Browsing by Author "Gouws, Emeline Jeanne"

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    Intraspecific body size variation in insects
    (Stellenbosch : Stellenbosch University, 2007-03) Gouws, Emeline Jeanne; Chown, Steven L.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: This thesis investigates several aspects of intraspecific variation in the body sizes of insects. More specifically, it concerns how body size is distributed within populations of a species and how body size within populations varies over space and time. The motivation for this study is the relative paucity of information in the literature pertaining to how body size varies at the intraspecific level for insects, and what mechanisms might underlie this variation. In particular, it is shown that although a lognormal frequency distribution in body size is expected at all taxanomic levels, there is great variation in these body size frequency distribution patterns at the intraspecific level for insects. This study also highlights the need to consider all possible factors that might influence the pattern of body size frequency distributions, including sexual size dimorphism of a species, how many size classes or bins are used in the distributions and the sample size. Furthermore, if a better understanding of these patterns is sought, especially with regard to the mechanisms underlying how body size of a population is distributed, factors affecting the life history, physiological and ecological responses of individuals in a population need to be considered. This is also the case for geographical variation in body size of insects. Altitudinal variation in insect body size therefore, is of particular interest, and here it was used as the basis for an investigation of the possible mechanisms underlying clinal patterns in body size. Variation was found in the patterns observed for the beetle species considered in this study. Although one species (Sternocara dentata) did not vary significantly in mean size along the altitudinal gradient, Thermophilum decemguttatum and Zophosis gracilicornis both showed a decrease in size with altititude, contrary to what is expected from the temperature-size rule for ectotherms. The responses in the body sizes of the latter two species to several environmental variables along the altitudinal gradient, including mean annual temperature and some vegetation variables indicated that the size variation is subject to the combined effects of temperature, resource availability and resource acquisition. This finding provides support for the resource allocation switching curve mechanism (one of several alternative mechanisms) thought to underlie clinal size variation.
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    Intraspecific body size variation in insects
    (Stellenbosch : Stellenbosch University, 2007-03) Gouws, Emeline Jeanne; Chown, S. L.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: This thesis investigates several aspects of intraspecific variation in the body sizes of insects. More specifically, it concerns how body size is distributed within populations of a species and how body size within populations varies over space and time. The motivation for this study is the relative paucity of information in the literature pertaining to how body size varies at the intraspecific level for insects, and what mechanisms might underlie this variation. In particular, it is shown that although a lognormal frequency distribution in body size is expected at all taxanomic levels, there is great variation in these body size frequency distribution patterns at the intraspecific level for insects. This study also highlights the need to consider all possible factors that might influence the pattern of body size frequency distributions, including sexual size dimorphism of a species, how many size classes or bins are used in the distributions and the sample size. Furthermore, if a better understanding of these patterns is sought, especially with regard to the mechanisms underlying how body size of a population is distributed, factors affecting the life history, physiological and ecological responses of individuals in a population need to be considered. This is also the case for geographical variation in body size of insects. Altitudinal variation in insect body size therefore, is of particular interest, and here it was used as the basis for an investigation of the possible mechanisms underlying clinal patterns in body size. Variation was found in the patterns observed for the beetle species considered in this study. Although one species (Sternocara dentata) did ' not vary significantly in mean size along the altitudinal gradient, Thermophilum decemguttatum and Zophosis gracilicornis both showed a decrease in size with altititude, contrary to what is expected from the temperature-size rule for ectotherms. The responses in the body sizes of the latter two species to several environmental variables along the altitudinal gradient, including mean annual temperature and some vegetation variables indicated that the size variation is subject to the combined effects of temperature, resource availability and resource acquisition. This finding provides support for the resource allocation switching curve mechanism (one of several alternative mechanisms) thought to underlie clinal size variation.