Modelling the spatial and genetic response of the endemic sparid: Polysteganus praeorbitalis (Pisces: Sparidae) to climate change in the Agulhas Current system
- Authors: Isemonger, Devin Neil
- Date: 2014
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/54509 , vital:26576
- Description: The Scotsman Seabream, Polysteganus praeorbitalis, is one of several large, slow-growing members of the Sparidae family of fishes endemic to the Agulhas Current system in the Western Indian Ocean (WIO). Relatively little research has been conducted on this species despite its importance to both recreational and commercial line fisheries in South Africa and the drastic decline in catch per unit effort (CPUE) that has been recorded since the 1940s. Changing sea temperatures as a result of global climate change are further expected to affect the distribution and abundance of many fish species based on their thermal tolerances, life histories and population structures. The ability of these species to shift their distribution and adapt to new environments and thermal conditions will depend to some degree on the levels of genetic variation and gene flow, within and between populations. A combined approach using species distribution modelling and genetic analyses may prove to be a useful tool in investigating the potential effects of climate change on the distribution and genetic diversity of species. An ensemble species distribution model (SDM) based on 205 occurrence records and 30 years of Reynolds Optimum Interpolated (OI) sea surface temperature data was constructed to predict the distributional response of P. praeorbitalis to climate change in the Agulhas Current system. The ensemble SDM displayed a true skill statistic (TSS) of 0.975 and an area under the receiver operating curve (ROC) of 0.999, indicating good model fit. Autumn and winter minimum temperatures, as well as bathymetry, were the most important predictor variables in the majority of models, indicating that these variables may directly constrain the distribution of P. praeorbitalis. In particular, the southern range edge of this species appeared to be constrained by autumn and winter minima, with high model agreement on this range edge. Conversely, the northern range limit showed poor model agreement leading to a gradual reduction in occurrence. This indicates that this range edge may be constrained by other factors not included in the models such as species interactions. The ensemble SDM projected the current range of P. praeorbitalis to be 1500 km², smaller than the published range for this species. The model underestimated the northern range edge of this species by approximately 5° latitude when binary transformed. This is probably due to the rarity of this species in the landings of the Mozambican linefishery, which was assumed to be an indication of low abundance of P. praeorbitalis in these waters. The absence of a specimen to verify the published northern range edge of this species indicates that the northern range edge produced by this model is likely to be closer to the actual range limit of the species. A range contraction of 30% occurring at both the northern and southern edge of P. praeorbitalis’ range and range fragmentation occurring, towards its northern range edge by 2030, was predicted. These changes are modelled to be the results of cooling related to the intensification of the Port Alfred upwelling cell and of warming predicted north of the Natal Bight and in southern Mozambique. Genetic analyses of the nuclear DNA (nDNA) S7 intron 1 and mitochondrial DNA (mtDNA) control region genes were carried out using 118 tissue samples of P. praeorbitalis collected at four main localities: the Eastern Cape, Transkei, southern KwaZulu-Natal and northern KwaZulu-Natal. Analyses of genetic diversity levels revealed relatively low diversity in the mtDNA dataset (Hd = 0.488; π = 0.004) and moderate levels of diversity in the nDNA dataset (Ad = 0.922; π = 0.005). The low levels of diversity observed in the mtDNA dataset might be explained by a number of factors, including high variation in spawning success, the negative effects of over-harvesting, or a recent population bottleneck. The last explanation is supported by characteristic star-shaped haplotype networks and unimodal mismatch distributions displayed by both datasets. These results, in conjunction with a significant (p = 0.005) negative Tajimas D value (-2.029) in the mtDNA dataset and significant (p = 0.0005) negative Fu’s F statistic in both the nDNA (F = -26.5) and mtDNA (F = -11.9) datasets, provide strong evidence for a recent population expansion after a bottleneck event in this species. Spatially, mtDNA diversity was highest in the Eastern Cape and lowest in the middle localities, while nDNA diversity showed the opposite pattern. These results may be indicative of differences in the sex ratio between localities, possibly as a result of the protogynous hermaphroditism that has been postulated for this species. Although pairwise comparisons and exact tests of population differentiation revealed no significant geneticdifferentiation between populations in the mtDNA dataset, there was some evidence of low levels of differentiation in the nDNA dataset. This occurred for comparisons between the Eastern Cape and Transkei (Fst = 0.039; p <0.05), and the northern KwaZulu-Natal (Fst = 0.045; p < 0.05).. This might be the result of one or a combination of factors including the effects of the Port Alfred upwelling cell on dispersal and gene flow, or the possibility of more than one spawning ground for this species promoting sub-structuring. A SAMOVA analyses run on the nDNA dataset maximised variance by grouping the Eastern Cape and southern KwaZulu-Natal together and Transkei and northern KwaZulu-Natal together in two groups. This revealed no evidence of spatial structure (p = 0.36), with only 3.30% of variation explained by this grouping. The removal of individuals below the estimated length at 50% maturity in the nDNA dataset, in order to test for temporal structure, resulted in stronger evidence of differentiation between the Eastern Cape and all other localities: Transkei (Fst = 0.081; p< 0.05), southern KwaZulu-Natal (Fst = 0.031; p<0.05), and northern KwaZulu-Natal (Fst = 0.078; p< 0.05). This indicates that some temporal genetic structure may exist between age classes within this species. The differentiation observed between the Eastern Cape and other localities, coupled with the high percentage of private haplotypes in the mtDNA dataset in this locality, indicates that this area is where P. praeorbitalis is most vulnerable to the potential negative effects of climate change on its genetic diversity. However, the vast majority of this species genetic diversity appears to reside towards the centre of its range where it is most abundant and the lack of strong genetic structure indicates high levels of gene flow. In conclusion, while P. praeorbitalis is vulnerable to range loss as a result of climate change, its genetic diversity is unlikely to be greatly affected.
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- Date Issued: 2014
Dangerous liaisons or critical alliances: student perceptions of community engagement at Rhodes University, South Africa
- Authors: Levy, Simone Arielle
- Date: 2018
- Subjects: Rhodes University -- Students -- Public services , Community and college -- South Africa -- Eastern Cape , Education, Higher -- Social aspects -- South Africa
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/57411 , vital:26907
- Description: Community Engagement (CE) in South Africa is an increasingly important feature of the relationship between the university and a broader community, and may aid in bridging the entrenched social divisions of this nation. This will only be possible if CE succeeds in uniting the knowledge production interests of the university and the broader community. Through CE, knowledge production and dissemination from within the university should be made more relevant and applicable because it is based on a relationship or engagement with a community. Based on the perceptions of student volunteers in a CE programme at a South African university, this thesis set out to ask whether or not students are transformed through university-community collaboration. This research examines the perceptions and motivations of student volunteers entering community partnership programmes. More importantly, it asks whether these engagements are merely a “weekend special” consisting of shallow engagements, which last only a few hours a week that provide institutional window dressing; or well-intended engagements through which students build meaningful relationships and experience learning opportunities that prepare them for real world civic participation. As this thesis focuses on the student perspective, it explores whether or not CE has an impact, both personally and educationally or academically, on the lives of individual student volunteers. The literature on CE argues that students’ participation in CE opportunities should enhance academic learning, personal growth and promote a sense of citizenship or civic responsibility. Based on the perceptions of a small group of student volunteers at one university, this thesis identifies possible successes and limitations of CE volunteering programmes in order to see if what is promoted in the literature or institutional policies is being experienced or achieved in practice at universities. I argue that students are indeed transformed through processes of CE, often in unexpected ways, and despite many difficulties. Therefore, if CE provides students with more holistic learning opportunities while attending universities for academic ends, it is important to look at in what ways this is achieved.
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- Date Issued: 2018
Factors influencing survivorship of Portulacaria afra cuttings in restoration of degraded lands
- Authors: Sholto-Douglas, Craig
- Date: 2019
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/92230 , vital:30692
- Description: Heavy over-browsing, over-grazing, and over-trampling has caused the degradation of vast areas of subtropical thicket, including parts of the Greater Addo Elephant National Park (GAENP). Severe degradation has resulted in the loss of vegetation cover and the deterioration of soils and soil functioning. The South African Department of Environmental Affairs (DEA), and specifically the Natural Resource Management Programme (NRM), have invested in restoration initiatives such as the Subtropical Thicket Restoration Programme (STRP), which has aimed to demonstrate the logistical and practical feasibility of restoring these degraded thickets by planting en masse Portulacaria afra (spekboom) cuttings. However, the planted P. afra cuttings often succumb to various abiotic and biotic stresses. This project aimed to identify various factors which may influence the survival of P. afra cuttings, including i) soil properties, ii) water (rainfall, infiltration, run-off, etc.), iii) browsing by mega-herbivores, iv) topographical features such as slope and aspect, or v) plant species or communities. Biodiversity and carbon baselines were carried out at 50 plots within the Main Camp, Darlington and Kabouga sections of the GAENP, providing pre-planting vegetation and soil data. The en masse planting of P. afra occurred following the completion of the baselines. Following a minimum rest period of three months after planting, survivorship counts were carried out at all plots. Infiltration rate had a significant positive relationship with planted P. afra survivorship across all of the sites. Positive trends between increases in litter and root biomass and planted P. afra cuttings survivorship in Kabouga were also evident. Magnesium, water-holding capacity and increasing soil clay percentage were found to have a significant negative relationship with planted P. afra survivorship in Kabouga. Aluminium, magnesium, and boron all had significant positive relationships with planted P. afra cuttings survivorship in Addo Main Camp. No soil variables had any significant relationship with survivorship of planted P. afra cuttings at Darlington. The presence of elephants (Loxidonta africana) had a significant negative relationship with planted P. afra survivorship. Plant communities in more ‘moderately’ degraded states, characterized by the retention of canopy dominant species, woody vegetation cover, limited bareground and higher cover of litter had higher survivorship of planted P. afra cuttings than those in more severely degraded states. The grass Panicum maximum, and forb Atriplex semibaccata were associated with positive relationships with planted P. afra survivorship across all sites. Future research should aim to develop matrices which plot likely survivorship percentages with parameters of measurable variables, such as infiltration, severity of soil capping, browsing densities, chemical indicators, and degradation severity, to identify suitable biophysical planting conditions for P. afra cuttings. Further research should assess whether the presence of elephants, in high densities, can reduce the economic feasibility of the en masse plantings of P. afra cuttings in attempts to restore degraded landscapes.
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- Date Issued: 2019