School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe ecological costs and benefits of urban stormwater wetlands to frogs( 2018)The speed and scale at which humans are altering natural systems creates novel challenges for many species. Some species can cope with human-induced rapid environmental change by exhibiting adaptive behavioural or phenotypic plasticity. Many others, however, respond maladaptively in ways that can impact individual fitness. When rapid environmental change triggers mismatches between perceived and actual habitat quality, animals can prefer inferior habitats, that are known as ecological traps. Using a meta-analysis, I show that ecological traps are an unexplored but potentially important conservation risk to animals within wetland habitats (Chapter 2). Focusing on urbanisation and stormwater wetlands as a case study, I assess how anthropogenic environmental change affects frogs, in terms of the environmental variables influencing species occurrence (Chapter 3), the capacity of individuals to make adaptive habitat selection decisions (Chapter 4), and the fitness and behavioural consequences of these decisions (Chapter 4 and 5). I show that frogs occupied wetlands across a broad spectrum of pollution levels, including even the most contaminated, and that pollution exposure reduced survival and impaired predator avoidance behaviours. Breeding frogs did not avoid wetlands where these fitness reductions occurred, demonstrating that stormwater wetlands can function as ecological traps. Collectively, my results highlight the need for a greater focus on individual-level metrics (e.g. fitness and habitat preferences) in addition to the more commonly measured population- and community-level metrics (e.g. richness and abundance). Based on my research, I propose three key recommendations to maximise biodiversity at wetlands within urban landscapes. Firstly, appreciate that poor water quality at stormwater wetlands may impact resident wildlife, and attempt to reduce the causal factors. Second, despite this, do not ignore the potential value of stormwater wetlands in providing habitat and enhancing connectivity amongst aquatic habitats, particularly when they are appropriately designed and managed. Finally, it is important to design and construct wetlands for wildlife that are not connected to stormwater networks, with their placement within the landscape carefully considered.
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ItemFire, resources and behavioural responses of ground-dwelling mammals( 2015)Planned fire is commonly used to reduce adverse effects of bushfire to human life and property, but may also be used to conserve biodiversity. However, there is a dearth of information regarding the effect of these fires on fauna. I investigated the response of ground-dwelling mammals to a planned fire event in the Otway Ranges, south-eastern Australia. Bush rats (Rattus fuscipes) and swamp wallabies (Wallabia bicolor) were chosen as study species given that they are expected to be affected by a change in vegetation resources due to fire. The differences in body size of the two species provided the scenario to study fire effects at two different spatial scales. At a small scale, I studied changes in abundance of bush rats as a consequence of fire, plus the role of unburnt areas as refuges. I used microsatellite markers to study movement of individuals between slopes and gullies. At a larger scale, I used GPS technology to track swamp wallabies before, during and after fire, to study changes in home range and habitat selection, as well as behaviour during fire. The studies included different temporal levels as well, the study on abundance and movement of bush rats, and on habitat selection of swamp wallabies, compared data from two months before with two months after fire. Home range data of swamp wallabies compared data two months before fire with data from up to eight months after the fire. Finally, the study on movement of wallabies during the fire, included data from 36 hours when the fire was burning compared to pre-fire data. The study on bush rats corresponded to a Before-After Control-Impact (BACI) design using a paired catchment approach, while the study on wallabies corresponded to an Impact Analysis (IA) design, comparing responses not only before and after, but also during fire. There was no strong relationship between the different responses that were quantified and the amount of area that was burnt within transects and home ranges, possibly because there were enough unburnt areas available in the post-fire landscape, emphasizing the importance of keeping areas of unburnt vegetation when applying planned fires. Yet, the impact of fire was presumably larger on bush rats; this was reflected in the reduction of abundance of individuals, while all swamp wallabies survived. The impact of fire varied between the two study species, reflecting the importance of investigating the effect of planned burns at different spatial and temporal scales. The strategy used in the fire event that I studied, i.e. of low intensity, progressively and in patches across the targeted area did not have major effects on the study species. The information provided in this thesis intends to improve the capacity for land managers to consider the ecological effects of planned fire by adding to current knowledge linking fire, resources and behavioural responses. Further assessment involving more intense fire would be necessary to assess the response of bush rats and swamp wallabies, and to predict the possible consequences that a wildfire could have on these species.