Electronic Theses and Dissertations (PhDs)

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Cognition in urban-dwelling yellow mongoose, Cynictis penicillata
(University of the Witwatersrand, Johannesburg, 2024) Muller, Mijke; Pillay, Neville
Cognition involves perceiving and processing environmental cues and devising appropriate behavioural responses to act on the acquired information. Studying animal cognition in an urban setting provides insight into the occurrence of behavioural changes in urban-adapted animals. This thesis aimed to investigate the cognitive abilities of a population of yellow mongoose, Cynictis penicillata, inhabiting locations with differing extents of urbanisation in South Africa. First, I investigated whether mongooses could learn to solve a puzzle box problem of increasing complexity. The mongooses were able to solve the problem at each stage of complexity, but took longer in a residential ecological estate than those frequently visiting a residential garden. These results indicated that mongooses were capable of innovation, but their problem-solving abilities were influenced by the level of disturbance in their environment. Secondly, I investigated whether mongooses exhibited cognitive flexibility. The mongooses were able to inhibit a non-rewarding behaviour, even when it was previously rewarded, in favour of a newly rewarded behaviour during the puzzle box task. Additionally, they could solve the puzzle box problem during distraction, but took longer with the most distraction, likely splitting their attention between solving the problem and remaining vigilant. Combined, the mongooses were capable of reversal learning and divided/alternating attention, providing evidence of cognitive flexibility in this mongoose population. Thirdly, I investigated the effects of a direct human approach on the problemsolving ability of mongooses. In areas of heightened human disturbances, the mongooses had reduced tolerance to humans, but were equally efficient at solving the puzzle box problem following human disturbance than those in areas of reduced human disturbance. Those more tolerant of humans improved their problem-solving efficiency, likely adapting to the disturbance. Finally, I investigated whether mongooses experienced a paradox of choice (i.e. whether too much choice can be cognitively challenging). The mongooses in my study appeared to experience cognitive difficulties when presented with extensive choice, providing support for a paradox of choice. These results provide evidence that urban-living yellow mongooses’ successful adaptation to an urban habitat may be attributed to their cognitive abilities, allowing them to exploit novel resources and flexibly adapt to the rapid environmental changes associated with urbanisation. However, the disturbance associated with urbanisation may negatively affect problem-solving efficiency, which may impact successful food acquisition, and the increased availability of resources may be cognitively challenging for urban-living yellow mongooses.
Factors limiting karoo shrub populations in the Nama-Karoo
(University of the Witwatersrand, Johannesburg, 2023-09) Hebbelmann, Lisa; O’Connor, Tim; Witkowski, Ed
The Nama-Karoo Biome occupies the central and western region of South Africa. Nama-Karoo shrublands are dominated by karoo dwarf shrubs and in the wetter eastern regions annual and perennial grasses are interspersed among shrubs. Rainfall and grazing are the main drivers of vegetation change in the Nama-Karoo. Stocking rate, season of grazing and animal type are important influences on vegetation community composition, and rainfall determines shrub growth and the abundance of grass. More recently, fire has been identified as a driver of vegetation change. Understanding vegetation change is important for land managers in the Nama-Karoo as changes in karoo shrub communities have implications for forage availability. This thesis is focused on understanding how grazing, fire, grass-shrub competition, and soil moisture and temperature affect the composition, structure, growth and phenology of karoo shrubs in the Eastern Upper Karoo. Livestock type and stocking rate vary greatly over the greater Nama-Karoo area. Plant composition data from the Afrikaner-Hereford grazing trial at Grootfontein show that grazing has a strong legacy effect on Karoo rangelands and grazing-induced compositional and structural changes are clear many years after grazing has ceased. Different sheep breeds affect karoo shrub communities in different ways. There was a severe negative effect of heavy stocking with dorper sheep on karoo shrub communities and their structure; the impacts of merino sheep were significant but less severe. Effects of animal type and stocking rate were not consistent across the sites but appear to be dependent on edaphic factors. Soil physical properties appear to play an important part in determining the long term effects of grazing on karoo shrub communities. Fire is a novel disturbance in the Karoo. Nine sites which had experienced fire for the first time in history were studied for the effect of fire on the composition and structure of their shrub communities. The immediate effect of fire on karoo shrub communities was severe and the legacy effect of fire was significant. The nature of recovery after a fire depended on the abundance of fire-intolerant obligate reseeder shrubs that are killed by fire compared to the abundance of fire-tolerant resprouting shrubs. Rainfall and grazing management were important determinants of shrub recovery after a fire. As rainfall increases, grass biomass is predicted to increase, and this may result in fire becoming a more frequent occurrence in the Nama-Karoo. During periods of high rainfall, the biomass of grass in the Nama-Karoo increased at the expense of shrub cover. The effect of grass-shrub competition on shrub growth and phenology is not adequately explained by existing hypotheses of niche separation and succession. A field experiment which examined the growth and phenology of karoo shrubs in the presence of grass (unclipped control) and the absence of grass (grass removed by clipping) did not provide evidence of a competitive effect from grass on shrub growth or phenology. It did, however, provide valuable insight into how shrub growth and phenology are influenced by soil moisture and temperature. Rainfall in the Nama-Karoo is sporadic and a karoo shrub’s ability to utilise soil moisture will determine its ability to grow and successfully recruit. Shrub growth, with or without grasses in the vicinity, was strongly correlated with rainfall, but this was modified by temperature. Similarly, soil moisture and temperature were important for stem growth and phenology. Flowering occurred in response to soil moisture all year round but seeding occurred mainly during summer. Patterns of growth and phenology can be used by land managers to optimise shrub production while allowing phenological processes to take place. The findings of this study provide further insight into how grazing, fire, competition, soil moisture and temperature influence shrub populations and their structure, and these are discussed in the context of an existing state-and-transition model for the Eastern Upper Karoo. The importance of animal type and stocking rate, and how they vary across Nama-Karoo landscapes, is highlighted. The legacy of both grazing and fire reveal that the transitions between the alternate states of Nama-Karoo shrublands are not easily reversed in a management timeframe. It may take decades for a community changed by grazing or fire, acting independently or in conjunction, to return to their former state even under benign management. These findings along with a description of how soil moisture and temperature influence shrub growth and phenology have been used to make ecologically sound recommendations for the management of Nama-Karoo rangelands. Future research is needed to improve our understanding of how edaphic factors limit and influence karoo shrub populations across a variety of karoo landscapes, how repeat fires might change karoo vegetation, and whether temperature and the presence of pollinators influences shrub seed set. An assessment of the economic implications of vegetation change in the Nama-karoo is warranted so that management recommendations can be made with both ecology and economy in mind.
The effects of concurrent extreme temperature and water deficit on the phytochemical profile and phytopharmacological activities in Portulacaria afra Jacq
(University of the Witwatersrand, Johannesburg, 2024) Adeleye, Oluwafunbi Christianah; Risenga, Ida
In nature, all plants are exposed to stress which are mostly biotic and abiotic stress factors. Previous studies have demonstrated the impact of various abiotic stress factors on the production of secondary metabolites in therapeutic plants. Plant responses to stressors brought on by a combination of antagonistic abiotic factors have shown to be phenomenal compared to when plants are exposed to single a factor. According to latest climate change models, it is believed that plants would suffer unique or demanding concurrent abiotic stresses in the years to come. South Africa has been experiencing increasing temperatures over last 40 years and being regarded as a climate change ‘hot spot’ by the Intergovernmental Panel on Climate Change (IPCC). Therefore, it is critical to conduct research on the impact of climate change on the bioactive compounds in therapeutic plants. The overarching aim of this study was to establish and scientifically document, for the first time to our knowledge, the phytochemical profile, medicinal properties and phytopharmacological attributes of Portulacaria afra, a widely renowned medicinal plant used for treating several skin conditions and oral infections which also includes the assessment of the effects of concurrent extreme temperatures and water deficit/drought on species’ biological activities. In this study, South African Portulacaria afra plants were selected from healthy parent plants and propagated from cuttings. Samples were allowed to grow and establish a root system in the greenhouse for up to three months. After three months, 180 potted plant samples were exposed to treatments and not watered for up to 144 hours (6 days), and 45 control samples were placed under 25oC (ambient) and watered every second day with 500ml of water. The control samples were kept at 25°C maximum night-time temperature (7pm to 5am) and 27°C maximum day time temperature. Plants undergoing treatment (coded as treatment A, B, C, D) were treated as follows: A and B were exposed to 0/10ºC (night/day) and 5/15ºC (night/day) respectively, while C and D were exposed 20/40°C (night/day) and 35/45°C (night/day), respectively. Five potted plants were harvested in each treatment three times for up to 6 days (144hrs). Sample harvesting was scheduled episodically every 48hrs (48, 96, 144) and were then airdried under 40°C for 2 to 3 days. The aqueous (water) extracts at a temperature of 60°C, alongside methanol, n-hexane, and ethyl acetate extracts were derived from the leaves, stems, and roots. The extracts were then used to investigate the phytochemical composition, antibacterial efficacy, antioxidant capacity and antidiabetic potential. The qualitative phytochemical screening encompassed the preliminary assessment of saponins, flavonoids, glycosides, quinones, phenols, terpenoids, steroids, phytosteroids, volatile oil, carbohydrates, amino acids, and coumarins. The quantitative analyses were performed to determine the total phenolic content (TPC), total flavonoid content (TFC), while the antioxidant assays were performed to determine the reducing, scavenging and chelating abilities against DPPH, H2O2 and metal (Iron) chelating. The antibacterial activities against gram-negative Escherichia coli and gram-positive Staphylococcus aureus, Streptomyces griseus were assessed through agar well diffusion assay. The antidiabetic potential was evaluated using In vitro inhibitory α-amylase assay. Chemical profiling of various extracts from the leaves, stems, and roots of P. afra was conducted to identify and quantify some secondary metabolites. The methanolic leaf extracts exhibited a notable presence of quinones, phenols, steroids, and coumarins, whereas the aqueous leaf extracts contained moderate presence of saponins, terpenoids, quinones, and coumarins. Ethyl acetate leaf extracts were characterized by a strong presence of tannins and a moderate presence of phytosteroids. Conversely, n-hexane leaf extracts showed considerable saponin levels, moderate tannins, and terpenoids. Significantly strong presence of secondary metabolites was observed in methanolic stem extracts, particularly terpenoids, steroids, phenols, and coumarins. Notably, coumarins, known for their anticancer properties, were prominently present in methanolic leaf and stem extracts, with a moderate presence in root extracts, hinting at potential pharmaceutical applications and future roles in public health. Aqueous stem extracts exhibited strong glycoside presence, while ethyl acetate and n-hexane stem extracts exhibited few fewer secondary metabolite groups, ranging from moderate to weak presence. Distinctive chemical profiles were observed in root extracts, with ethyl acetate extracts showing significantly stronger quinone presence. Methanolic root extracts displayed moderate presence of coumarins and glycosides, whereas aqueous root extracts showed a low glycoside presence. The highest total phenolic contents (TPCs) and total flavonoid contents (TFCs) were found in methanol stem extracts and aqueous root extracts, respectively. Notably, aqueous root extracts exhibited the highest TPC and TFC among all root extracts. Antibacterial activity assays showed a wide range on inhibitory effects of n-hexane extracts from leaf, stem, and root against test microorganisms. Ethyl acetate leaf extracts demonstrated considerable inhibitory efficacy against Staphylococcus aureus, while methanolic extracts showed zero zone of inhibition. Aqueous root extracts showed strong antibacterial activity against Staphylococcus aureus, whereas other extracts showed no significant activity. Inhibition zones ranged from 13 to 24 mm for the plant extracts. The assessment of antioxidant potential through DPPH, H₂O₂ scavenging, and metal chelating assays showed varied activity among extracts. Ethyl acetate root extracts showed the strongest H₂O₂ scavenging activity, while aqueous stem extracts showed the strongest antioxidant activity against DPPH radicals. Aqueous and n-hexane root extracts showed the strongest metal chelating ability. The in vitro antidiabetic activity showed that all plant parts were active against α-amylase, with the highest inhibitory action recorded from the methanolic leaf extracts, followed by the methanolic root extracts
The value of large trees and their protection where elephants and trees co-exist
(University of the Witwatersrand, Johannesburg, 2024) Cook, Robin Michael; Henley, Michelle; Witkowski, Edward
Increasing African elephant (Loxodonta africana) numbers in many southern African protected areas have raised concerns about their impact on large tree species and subsequent effects on biodiversity. However, sustainable strategies for managing elephant impact on particular large trees of concern require stakeholder support. Concerned stakeholders in South Africa's Associated Private Nature Reserves (APNR), a protected area containing a high density of waterholes and elephants, are implementing tree protection methods to protect large trees from elephant impact, but few studies have assessed these methods’ efficacy. This thesis aimed to understand stakeholder perception of the value of large trees. Thereafter, I investigate elephant impact on the large tree component within the APNR over a 12-year period while also assessing the relationship between the persistence of the nests of large tree nesting birds and that of the trees themselves. Lastly, I assessed the effectiveness of various implemented tree protection methods to mitigate against elephant impact. A combination of qualitative and quantitative analysis was used to measure stakeholders’ values on large tree and elephant population dynamics, as well as management strategies to reduce the impact on large trees. The results show that stakeholders were concerned about the loss of large trees and its impact on other species. However, they disagreed on the most effective management strategy to minimise elephant impact, with varying values across stakeholder generations and professions. The persistence trends of 2,758 large trees comprising three species of concern were analysed between 2008-2020 to understand the impact of elephants and other environmental factors on tree mortality. The annual large tree mortality rate from 2008-2020 was 5.6%, with varying declines among tree species and the most significant declines occurring during dry periods. Furthermore, the long-term impact of elephants on trees nested in by the critically endangered white-backed vulture (WbV, Gyps africanus) was studied in riparian and woodland habitats to investigate both tree and nest persistence. Ten tree species were utilised for nesting sites, with woodland trees more at risk to elephant impact verses those in the riparian habitat. However, there was no direct correlation between WbV nest loss and tree fall. Lastly, when considering tree protection methods, about half of the 2,758 trees surveyed were wire-netted as potential elephant impact mitigation strategy. Trees with a stem diameter >40 cm that were wire-netted had the highest persistence rates, but the wire-netting needed replacing after four years. Overall, wire-netting was the most practical method for larger- scale implementation, particularly on larger trees elephants cannot push over. Of the four tree protection methods evaluated in this study in terms of their effectiveness and practicality as a mitigation strategy, beehives were found to be the most effective at protecting trees but proved to be the most expensive in comparison to wire-netting, concrete pyramids and creosote jars
Tracing multiple aquatic ecosystem stressors across a land-use intensification gradient: A multi-tooled environmental forensic approach
(University of the Witwatersrand, Johannesburg, 2024) Levin, Jonathan Chaim; Woodford , D.J.; Curtis, C.J.
South Africa requires advanced freshwater management approaches to address complex catchment stressors acting on aquatic ecosystems. An environmental forensics toolbox could help disentangle pollution sources, informing stressor-focused adaptive management. Existing national, spatial resource strategies that define aquatic resource objectives, overlook modelling different aquatic stressor-linked components across spatio-temporal scales to disentangle individual stressor effects along land-use intensification gradients. This thesis investigated how spatio-temporal, physico-chemical water quality parameters, dissolved and sediment-bound trace metals as well as fish tissue δ34S all collected from 15 river sites in the tributaries of the Gwathle River Catchment, positioned in the Platinum Belt of South Africa across a land-use intensification gradient, can be used to disentangle aquatic stressors. Through using a spatio-temporal generalised linear mixed effects model (GLMM) approach, the importance of employing a multi-hydrological-spatial (sub-basin, cumulative basin and riparian buffer) scale approach to link stressors (drivers) to changes in key catchment water quality parameters as opposed to a single scale approach was identified. At the sub-basin scale, ammonium concentrations were best explained by urban stress through wastewater effluent, Cu increased with mining via leaching from pollution control dams and mineral discharges, while turbidity increased with higher agricultural coverage, following greater tillage practices and irrigation. River pH was positively predicted for by slope heterogeneity at the cumulative-basin scale, while sulfate increased with mining at the cumulative 100 m riparian buffer, from leaching and discharges. Dissolved inorganics, including trace metals, are routinely assessed in national aquatic resource assessments, yet metals in sediments demonstrating legacy effects, are yet to be integrated. Using geo-spatial models across seasons, dissolved and sediment Cr concentrations were found to be driven primarily by mining both at the sub-basin scale, while dissolved Zn concentrations reflected sub-basin lithology and sediment-bound Zn reflected cumulative basin scale urban stress and lithology. Concordance correlation indicated that the Cr had a substantial positive stress-tracking agreement between the two media, with both tracking Cr land-use intensification gradient inputs while Zn displayed negligible concordance. While fish tissue δ15N has been used to trace nutrient pollution, no local or international research has assessed time-integrated fish tissue δ34S as a sulfur stress-tracer from interacting urban, agricultural and mining stressors. Using a spatio- temporal GLMM modelling approach, it was found to be possible to distinguish key agricultural and mining stressors on aquatic ecosystems, with δ34S being relatively enriched following sub-basin scale agriculture and relatively depleted following cumulative basin scale mining activities. The outcomes of this research expands our knowledge base on using aquatic physico-chemical parameters, inorganic media indicators, and biotic tracers, towards the development of a potential environmental forensic toolbox to elucidate complex pollution sources and pathways for enhanced catchment management and freshwater governance in South Africa.
Understanding disturbance, vegetation density, seed banks and pollination for the conservation of Protea curvata
(University of the Witwatersrand, Johannesburg, 2023) Mabuza, Precious Gugulethu Babalwa; Balkwil, Kevin
Background Aims: Protea curvata (Proteaceae) is a threatened species endemic to Mpumalanga, South Africa. Previous records of the species showed discrepancies in location data and information on population demographics was sparse. At the time of the study (2018), the last IUCN assessment of P. curvata was 20 years ago and one subpopulation of the species was reported to have a low number of mature individuals. In 2017, a census of another subpopulation indicated that the mature individuals were the most abundant cohort and there was no recruitment of P. curvata seedlings. Thus, there was uncertainty regarding how population size, population demographics and threats faced by the species may have changed over the last 20 years. The study aimed to update the IUCN status of P. curvata and to assess factors relating to P. curvata recruitment, namely the breeding biology of the species and the woody species composition on P. curvata sites. Methods: A census was conducted on P. curvata sites. Census data and site composition was compared between sites with contrasting management. Soil samples were collected from six sites. Pollination modes in P. curvata were investigated by manually pollinating inflorescences that were covered at bud phase to exclude animal pollinators. Five treatments were tested: autogamous selfing, tree geitonogamous selfing, inflorescences geitonogamous selfing, natural outcrossing and pollen supplemented outcrossing. Seeds from each treatment were weighed and tested for viability using TTZ staining. Animal pollinators were observed in the field and through camera traps positioned in front of non-covered inflorescences. Key Results: Five subpopulations were identified. P. curvata recruitment was low in two subpopulations and absent in three subpopulations. When comparing the site with the lowest recruitment (Site A) to the site with the highest recruitment (Site C), woody cover and tree density was higher on the site with low recruitment – indicating bush encroachment. This was attributed primarily to long intervals between fires at Site A. Site A showed a concerning net decline in subpopulation size (3% loss per year). Despite having more P. curvata juveniles, Subpopulation C showed a similar rate of decline (2% loss per year). The species was identified as endangered; with severe hailstorms and delayed, intense fires posing the major threats. Hailstorms compounded fire-induced damage on P. curvata bark. Flowering declined significantly after a hailstorm. (x̄pre-hail = 10.94 inflorescences per tree, x̄post-hail = 4.28 inflorescences per tree, p-value = 0.0031). During pollination experiments, Protea curvata was able to self-pollinate. However, seed mass and viability were significantly higher in outcrossed treatments. Viability in naturally outcrossed treatments (x̄=42.7%) was similar to pollen-supplemented outcrossed treatments (x̄=32.1%), but significantly higher than treatments of autogamous selfing (x̄=21.95%), geitonogamous selfing within inflorescences (x̄=27.1%) and geitonogamous selfing within trees (x̄=26.2%) [C.I= 95%; d.f.= 4, 95; Fcalc= 4.5; p = 0.0021]. Colletid bees and Apid bees contributed to P. curvata pollination via geitonogamy and early removal of self-pollen from stigmas. Birds were the most frequent visitors of P. curvata and were the most effective pollinators due to their prominent role in natural outcrossing. Bats infrequently visited inflorescences but may possibly complement outcrossing since they make contact with stigmas and do not spend their visit time restricted to one inflorescence or tree. P. curvata was non-serotinous and possessed a short-lived, soil seed bank. Across all sites, the average viability of seeds in the soil was well below that of freshly collected seeds from pollination experiments (4–9% for soil seed bank; 22.0–42.6% for fresh seeds). Seed bank size was surprisingly low in subpopulations with high flowering. Conclusions: Reducing seed loss after release from the canopy appeared to be more important than high flowering for maintaining a large seed bank. Therefore mild, frequent fires will be essential for reducing bush encroachment, making way for seed deposition and encouraging seedling survival

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Browsing Electronic Theses and Dissertations (PhDs) by SDG "SDG-15: Life on land"

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