Browsing by Author "Robertson, Hamish"

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    The impacts of different methods of alien plant control on the recovery of Fynbos ecosystems
    (2002) Parker, Fatima; Richardson, Dave; Van Wilgen, Brian; Robertson, Hamish
    This study investigated the effects of past management aimed at clearing invasive alien plants in South African fynbos ecosystems. The treatments included "bulldozing and aerial-spraying", "aerial-sprayiing", "boom-spraying" and "spot-spraying". Both an ant study and vegetation survey was conducted to test the hypothesis that fynbos is resilient to all kinds of pertubation (including the most severe alien plant management treatments employed) and that natural recovery over time is adequate to restore fynbos (without human intervention).
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    A macro- and micro-evolutionary investigation of African Camponotus ants
    (2002) Eick, Brigitte N; O'Ryan, Colleen; Robertson, Hamish; Harley, Eric
    Camponotus than the cytochrome oxidase II gene, based on almost all measures of phylogenetic utility. The primary hypothesis proposed to account for this observation is that these two mitochondrial genes are evolving under different evolutionary constraints. Specifically, the cytochrome oxidase II gene displays greater rate heterogeneity than the cytochrome b gene, thereby decreasing its utility for phylogenetic analyses. Combining sequence data from both genes resulted in more robust phylogenetic hypotheses, with the combined topologies displaying greater congruence with the cytochrome b topologies than those based on cytochrome oxidase II sequence data. The morphological data produced a topology that was congruent with that obtained from molecular data, and provided increased support for certain nodes in the context of a combined molecular-morphological framework. The hypothesis that subgeneric classifications within Camponotus do not accurately reflect phylogenetic relationships was supported by the molecular phylogenies. An exception to this hypothesis was the monophyly of the subgenus Myrmosericus, based on cytochrome b data. The morphological and behavioural data provided support for a monophyletic group comprising the four species assigned to the subgenus Myrmopiromis. However, although these four species associated together in a group based on combined cytochrome oxidase II and cytochrome b sequences, this group was paraphyletic in the combined molecular topology, with two species in subgenus Myrmopsamma also falling within this group.