Zoology - Theses
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ItemUnderstanding how climate affects the koala, Phascolarctos cinereus: the roles of behaviour, morphology and physiology( 2013)Understanding why species live where they do and not elsewhere, and what it is about their traits or the properties of their environment that has led to this distribution, is one of the fundamental aims of ecology. The role of climate in setting species distribution limits has become a topic of much research in recent times, as ecologists seek to predict how species’ ranges may expand, shift, or contract under future climate change. How climate influences species is mediated by the physiology, morphology and behaviour of individuals and how these interact with each other and the local environment. Understanding how climate limits species distribution therefore requires an approach that accounts for both exposure to climate (as mediated by behaviour, local climate and habitat features) and sensitivity (as influenced by physiological and morphological traits). Mechanistic models of species distributions aim to explicitly capture the links between the functional traits of organisms and their environments, based on the principles of biophysical ecology. For broadly distributed species, both the exposure and sensitivity of individuals to climate can vary substantially across their geographic range, along with the processes and key traits that determine the species’ range limits. In this thesis I investigate how climate influences the energy and water requirements of a broadly distributed arboreal marsupial: the koala, Phascolarctos cinereus. I focus particularly on how behaviour and morphological variation mediate the effect of climate on koalas. To evaluate whether koalas use behaviour to buffer themselves against variation in climate I collected microclimate data and behavioural observations of koalas under a range of environmental conditions at sites near the northern (Magnetic Island) and southern (French Island) edges of their geographic range. Using museum specimens I also quantified variation in two key morphological traits that influence heat exchange – fur depth and body size. Data on koala behaviour, morphology and physiology were incorporated into a mechanistic model that predicts energy and water requirements of koalas with different behavioural and morphological traits, exposed to different environments. To test the model, I measured energy and water turnover of free-ranging koalas at both Magnetic Island and French Island over summer using the doubly-labelled water technique. Using this model, I was able to quantify the importance of behavioural and morphological variation in koalas, and how these traits interact with each other and the local environment to influence energy and water requirements. By coupling the models with spatial climate datasets I was able to predict daily energy and water requirements of koalas across the Australian landscape for the last 20 years. This modelling approach is unique in its capacity to identify key processes limiting the current distribution of this species, and to predict responses to future climate change.
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ItemPredicting responses to climate change: ecophysiology of the common brown butterfly, Heternoympha merope( 2013)Understanding the processes through which climate limits the distribution and abundance of organisms is a fundamental question in ecology, and is particularly important in light of recent, on-going, climate change. Variation in temperature in particular, can have substantial impacts on the fitness and survival of organisms, through its ubiquitous effects on biological rates. However, animals have the capacity to construct their own thermal environment through behaviour, and so to understand the impacts of temperature on species’ ecology, interactions between the organism and its environment must be accounted for. Holometabolous insects make fascinating systems with which to explore the impacts of temperature on fitness, because the different life-cycle stages vary in thermal sensitivity, their capacity to behave, and in the environments encountered. Furthermore, the different life-history stages are invariably linked: conditions experienced by one life-cycle stage have a direct impact on the fitness and survival of subsequent stages and generations. Consequently, understanding how climate constrains the survival of such species requires a holistic approach, in which all stages of the life-cycle are considered. This thesis focuses on an endemic, widespread Australian butterfly, the common brown, Heteronympha merope. To ascertain how the life-cycle phases of H. merope differ in their thermal sensitivities, I measured the impact of temperature on a suite of fitness traits including development time, growth rate, body size, flight, longevity, starvation and fecundity. As adult butterflies have a broad scope for behavioural thermoregulation, I also quantified how basking posture affects the core-body temperature of H. merope. These empirical datasets were subsequently incorporated into a mechanistic model, which was run across the Australian landscape with high-resolution, spatial climatic datasets to identify processes that constrain H. merope’s distribution. These models incorporate variation in thermal sensitivities, behaviour and dispersal potential of the different life-history phases to attain a comprehensive understanding of how climate limits the common brown’s survival. The final model provides a powerful tool for holistically assessing how organisms with complex life cycles, such as butterflies, are likely to respond to future climate change.