hooks/prickles or bristles. Longawned species were more likely to be found in frequently burned environments and were also usually taller than species without awns. Grazer-dominated systems appear to select for two different floral trait syndromes. The study has improved our ecological and taxonomic 5 understanding of how floral traits differ among the range of tribes in one family across African countries. It can help in understanding dispersal limitations in grasses and predicting which species are likely to flourish in particular grassland habitats. The grass family (Poaceae), despite having only emerged and spread in the last 50 million years, is cosmopolitan, and many species have large, almost cosmopolitan distributions. Lineage age and dispersal ability are two factors thought to explain the variation of range size and grasses show a wide range of floral structures and heights associated with different dispersal strategies. In Chapter 4 I aimed to assess how dispersal syndrome (inferred from floral structures and other functional traits) and evolutionary history affect range size in the grass subtribe Eleusininae – a tropical grass clade with variation in floral structures. Global location records for 97 grass species of 29 Eleusininae genera were used to quantify range size, and linear models were used to test the relationship between range size and interaction between plant height, and lemma awn state (absent/present), caryopsis length (mm) and genus age. Taller grass species with awned lemmas were found to have a larger range size, and this supports my hypothesis (developed in Chapter 2) that the importance of grass height in driving range size depends on the dispersal syndrome. It was found that there is no relationship between genus age versus floral and functional traits used in this analysis. The study can help to explain some of the differences in biogeographic history between different lineages and also determine dispersal syndromes. In Chapter 5 I compiled general discuss or overview of the study, including geographical distribution of the southern African grasses, grass clades co-vary according to their floral traits, conservation and management implications, limitations of this study and needs for future research and conclusion.
Re-assessment of the threat status of three Red Data List plant species: brachystelma gerrardii, senecio triodontiphyllus and streptocarpus fasciatus
(2022) Makgopo, Katlego
Plants provide fundamental support systems and resources for life on earth, they serve as the foundation of ecosystems. However, many plant species are rapidly going extinct and will soon disappear. The threat assessments of plants are important as they inform which species are most at risk and call for immediate management attention and conservation. The first step to initiate conservation actions for endangered organisms is identifying species that are in decline or face extinction. A previous study for the management of Pullen Nature Reserve found that there are threatened plant species that occur on the property and in the conservancy. These plants are: (1) Brachystelma gerrardii Harv., (2) Senecio triodontiphyllus C. Jeffrey, and Streptocarpus fasciatus T. J Edwards & Kunhardt. Brachystelma gerrardii has a distribution from KwaZulu-Natal to the Waterberg in Limpopo, and is currently classified as Endangered (EN) according to the IUCN Categories and Criteria,. Senecio triodontiphyllus has a distribution that is restricted to the Mpumalanga province, from Barberton to Kaapmuiden. This species is currently classified as Vulnerable (VU). Streptocarpus fasciatus is endemic to South Africa and occurs in Mpumalanga. Its distribution ranges from Nelspruit to Kaapmuiden. This species has a current threat status of VU. Brachystelma gerrardii, S. triodontiphyllus and S. fasciatus were chosen for this study because they are rare, endangered and have restricted distributional ranges. A re-assessment of their threat status is important as the previous assessments are out of date. Thus, the aim of this project is to re-assess the threat status of three plant species B. gerrardii, S. fasciatus and S. triodontiphyllus; to assess the potential effect of climate change on current and future distributions of these plant species; as well as to investigate aspects of the reproductive ecology of S. fasciatus. The IUCN Red List Categories and Criteria were used to perform the assessments; these criteria are objective, quantifiable and have been used over many years. This project was carried out in three stages, (1) an analysis of herbarium specimens as well as fieldwork to collect data on species habitats, range sizes, population sizes, as well as Area of occupancy (AOO) and Extent of occurrence (EOO) among other information to determine the current threat status of the species; (2) an analysis of current and future climate data to determine the impact of climate change on plant species distributions; and lastly, (3) investigating the breeding strategy used by S. fasciatus, to determine whether pollination and germination have implications for the threat status. Results from herbarium records and fieldwork revealed eleven, five and six sub-populations for B. gerrardi, S. fasciatus and S. triodontiphyllus respectively. According to the MaxEnt models for B. gerrardii and S. triodontiphyllus, areas that are currently suitable for the growth of these plants are predicted in the eastern parts of South Africa from East London through KwaZuluNatal and Mpumalanga, towards the northern parts of Limpopo. Current suitable areas for S. fasciatus are predicted as patches along the coast in Western cape, along the border of Lesotho in KwaZulu-Natal, in parts of Gauteng as well as the eastern parts of Mpumalanga. Future iv predictions for 2050 using the A1B and A2 emission scenarios showed a decrease in suitable habitats for B. gerrardi and S. triodontiphyllus, but a significant increase in the suitable habitat for S. fasciatus. Field studies on the pollination of S. fasciatus show that this plant may be pollinated by a nemestrinid fly belonging to the genus Stenobasipteron, and the results also indicate the presence of a mixed breeding system involving self-pollination and cross-pollination. A low seed set was observed in open pollinated flowers, indicating that the species may be pollinator limited, however, this observation may also be as a result of the species’ very specific habitat requirements. This may contribute to its low population size and thus its threatened status. According to the results of the IUCN threat assessment, S. fasciatus was found to be vulnerable (VU) under Criterion D (subcriteria D1 and D2), and S. triodontiphyllus was found to be endangered (EN) under subcriteria D1. Brachystelma gerrardii remains classified as EN as per the threat assessment by Styles and von Staden in 2007. Based on the results of this study further investigations are required with regards to the breeding system of S. fasciatus, and all three of these plant species are in need of immediate conservation actions.
Scaling of ecosystem phenology across satellite sensors and field-based observations: a case-study of contrasting vegetation types in a semi-arid savanna
(2022) Damant, Richard John
Savannas are characteristically heterogenous and are driven by factors such as rainfall, herbivory, fire, and soil nutrients. All these factors interact differently at different spatial and temporal scales. Savanna phenology is highly unpredictable and is influenced predominantly by rainfall among other environmental factors. Climate change is therefore likely to alter phenological responses which emphasises the need for monitoring. However, the heterogeneous nature of savanna phenology makes it difficult to monitor as savanna treegrass ratios are unpredictable and are not comparable across spatial scales. This similarly applies to the use of remotely sensed data sources used to estimate phenological events, which have different spatial and temporal properties, thus phenological observations are limited to the scales they were derived from. Many studies have made use of the Normalised Difference Vegetation Index (NDVI) to estimate both vegetation biomass and phenological metrics from a variety of different satellite products. However, no studies were found that explicitly investigated how spatial scale influences phenological metric and vegetation biomass estimates in a southern African savanna setting. Therefore, this study aimed to explore the influence of spatial scale on phenology and biomass estimates derived from remotely sensed products in a semi-arid savanna. A spatially nested data collection process was followed from which in situ biomass and remotely sensed NDVI products were collected. Results suggest that finer scale NDVI products are better predictors of herbaceous biomass and, on average, phenological metrics occurred later at coarser scale and earlier at finer spatial scales (~17 days). The conclusions from this study highlight the need for monitoring programs to carefully consider the use of coarse scale NDVI products as a proxy for biomass, particularly in heterogeneous landscapes, and the need to use a multi-scale approach when estimating phenological processes.

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Browsing 3. Electronic Theses and Dissertations (ETDs) - All submissions by School "Animal, Plant and Environmental Sciences"

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