School of Agriculture, Food and Ecosystem Sciences - Theses
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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.
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ItemInteractions between fire, environmental heterogeneity and ground-dwelling mammals( 2014)Environmental heterogeneity is known to influence a range of ecological processes at various spatial scales, from individual habitat selection and interspecific interactions, to species’ distributions and diversity. Fire regimes can influence environmental heterogeneity by altering the spatial and temporal distribution of resources. In this thesis I used the ground-dwelling mammals of south-eastern Australia as a focal group to explore the role of fire-mediated heterogeneity in driving individual species distributions, abundance and species diversity. I focussed on two aspects of fire regimes as drivers of environmental heterogeneity at different spatial scales; time since fire at a landscape scale and spatial extent of fire within an individual planned burn. As a secondary objective I also evaluated techniques used to detect ground-dwelling mammals. I investigated relationships between fire-mediated heterogeneity and species diversity at the landscape scale. I compared heterogeneity defined by spatial pattern metrics based on fire age and vegetation type, versus heterogeneity derived from site-based habitat structural measurements. I used two complementary diversity metrics, species richness and beta diversity as response variables. Heterogeneity defined by habitat structural contrasts was positively correlated with beta diversity, however heterogeneity defined by mapped post-fire age classes and vegetation types did not influence beta diversity, and neither measure of heterogeneity was related to species richness. The mammal communities in our study area were influenced by environmental heterogeneity but only if it was present in specific structural attributes of the environment. This suggests that relationships between heterogeneity and diversity depend on how variables representing these properties are quantified. The spatial pattern metrics based on fire age and vegetation type did not reflect physical contrasts that are important for maintaining ground-dwelling mammal diversity. Building on the knowledge at the mammal community level, I investigated individual species responses to time since fire at the landscape scale. Specifically, I used a space for time substitution to investigate interrelationships between the occurrence of eight ground-dwelling mammals, time since fire, and structural resources. Individual species distributions were not well predicted by time since fire. Time since fire was moderately correlated with habitat structure yet was a poor surrogate of mammal occurrence. Variables representing habitat structure were better predictors of mammal occurrence than time since fire for all species considered. These results suggest that time since fire is unlikely to be a useful surrogate for ground-dwelling mammals in heterogeneous landscapes. At a smaller spatial scale, I used a before-after-control-impact experiment, focussed on a planned fire, to investigate the role of unburnt patches in providing post-fire refugia for Agile Antechinus Antechinus agilis and Bush Rats Rattus fuscipes. The two species responded differently to the presence of unburnt patches associated with wet gullies in the burnt landscape. Relative to controls, fire had little effect on Bush Rat abundance in unburnt gullies. In contrast, the fire caused Agile Antechinus abundance to increase in gullies, indicating a shift of individuals from burnt parts of the landscape. Bush Rats that previously occupied burnt parts of the landscape most likely perished in the aftermath of the fire. These differences are likely driven by differences in habitat use and intraspecific competition between these species. I evaluated the three techniques used to detect mammals, live trapping, camera trapping and hair detection. The camera traps detected more species than the other two techniques but live trapping consistently complemented the cameras by detecting unique species. Furthermore the effectiveness of the different techniques varied across the landscape, with live trapping detecting more unique species in wetter, more productive vegetation types, whereas in dry vegetation types the camera trapping alone detected all species present in the sample. I also evaluated two different camera trap models. I found that Reconyx cameras consistently detected more species than Scoutguard camera, mostly because they detected small and medium species more frequently. The results showed that the use of Scoutguard cameras in isolation would have led to erroneous conclusions about the main drivers of species distributions across the landscape.