Browsing by Author "Irlich, Ulrike Marianne"
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- ItemInsects, temperature and the metabolic theory of ecology(Stellenbosch : Stellenbosch University, 2007-03) Irlich, Ulrike Marianne; Chown, S. L.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Metabolism is a fundamental characteristic of all living organisms. That metabolic rate vanes substantially between species and environments has long been recognized and the significance of this variance has gained renewed interest with the introduction of the metabolic theory of ecology (MTE). The theory states that variation in metabolism accounts for variation in a large number of organismal traits, such as development and speciation rates and a range of population parameters. This quantitative theory is based on the assumption that metabolic rate varies principally as a consequence of body mass and temperature. Thus the MTE can be divided into two main components, the mass component and the temperature component, both of which are heavily debated. The empirical values and theoretical explanations underlying the mass scaling of metabolic rate remain a subject of contention. To date, the temperature component, the Universal Temperature Dependence (UTD) of metabolism, has received far less attention than the mass component. In this study the effect of temperature on insect metabolic rate and development rate in the context of the MTE was investigated. The four main predictions of the MTE were examined: (i) the mean activation energy should not be significantly different from the mean value of 0.65 e V, with most values lying between 0.6 and 0.7 eV; (ii) little phylogenetic signal should be evident in the slopes of the rate-temperature relationships; (iii) slopes of the rate-temperature relationships should show minimal environmental variation; (iv) intra- and interspecific rate-temperature relationships should not differ. This study clearly illustrated that the first step in any assessment of the MTE must be to understand the artefacts that might be associated with the data collection, specifically the methods used to measure metabolic rates. Although the intraspecific activation energies were close to the predicted value of 0.65 e V, only 21-31 % of all values fell within the predicted range. Consistent variation about the rate-temperature relationships was found in the form of a weak phylogenetic signal, explaining a small proportion of the variation. A greater proportion of variance was however explained by a set of environmental variables, specifically geographic locality and environmental temperature. In the case of development rate the slopes of the interspecific relationship were typically lower than the mean slopes of the intraspecific relationships, while for metabolic rate this pattern was only apparent in some cases, depending on the method used to calculate the interspecific slopes. Furthermore, this study showed that the environmental temperature at which the insect was thought to live its adult life, or its entire development, plays a pivotal role in shaping the between species rate-temperature relationships. This study showed that the hard version of the UTD of metabolism does not appear to be supported by the data for insect metabolic and development rates, and thus the MTE is rejected. However, some support was obtained for the soft UTD as well as the evolutionary trade-off hypothesis.