Zoology - Theses
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ItemThe effects of copper antifouling paints and marinas on the ecology of marine sessile epifaunal assemblages(University of Melbourne, 2000)An experimental field study was undertaken to evaluate the effects of copper dosed from antifouling paints on the development of sessile epifaunal fouling assemblages in southeastern Australia. The study system was chosen because of the importance of copper pollution in the marine environment and the fact that members of assemblages of this type are the target organisms of antifouling compounds. Experiments were conducted inside and outside of enclosed marinas, as it was hypothesised that the conditions found inside marinas may have led to differential effects of copper dose in this environment. Initially, I developed a system to dose copper to settlement plates in the field. After several pilot experiments, I chose a system that used a laboratory-made antifouling compound painted onto a collar around a settlement plate as the dosing method. Field tests established that this system exerted biological effects over the settlement plates, and that these effects lasted for at least four weeks. Field-measurement at four sites, of copper doses delivered to plates demonstrated that dose differed among sites and times of year. The difference appeared to be in part related to the amount of water movement. A field-study that compared fouling assemblages developing in two marinas near Melbourne, Victoria to assemblages at each of three nearby control sites, confirmed that the marinas affected assemblage structure. For each marina, a number of species showed an effect, but very few species showed the same effects across both marinas. After aggregation of the species to functional groups, some effects were found across both marinas. Three approaches were undertaken to investigate the effects of dosed copper and the marinas on establishment of sessile epifaunal assemblages. The first experiment examined early recruitment of assemblages and found that copper dose affected a number of species recruiting to the plates. Recruitment varied widely with time and between sites inside and outside the marinas, but the results seemed to reflect normal temporal and spatial heterogeneity characteristic of the recruitment of fouling organisms. The second approach examined growth rates and competitive abilities of colonial fouling organisms. By using clonal replicates of colonies, I was able to show that the populations studied showed heterogeneity in growth rates, and occasionally showed heterogeneity in the effects of treatments on growth rates. Partially as a result of this variability, significant treatment effects on growth rates were rare. I did not find any effects of dose or marinas on the competitive ability of colonies, but the number of experiments that examined this feature was very low. Finally, a longer-term experiment that utilised reciprocal transplants of plates between sites and doses showed that effects of the marinas on assemblages were more important than effects of dose. Once again, some results indicated that some species showed variability in the degree to which different populations were affected by treatments. Overall, I found that locations (inside or outside the marina) had a greater effect on determining the assemblage structure than did dosed copper, despite these dosing levels being well above background levels of copper in these marinas. This is probably due to a large number of factors associated with marinas over and above increased background heavy metal pollution. Several taxa appeared to show adaptation to local conditions or copper doses, and some appeared to show either heterogeneity in response to dosing or an ability to acclimate to dose. These types of findings have important implications for the manner in which we apply the findings of traditional laboratory-based ecotoxicology experiments to environmental management.
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ItemPopulation dynamics of Australasian gannets (Morus serrator) breeding in Port Phillip Bay, Victoria; competition with fisheries and the potential use of seabirds in managing marine resources( 2000)Increasing exploitation of pelagic fish populations worldwide has often resulted in overfishing and the collapse of commercial fisheries and associated serious declines in many marine predator populations, including seabirds. These events highlight the competing demands for limited marine resources. Recent emphasis for the ecologically sustainable management of commercial fisheries has stimulated attempts to manage fisheries by incorporating knowledge of trophic interactions and ecosystem functioning, known as ecosystem-based fisheries management. Seabirds are often highly visible, wide-ranging upper trophic level consumers that aggregate in areas of increased ocean productivity and therefore be used as natural monitors of marine environmental conditions. Further, many seabirds commonly fed on commercially-exploited fish stocks (often targeting prey of similar size). In this study, the population dynamics of Australasian gannets (Morus serrator) breeding in Port Phillip Bay, Victoria, is investigated and competition between gannets and commercial fisheries is determined. In addition, the potential use of seabird reproductive and population parameters as indicators of the abundance of commercially exploited fish stocks, and pelagic conditions generally, is assessed.
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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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ItemEvolution of the Proboscidea and the Sirenia( 2000)Sixteen African elephant (Loxodonta africana), two dugong (Dugong dugon) and four manatee (Trichecus manateus) fetuses were collected for this study. The fetuses were measured, dissected and serially sectioned. Aspects of development were described and discussed in the context of the evolution of the elephant, dugong and manatee and the possible aquatic ancestry of the elephant. The consequences of an aquatic ancestry of the elephant are reflected in numerous ways during its development: the specialisation of the lungs and respiratory system and the trunk, the presence of nephrostomes in the fetal kidney and the permanent intra-abdominal location of the testes. The trunk is obviously an ancient feature of the elephant and this is reflected in its development and is present in even the earliest stages. The lungs of the elephant develop in a pleural cavity and then adhesions develop, obliterating the cavity, at birth. The adhesions are thought to provide support for the lungs as the elephant sucks water up its trunk and to support the lungs whilst using the trunk as a snorkel when swimming. The adhesions could be a more recent adaptation as the elephant evolved from an aquatic to a terrestrial mammal. Nephrostomes were observed in the mesonephric kidney of the elephant. Nephrostomes are a feature of primitive vertebrates and the presence of nephrostomes, are a clear example of ancient structures persisting in development. The manatee does not have nephrostomes in the mesonephros late in gestation although it is possible that nephrostomes were present in early gestation. The elephant, dugong and manatee are primary testiconda, a feature also consistent with an aquatic origin. The position of the testes in the elephant, dugong and manatee clearly represents a pleisomorphic condition. Elephants do not have a sexually dimorphic ano-genital distance unlike their closest relatives the dugong and manatee. This could be due to androgens produced by the fetal adrenal that are causing the masculinisation of the female genitalia and perhaps also masculinise the brain, and ultimately behaviour. In summary, the study of the development of the fetuses of these three closely related groups has furthered our knowledge about the development and evolution of testicond species. The finding of nephrostomes in the mesonephros of the elephant has reinforced the idea that ontogeny can provide clues about phylogeny. The development of the elephant has strengthened the evidence for an aquatic ancestry of the elephant. Additionally, the similar ana-genital distances in male and female fetal elephants, has provided a step to a fascinating area of future research.
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ItemAspects of the reproductive endocrinology of the echidna, Tachyglossus aculeatus( 2000)This thesis investigated some aspects of the reproductive endocrinology the shortbeaked-echidna, Tachyglossus aculeatus. Measurements of seasonal changes in plasma steroid testosterone and corticosteroids were made in captive and free-ranging male echidnas. Non-invasive faecal sampling techniques were developed as an alternative to blood sampling for measuring endocrinological changes in both sexes. This thesis focussed on male reproduction for two reasons. First, it has long been suggested that female echidnas do not breed every year and will enter periods of torpor or inactivity during the breeding season if they are non-breeding (Broom, 1895; Griffiths, 1968; Rismiller, 1992; Rismiller and McKelvey, 1996). Males, however, are generally more active during the breeding season and have been observed to actively seek out females moving from train to train (Rismiller, 1992), thus making them easier subjects for study. Secondly, none of the females used for the blood sampling study were observed to mate or produce young during the course of the study, so making it difficult to adequately describe female reproduction in terms of the changes that occur in plasma concentrations of steroids. (From Abstract)