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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ItemHistory, habitat and management: considerations in the selection of potential reintroduction and translocation sites for the brush-tailed rock-wallaby, Petrogale penicillata, in East Gippsland Victoria( 2002)Currently, there are estimated to be no more than 25 Brush-tailed Rock-wallabies, Petrogale penicillata, of Victorian origin remaining, with half of these in captivity as part of a breeding program. The decline of Brush-tailed Rock-wallabies has been attributed to several factors including hunting, predation, competition and stochastic events such as wildfire and disease. In Victoria, rock-wallabies have continued to decline in number, even after the cessation of hunting and implementation of an intensive predator control program. Without the intervention of captive-breeding and reintroduction or translocation programs, this critically endangered species will soon become extinct in Victoria. Reintroduction and translocation are becoming increasingly popular in the recovery of endangered species, however, many past attempts have had unknown or poor success rates. Conditions influencing the success of reintroduction and translocation programs are not well understood and for the most part, past efforts have been conducted in an ad hoc manner with little monitoring and documentation. One of the factors considered important in success is identification and selection of sites with high habitat quality, as unfavourable habitat is likely to result in the loss of animals through dispersal, predation or lack of other essential requirements. In addition to Wakefield (1961) and Short's (1980) observations of Brush-tailed Rock-wallabies occupying restricted habitat, presumably in response to the introduction of the Red Fox, Vulpes vulpes, this study found that there has been further restrictions in habitat use in East Gippsland, Victoria since the 1960s. Extant Brush-tailed Rock-wallabies sites were found to be larger than unoccupied sites, face predominantly north to north-east, have a general slope greater than 45° and a greater number of ledges per 100m of transect. It was also found that rock-wallabies preferred larger refuges with more than one entrance, low exposure to weather and another refuge or ledge within 10m. Preferred ledges were also large, faced predominantly north to east and within 10m of another refuge or ledge. The advantages these characteristics offer in the selection of future reintroduction and translocation sites are discussed. However, habitat suitability is not the only factor important to the selection of reintroduction or translocation sites. The selection of release sites will need to consider the ability to effectively undertake monitoring and management activities, and balance these requirements with the ecological requirements. This study also investigated past and current management (e.g., burning and predator control) of the study area and found that there has been a substantial change in land use that may have contributed to the persistence of Brush-tailed Rock-wallabies at the current sites in East Gippsland. This knowledge offers clues to future management. Other factors influencing site management are also discussed, and release sites with secure land tenure, which are easily accessible throughout the year and have a good network of vehicle tracks are considered favourable for reintroduction and translocation. In addition, release sites should not be in areas that conflict with visitor activities and should have strong community support.
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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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ItemPatterns in the distribution and abundance of reef fishes in South Eastern Australia( 2011)This research investigated patterns in the distribution and abundance of nearshore fishes of south-eastern Australia. I used two methods to survey fishes, underwater visual census (UVC) and baited remote underwater video (BRUV). A comparison between these methods revealed that BRUV recorded higher relative abundance of mobile predators, while UVC observed higher relative abundance of herbivores, territorial species, and small site-attached species. These results suggest that studies surveying diversity would do best to employ multiple methods. In cases where funds are limited, UVC may provide a more complete estimate of diversity than BRUV as UVC recorded higher diversity, species richness and more individuals. Combining measures of abundance with habitat data, I investigated fish-habitat associations, specifically exploring how altering spatial grain influenced the strength of correlations between fish and habitat. Species of different sizes responded to habitat measured over different scales, with large-bodied species only displaying strong correlations with habitat when it was measured over large scales. These results suggest that research quantifying fish-habitat associations needs to take spatial grain into account. In addition, many species may respond to changes in habitat at scales larger than are typically investigated. Understanding not only how species interact with their environment but also the scale at which these associations occur is essential for management and conservation. I investigated biogeographic patterns in the distribution of fishes in Victoria using abundance measured by BRUV and UVC. The BRUV data displayed a cline in change across the state in which dissimilarities between locations were linearly related to distance. In contrast, data collected using UVC indicated the presence of a large faunal break in the vicinity of Ninety Mile Beach, and a second break between Cape Conran and Cape Howe, suggesting that contemporary habitat discontinuity, flow and/or temperature may be important factors structuring communities in this region. At a still larger scale, I explored relationships at upper and lower bounds between body size, geographic range size and abundance using data collected from Australia and New Zealand. At maxima, the relationship between body size and abundance was negative but steeper than expected, possibly driven by diver-averse behaviour of large species. At minima, body size and geographic range size were positively related, implying that body size determines the minimum area that a species must occupy. In contrast, at the upper bound this relationship was negative for non-perciform fishes, a K-selected group whose geographic range size could be constrained by their limited dispersal capacity. Distribution-abundance relationships deviated from predictions, with a negative relationship at the upper bound for Perciformes, which could be driven by the high dispersal potential of widespread species that results in diffuse low-density populations. From these results, I concluded, first, that fishes appear to differ from terrestrial taxa, which may be attributed in part to large-bodied fishes’ limited capacity for dispersal. Second, the approach of applying regressions to maxima and minima uncovered relationships that would have been obscured had they been investigated at the mean, highlighting the importance of exploring limits in macroecological relationships.
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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.
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ItemResource partitioning among five sympatric mammalian herbivores on Yanakie Isthmus, south-eastern Australia( 2010)This thesis combines multiple approaches to improve our understanding of large herbivore ecology and organisation in a contemporary assemblage made up of species with independent evolutionary histories on Yanakie Isthmus, Wilsons Promontory National Park, Victoria, Australia. In particular, this thesis compares niche parameters among populations of five sympatric native and introduced herbivore species by simultaneously assessing overlap in resource use along two dimensions (spatial and trophic) at multiple scales, thereby providing insight into resource partitioning and competition within this herbivore assemblage. Faecal pellet counts demonstrated that inter-specific overlap in herbivore habitat use on Yanakie Isthmus was low, suggesting that spatial partitioning of habitat resources had occurred. However, resource partitioning appeared to be independent of coevolutionary history. Low overlap in habitat use implies low competition, and the lack of clear shifts in habitat use from preferred to suboptimal habitats suggested that inter-specific competition was not strong enough to cause competitive exclusion. However, low overlap in habitat use between the European rabbit Oryctolagus cuniculus and other species, and preferential use by rabbits (and avoidance by other species) of the habitat that appeared to have the highest carrying capacity, suggested that rabbits excluded other grazing herbivores from preferred habitat. High overlap in habitat use was apparent between some species, particularly grazers, indicating some potential for competition if resources are limiting. In particular, the eastern grey kangaroo Macropus giganteus had a narrow niche, occurred at low densities and had low population metabolism relative to other species, consistent with competitive suppression. In contrast, the common wombat Vombatus ursinus appears to be the strongest competitor in this assemblage, being numerically dominant, utilising the greatest proportion of resources, and displaying a relatively broad habitat niche. Habitat modification by fire, including changes in vegetation composition and structure, altered fine-scale partitioning of habitat resources by sympatric herbivore species, and changed the composition of the herbivore community. Faecal pellet counts demonstrated a decrease in herbivore densities, particularly grazers, following the burn, probably associated with reduced ground layer vegetation cover. In contrast, there was an increase in the density of browsers, particularly the swamp wallaby Wallabia bicolor, probably associated with increased shrub cover. Fine-scale partitioning of habitat resources was evident through inter-specific differences in abundance, population metabolism and use of fine-scale vegetation strata prior to and after the burn. Inter-specific differences in feeding strategies and thus resource requirements appear to facilitate coexistence within this assemblage. Further, overlap in fine-scale habitat use appears to be greater between native and introduced species than between native species, suggesting that species with independent evolutionary histories have inherently less resource partitioning than species with long coevolutionary histories. Microhistological diet analysis showed that the diets of the relatively large-bodied introduced hog deer Axis porcinus and relatively small native swamp wallaby consisted mainly of dicots. The diet of the small, introduced European rabbit contained similar proportions of monocots and dicots. The diets of the native eastern grey kangaroo, intermediate in size, and large native common wombats, consisted mainly of monocots, but kangaroos also consumed moderate amounts of dicots. Overlap in food use by the five species was high, particularly between native and introduced species, but also between some native species. Despite a high potential for food resource competition, it appears that coexistence of herbivores on Yanakie Isthmus is facilitated by ecological separation. However, patterns of ecological separation, niche breadth and diet overlap in this guild did not conform well to body-size related predictions: the species with the narrowest and the broadest diet niches were intermediate in size, and the largest species consumed a greater proportion of dicots than did several smaller species. Interactions between intrinsic and extrinsic constraints on diet choice are likely to influence the diet of herbivores on Yanakie Isthmus. This study provides important preliminary insights into herbivore community niche dynamics on Yanakie Isthmus. High diet overlap and overlap in habitat use at some scales between some species, coupled with resource limitation is likely to result in inter-specific competition, particularly given indications of resource limitation through diet niche adjustments, broad niches and high diet overlap between the native and introduced herbivores in this community. Experimental manipulation is required to obtain a mechanistic understanding of species interactions and conclusively demonstrate competition.