Insects, temperature and the metabolic theory of ecology

Irlich, Ulrike Marianne (2007-03)

Thesis (MSc)-- University of Stellenbosch, 2007.

Thesis

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.

AFRIKAANSE OPSOMMING: Metabolisme is 'n basiese eienskap van alle lewende organismes. Dit is lankal bekend dat metaboliese tempo substantieel varieer tussen spesies en omgewings en die belangrikheid van hierdie verskil het nuutgevonde belangstelling met die inleiding van die Metaboliese Teorie van Ekologie (MTE) tot gevolg gehad. Die teorie verklaar dat variasie in metabolisme gee aanleiding tot variasie in 'n groot getal organismiese kenmerke, soos die tempo van ontwikkeling en soortvorming en 'n verskeidenheid van populasie parameters. Hierdie kwantitatiewe teorie mik op 'n verduideliking van hoe metaboliese tempo op grondvlak varieer as 'n gevolg van liggaamsmassa en temperatuur. Dus kan die MTE verdeel word in twee hoof komponente, die massa en die temperatuur komponent waarvan albei emstig gedebateer word. Die empiriese waardes en teoretiese verduidelikings, wat die massa komponent onderlig, bly onderworpe aan bewering. Die temperatuur komponent, die Universele Temperatuur Afhanklikheid (UT A) van metabolisme het tot op datum veel minder aandag geniet as die massa komponent. In hierdie studie is die effek van temperatuur op insek metaboliese tempo en ontwikkelings tempo in die konteks van die MTE bestudeer. Die vier hoof voorspellings van die MTE was ondersoek: (i) die gemiddelde aktiverings energie behoort nie kenmerkend te verskil van die gemiddelde waarde van 0.65 eV met meeste waardes tussen 0.6 an 0.7 eV; (ii) min filogenetiese seine mag sigbaar wees in die hellings van die temperatuur-tempo verhoudings; (iii) die hellings van die temperatuur-tempo verhoudings mag minimale variasie wys as gevolg van omgewings veranderlikkes; (iv) intraen interspesiefieke temperatuur-tempo verhoudings behoort nie te verskil nie. Hierdie studie illustreer duidelik dat die eerste stap in enige bepaling van die MTE is die begrip van die artefakte wat met die data versameling geassosieer mag word, spesifiek die metodes wat gebruik is om metaboliese tempo te bereken. Alhoewel die intraspesifieke aktiverings energiee na aan die voorspelde waarde van 0.65 e V was, het slegs 21-31 % van al die waardes binne die voorspelde reeks geval. Konstante variasie oor die temperatuur-tempo verhoudings was gevind in die vorm van swak filogenetiese seine wat n klein deel van die variasie verduidelik. 'n Groot deel van die variasie was verduidelik deur n stel omgewings veranderlikes, spesifiek geografiese lokasie en omgewings temperatuur. In die geval van ontwikkelings tempo was die hellings van die interspesifieke verhoudings tipies laer as die gemiddelde hellings van die intraspesifieke verhoudings, terwyl ten opsigte van metaboliese tempo hierdie patroon slegs in sekere gevalle bekend was, afhanklik van die metode wat gebruik is om die interspesifieke hellings te bereken. Verder het hierdie studie gewys dat die omgewings temperatuur waarby die insek skynbaar sy volwasse lewe uitleef of <lat sy volkome ontwikkeling 'n wesenlikke rol speel in die vorming tussen spesies se temperatuurtempo verhoudings. Hierdie studie het verder gewys <lat die harde weergawe van die UT A van metabolisme blyk nie ondersteun te wees deur die data vir insek metaboliese en ontwikkelings tempos en dus word die MTE verwerp. Alhoewel 'n bietjie ondersteuning verwerf is vir die sagte UTA sowel as die evolusionere kompromis hipotese.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/50721
This item appears in the following collections: