Browsing by Department "Botany"

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    Local benefits of retaining natural vegetation for soil retention and hydrological services
    (2009) O'Farrell, P. J.; Donaldson, J. S.; Hoffman, M. T.
    Renosterveld is a grassy shrubland with a diverse understory of geophytes. Exceptional plant diversity and endemism, combined with considerable fragmentation due to transformation to cropland, make this vegetation type a conservation priority. The provision of formal reserves is difficult in highly fragmented landscapes. One possible way of motivating for conservation is to demonstrate the ecosystem services derived from the retention of remaining natural fragments, as a motivation for their conservation on private land. This study explored the benefits of retaining renosterveld fragments at the farm-scale based on the hydrological and soil retention services they provide. Rainfall simulations were carried out at paired sites of renosterveld and transformed renosterveld, and renosterveld and managed transformed renosterveld (requiring physical inputs). Infiltration rates, runoff volumes, sediment loads and plant species cover were recorded. This study found that infiltration was linked primarily to vegetation cover, with the highest infiltration rates experienced in renosterveld and managed transformed renosterveld dominated by alien grasses. Similarly aeolian loads and wind speeds among these three vegetation states were explored using suspension traps and hand-held anemometers. Renosterveld remnants were demonstrated to significantly reduce wind speed and aeolian load. Renosterveld provides an important service in reducing runoff, facilitating infiltration and retaining topsoil without expensive management interventions.
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    Nuclear and chloroplast DNA-based phylogenies of Chrysanthemoides Tourn. ex Medik. (Calenduleae; Asteraceae) reveal extensive incongruence and generic paraphyly, but support the recognition of infrasp
    (2009) Barker, N. P.; Howis, S.; Nordenstam, B.; Källersjö, M.; Eldenäs, P.; Griffioen, C.; Linder, H. P.
    The small genus Chrysanthemoides comprises two species within which a number of infraspecific taxa have been recognized, some of which are invasive aliens in Australia and New Zealand. Here we investigate the relationships of the species and infraspecific taxa using both chloroplast and nuclear non-coding DNA sequence data. Results of the analyses of the plastid and nuclear data sets are incongruent, and neither Chrysanthemoides nor Osteospermum is resolved as monophyletic, although there is some support for the recognition of infraspecific taxa. Analyses of the separate and combined data sets resolve two clades within Chrysanthemoides (which include some species of Osteospermum), and these appear to have a geographic basis, one being restricted to the mainly winter rainfall region, the other the eastern bi-seasonal rainfall area. Our results suggest that there is evidence of past or ongoing hybridization within and possibly between these two lineages.
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    Rodent pollination in Protea nana
    (2009) Biccard, A.; Midgley, J. J.
    Floral morphology, late winter flowering time and a distinct yeasty odour in Protea nana suggest that it is adapted for rodent pollination. To test this hypothesis, rodents were trapped in a stand of P. nana, examined for presence of pollen (on their noses and in their scats) and then observed in the laboratory for pollination behaviour. Inflorescences were placed in wire and shade-cloth exclosures and seed-set compared to controls in the field. Otomys irroratus, Aethomys namaquensis, Rhabdomys pumilio and Myomyscus (Praomys) verreauxi were captured and all tested positive for the presence of protea pollen. All, except O. irroratus, displayed legitimate pollination of P. nana. Myomyscus verreauxi was regarded as the most competent pollinator as it displayed superior climbing ability in comparison to the other rodent species. R. pumilio sometimes displayed highly destructive behaviour of P. nana inflorescences and is the likely explanation for the observed 20% reduction in average number of inflorescences per plant over a two month period. Seeds per inflorescence were lowest in shade-cloth covered inflorescences (total pollinator exclusion), but not significantly lower in wire exclosures which provided access for insects. A high percentage of sugar (29.4% by weight) in the nectar of P. nana is similar to known rodent pollinated species. We conclude that P. nana is at least partially rodent pollinated.
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    The rediscovery of Schizostephanus gossweileri and its phylogenetic position
    (2009) Bruyns, P V; Klak, C
    Two new records of Schizostephanus gossweileri (S. Moore) Liede from north-western Namibia and south-western Angola are documented and an amplified description is provided for the species. Analysis of ITS and trnL–F data provides additional evidence that this species belongs to Schizostephanus Hochst. ex K. Schum., where its relationship to S. alatus is strongly supported. The two species of Schizostephanus form a lineage that is either unsupported or weakly supported as sister to Cynanchum L. s.l.
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    Variation in seed set amongst populations of a redent pollinated geophyte, Colchicum coloratum
    (2009) Kleizen, C; Midgley, J J; Johnson, S. D.
    Agricultural activities around the rural village of Nieuwoudtville in the Succulent Karoo region of South Africa has lead to the confinement of many plant and animal species to fragmented patches of relatively untransformed habitat. The geophyte Colchicum coloratum subsp. coloratum (Colchicaceae) was studied in five patches of variable size in and around Nieuwoudtville. This species is dependent on rodent visitation for seed production. The influence of variation in population size and plant size on seed set was investigated, as well as whether there is pollen limitation in this species. A pollen-supplementation experiment indicates that there is pollen limitation in C. coloratum, and that much of the natural seed set could be the result of pollinator-mediated selfing. The five populations appeared to have different rodent abundances, however, neither population size nor the abundance of rodents in the area have an effect on seed set. This suggests that the mutualism between C. colchicum and its rodent pollinators is robust, and that habitat fragmentation in Nieuwoudtville has not yet affected the seed production of this geophyte.