Browsing by Author "Mgidi, Theresa Nobuhle"

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    Attributes that make Acacia karroo dominant : stable N and C isotope analysis of nine Acacia species from KwaZulu-Natal (South Africa)
    (2006) Mgidi, Theresa Nobuhle; Midgley, Jeremy J; Stock, WD
    This study focuses on nine Acacia species from Hluhluwe-Imfolozi Park in KwaZulu-Natal, South AFrica. The study was motivated by the need to understand the dominance of legumes in the process of bush encroachment in Southern Africa. A. karroo has been identified as a particularly invasive species in HUP, and determining what makes this Acacia species and any of the other acacias in HUP invasive formed the foundation of this study.
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    The effects of size and habitat on δ N-15 of carnivorous plants (Drosera spp.)
    (1999) Mgidi, Theresa Nobuhle; Midgley, Jeremy J; Stock, WD
    The δ N-15 natural abundance method was used to investigate the role of nutrient-poor habitats in carnivorous Drosera capensis and Drosera aliciae, and how that role changes under sunny and shady environmental conditions. The main purpose of the study was to evaluate Givnish's (1984) cost/benefit model used to explain the evolution of carnivory in nutrient-poor, sunny and moist habitats. δ N-15and total nitrogen values of the Drosera species were compared against each other, as well as against the non-carnivorous reference plants collected from each of the two habitats. Generally, data indicated significant differences between the carnivorous plants and their reference plants in terms of δ N-15 values. However, there was no significant difference between plants collected from the shade and those collected from the sun for both Drosera species. Total nitrogen results revealed higher values for Drosera plants from Camp's Bay than those from Table Mountain did. This indicated that there was a bigger source of insect nitrogen at that site, meaning more insects were available and being caught by the plants at Camp's Bay. Further investigations were performed on the two Drosera species in order to find the influence of altitude, leaf-size and plant form, on the degree of carnivory. There was an overall, higher degree of carnivory at Camp's Bay where it is, seasonally wet and the plants have longer leaves and a stem-like rosette. On Table Mountain it is cooler, waterlogged, and the plants have short leaves and ground-level rosettes therefore, the degree of carnivory there was lower. Lastly, chlorophyll and anthocyanin contents were measured and compared between the sun and shade collected D. capensis plants, with tentacles intact and with them removed. Chlorophyll investigations showed significant differences between sun and shade collected D. capensis plants but these were not affected by the removal of tentacles. Alternatively, anthocyanin measurements indicated that sun and shade collected D. capensis plants have similar amounts of anthocyanins, but the removal of tentacles results in a decrease (about four times lower) in the anthocyanin content.
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    Variation in Thamnocortus insignis - genetically and environmentally plastic?
    (1999) Mgidi, Theresa Nobuhle; Linder, H Peter
    Environmental variation of Thamnocortus insignis Mast. (Restionaceae) is presented, by using average dry weight measurements of six populations of this species found along the coast of the Cape Province. The dry weight measurements were used to detect variation in the growth rates of the six populations, which in tum indicates the environmental variation among the populations. The results were showed no significant difference between all six populations and this was due to the relatively very small sizes of the seedlings when the measurements were taken. Genetic variation was investigated by using isozyme electrophoresis of the EST locus. One population (Puntjie) showed significant deviation from the Hardy-Weinberg equilibrium, whilst all the others agreed with the assumptions of the model except for the Superthatch-extra tall population, which was homologous. Estimation of allelic diversity among the populations produced a Fst of 0.098 that implies that there is a high level of gene flow among the six populations of the species. The allelic diversity estimate within populations was also very low (Fis = 0.079) implying that the genetic neighbourhoods are relatively large and there is a high incidence of gene flow within the populations. Both estimation results support the predicted results for dioecious wind-pollinated species such as T. insignis.