Scielo RSS <![CDATA[South African Journal of Science]]> vol. 113 num. 9-10 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>When personal opinion trumps science</b>]]> <![CDATA[<b>Ancient DNA comes of age, but still has some teenage problems</b>]]> <![CDATA[<b>The privileges and opportunities of a research sabbatical</b>]]> <![CDATA[<b>Searching for a symbolic shipwreck in Table Bay: <i>Haarlem </i>(1647)</b>]]> <![CDATA[<b>Racism: The 'soft touch' does not work</b>]]> <![CDATA[<b>Human evolution and South African science: Darwin's hunch in context</b>]]> <![CDATA[<b>The complex origin of modern humans</b>]]> <![CDATA[<b>The Extended BSc Programme: Performance of students in Chemistry</b>]]> <![CDATA[<b>Towards an integrated ecological restoration approach for abandoned agricultural fields in renosterveld, South Africa</b>]]> <![CDATA[<b>Pollination: Impact, role-players, interactions and study - A South African perspective</b>]]> Plant-pollinator interactions are essential for maintaining both pollinator and plant communities in native and agricultural environments. Animal-instigated pollination can be complex. Plants are usually visited by a number of different animal species, which in turn may visit flowers of several plant species. Therefore, the identification of the pollen carried by flower visitors is an essential first step in pollination biology. The skill and time required to identify pollen based on structure and morphology has been a major stumbling block in this field. Advances in the genetic analysis of DNA, using DNA barcoding, extracted directly from pollen offers an innovative alternative to traditional methods of pollen identification. This technique, which is reviewed in detail, can be used on pollen loads sampled from bees in the field and from specimens in historic collections. Here the importance of pollination, the role-players involved, their management and the evolution of their interactions, behaviour and morphology are reviewed - with a special focus on South African bees. SIGNIFICANCE: • Pollen metabarcoding will enable the identification of pollen for a multitude of uses, including agriculture, conservation and forensics. • Plant-pollinator interaction documentation through pollen identification gives a more certain record of a visitor being a pollinator rather than a flower visitor that could be a nectar gatherer. <![CDATA[<b>Resilience processes in sexually abused adolescent girls: A scoping review of the literature</b>]]> Childhood sexual abuse is often associated with a number of deleterious psychological and behavioural outcomes for survivors. However, some research suggests that this impact is variable and that some survivors adapt positively. An ability to adapt positively to adversity, under any circumstances, has been termed resilience. Drawing on a socio-ecological understanding of resilience, the aim of this scoping review was to comprehensively map existing empirical studies on resilience processes in sexually abused adolescent girls and to summarise emerging resilience-enabling factors. We also considered the implications of the findings for practice and research. A total of 11 articles met the criteria for inclusion in the review. Findings from these studies suggest that internal factors (meaning making, optimistic future orientation, agency and mastery) and contextual factors (supportive family, social and educational environments) function interdependently to enable resilience in sexually abused adolescent girls. Practitioners should leverage these complementary and interdependent resilience-enabling mechanisms by encouraging greater involvement of girls in the planning of interventions and by assisting girls in developing meaningful narratives about their abuse experiences. Interventions should also encourage greater involvement from supportive structures, while challenging social and cultural norms that inhibit resilience. Resilience researchers should be cognisant of the paucity of research focusing on resilience processes in sexually abused adolescent girls as well as the absence of innovative, participatory methods of data collection. SIGNIFICANCE: • The review adds to a body of literature on resilience processes with implications for resilience researchers. • The findings have implications for a range of practitioners (psychologists, social workers, teachers etc.) who work with sexually abused girls. <![CDATA[<b>Potential of interval partial least square regression in estimating leaf area index</b>]]> Leaf area index (LAI) is a critical parameter in determining vegetation status and health. In tropical grasslands, reliable determination of LAI, useful in determining above ground biomass, provides a basis for rangeland management, conservation and restoration. In this study, interval partial least square regression (iPLSR) in forward mode was compared to partial least square regression (PLSR) to estimate LAI from in-situ canopy hyperspectral data on a heterogeneous grassland at different periods (onset, mid and end) during summer. The performance of the two techniques was determined using the least relative root mean square error to the mean (nRMSEP) and the highest coefficients of determination (R²p) between the predicted and the measured LAI. Results show that iPLSR models could explain LAI variation with R²p values ranging from 0.81 to 0.93 and low nRMSEP from 9.39% to 24.71%. The highest accuracies for estimates of LAI using iPLSR were at mid- and end of summer (R²p = 0.93 and nRMSEP = 9.39%; R²p = 0.89 and nRMSEP = 10.50%, respectively). Pooling data sets from the three assessed periods yielded the highest prediction error (nRMSEP=24.71%). Results show that iPLSR performed better than PLSR, which yielded R²p and RMSEP values ranging from 0.36 to 0.65 and from 28.44% to 33.47%, respectively. Overall, this study demonstrates the value of iPLSR in predicting LAI and therefore provides a basis for more accurate mapping and monitoring of canopy characteristics of tropical grasslands. SIGNIFICANCE: • The relationship between LAI and canopy reflectance can be used in iPLSR modelling to provide more accurate mapping and monitoring of canopy characteristics for land management and conservation <![CDATA[<b>The benefits of segmentation: Evidence from a South African bank and other studies</b>]]> We applied different modelling techniques to six data sets from different disciplines in the industry, on which predictive models can be developed, to demonstrate the benefit of segmentation in linear predictive modelling. We compared the model performance achieved on the data sets to the performance of popular non-linear modelling techniques, by first segmenting the data (using unsupervised, semi-supervised, as well as supervised methods) and then fitting a linear modelling technique. A total of eight modelling techniques was compared. We show that there is no one single modelling technique that always outperforms on the data sets. Specifically considering the direct marketing data set from a local South African bank, it is observed that gradient boosting performed the best. Depending on the characteristics of the data set, one technique may outperform another. We also show that segmenting the data benefits the performance of the linear modelling technique in the predictive modelling context on all data sets considered. Specifically, of the three segmentation methods considered, the semi-supervised segmentation appears the most promising. SIGNIFICANCE: • The use of non-linear modelling techniques may not necessarily increase model performance when data sets are first segmented. • No single modelling technique always performed the best. • Applications of predictive modelling are unlimited; some examples of areas of application include database marketing applications; financial risk management models; fraud detection methods; medical and environmental predictive models. <![CDATA[<b>The potential of South African timber products to reduce the environmental impact of buildings</b>]]> South Africa was the first country in Africa to implement a locally developed green building rating tool and has a growing number of rated green building projects. The method of life-cycle assessment can help to compare and assess the environmental performance of building products. At present, more than 70% of all sawn timber in South Africa is used in buildings, mainly in roof structures. Light gauge steel trusses have recently also been gaining market share. However, to date, no studies have been conducted that quantify and compare the environmental impacts of the different roof truss systems in South Africa. We thus compared several roof truss systems (South African pine, Biligom and light gauge steel) found in low- and medium-income house designs in South Africa using a simplified life-cycle assessment approach. Our results show that the two timber systems had overall the lowest environmental impact. Although the difference between the timber systems was small, light gauge steel had a 40% higher normalised impact over all assessed environmental impact categories. The benefit of biogenic carbon dioxide present in timber proved to play a significant positive role in the global warming potential impact and could even be further reduced if wood were used to generate energy at its end-of-life. This study demonstrates the potential advantage of using local timber products to reduce the environmental impact of the truss and building industry in South Africa. SIGNIFICANCE: • Timber truss systems showed overall lower environmental impact than light gauge steel trusses, with implications for green building. <![CDATA[<b>Perspectives of wild medicine harvesters from Cape Town, South Africa</b>]]> Cape Town is a fast-growing cityscape in the Cape Floristic Region in South Africa with 24 formally protected conservation areas including the World Heritage Table Mountain National Park. These sites have been protected and managed as critical sites for local biodiversity, representing potentially one-third of all Cape Floristic Region flora species and 18% of South Africa's plant diversity. Cape Town is also inhabited by a rapidly growing culturally and economically diverse citizenry with distinct and potentially conflicting perspectives on access to, and management of, local natural resources. In a qualitative study of 58 locally resident traditional healers of distinct cultural groups, we examined motivations underlying the generally illicit activity of harvesting of wild resources from Cape Town protected areas. Resource harvester motivations primarily link to local economic survival, health care and cultural links to particular resources and practices, 'access for all' outlooks, and wholesale profit-seeking perspectives. We describe these motivations, contrast them with the current formal, legal and institutional perspectives for biodiversity protection in the city, and propose managerial interventions that may improve sustainability of ongoing harvest activities. SIGNIFICANCE: • The study reveals, for the first time in the Cape Floristic Region, informal economy viewpoints on terrestrial nature and how its direct use has important economic and cultural roles - specifically in wild medicine harvesting and trade. • We contrast the formal and informal approaches to nature conservation in the city and propose new considerations for conservation managers. <![CDATA[<b>Externality costs of the coal-fuel cycle: The case of Kusile Power Station</b>]]> Coal-based electricity is an integral part of daily life in South Africa and globally. However, the use of coal for electricity generation carries a heavy cost for social and ecological systems that goes far beyond the price we pay for electricity. We developed a model based on a system dynamics approach for understanding the measurable and quantifiable coal-fuel cycle burdens and externality costs, over the lifespan of a supercritical coal-fired power station that is fitted with a flue-gas desulfurisation device (i.e. Kusile Power Station). The total coal-fuel cycle externality cost on both the environment and humans over Kusile's lifespan was estimated at ZAR1 449.9 billion to ZAR3 279 billion or 91c/kWh to 205c/kWh sent out (baseline: ZAR2 172.7 billion or 136c/kWh). Accounting for the life-cycle burdens and damages of coal-derived electricity conservatively, doubles to quadruples the price of electricity, making renewable energy sources such as wind and solar attractive alternatives. SIGNIFICANCE: • The use of coal for electricity generation carries a heavy cost for social and ecological systems that goes far beyond the price we pay for electricity. • The estimation of social costs is particularly important to the electric sector because of non-differentiation of electricity prices produced from a variety of sources with potentially very dissimilar environmental and human health costs. • Because all electricity generation technologies are associated with undesirable side effects in their fuel-cycle and lifespan, comprehensive comparative analyses of life-cycle costs of all power generation technologies is indispensable to guide the development of future energy policies in South Africa. <![CDATA[<b>Exploring the relationship between entry requirements and throughput rates for honours students</b>]]> In order for a student to enrol in an honours programme at the University of KwaZulu-Natal (UKZN), a weighted average mark for their final year of undergraduate study must exceed a particular threshold value. Students are then ranked according to this weighted average mark, with entry into the honours programme offered on a top-down basis, within the constraints of teaching resources and space. A proposal has been made at UKZN to remove existing barriers for entry into an honours programme, i.e. to allow entry to any student who has completed a 3-year undergraduate degree with a major in that discipline. The impact of such a decision was investigated. By lowering the requirement for entry into an honours programme, one is expected to predict how a new cohort of students will perform. Apart from obviously having a lower weighted average mark for their final year of undergraduate study, these new students may also differ in other unobservable ways which need to be accounted for. In a regression modelling context, one is asked to predict outside the range of a collected data set. A Heckman selection model was used to account for a possible self-selection bias that may arise because the subpopulation for which a prediction is required (namely those new students who will now be able to enter an honours programme), may be significantly different from the population of UKZN undergraduate students who are currently permitted entry to an honours programme. SIGNIFICANCE: • A modelling technique that accounts for a possible sample selection bias was used to determine the impact of lowering the entry requirements into the honours programme at UKZN to allow entry to any student who has completed a 3-year undergraduate degree. <![CDATA[<b>Deflating the shale gas potential of South Africa's Main Karoo basin</b>]]> The Main Karoo basin has been identified as a potential source of shale gas (i.e. natural gas that can be extracted via the process of hydraulic stimulation or 'fracking'). Current resource estimates of 0.4-11x10(9) m³ (13-390 Tcf) are speculatively based on carbonaceous shale thickness, area, depth, thermal maturity and, most of all, the total organic carbon content of specifically the Ecca Group's Whitehill Formation with a thickness of more than 30 m. These estimates were made without any measurements on the actual available gas content of the shale. Such measurements were recently conducted on samples from two boreholes and are reported here. These measurements indicate that there is little to no desorbed and residual gas, despite high total organic carbon values. In addition, vitrinite reflectance and illite crystallinity of unweathered shale material reveal the Ecca Group to be metamorphosed and overmature. Organic carbon in the shale is largely unbound to hydrogen, and little hydrocarbon generation potential remains. These findings led to the conclusion that the lowest of the existing resource estimates, namely 0.4x10(9) m³ (13 Tcf), may be the most realistic. However, such low estimates still represent a large resource with developmental potential for the South African petroleum industry. To be economically viable, the resource would be required to be confined to a small, well-delineated 'sweet spot' area in the vast southern area of the basin. It is acknowledged that the drill cores we investigated fall outside of currently identified sweet spots and these areas should be targets for further scientific drilling projects. SIGNIFICANCE: • This is the first report of direct measurements of the actual gas contents of southern Karoo basin shales. • The findings reveal carbon content of shales to be dominated by overmature organic matter. • The results demonstrate a much reduced potential shale gas resource presented by the Whitehill Formation.