Zoology - Theses
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ItemThe ecology and conservation management of Murray Cod Macullochella peelii peelii( 2006)Murray cod Maccullochella peelii peelii is an iconic freshwater angling species that has suffered declines in abundance and is now listed as a nationally vulnerable species. Despite recognition of the need for biological knowledge to provide future management directions, little is known of its ecology. This thesis examines that ecology to provide new knowledge and recommendations for improved conservation management. (For complete abstract open document)
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ItemThe impact of kangaroo grazing on sediment and nutrient mobilisation( 2000-05)The adverse impacts on vegetation and soils due to livestock grazing have been extensively studied for many years. The extent to which native wildlife may also be causing change to their environment, as a result of local increases in population density, has been the subject of debate in a number of countries. In Australia there has been a growing awareness in recent years that native herbivores, particularly kangaroos and wallabies, may also be causing changes to ecosystem dynamics. Environmmental changes, produced firstly by the aboriginal people and then by Europeans, have favoured the larger macropods, resulting in increased population levels. These impacts can also be seen in areas around cities, where pressure from urbanisation has restricted populations to smaller and smaller patches of remnant vegetation and reserves, increasing the pressure on diminishing food resources within these patches. This study focuses on one of the areas that supplies drinking water to Melbourne, the Yan Yean Reservoir catchment, which is situated 37 km north east of Melbourne. This study adds to our understanding of the impacts of native wildlife populations by investigating the extent of some of these possible changes to ecosystem dynamics.
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ItemThe effect of disturbance on the breeding biology of hooded plovers( 2000)Disturbance of birds by humans is a growing problem. This thesis examines the mechanisms through which disturbance may reduce reproductive success in the Hooded Plover Thinornis rubricollis, a solitary-nesting shorebird for which disturbance is thought to constitute a conservation threat. As a precursor to examining disturbance in this species, breeding biology, life history and parental care were investigated in a colour-banded population of Hooded Plovers in coastal Victoria, Australia. Pairs bred in widely dispersed territories, and intact pairs bred in the same territories year after year. The breeding season was asynchronous and protracted, lasting up to eight months. Breeding success was low, but pairs re-nested frequently and rapidly after nest and brood failure, and sometimes after successfully fledging young. Survival of juveniles was similar to that reported for other plovers, and adult survival was high compared with other plovers. However, it was estimated that only 34% of adults were expected to live 11 years, the average period needed for a pair to replace itself (produce two young). One unusual feature of the life cycle of Hooded Plovers was the complete temporal overlap of adult wing moult with breeding. Complete biparental care occurred throughout the breeding cycle. There is some evidence that males undertook more of the nocturnal incubation while females undertook more of the diurnal incubation but overall, pair members shared incubation equally. Levels of incubation were high and constant over the incubation period. Once chicks hatched, the average number of parents nearby and the frequency of distraction displays increased. Additionally, adults fed less after their chicks hatched, and adult body mass decreased. Brooding decreased as chicks grew. A number of mechanisms through which disturbance could reduce reproductive success were examined. Disturbance resulted in egg temperatures moving above and below benchmark values, potentially leading to thermal stress in eggs. At least some recorded egg temperatures were potentially lethal. The proportion of abandoned eggs was highest in foredune nests, followed by beach then dune nests. This pattern mirrored the pattern of disruption of incubation by humans between habitats, suggesting thermal stress due to disturbance caused egg mortality. Thermal stress could also kill chicks, and disturbance disrupted brooding. Failure of adults to defend eggs or chicks due to disturbance did not lead to nest or brood failure. Adults defended nests and broods, but predation events were only observed during undisturbed conditions. For broods, foraging time decreased and the level of the habitat used for foraging changed with increasing levels of disturbance. Energetic stress is therefore another potential mechanism that could decrease chick survival. This study uncovered potential mechanisms through which disturbance could decrease hatching and fledging success in Hooded Plovers. Identification of the mechanisms through which disturbance acts, suggests that a management approach that emphasises managing the effect of disturbance rather than the response to it, will be a necessary component of the recovery of this species.
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ItemAn investigation of hypothesis testing and power analysis in impact assessment, using case studies of marine infauna( 2002)Statistical analysis is now widely used in impact assessment, and a common approach is to use a BACI design which considers changes Before and After a disturbance occurs, in conjunction with differences between the potentially Impacted location and one or more Control locations. The statistical power of an assessment is the confidence with which a nominated difference may be detected by a formal hypothesis test, and power analysis provides a means of quantifying this confidence. Despite the effort that goes into many impact assessments, results may be inconclusive or even wrong. Retrospective examination of completed assessments is one means of identifying factors which contribute to their success or failure. In this thesis, several BACI-style statistical tests for impact and their statistical power were examined, using case studies of marine infaunal assemblages in the vicinity of coastal wastewater discharges. The infauna is an assemblage often used in impact assessment, but is also known for large and often unpredictable natural changes in abundance which can make the identification of disturbance-related changes particularly difficult. Estimates of variance of infaunal abundance generated from the case study data were themselves extremely variable, with 43% differing from a best estimate by 50% or more. Even estimates for the same taxon, from studies in the same region and using identical sampling methods, differed by an order of magnitude or more in 25% of cases. The worst estimates of variance were usually obtained from single surveys, which had no component of large-scale temporal variation. Such variability in estimates of variance suggests that those based on single sampling times may be particularly unreliable, and that it may be desirable to allow for a larger than expected error variance by initially sampling more replicates than are expected to be needed. The specification of an alternate hypothesis, and subsequently an effect size, is an essential step in calculating the power of an hypothesis test, but it may be difficult to specify an effect size that is meaningful for the particular situation. The effect sizes actually observed in the infaunal data were very variable, with the most extreme being in excess of 10000% change. However, many of the observed effects, including some of the most extreme cases, appeared to be natural events rather than the result of a disturbance. The main alternative to the Control versus Impact designs is a gradient approach, which identifies changes in an ecological variable along a disturbance-related environmental gradient. This is usually done at a single time, resulting in possible confounding of a naturally-existing gradient with one imposed on the fauna by a disturbance. Including Before/After comparisons of gradients from multiple times within each period in a BAG design reduces this confounding. In contrast to the more common BACI-style assessments, it also provides an indication of the spatial extent of an impact, although comparison with a more conventional BACIP design suggested it might be more costly to undertake. The use of soft sediment infauna in impact assessment is often an expensive undertaking, because manual sorting of macrofauna from large quantities of sediment can be very time consuming. A process of compositing and subsampling may be effective for infaunal samples in assessments where random samples are taken at a range of spatial scales. When hierarchical analysis of variance is used, an arithmetic averaging of data from lower levels in the hierarchy occurs for tests which use the variance among higher levels as their error term. Subsampling of composite samples for each location in an MBACI design would produce physically averaged values which reflect the overall state of each location. Using these physical means would result in an identical test statistic to that resulting from the arithmetic averaging of lower level data within the hierarchical anova, provided that the compositing and subsampling process itself did not bias the estimates of the location means. Data from infaunal samples collected specifically for this compositing exercise established that the process did not appear to generate bias. Using hypothetical monitoring programs, cost savings of approximately 40% were possible with the use of compositing and subsampling in one scenario, while in another, additional sampling could be undertaken to increase power from 0.47 to 0.81 while still achieving an overall cost saving of 17%. The patterns of variability seen in the case studies, particularly in the space x time interactions, resulted in some large and unpredictable error variances and observed effect sizes. These patterns were not dissimilar to those seen in other published studies, suggesting that impact assessments in general could be prone to the problems identified in this study. Thus, responses to those problems, such as not relying on single sampling times for estimates of error variance in long-term programs, or considering compositing and subsampling when laboratory processing time is a concern, may also be applicable.