Browsing by Subject "Plants"

Now showing 1 - 6 of 6
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    Aspects of plant dispersal in the southwestern Cape with particular reference to the roles of birds as dispersal agents
    (1988) Knight, Richard Spencer; Knight, Richard Spencer; Siegfried, Roy; Moll, Eugene J
    The dispersal of plants with particular attention to the roles birds play as dispersal agents was studied in the southwestern Cape, South Africa from 1983 to 1985. The research was organized as ten inter-related studies, each with an independent data base. Each chapter focused on a different scale of plant dispersal processes ranging from regional assemblages of plant species to individual species. At the largest scale, the seven vegetation types commonly occurring in the southwestern Cape were examined for incidence of vertebrate-dispersed plants. Coastal Thicket and Afromontane Forest were found to be the richest in these species. The colonization of vertebrate-dispersed plants was examined in an artificially cleared area of Mountain Fynbos vegetation. Enhanced densities of vertebrate-dispersed species were found in areas where perches had been provided. The seasonal availability of vertebrate-dispersed species was found to be most continuous in Coastal Thicket vegetation. Fruit displays of vertebrate-dispersed indigenous plants were found to vary from those that were sporadic and inconspicuous, to those that were conspicuous and predictable, whereas those of alien plants were usually large and conspicuous. Avian use of these fleshy fruits in Coastal Thicket was examined and found to be proportional to their availability. A study of fruit presentation in relation to leaf number and stem thickness suggested that sessile, stem attached fruits have fewer local leaves at time of ripening than fruits which are presented in panicles. This may enhance accessibility and conspicuousness of stem attached fruits for dispersal by birds. Four autecological studies tested certain predictions arising from models developed to describe fruit/frugivore interactions. The dispersal of the alien Acacia cyclops seeds by the indigenous Black Korhaan Eupodotis afra suggested that successful fruit/frugivore relationships are not necessarily the product of reciprocal evolution. The study on Chrysanthemoides monilifera found that efficient dispersal systems are not limited to plants producing small quantities of lipid-rich fruits and to dispersal by obligate frugivores. The abiotic dispersal of Quercus robur was found to be efficient in relation to vertebrate-dispersal. The study on Protasparagus aethiopicus found that the morphology of fleshy fruits may also reflect attempts to overcome the effects of non-dispersing seed predators. 1It is concluded that a gradient from a predictable to unpredictable fruit availability provides a better basis for studying fruit/frugivore interactions than the coevolutionary models. previously presented.
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    Intravaginal practices, bacterial vaginosis, and HIV infection in women: individual participant data meta-analysis
    (Public Library of Science, 2011) Low, Nicola; Chersich, Matthew F; Schmidlin, Kurt; Egger, Matthias; Francis, Suzanna C; Van de Wijgert, Janneke H H M; Hayes, Richard J; Baeten, Jared M; Brown, Joelle; Delany-Moretlwe, Sinead
    Pooling of data from 14,874 women in an individual participant data meta-analysis by Nicola Low and colleagues reveals that some intravaginal practices increase the risk of HIV acquisition.
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    Investigating the role of phytohormones during desiccation in two evolutionarily distinct resurrection plants
    (2025) Kirchner, Sabine Maye; Farrant, Jill Margaret; Vothknecht, Ute; Van de Pas, Llewelyn
    Most plants encounter challenges brought on by various abiotic stressors which subsequently prompt adaptations to mitigate these challenges. Water deficit brought about by drought conditions is a significant abiotic stressor that impacts crop productivity, ultimately threatening global food security. Significant effort has thus gone into researching the unique adaptations that have allowed a remarkable group of angiosperms termed resurrection plants, to survive extreme water loss. This thesis focused on profiling phytohormone abundances in two evolutionarily distinct resurrection plant species; Craterostigma pumilum and Xerophyta schlechteri, during a dehydration time course. The objective was to elucidate some of the molecular processes that occur in the context of differing desiccation tolerance strategies, namely homoiochlorophylly and poikilochlorophylly. Hormone profiles were then followed up with gene expression analysis of desiccation-responsive genes RD29B and GASA3 in C. pumilum to further explore hormone signalling associated with jasmonates. In order to do this, and because the major findings on the roles of these genes in relation to jasomonate emanate from work on the model plant Arabidopsis thaliana, protocols designed for their analyses in that species were tested against C. pumilum to investigate their effectiveness when implemented in a non-model species. Species-specific hormone profiles were identified not only between the two resurrection plants, but also within their leaf and root tissues. ABA emerged as a central regulator of stress responses, while jasmonic acid (JA) appeared to play more of a supporting role, and the dynamics of OPDA, a precursor of JA, suggested a potential alternative signalling pathway that may occur in resurrection plants during desiccation. Overall, the findings point to species-specific hormone profiles that may be unique to resurrection plants and underscore the complexity of hormonal interactions in plant responses to water deficit stress. Additionally, results highlighted the need for further optimization of laboratory protocols designed with specific species in mind and warn against a potential over-reliance on protocols designed for model species.
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    Optimising regionalisation techniques: identifying centres of endemism in the extraordinarily endemic-rich Cape Floristic Region
    (Public Library of Science, 2015) Bradshaw, Peter L; Colville, Jonathan F; Linder, H Peter
    We used a very large dataset (>40% of all species) from the endemic-rich Cape Floristic Region (CFR) to explore the impact of different weighting techniques, coefficients to calculate similarity among the cells, and clustering approaches on biogeographical regionalisation. The results were used to revise the biogeographical subdivision of the CFR. We show that weighted data (down-weighting widespread species), similarity calculated using Kulczinsky's second measure, and clustering using UPGMA resulted in the optimal classification. This maximized the number of endemic species, the number of centres recognized, and operational geographic units assigned to centres of endemism (CoEs). We developed a dendrogram branch order cut-off (BOC) method to locate the optimal cut-off points on the dendrogram to define candidate clusters. Kulczinsky's second measure dendrograms were combined using consensus, identifying areas of conflict which could be due to biotic element overlap or transitional areas. Post-clustering GIS manipulation substantially enhanced the endemic composition and geographic size of candidate CoEs. Although there was broad spatial congruence with previous phytogeographic studies, our techniques allowed for the recovery of additional phytogeographic detail not previously described for the CFR.
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    A rapid multi-disciplinary biodiversity assessment of the Kamdebooberge (Sneeuberg, Eastern Cape, South Africa): implications for conservation
    (Springer, 2012) Clark, Vincent; Perera, Sandun; Stiller, Michael; Stirton, Charles; Weston, Peter; Stoev, Pavel; Coombs, Gareth; Morris, Dale; Ratnayake-Perera, Dayani; Barker, Nigel; McGregor, Gillian
    Botanical work since 2008 on the Sleeping Giant section of the Kamdebooberge (Sneeuberg mountain complex, Eastern Cape, South Africa) has indicated that these mountains may be of significant conservation value. Accordingly, a precursory, rapid multi-disciplinary biodiversity assessment was undertaken in January 2011, focusing on plants, tetrapod vertebrates and leafhoppers. The botanical results confirm the Kamdebooberge as being of high botanical conservation value, hosting three strict endemics, healthy populations of five other Sneeuberg endemics, and fynbos communities comprising species not found elsewhere in the Sneeuberg. The Kamdebooberge are important for herpetofauna (excluding serpentoids) and mammals, hosting several range-restricted and regional endemics. The expedition uncovered three new leafhopper species, together with several species previously only known from the Cape Floristic Region. Further detailed faunal work may provide further interesting results from these mountains, which show a high conservation value unique to the southern Escarpment.
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    The Pharmacological actions of Plants of the Genera Cotyledon and Crassula, N.O. Crassulaceae, with other Papers
    (1935) Sapeika, Norman
    The disease known as "Krimpsiekte" (Nenta, Kraamsiekte, cerebrospinal meningitis, Cotyledonosis) has been recognised in South Africa for ma.ny years. It appears in arid parts of the Cape Province, and affects animals which have ingested certain members of the genus Cotyledon (N.O. Crassulaceae).