The invasion ecology of Pontederia cordata L. (Pontederiaceae) in South Africa
- Authors: Wansell, Sage Nora-Lee
- Date: 2021
- Subjects: Plant invsions -- South AFrica , Invasive plants -- Ecology -- South Africa , Pontederiaceae -- South AFrica
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/172433 , vital:42200
- Description: Pontederia cordata L. (Pontederiaceae) is a tristylous invasive macrophyte – originating from North and South America – that has caused detrimental environmental, agricultural and socio-economic impacts in South Africa (SA). This novel study investigates the invasive ecology of P. cordata in SA by determining population genetics, pollination ecology and floral traits. Preliminary field surveys suggest that only one of three tristylous forms of P. cordata is invading SA and no seeds have been observed in any invasive populations. This study therefore determined the population genetics, mode of spread of P. cordata in SA and possible reasons for the lack of seed production, as well as providing suggestions for future control and management strategies. Inter Simple Sequence Repeats of leaf samples from invasive populations in SA and the native range of the United States of America (USA) were performed to determine the population genetics of P. cordata. The clarification of population structure of an alien invasive plant can provide insight into founder effects, introduction events and modes of spread and is important for the development of management plans such as biological control. Results from the genetic analyses indicated that P. cordata populations have low genetic diversity within and amongst invasive populations in comparison to native populations. This suggests that high gene flow and sexual reproduction is not present in invasive populations, and that only a single or very few introductory events have occurred in SA. Furthermore, invasive P. cordata populations shared the highest genetic similarity with native samples from Belle Haven, Virginia, USA, and thus further sampling and future genetic surveys should be conducted in this area to identify source populations to survey for potential biological control agents. Following these findings, I investigated whether sexual reproduction and seed production is absent from invasive P. cordata populations in SA as speculated. Floral traits from populations throughout all the invaded provinces were measured and, along with pollen grain measurements, it was determined that only short-morphed plants are present in SA. It was speculated that the absence of native pollinators in the invasive range may be responsible for the absence of sexual reproduction. However, a pollination study confirmed the presence of generalist insect pollinators. Thereafter, artificial pollination experiments on 8 865 flowers were conducted to determine whether an incompatibility system was present which prevented seed production. No seeds were produced and it was concluded that illegitimate pollination of the short-morphed plants prevented seed production and rhizomes are responsible for the invasion of P. cordata throughout SA. The implications of these findings and possible management strategies such as biological control is discussed in Chapter 4. These findings suggest that control programmes should target the plants rhizomes to prevent and reduce spread. Preventing the introduction of medium- and long-morphed plants into SA is crucial to prevent P. cordata from producing seeds and intensifying invasion further through both asexual and sexual spread.
- Full Text:
- Date Issued: 2021
Growth and photosynthetic responses of Acacia (Vachellia) seedlings to atmospheric CO2 increased from glacial to current concentrations: underlying mechanisms and ecological implications
- Authors: Anderson, Bruce Maurice
- Date: 2020
- Subjects: Acacia vachellia , Acacia vachellia -- Growth , Acacia -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/138182 , vital:37604
- Description: The African Acacia species Vachellia karroo, V. robusta, V. nilotica, and V. tortilis are some of the most invasive species implicated in bush encroachment and woody thickening of historically open savannas in southern Africa. This is partially explained by historic increases in atmospheric CO2 concentrations, which are proposed to have promoted the growth and survivorship of C3 tree seedlings relative to C4 grasses. However, the uniformity of CO2 responsiveness and differences among Vachellia species remain largely undetermined. Here we investigate the growth and photosynthetic responses of four Vachellia species, all implicated in woody encroachment, but originating from distinct climatic niches. Exposing these species to a range of sub-ambient CO2 concentrations (12 – 40 Pa) showed that V. karroo, V. robusta, V. nilotica and V. tortilis all responded strongly and fairly consistently to increasing CO2 concentrations, acting as a ‘functional type’ despite being selected from different geographic regions and having different climatic niches. Combined average net CO2 assimilation rates increased by 130% despite significant, but low levels of down-regulation and decreased stomatal conductance. The increased photosynthetic rates stimulated growth and biomass production in all compartments, with no significant differences in interspecific above and below ground allocation. Growth rates and dry biomass increased by 50% and 186%, respectively, while leaf level water use efficiency (ratio of net CO2 assimilation rate to transpiration rate) increased by an average of 218%. When this was scaled to the whole plant level, this stimulation was decreased to 80%. The decrease was the result of the CO2 stimulated increase in canopy areas, which increased leaf area for water loss. The seedlings’ total number of spinescent physical defenses, as well as the average mass and spine mass fraction also increased with rising CO2. These thicker spines could act as better deterrents against vertebrate browsers. Spine density was unchanged, however, showing that the increased spine numbers were associated with larger seedlings at higher CO2 rather than an increase in the number of spines per stem length. The stimulatory effects of increasing CO2 concentrations since the last glacial maximum and resultant increases in seedling growth and biomass are likely to have had important consequences for the survival and establishment of Acacia seedlings. Tolerance of drought and disturbance has been related to seedling size, hence stimulating the growth rate could confer disturbance tolerance and this tolerance would develop more rapidly with increasing CO2 concentrations. Furthermore, increased nitrogen and water use efficiency have the potential to support seedling establishment in environments where these resources would otherwise be limited at lower atmospheric CO2 concentrations. Resulting in a larger proportion of CO2 fertilization responsive woody seedlings surviving the seedling size classes, and persisting within historically open savannas. Where interspecific differences occurred they are likely to have arisen from adaptation to specific climates where these species are native and selection would have been driven by factors such climate, resource availability, levels of disturbance and competitive interactions. V. karroo had the highest growth rates and strong CO2 driven increases in biomass accumulation, despite having the lowest inherent photosynthetic rates. V. karroo also had the lowest increase in water use efficiency and high transpiration rates could potentially increase access to soil nutrients through mass flow. This species had the highest mean spine mass and showed significant increases in spine mass fraction at elevated CO2 concentrations, which may be important for deterring herbivores. V. robusta’s distribution to the mesic east coast of Africa suggests that water is an important limitation to its distribution. Hence, the CO2 stimulated increase in water use efficiency at both leaf and whole canopy level allows speculation that this may be an important driver of this species’ range expansion, which might continue if increasing levels of CO2 continue to promote water use efficiency. V. nilotica occupies a broad range of habitats, inhabiting large areas of the subtropics both north and south of the equator, with the strongest climatic correlates being the precipitation of the wettest quarter followed by high temperature seasonality. In response to increasing CO2, V. nilotica showed overall strong increases in growth, water use efficiency, and physical defenses. These responses may explain why V. nilotica has been such a successful encroacher in a broad range of habitats where limitations are likely to include multiple climatic factors and disturbances. V. tortilis has the widest distribution of all the species studied, covering broad ranges of Africa and only being excluded from the wettest parts of the equator and driest parts of the deserts. In these experiments this species showed the lowest biomass responsiveness to CO2, but had especially large increases in water use efficiency at both the leaf and canopy level. This may have been an important driver for this species’ encroachment into the more arid parts of its distribution, however this link will need to be verified with further experimentation.
- Full Text:
- Date Issued: 2020
The effects of elevated atmospheric CO2 on the biological control of invasive aquatic weeds in South Africa
- Authors: Baso, Nompumelelo Catherine
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa , Plants -- Effect of atmospheric carbon dioxide on , Atmospheric carbon dioxide -- Environmental aspects
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140772 , vital:37917
- Description: There has been a rapid increase in atmospheric CO2 concentration, from pre-industrial values of 280 ppm to more than 400 ppm currently, and this is expected to more than double by the end of the 21st century. Studies have shown that plants grown above 600 ppm tend to have an increased growth rate and invest more in carbon-based defences. This has important implications for the management of invasive alien plants, especially for the field of biological control which is mostly dependent on herbivorous insects. This is because insects reared on such plants have been shown to have reduced overall fitness. Nevertheless, most of the studies on potential changes in plant-insect interactions under elevated CO2 are based on agricultural systems, with only a limited number of these types of studies conducted on alien invasive weeds. However, climate change and invasive species are two of the most prevalent features of global environmental change. Therefore, this also warrants active research and experimental studies to better understand how these systems will be affected by future climates. Thus, the aim of this study was to investigate the effects of elevated atmospheric CO2 on the biological control of four invasive aquatic weeds (Azolla filiculoides, Salvinia molesta, Pistia stratiotes, and Myriophyllum aquaticum). These species are a threat to natural resources in South Africa but are currently under successful control by their biological control agents (Stenopelmus rufinasus, Cyrtobagous salviniae, Neohydronomus affinis, and Lysathia n. sp.). To achieve this, the selected plant species were grown in a three-factor experimental design in winter (CO2 X nutrients X herbivory), and another two-factorial design in summer (CO2 X herbivory). Atmospheric CO2 concentrations were set at ambient (400 ppm) or elevated (800 ppm), as per the predictions of the IPCC. As per my hypothesis, the results suggest that these species will become more challenging in future due to increased biomass production, asexual reproduction and a higher C: N ratio which is evident under high CO2 concentrations. Although the biological control agents were in some instances able to reduce this CO2 fertilisation effect, their efficacy was significantly reduced compared with the levels of control observed at ambient CO2. These results suggest that additional biological control agents and other management methods may be needed for continued control of these invasive macrophytes, both in South Africa and further afield where they are problematic.
- Full Text:
- Date Issued: 2020
The invasion ecology of Nymphaea mexicana Zucc. (Mexican Water lily) in South Africa
- Authors: Naidu, Prinavin
- Date: 2019
- Subjects: Nymphaea Mexicana zuccarini , Nymphaea , Nymphaea -- Biological control -- South Africa , Water lilies , Nymphaea -- Ecology -- South Africa , Water lilies -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Water lilies -- Ecology -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/92920 , vital:30763
- Description: The Mexican water lily, Nymphaea mexicana Zuccarini, is an aquatic perennial, native to southern USA and Mexico, and has been introduced to South Africa via the ornamental plant trade. This species has rapid growth rates and becomes weedy in dams, ponds and rivers. It is currently listed as a NEM:BA category 1b invasive plant in South Africa. One possible management measure for this weed is biological control, but it is a novel target because no biological control programme has been initiated against it anywhere in the world. This study is intended as a baseline for the biological control programme against this plant in South Africa. Assessing the population structure and mode of reproduction of invasive alien plants is an imperative aid to determining if biological control is a suitable management option. Using amplified fragment length polymorphism (AFLP) molecular markers, I compared the amount of genetic variability and differentiation of N. mexicana in its native range (USA), and invasive range (South Africa). Results indicated a large genetic distance between populations in the USA and South Africa, compared to populations within each country. The genetic variability of the invasive populations was higher than that found in the native distribution. This could be due to hybridization in the introduced range, and/or multiple introductions from different source populations. Differences in the morphology of N. mexicana plants in the invasive range and South Africa were also observed which confirm the results of the genetic analyses. I also assessed the reproductive mode of N. mexicana cultivars/hybrids by conducting breeding system experiments and field pollinator studies. Results indicated that the cultivars are sterile, suggesting that the primary mode of reproduction is asexual via fragmentation of tubers. The main pollinators that were found to be associated with the cultivars in South Africa were honeybees, sweat bees, flies and beetles. These insect groups were the same as those that were observed in another study which was conducted on the pollinators associated with the pure N. mexicana in the native range in southern USA. Mechanical and chemical control of N. mexicana and its multiple genotypes have been applied but have not been efficient due to the fast regeneration of shoots, especially in summer. Therefore, these two management options are not long–term solutions and will also be costly due to the widespread occurrence of the hybrids in South Africa. Thus the only cost–effective, environmentally friendly, self–sustainable and long–term management option is biological control. The significant divergence between native and invasive populations of N. mexicana, as well as the possibility of numerous invasive cultivars, may limit future prospects of biological control of this species. However the differences in the root structures between native South African waterlilies, such as N. lotus and N. nouchali, and the introduced waterlilies, such as N. mexicana and its associated hybrids, may play a pivotal role in the success of biological control of the N. mexicana hybrid complex in South Africa. Natural enemies which feed on the hard tuberous roots of N. mexicana and its hybrids, as opposed to the soft bulbs of the native N. nouchali and N. lotus, should be prioritised.
- Full Text:
- Date Issued: 2019
Assessing the potential impact of climate change in the south-eastern Great Escarpment, Southern Africa
- Authors: Bentley, Luke Kinross
- Date: 2017
- Subjects: Mountain plants -- Climatic factors -- Drakensberg Mountains , Mountain biodiversity -- Drakensberg Mountains , Climatic changes -- Drakensberg Mountains , Rain and rainfall -- Drakensberg Mountains , Plant diversity -- Climatic factors -- Drakensberg Mountains
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4657 , vital:20709
- Description: Rapid, anthropogenic climate change is a contemporary phenomenon which is threatening natural ecosystems. Mountains are globally important, housing high levels of plant and animal biodiversity, as well as being important suppliers of water with 50% of mountainous regions being essential for the provision of water to downstream inhabitants. Owing to their importance, an assessment of the historical, current and potential impacts of climate change on the south-eastern Great Escarpment encompassing South Africa and Lesotho is necessary and is the primary aim of this thesis. In order to assess the historical and current impacts of climate change, historical rainfall records were collected from 78 sites throughout the Eastern Cape. These records were used to determine rainfall trends and trends in the frequency of daily extreme events. Climate change projections predict increasing trends in summer and annual rainfall, and a marginal increase to a slightly decreasing trend in winter rainfall, depending on if statistically downscaled or dynamically downscaled projections are examined. Extreme events are also predicted to increase in frequency. Results showed trends which generally agree with the predictions, except for extreme events for which there was insufficient data to support the projections. This has implications for farmers in the area and validates the downscaled Regional Climate Models (RCMs) to be used for the predictive analysis determining the potential future impacts of climate change on plant species' distributions in the south-eastern Great Escarpment. In order to assess montane plant species to future climate predictions, occurrence records of 46 species were correlated to rainfall and temperature predictor variables and predictions for species richness and beta diversity were made for current and future climates. This predictive analysis used and compared two correlative species distribution modelling methods - one method used one correlating algorithm in a nuanced manner and the other method used five correlating algorithms in an ensemble. A trend of range restriction to higher elevations for the 46 species analysed was as expected from a warming climate. The nuanced, single algorithm modelling method produced less conservative models. The predicted trend of an elevational increase in montane vegetation in this region points to Lesotho and the Drakensberg highlands as being an important refugium for montane plant taxa of the southeastern Great Escarpment. The Maloti Drakensberg Transfrontier Conservation Area hence needs to be expanded and its mandate properly enforced to protect this region adequately.
- Full Text:
- Date Issued: 2017
Browsing as a demographic bottleneck in a semi-arid savanna: the effect of size and age on compensatory responses of Vachellia karroo seedlings after simulated herbivory
- Authors: Perumal, Lavinia
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4899 , vital:20741
- Description: Savannas are characterised by a continuous grass layer with scattered trees at varying densities. This vegetation structure is determined by several interacting factors, including fire, herbivory, resource competition and atmospheric CO2 concentration. The preservation of savanna biomes is important and a shift towards a woody biome threatens savanna globally. Bush encroachment which describes the shift towards domination of savannas by C3 woody plants, is especially acute in southern Africa. In semi-arid rangelands, encroachment progresses to dense thickets dominated by thorny and unpalatable bushes and trees. There is evidence that bush encroachment is driven by a reduction in fire and browsing events as well as their interaction. Despite browsing having strong effects on African savannas its isolated role in maintaining tree-grass coexistence has not received as much attention as the role of fire. Therefore the overall aim of this study was to examine the effects of browsing on seedlings of a commonly encroaching species, Vachellia karroo. Browsing was hypothesized to be a demographic release bottleneck for bush encroachment in a semiarid (MAP ~550mm) savanna in the Eastern Cape of South Africa, where fire has been historically rare. In a single study I explored the fate of V. karroo seedlings (less than a year old) following browsing in sub canopy and inter canopy microhabitats. Additionally, I explored how the fate of a seedling changed under high and low tree cover. Firstly, I investigated the type, intensity and frequency of herbivory, from both small and large herbivores, which seedlings were subjected to. Results revealed that browsing was severe and frequent with the majority of seedlings browsed more than twice over a 12 month period. Large browsers such as kudu and impala caused high seedling mortality (46%) while smaller browsers such as invertebrates were more effective at suppressing growth. Microhabitat had little impact on seedling survival, but significantly influenced plant compensatory growth. Reduced seedling growth following browsing was observed in the sub-canopy in comparison to seedling growth in full sunlight in the intercanopy, suggesting V.karroo may be shade intolerant. Secondly, the effect of tree cover on browsed seedlings was determined by quantifying browsing frequency and intensity at high and low tree cover. No differences in browsing intensity and frequency were observed between high and low tree cover. However, high tree cover due to bush encroachment limited seedling above ground growth. The aim of the second study was to investigate how V.karroo survival and growth were influenced by its age and size following simulated browsing. I explored this aim through field and greenhouse experiments. I was particularly interested in testing how plant sensitivity to varying defoliation intensities of repeated browsing varied with plant age (known ages of 6, 12, 16 and 30 weeks). There were large differences in mortality between the different age groups. Furthermore, age interacted with repeated browsing and negatively influenced seedling survival and regrowth. Older seedlings (16 and 30 week old) had greater survival and higher browsing frequencies resulted in greater mortality and reduced growth. The threshold age after which seedlings become more tolerant to herbivory occurs at an age of 28 weeks. Seedlings less than six weeks old experiencing intense (100 % defoliation)browsing had a very low probability (33%) of survival following just a single defoliation. Interestingly, all 16 week old seedlings regrew most of their foliage following a moderate (50%) defoliation with some plants overcompensating for leaf loss. The field study revealed two distinct demographic stages based on age and size (seedlings< 9 mm and saplings >9 mm in stem basal diameter (SBD)). Browsing had a strong negative effect on seedlings, resulting in reduced investment in leaf biomass. These findings suggest plant size and age can be used as robust predictors of a plants vulnerability to browsing. An increase in tree cover requires successful transitions of seedlings to saplings (also known as release). The results of this study suggest that in semi-arid savannas, browsing can impact tree cover through imposing a release bottleneck for tree seedlings and to lesser extent saplings. By limiting tree growth plants are kept in a disturbance trap and will therefore be exposed to not only browsers but fire. These findings also have important implications for tree-grass coexistence dynamics, suggesting that specific size and browsing thresholds should be considered in savanna management.
- Full Text:
- Date Issued: 2017
Patterns of plant diversity and cultural meaning in a rural landscape in the Albany Thicket: effects of land-use and topography
- Authors: Ngqiyaza, Nozuko Princess
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50237 , vital:25969
- Description: South Africa is the world's third most bio-diverse country, but pressures on this biodiversity are many and widespread. It is now well recognised that protected areas on their own are insufficient to protect biodiversity, and increasing emphasis is placed on developing models for ensuring the persistence of biodiversity in agricultural and rural landscapes. One of the major challenges, especially in rural areas, is the need to reconcile people’s need to use natural resources with biodiversity conservation. This study aimed to (1) examine the ecosystem services people derive from the natural vegetation and how this is distributed in space and (2) the effects of land use and topo-edaphic factors on species richness, composition and structure and how this is spatially distributed. I investigated two land-use types, i.e. a rural village and adjacent lightly used game farm(s) by comparing 20 sites under each land-use representing the range of topographic position. I sampled respondent’s uses and values, species richness and composition, woody density, structure and composition at these 40 sites. This allowed for comparison between the two land uses but also allowed me to examine the effect of topography and relative soil moisture (both known to have a string influence on vegetation in semi-arid areas), and to relate the ecosystem services to plant species richness, structure and woody composition. People derived a wide range of ecosystem services and this differed with distance from the village and vegetation type. Men and women performed different tasks and had different feelings and derived different use values across the landscapes. Both men and women showed a great appreciation for the thicket forest, Pteronia-dominated and grasslands sites. They recognised these areas and as sacred grounds where they have a strong connection with their ancestors. Women preferred utilising areas closer to the village because they feared crime and wild animals in more remote thicket or forest, while men utilised all areas across the land, but more frequently closer to the village. The older generation had a strong attachment to nature, perceiving it as a provider. The younger generation, especially the young women did not express such a deeply felt connection, but enjoyed getting to see where some of the medicinal plants and useful wood structures were harvested. Younger men would go far into the forest quite regularly, often as far the Great Fish River, when they hunt with their peers. Although a diversity of perceptions were presented, and not all conformed to traditional views and practices, most respondents derived a mix of ecosystem services, with the areas closer to the village providing recreational and direct use value to more people on a more regular basis but spiritual values associated with deep forest persisted, especially among the older generation. Species richness and composition was analysed in relation to Topographic Relative Moisture Index (TRMI), land use and distance from the village to see the effect of topography versus land use on the vegetation. The total number of plant species recorded was 386 for both study sites. Two hundred and ninety two species were recorded in Ntloko and 265 on the game farms. Of the species that were sampled, 121 were recorded in Ntloko only, 94 in the game farms only, and 171 species were shared. The number of useful plant species (fuel, medicine, forage, cultural and edibles) was recorded to be 110, 83 in Ntloko and 63 on the game farms. There was no significant difference in species richness and alpha diversity between the study sites, but the game farms had a higher projected total number of species, reflecting higher beta diversity in the game farms than the communal area. The point-centered quarter method (PCQ) was used to describe woody plant composition, tree density and structure. The woody structure and composition was analysed in relation to the above-mentioned factors and I found no significant difference in the density and overall woody structure and composition between the two study sites. Sites at Ntloko had a positive correlation between soil moisture and woody plant density and a higher density of palatable and unpalatable species. The game farms showed no significant changes in woody plant density with TRMI. This study showed that the communal area maintained comparable plant species richness and vegetation structure and composition to game farms. The rural landscape comprised a gradient from sites close to the village that were heavily impacted, not considered particularly special or sacred but safe, familiar and of utilitarian importance, to sites farther away with denser, less transformed thicket vegetation, which are considered to be of greater cultural, spiritual and aesthetic importance but less safe, familiar and accessible. This suggests that conservation outcomes can be achieved outside protected areas, and that biodiversity is valuable to local residents. Resource management should be implemented to maintain the ecosystem services provided in rural areas in a way that integrates local peoples’ perceptions, goals and values with ecological evidence.
- Full Text:
- Date Issued: 2017
Photosynthetic and growth responses of C3 and C4 grasses to short- duration sunflecks and resultant consequences for their performance in understory environments
- Authors: Adams, Claire Elizabeth
- Date: 2017
- Subjects: Understory plants -- Effect of light on , Grasses -- Effect of light on -- South Africa , Erharta -- Effect of light on , Brachiara -- Effect of light on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5016 , vital:20753
- Description: Low C4 grass species abundance in understory environments is thought to be as a result of their high-light requirements, lack of photosynthetic advantage relative to C3 species in cooler environments, and an inability to adequately utilise sunflecks. This study sets out to investigate this theory, hypothesizing that C3 grass species outperform C4 grass species under the canopy, not as a result of quantum efficiency temperature effects, but as a result of C4 species inability to utilize short-duration sunflecks. Short sunflecks could result in a breakdown in assimilate movement between the mesophyll (MSC) and bundle sheath (BSC) cells. The role of BSC leakiness, stomata and PSII efficiency on the ability of C3 and C4 Alloteropsis semialata to utilize short-duration sunflecks was investigated using gaseous exchange and chlorophyll fluorescence techniques, while the growth of both subspecies under a simulated flecking-light environment tested whether these measured responses translated into effects on growth. As C3 grasses are known to possess higher levels of stomatal conductance in relation to C4 species, results showed that C3 A. semialata was able to utilize short-duration sunflecks as a result of increased stomatal conductance and an ability to induce photosynthesis under various light flecking conditions. In contrast, C4 A. semialata was unable to utilize sunflecks possibly as a result of energetic limitations of the carboxylation mechanism (PSII) and not because of increased bundle sheath leakiness. These photosynthetic responses translated into growth differences when both types were grown in an artificially flecking light environment. The photosynthetic differences noted for C3 and C4 A.semialata were also evident in shade adapted understory grasses; Erharta erecta (C3), Dactylotenium australe (C4) and Brachiaria chusqueoides (C4). As photosynthetic induction was marginally more rapid in all species relative to A. semialata it suggests some degree of adaptation in shade grasses, however the inability of the C4 species to utilise short sunflecks remained. As a result, it was hypothesized that C3 shade adapted E. erecta and C4 B. chusqueoides, co-inhabiting the same forest understory, are able to do so because of differences in light micro-environments associated with each species. However, canopy openness and light profiles determined for theses micro-climates showed no differences and that both species have persisted within a relatively stable understory environment. The coexistence was possible as the understory was supplied with a significant proportion of its daily light in flecks sufficiently long as to not compromise C4 productivity. A survey of 10 species of grasses under various canopy densities and in the open showed a strong negative linear relationship between canopy openness and the rate at which photosynthesis was induced by flecking light, which has not been shown before. This did not result from the phylogenetic relationship between species and could be shown for a single species (E. erecta) growing in a range of light environments. This demonstrates that C4 grasses, despite adaptation, would be limited from sunfleck environments if a significant proportion of the daily light available consists of flecks of short-duration. The generation of such environments may occur as a result of woody thickening and could help explain the observed decline in C4 grasses under these conditions.
- Full Text:
- Date Issued: 2017
Revising the distribution of mangrove forests in South Africa and changes in growth of mangrove species along a latitudinal gradient
- Authors: Bolosha, Uviwe
- Date: 2017
- Subjects: Mangrove ecology -- South Africa , Mangrove forests -- South Africa , Mangrove plants -- South Africa -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7544 , vital:21271
- Description: Mangrove forests are a diverse assemblage of trees and shrubs that are adapted to a saline and tidally inundated environment. The global spread of mangrove species is affected by climate, with most confined to areas that are warmer and moist. At a global scale, temperature limits the distribution of mangrove forests but on a regional scale and local scale, rainfall, river flow and tidal exchange have a strong effect on the distribution and biomass of mangrove forests. Other factors that play a role in limiting growth and distribution of mangroves include accessibility of suitable habitats for growth and also conditions that are suitable for propagule dispersal. The objectives of this study were to review the distribution of mangroves in South Africa and determine the number of extreme temperature events that may limit further distribution and secondly to measure growth rates of mangrove species at Mngazana and Nahoon Estuary and the nutrient pools in the sediment of these forests. In 1982, Ward and Steinke published a list of estuaries where mangroves were present. The current study sampled the population structure, microclimate and level of expansion in two estuaries within and outside of the published range. The minimum, maximum temperature and number of extreme temperature events were measured using iButtons. Mangrove expansion will be limited by minimum temperatures (1.1 ° C) and an increase in extreme temperature events (830) (<5 ° C and 5- 10 ° C) at the latitudinal limits. Expansion of A. marina at Kwelera and Tyolomnqa Estuary was evident but sapling survival was low. Mangroves have expanded within and outside the range proposed by Ward and Steinke (1982), but are limited by physical factors, restricted by the presence of saltmarsh and other estuarine macrophytes and natural disturbance regimes. An increase in population growth was recorded over the years at both Mngazana and Nahoon Estuary. Nutrients, (ammonium, nitrates + nitrites and soluble reactive phosphorus) varied amongst sites and were related to seasonality. Nitrogen in both estuaries was available in the form of ammonium (NH4) and its concentration was generally higher (1.3-76.2 pm) than other forms of nitrogen (0.07-6.3 µm). Soluble reactive phosphorus (SRP) was higher during the wet seasons in both estuaries. An increase in porewater salinity since 2007 (41.3 practical salinity unit (PSU)) was measured at Mngazana and this is a result of freshwater abstraction and low rainfall. A. marina saplings and adults grew significantly faster at Nahoon Estuary (the distributional limit) (11.1 ± 1.1 cm year-¹) compared to Mngazana Estuary (5.3 ± 1.8 cm year-¹). Different mangrove species and forests respond differently to environmental factors and changes in mangrove distribution is expected in South Africa but changes are expected to happen slowly and opportunistically.
- Full Text:
- Date Issued: 2017
The response of microalgal biomass and community composition to the chemical and physical dynamics of two Eastern Cape estuaries
- Authors: Cotiyane, Phumlile L
- Date: 2017
- Subjects: Estuarine plants -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape , Phytoplankton -- South Africa -- Eastern Cape , Algal blooms -- South Africa -- Eastern Cape , Algal blooms -- Monitoring-- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4999 , vital:20751
- Description: Water quality characteristics of estuaries are influenced by both natural and anthropogenic activities. Estuaries situated in coastal urban areas are exposed to more perturbations than those in rural settings. This study determined the drivers of phytoplankton biomass and community composition in two Eastern Cape estuaries and evaluated the anthropogenic activities that influence the overall health of each estuary. The estuaries were sampled in summer and winter (2014, 2015). The water quality of the estuaries was determined by measuring the variability in physico-chemical parameters (salinity, temperature, dissolved oxygen and pH), nutrients, phytoplankton biomass and composition and faecal bacteria. Results show that both Mngazana and Nahoon are well oxygenated (~ 6.0 mg l-¹) and are saline systems (~ 35 ppt) due to low freshwater inputs into both estuaries. Mngazana Estuary exhibited low nutrient inputs along the length of the estuary including Creeks 1 and 2 with low chlorophyll a (4.0 ± 0.2 µg Chl-a r¹) being recorded during this study while Nahoon Estuary had an overall chlorophyll a of 3.5 ± 0.3 µg Chl-a r¹. The two estuaries were dominated by flagellates with phytoplankton blooms recorded seasonally. Possible eutrophic conditions were evident along the upper reaches of Nahoon indicated by nutrient accumulation and by the presence of cyanobacteria. This also this reflected the possible anthropogenic nutrient inputs originating from the Nahoon catchment despite the low freshwater inflow. The presence of faecal bacteria counts along both estuaries indicates the need for further investigation into the source of faecal contamination. The use of nutrient analyses and phytoplankton composition during this study enabled a clear description of the water characteristics of the investigated estuaries. Furthermore, the need for the adherence to freshwater flow requirements of estuaries to limit the dominance of marine waters was clearly illustrated. Urban runoff due to impervious surfaces increases nutrient inputs into estuaries while rural use of estuarine waters introduces contaminants into the system; coupled with low freshwater inputs and eutrophic conditions, the deterioration of estuarine water quality over time demonstrates the need for effective monitoring of these systems.
- Full Text:
- Date Issued: 2017
An investigation of the aquatic macroinvertebrate fauna of the southern Great Escarpment (South Africa): insights from ecological and genetic studies
- Authors: Taylor, Chantal Lee
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4275 , http://hdl.handle.net/10962/d1020839
- Description: Biological diversity in freshwater biomes is vital to maintain healthy, functioning ecosystems with resilience to disturbance and the impacts of climate change. Freshwater ecosystems provide essential resources to life on Earth. However, as increasing pressure is being placed on the environment by human population growth, the quality of freshwater resources and the health of these ecosystems are at risk. Mountain streams provide an important source of water and are usually less affected by anthropogenic stressors, compared to lowland freshwaters. These montane streams are therefore of important conservation value and due to their untransformed nature serve as ideal ecosystems for biodiversity studies and as reference sites for studies on environmental change. This study explores aquatic macroinvertebrate biodiversity of the southern Great Escarpment in South Africa. Species assemblages and the environmental variables of each site were sampled from first order streams across five different mountain blocks along the Great Escarpment. Additionally, mitochondrial DNA of three mayfly species (Afroptilum sudafricanum, Demoreptus natalensis and Demoreptus capensis), commonly occurring in the study area, was analysed to compare the genetic diversity between habitat specialist and habitat generalist species. A total of 2 595 macroinvertebrate specimens from 47 families and 86 species were collected with several interesting and potentially new species being discovered. Partitioned diversity analyses indicate that macroinvertebrate diversity varies across mountain blocks. Multivariate analyses indicate that differences in assemblages could be attributed to differences in environmental variables between sites, particularly water velocity, total dissolved solids and salinity. As these environmental variables reflect of the topography of the sites, differences in species assemblages was attributed to difference in topography and therefore biotopes present. Habitat-restricted mayfly species (D. natalensis and D. capensis), occur in distinct populations confined to mountains blocks. Isolation-by-distance analyses further emphasis that these species are genetically restricted by their habitat preference for mountain streams. In contrast, A. sudafricanum, a habitat generalist, showed no indication of genetic structure due to location or distance. Possible cryptic taxa and new species were identified within A. sudafricanum and Dermoreptus respectively. This study provides an important contribution to the baseline data of freshwater macroinvertebrate diversity for the southern Great Escarpment region and provides insights into the considerable genetic diversity of selected aquatic taxa across this region.
- Full Text:
- Date Issued: 2016
An investigation on the effect of Russian wheat aphid (Diuraphis noxia Kurdjumov) population growth and feeding damage on selected barley (Hordeum vulgare L.) cultivars under ambient and elevated CO2
- Authors: Sacranie, Sattar Farouk
- Date: 2016
- Subjects: Russian wheat aphid -- Research -- South Africa Barley -- Disease and pest resistance -- South Africa Callose Aphids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50311 , vital:25975
- Description: The Russian wheat aphid (RWA) (Diuraphis noxia Kurdjumov) is a major pest of cultivated small grains. It is particularly devastating because of is high reproductive rate which results in the growth of large populations which become damaging to its host plants. Development of resistant barley (Hordeum vulgare L.) cultivars is complicated as resistance is polygenic. As a result, the industry remains at risk now that the RWA has spread throughout South Africa. It has, as recently as, 2013, been identified in the SW Cape, which was previously geographically isolated. This is South Africa‟s principle barley growing region. Now a potentially huge problem exists. Therefore, it is imperative that an alternative to pesticide use is found. Testing potential innate resistance in barley cultivars is thus, critical. In this thesis, I present data on four barely cultivars where I have examined their resistance/ lack of resistance to three known RWA biotypes, RWASA1, RWASA2 and RWASA3. The barley varieties used were two economically important South African malt barley cultivars (S5 and SSG 564) along with two potentially RWA resistant Afghan accessions (CIho 4125 and CIho 4159). The RWA biotype population growth rates on each of the plants were determined over a 14 day period. The aim was to establish baseline data of the effects of RWA population growth on the host plants under ambient CO2 (380 – 400 ppm) conditions. The extent of RWA feeding damage was investigated at the cell level by examining saliva deposition and cell disruption using Transmission Electron Microscopy; at the tissue/vascular level using fluorescence microscopy, to determine the extent of callose formation; at a whole leaf level by recording percent chlorosis and leaf roll; and finally, at a whole plant level by measuring biomass loss.The experiments were repeated under elevated CO2 (450 ppm) to model any changes in RWA/plant interaction with respect to future climate change. The effects of an elevated CO2 environment and RWA feeding on host plant foliar N and C:N ratio were compared to ambient CO2 conditions, to provide a clearer picture of the potential nutrient drain that a feeding RWA colony exacts on its host. Of the varieties tested, the CIho accessions performed better than the two SA barley cultivars as the CIho accessions appeared to express a mild antibiosis resistance response as RWA populations, particularly those of RWASA1, were smaller than those observed on either S5 or SSG 564. In addition, less damage was evident in the two CIho accessions due to RWA feeding. II RWASA2 was the most virulent of the three RWA biotypes tested, followed by RWASA3 while RWASA1 was the least virulent. Under elevated CO2 conditions, RWA feeding damage was exacerbated but the trend of biotype virulence remained the same. Higher aphid population sizes were recorded under elevated CO2, meant that even the more resistant CIho accessions were overcome by the increased demand made by the larger aphid colonies on the host plants. The % foliar N data showed that under elevated CO2 aphid-free control plants had increased N levels in their leaves. Increased “food” supply (as shown by the increased N levels) therefore allowed significantly larger aphid populations to develop on the plants exposed to elevated CO2, due to improved nutrient status of the phloem sap taken up by RWA. The knock-on effect of a higher aphid population was increased cell disruption as a result of extensive probing, extensive formations of wound callose, with the result that phloem damage impeded nutrient flow through the vascular tissues which contributed to chlorosis and (eventually plant) death. The major conclusion from this study is that even a mild CO2 elevation resulted in an increase aphid population which may pose a severe and very real threat to a barley crop. Therefore, without effort to identify and deploy resistant barley cultivars, it could well be possible that future barley cultivation in South Africa may no longer be viable.
- Full Text:
- Date Issued: 2016
Assessing estuarine nursery habitats for Cape Stumpnose (Rhabdosargus holubi), (Pisces: Sparidae) in a warm-temperate estuary in the Eastern Cape, South Africa
- Authors: Leslie, Timothy David
- Date: 2016
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3178 , vital:20381
- Description: The nursery role hypothesis provides an approach for assessing the nursery function of habitat types within estuaries. This study attempted to assess the nursery value of the dominant estuarine habitats in the Bushmans Estuary for Rhabdosargus holubi (Steindachner 1881) by analysing habitat complexity, relative abundance and behaviour of R. holubi and using stomach contents analysis and dietary diatom composition as indicative of feeding habitat. Structural habitat complexity was assessed in Zostera capensis (Setchell) seagrass and Spartina maritima (Curtis Fernald) salt marsh by sampling above-ground stem density and length, and total cover per unit area (Ct/At). Dimensionless habitat complexity indices such as the interstitial spatial index (ISI) at three magnifications and fractal geometry at two magnifications were used to further analyse habitat complexity. Above-ground biomass (P<0.05) in each season and canopy height (P<0.001) were significantly higher in salt marsh than in seagrass whilst stem density was significantly higher in seagrass than in salt marsh in each season (P<0.001). Each dimensionless index indicated that complexity is notably higher in seagrass than in the salt marsh. Using dimensionless indices that analyse complexity at different spatial scales provided a better analysis of habitat complexity than canopy height and biomass as it allowed for direct comparisons between habitat types. Underwater video cameras were deployed in seagrass, salt marsh and sand flat habitats to assess the relative abundance and behaviour of R. holubi. The relative abundance of R. holubi was significantly higher in seagrass than salt marsh and sand flats, whilst the behaviour of R. holubi indicated a high degree of habitat use in structured habitats and a low degree of habitat use in unstructured sand flat habitats. This indicated that not only are juvenile R. holubi a vegetation-associated species, but also a species that prefers seagrass to salt marsh.
- Full Text:
- Date Issued: 2016
Local versus landscape effects of bush encroachment on plant available light, soil moisture, frost occurrence and herbaceous productivity and composition
- Authors: Klopper, Chrisna
- Date: 2016
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3137 , vital:20376
- Description: Bush encroachment is a global phenomenon and a pressing concern for South Africa rangelands. The expansion and increase in density of Vachellia karroo (hereafter referred to aAcacia karroo) has been documented in the Eastern Cape and KwaZulu Natal in South Africa. This increase in woody species in savannas is often at the expense of grass cover and thus is causing concern about how this will impact agriculture due to possible loss of grazing capacity. To understand the impacts of bush encroachment the effect of trees on their micro-climate and abiotic factors and in turn on the herbaceous layer needs to be examined. The objective of this study was to quantify the effect of Acacia karroo encroachment on the light environment, soil moisture and frost occurrence in the sub-canopy and inter-canopy micro-habitats, and how these changes affected herbaceous player productivity and composition. Another question that is being addressed here is whether, and how, the local tree effects scale up in the landscape and whether prediction can be made based on the effects of individual trees. The study was undertaken on a farm, Endwell, in the Smaldeel, Eastern Cape. At the study site, a semi-arid savanna, Acacia karroo has been encroaching since the 1980’s. The study was conducted at three scales: landscape, stand-wide and local scale. The landscape scale was represented by four areas with 0, 21, 45 and 72% tree canopy cover, the stand-wide scale consisted of transects with varying percentages of tree canopy cover within each of the four levels of encroachment. The local scale was represented by the sub-canopy and inter-canopy environment to test the effect of trees. At the local scale plant available light and soil moisture were lower in the sub-canopy than intercanopy regions, with leaf area index being higher in the sub-canopy. This local negative effect of the tree canopy on light and soil moisture in the sub-canopy did not scale up predictably in the landscape. At the stand-wide scale light in the inter-canopy was reduced as shading increased. Frost was excluded from under the canopies and frost incidence decreased at higher tree cover. Grass productivity was reduced in the sub-canopy, possibly due to lower light and soil moisture. Overall biomass increased from the low to medium level of encroachment but lowest at the high level of encroachment. Grass composition and cover was only slightly affected by tree canopies cover and C4 grass species were still present in the sub-canopy and at lower light environments. At the levels of Acacia karroo encroachment encountered at this study site, it seems unlikely that palatable or desirable C4 would be excluded from the system and that a shift from C4 to shade-tolerant species would occur. This is due to tree canopies at the site not reducing light to such anextent that they would outcompete grasses, and likely the very low grazing pressure at thesesites. Herbaceous biomass at these sites were still sufficient to carry a fire in the inter-canopyregion and sufficient grazing for herbivores. In the sub-canopy region fires will be excluded thus with higher the portion of sub-canopy areas increasing at the high levels of encroachment they may interrupt fire spread. Thus it was concluded that Acacia karroo encroachment up to 45% tree cover is currently not creating negative feedback on herbivory, but low stocking rates appear to be key to maintain this.
- Full Text:
- Date Issued: 2016
Reproductive biology of important invasive plants in the Eastern Cape Province of South Africa
- Authors: Thorne, Cara-Jayne
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3683 , vital:20535
- Description: Baker’s rule predicts species capable of uniparental reproduction are more likely to establish after long distance dispersal (or introduction in the case of invasive plants), thus the ability to undergo autonomous self-pollination should promote colonization. An investigation into the reproductive biology of eleven invasive species in the Eastern Cape Province of South Africa between 2012 and 2014 showed strong support for Baker’s law. Breeding system results showed evidence of self-compatibility in eight species, ten species were capable of autonomous self-pollination, and only three species showed evidence of varying levels of self-incompatibility. These results provide evdence that autonomous self-pollination occurs more frequently among invasive species, self-compatible species more frequently become invasive compared with self-incompatible species and that autogamous species should have a larger invasive range. Co-opting suitable local pollinators may be problematic for invasive plants, especially those with highly specialized pollination systems. The species investigated appear to be largely independent of pollinators, mostly setting seed in the absence of pollinators. Despite this, all eleven invasive plant species are regularly visited by a variety of generalist pollinators including Apis mellifera, Xylocopa bees and Allodapini species. Pollinators all carried substantial pollen loads, even managing to extract pollen from more specialized plants, such as the poricidal anthers of Solanum species, and frequently came into contact with both anthers and stigmas. Considering most of theses species are capable of autonomous self-pollination, their reliance on pollinators may be low. Even the most self-incompatible species, Passiflora caerulea, appears to have successfully co-opted local pollinators (honeybees and carpenter bees), ensuring successful pollination and seed set. The ability for cross-pollination by local pollinators allows for some degree of genetic variation within invasive plant populations, especially for self-incompatible species. Inadequate pollen deposition by unreliable or inefficient pollinators, or reduced resource availability, can result in pollen limitation. Invasive plant species may be especially susceptible, with three of the plant species investiagted showing possible pollen limitation at the level of seed set, while the remaining nine invasive plant species showed no evidence of pollen limitation in South Africa. The ability to utilize uniparental reproduction (as Baker’s law predicted), and co-opt local pollinators has allowed invasive plants in the Eastern Cape to successfully establish and persist after introduction. Hence, the inclusion of reproductive traits of plants should therefore be included in risk assessments for future plant invaders.
- Full Text:
- Date Issued: 2016
The phytogeography of Southern Mistbelt Forests of the Eastern Cape, South Africa
- Authors: Matiwane, Aviwe
- Date: 2016
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3224 , vital:20393
- Description: In the Eastern Cape, a moisture gradient (from west to east) exists along the Escarpment where patches of Southern Mistbelt Forests (SMF) occur. There is a notable profusion of plants in these forests, but the factors that drive plant species composition and abundance in these patches is poorly understood and such knowledge is critical if we are to address or mitigate the problems imposed by global change. Many of our ideas on plant community assembly are based on the premise that species differ in their environmental requirements for successful regeneration, especially when young. The aims of this study were to document the floristic diversity of poorly known patches of Southern Mistbelt Forests in the Eastern Cape and identify the environmental factors that influence plant community composition in these forest patches. Twenty six forest patches across the Eastern Cape were sampled. In each forest 400m2 circular plots were constructed. The diameter at breast height and stem counts for the tree species was taken and the % cover of the herbaceous species was recorded. General collections were also made to supplement the plot data in order to obtain a comprehensive flora for each forest patch. All sampling was done during the summer season of 2013 and 2014. Using plot data, Hierarchal Cluster Analysis and Multidimensional Scaling Analysis were done to compare similarities between patches. Plots from the same forest patch clustered which indicated that the species composition in each forest patch was unique. However, this pattern went down when only tree species were considered. Plant diversity also varied between patches; with those located in the east being generally more diverse than those in the west are. Clustering patterns in fragmented communities and differences in species diversity indicate evidence of species “nestedness”. Analysis of nestedness indicated that these forest patches were significantly nested. To identify which environmental variables might be correlated with both species diversity and nestedness, twelve environmental variables was selected for analysis using Canonical Correspondence Analysis and Principal Component Analysis. Results show that Mean Annual Precipitation, Mean Annual Potential Evapotranspiration, and percentage of Organic Matter of the soil were most strongly correlated with the patterns of diversity observed in these forest patches. Regression analysis indicated that Mean Annual Precipitation accounted for most of the variation in species diversity, especially for the herbaceous species. The herbaceous species thus show a greater sensitivity to “climate filtering” as a consequence of rainfall gradients. With the implementation of suitable monitoring programs, changes in abundance or even local extinction of these species can act as an early warning indicator of the possible long-term effects of climate change on forest communities.
- Full Text:
- Date Issued: 2016
Drought responses of selected C₄ photosynthetic NADP-Me and NAD-Me Panicoideae and Aristidoideae grasses
- Authors: Venter, Nicolaas
- Date: 2015
- Subjects: Aristida , Panicum , Switchgrass , Grasses -- Effect of drought on , Grasses -- Phylogeny , Photosynthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4272 , http://hdl.handle.net/10962/d1018549
- Description: Grass species within South Africa show a photosynthetic subtype and phylogenetic response to rainfall gradients, with Panicoideae species (NADP-Me and NAD-Me) inhabiting mesic environments, while Aristidoideae species (NADP-Me) inhabit more arid environments. It is predicted that climate change will alter rainfall patterns within southern Africa, which could have implications for grassland distributions and functional composition. Globally, and in South Africa, species distributions indicates that NAD-Me species have a preference for more arid environments, but this may be complicated by phylogeny as most NAD-Me species belong to the Chloridoideae subfamily. Additionally, differences in the metabolism and energetic requirements of different carboxylation types are expected to confer different ecological advantages, such as drought tolerance, but the role of these different pathways is not well understood. Based on natural distribution and photosynthetic subtype differences, it was hypothesised that Panicoideae NADP-Me species would be less drought tolerant than Panicoideae NAD-Me and Aristidoideae NADP-Me species and that subtypes and lineages would show different drought recovery rates. Furthermore, drought sensitivity would be of a metabolic and not a stomatal origin and plants that maintained favourable leaf water status would be more drought tolerant and recover faster. This was tested experimentally by comparing Panicoideae species (NADP-Me and NAD-Me) and NADP-Me species (Panicoideae and Aristidoideae). Plants were subjected to a progressive 58 day drought period and a recovery phase where gas exchange, chlorophyll fluorescence and leaf water relations were measured at select intervals. In conjunction with this, a rapid drought experiment was performed on Zea mays (NADP-Me: Panicoideae) plants where similar parameters were measured. Photosynthetic drought and recovery responses showed both a subtype and phylogenetic response. Panicoideae species were less drought tolerant than Aristidoideae species, although Panicoideae NAD-Me showed better recovery rates than Panicoideae NADP-Me species, while Aristidoideae species recovered the quickest. Panicoideae NAD-Me and Aristidoideae species maintained higher leaf water status during drought which contributed to the maintenance of PSII integrity and thus facilitated rapid photosynthetic recovery. During drought Panicoideae species showed greater metabolic limitations over Aristidoideae species and for the first time, lower metabolic limitations were associated with osmotic adjustment. This is a novel finding whereby osmotic adjustment and the subsequent maintenance of leaf water are key to preventing metabolic limitations of photosynthesis in C₄ grasses. Results from the Z. mays rapid drought study showed the limitations to photosynthesis were exclusively metabolic and unlikely to be a direct consequence of turgor loss. It was apparent that the response to drought was stronger amongst lineages, as NADP-Me species from different subfamilies showed a significant difference in drought tolerances. Aristidoideae species’ exceptional drought tolerance and predicted increased aridification could favour these species over Panicoideae species under future climates.
- Full Text:
- Date Issued: 2015
Montane Wetlands of the South African Great Escarpment : plant communities and environmental drivers
- Authors: Janks, Matthew Richard
- Date: 2015
- Subjects: Mountain plants -- South Africa -- Eastern Cape , Wetland plants -- South Africa -- Eastern Cape , Wetland plants -- Effect of altitude on -- South Africa -- Eastern Cape , Wetland ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4274 , http://hdl.handle.net/10962/d1018917
- Description: Wetlands provide a number of valuable functions to both the surrounding environment and society. The anaerobic conditions created by flooding in wetlands provide a habitat that supports unique assemblages of plant life. High altitude wetlands are amongst the most species-rich in South Africa. They house a number of rare species and play a vital role in the supply of water to lower lying areas. These are some of the reasons that mountain wetlands are of high conservation value. A phytosociological study was undertaken on the high altitude wetlands of the Great Escarpment with the aim of classifying the plant communities and identifying the environmental drivers of plant community patterns within these ecosystems. Data collection was focused in the Eastern Cape and was supplemented with data from existing studies to gain a more complete understanding of the wetlands of the Great Escarpment of South Africa. Using the Braun-Blanquet approach, Hierarchical Cluster Analysis and Indicator Species Analysis; five broad wetland groups were identified, comprised of 33 individual plant communities and 81 indicator species. Multivariate analysis, including Canonical Correspondence Analysis revealed that the effects of altitude, such as temperature and rainfall, are the most significant large-scale drivers of vegetation patterns. Smaller scale drivers include wetness and soil nutrients including nitrogen, phosphorus, electrical conductivity, sodium, and organic content. The identification of indicator species served to reveal potentially important wetland species across different areas of the Great Escarpment. The effects of altitude on plant community patterns highlights the susceptibility of the high altitude specific communities to upward temperature zone shifts resulting from global warming. Other threats include livestock trampling, water extraction, and land use change for agricultural purposes. The relative absence of alien species in these wetlands gives an indication of their pristine condition and therefore their importance as a reference from which they may be monitored. A large proportion of the wetlands studied here occur outside protected areas, and given the rate of wetland loss in South Africa, it is important that continued effective land management is practiced to ensure that these ecosystems are conserved in the future .
- Full Text:
- Date Issued: 2015
The role of seasonality, environmental correlates and edge effects on the diversity and abundance of small mammals in Afromontane forest patches, Eastern Cape, South Africa
- Authors: Junkuhn, Kyle Peter
- Date: 2015
- Subjects: Upland ecology -- South Africa -- Eastern Cape , Mammal populations -- South Africa -- Eastern Cape , Forest animals -- Adaptation -- South Africa -- Eastern Cape , Forest animals -- Climatic factors -- South Africa -- Eastern Cape , Forest animals -- Effect of habitat modification on -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4270 , http://hdl.handle.net/10962/d1018188
- Description: The Eastern Cape contains the majority of the remaining forested areas in South Africa (95.8 percent Coastal forests and 47.6 percent Afromontane forests), however these occur in fragments. Due to the rapid rise in the human population and its needs, conversion of forests to agricultural land and the extraction of timber increases, natural vegetation are lost and this therefore leads to forests becoming fragmented into small forest patches. One of the main consequences of forest fragmentation is loss of contiguous habitat, which is the dominant threat to species globally as it negatively affects both species richness and genetic diversity. This research investigates the effects that forest fragmentation has on small mammal diversity and abundance. The study sampled small mammals in Southern Mistbelt Afromontane forest patches in the Eastern Cape. The first aim of this study was to identify which environmental variable, or combinations of variables, affect the diversity and abundance of small mammals in fragmented forest patches in the Eastern Cape during the austral summer. The second aim was to compare seasonal changes in small mammal diversity and abundance at a forest edge compared to the forest core at Beggars Bush, an Afromontane forest in the Eastern Cape, South Africa. To identify the environmental impacts that different forests have on small mammals, nine different forests were chosen in the Eastern Cape and sampled during the summer in 2013. These nine forests were: Fort Fordyce Forest, Thaba Ndoda Forest, Hogsback Forest, Dassie Kraans Forest, Langeni Forest, Burchell’s Reserve Forest, Maiden Dam Forest and Kagaberg Forest. At each site, three transects of 30 Sherman Traps each were used. Trapping periods within each forest patch lasted between three to five consecutive nights and traps were inspected once a day in the morning. Nine environmental variables were initially identified and after being tested for normality and colinearity, five variables were chosen. These variables were Altitude, Mean Annual Temperature, Gradient, Patch Size and Mean annual potential evaporation. The number of individuals captures and species richness were then incorporated as dependent variables for best subset multiple regression model selection using the Akaike Information Criterion (AIC). For the second aim, the same trapping methods were used when comparing seasonal changes to diversity and abundance within the forest core. However at the forest edge, due to the small size of the forest, only 20 Sherman traps were used in each transect with five traps (25 percent) placed in the grassland and 15 (75 percent) placed in the forest along each transect. This study was one of few to survey small mammal diversity and abundance in fragmented forests in the Eastern Cape. Gradient, patch size and mean annual potential evaporation were the variables that best predicted the individual number of small mammal captures while only gradient best explained species richness. It does however, need to be noted that capture rates and species richness were very low and this would therefore effect the analysis of environmental variables. Future studies should have a larger sample size of forest patches and include more microhabitat environmental variables to determine their effects on small mammal diversity and abundance. However, it should be noted that through climatic extinction filtering, forest mammals are resilient generalists that can tolerate fragmentation effects. Furthermore, it was found that forest edges appear to play a significant role in small mammal diversity and abundance in the Beggars Bush Afromontane forest. Some species were habitat specialists such as Rhabdomys pumilio preferring the grassland habitat and Graphiurus murinus and Aethomys namaquensis the forest habitat, while Myosorex varius was the only species that was not habitat dependant. It was found that there was a greater diversity and abundance at the forest edge compared to within the forest core throughout most of the seasons. One possible flaw was that the sampling methods were different at the edge and within the forest and therefore future studies should ensure that the method stays uniform throughout the study.
- Full Text:
- Date Issued: 2015
Variation in breeding systems, floral morphology and nectar properties in three co-occurring Erica species with contrasting pollination syndromes
- Authors: Lombardi, Giorgio Colombo
- Date: 2015
- Subjects: Ericas -- South Africa -- Western Cape , Ericas -- Morphology , Ericas -- Reproduction , Ericas -- Pollination , Pollination by animals , Pollination by insects , Nectar
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4273 , http://hdl.handle.net/10962/d1018567
- Description: The genus Erica is the most species rich in the Cape Floristic Kingdom, yet there are limited data on the various flower-pollinator interactions and breeding systems for the majority of these species. Until recently research has focussed on predictive floral traits, including flower shape, length of corolla and corolla opening to identify likely pollinators in this genus. Field observations provide an empirical test of such predictions. This study investigated three species of Erica and compared their pollination and breeding systems and floral biology. Research, including field experiments and pollinator observations was undertaken in the Vogelgat Private Nature Reserve, Maanschynkop Nature Reserve and Boskloof farm in the vicinity of Hermanus in the Western Cape Province of South Africa. Field observations were conducted to determine what flower- visitor interactions occurred, while nectar volumes and sugar concentrations were measured to determine the value of the reward to the different visitors. Selective exclusion and breeding system experiments were carried out to determine whether these Erica species were capable of autonomous self-fertilization or whether they are pollinator dependent for breeding success. The unusual morphology of Erica lanuginosa suggested rodent-pollination. Field observations, including photographs of visits to plants in the field, the presence of pollen in scat sample and selective exclusion and breeding system experiments identified rodents, primarily Acomys subspinosus to be the primary pollinator. Long-proboscid flies of the family Nemestrinidae were found, on the basis of field observations to be responsible for pollination of the endemic Erica aristata. This was supported by with nectar volume and sugar concentration samples which are consistent with other long-proboscid fly-pollinated plant species. Selective exclusion and breeding system experiments undertaken confirmed that Erica aristata required a pollinator to set seed. Observations and breeding trials revealed bird-pollination in Erica sessiliflora. Nectar volume and sugar concentrations in Erica sessiliflora were in line with other sunbird-pollinated plant species, providing the necessary rewards for sunbirds visiting this species. Specialised pollination by single pollinators was found in all three species and results from breeding system experiments show that out-crossing is important. Further research into pollinator-flower interactions in the genus Erica is necessary, not least to understand more fully the conservation importance of specific pollinators.
- Full Text:
- Date Issued: 2015