| Summary: | Thesis (MSc)--Stellenbosch University, 2005. ENGLISH ABSTRACT: Evidence for widespread ecological impacts due to rapid climate change is on the increase, with further warming predicted over the next century. This increase in warming has lead to organisms adjusting their distribution range and where this is not possible organisms must cope with the stressful environments in a different way. One potential way to handle environmental stress is via a mechanism known as phenotypic plasticity, which allows an organism to express different phenotypes depending on the biotic or abiotic environment in a way that may alter that organism's fitness. Acclimation temperatures can potentially cause plastic (reversible and irreversible) changes in the response of individuals to stressful experimental conditions that could increase their survival. The issue of whether this acclimation will be beneficial to the organism or not remains contentious, with support offered both for and against the idea of beneficial acclimation. The aims of the investigation were to determine the thermal limits of five ameronothrid mite species (Halozetes marinus, H marionensis, H belgicae, H. fulvus and Podacarus auberti) from varying terrestrial habitats and to test whether there is beneficial acclimation on the thermal traits. Along with the beneficial acclimation hypothesis several alternative hypotheses were also tested. In addition, locomotor performance was determined as it has been suggested that locomotion performance is a reliable and practical measure of potential fitness of animals. The same hypotheses testing the effects of acclimation temperature on the thermal limits were tested on three performance traits; performance breadth, optimum speed and optimum temperature. Support for beneficial acclimation was found in the performance breadth and optimum speed traits for all species except for Halozetes marinus. For the optimum temperature trait the prediction for the compensation hypothesis was met and that of the beneficial acclimation ...
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