Zoology - Theses
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ItemA comparative study of the flora and fauna of exotic pine plantations and adjacent, indigenous eucalypt forests in Gippsland, Victoria( 1978-01)The introduction and establishment of a new and markedly different environment within a long established natural system provides an excellent opportunity to study the principles of adaptation and colonisation by native species. In Australia, an example is furnished by the conversion of large areas of native eucalypt forests to mono-cultured plantations of Monterey Pine (Pinus radiata). The principal aim of this study was to assess which species of native mammals, birds and higher plants are able to utilise or occupy such plantations. Successional aspects of community structure, and colonisation in pine forest systems, were investigated by considering stands of different ages. A variety of adjacent native eucalypt forests provided controls and indicated the range of potential colonisers. Various habitats in both forest types were studied with regard to potential nest sites and availability of food, in order to determine those habitats most favourable for mammals and birds. The effect, on wildlife, of clearing eucalypt forests, but leaving forest remnants along gullies, was also assessed.
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ItemLife-history strategies of five species of intertidal limpet( 1977)The life-long strategies of five species of intertidal limpet, Cellana tramoserica, Notoacmea petterdi, Patella peroni, Patelloida alticostata, and Siphonaria diemenensis, which occur on the same shore but in different tidal zones, are considered in relation to their different environments. Attention is focused upon reproductive effort, which is defined as the percentage of assimilated energy devoted to reproduction, and which is measured for each species by using annual energy budgets. Environmental and demographic factors, which previous workers have suggested may have important influences on the level of reproductive effort, are investigated. In particular, interspecific differences in reproductive effort are compared with differences in the availability of food resources, differences in the magnitude of density-independent causes of mortality, differences in adult mortality rates and differences in extrinsic adult mortality rates (i.e. the adult mortality rates that would occur in the absence of expenditure of energy in reproduction.) The results of the present study indicate that reproductive effort is correlated with the availability of food resources, but that the primary determinant of the optimum level of reproductive effort is the rate of extrinsic adult mortality.
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ItemImpacts of habitat fragmentation on dispersal of native mammals( 2011)Habitat fragmentation is widely regarded as a major threat to biodiversity worldwide. In addition to the reduction of the total area of habitat available for wildlife, clearing of native vegetation creates disconnected patches of habitat immersed in a matrix, which does not provide resources for most species of wildlife. The remaining habitat patches often accommodate small populations of native animals, which suffer increased susceptibility to extinction. Movement of individuals between habitat patches, however, can interconnect such populations so that they effectively behave as larger and more stable metapopulations. Hence the traversability of any matrix for wildlife is an important attribute of fragmented landscapes and impacts on their ability to support viable populations. Further, the capability of different species to cross various matrix types varies. ‘Landscape connectivity’ describes the functional isolation of remnant areas of habitat and considers not only the distance between them but also the species-specific ability to successfully move through the matrix. In this thesis I examine the dispersal behaviour and population genetic structure of two species of marsupials in a fragmented landscape. I describe the movements of bobucks (Trichosurus cunninghami) and agile antechinus (Antechinus agilis) in the Strathbogie Ranges in north-eastern Victoria. Being forest-dependent, both species occur solely in remnants of native forest. Both also have a life-history pattern that is characterised by the dispersal of subadult males. However, they differ greatly in body size. I used GPS (for bobucks) and VHF (for antechinus) tracking to monitor individuals within their home ranges in the pre- and post-dispersal stages of their life cycle as well as during dispersal. I also used genetic parentage assignment tests to identify movements of antechinus. While the literature reports that the vast majority of subadult males of both species disperse, in my study a high proportion remained philopatric. Exploratory movements, beyond the boundaries of their home ranges, were recorded for adult and subadult bobucks; however, subadult males that later dispersed rarely exhibited this behaviour. In the months before the dispersal season, subadult bobucks that would subsequently remain philopatric appeared to occupy larger home ranges than dispersers. One possible explanation for this observation is that resource availability drives dispersal in this species and only those individuals that cannot secure access to sufficient resources in their natal home ranges disperse. In order to examine the response of dispersers to different landscape elements I monitored individuals during dispersal. Some bobucks and antechinus dispersed long distances. The very detailed dispersal pathways of bobucks, that I recorded using GPS tracking, revealed a clear pattern with all individuals dispersing along wooded landscape elements when these were available. Individuals were able to cross considerable distances across pasture using paddock trees and linear forest remnants as stepping stones and dispersal corridors. While some antechinus are likely to have crossed small gaps in linear forest remnant habitat, they appeared to be more restricted to forest during dispersal than bobucks. Genetic parentage analysis revealed that some male antechinus moved very considerable distances during the mating season, a behaviour that could significantly increase gene flow in this species. I applied genotypic analyses to infer gene flow in this system and used a landscape genetic approach to determine the connectivity of habitat in the Strathbogie Ranges for both bobucks and antechinus. I also investigated the influence of wooded landscape elements on gene flow in these two species. These analyses indicated that the distribution of forest remnants and individual trees play no role in determining gene flow in bobucks or antechinus within the Strathbogie Ranges. Surprisingly higher spatial genetic structure, which could indicate restricted dispersal, was detected in the larger, more mobile bobucks compared to antechinus. This seems to contradict my findings based on direct observations of dispersers in both species, namely the importance of paddock trees and linear forest remnants as dispersal conduits for bobucks and stronger restriction to forest of dispersing antechinus in comparison to bobucks. In fact, however, this discrepancy emphasises the difference between measurements of dispersal via direct observations versus genotypic inferences of gene flow. While observations of individual dispersers can provide detailed information on the behaviour of animals when they are traversing fragmented landscapes, data on their survival and breeding success post-dispersal is virtually impossible to obtain for many species. In contrast, molecular genetic analyses yield information on the reproductive outcome of dispersal across several generations, but usually cannot inform about dispersal pathways. The two approaches that I used are complementary, and combining them can help to avoid inaccurate conclusions about landscape connectivity for metapopulations, that are based on either technique alone. In my study, the landscape genetic model applied may have underestimated the true value of paddock trees as conduits for bobuck dispersal. Also the small number of antechinus that I was able to monitor during dispersal probably led to an underestimation of this species’ ability to leave its preferred forest habitat and traverse the matrix. Overall, the availability of linear forest remnants, scattered paddock trees and small patches of forest in the Strathbogie Ranges appeared to create high functional connectivity for populations of both species. My research emphasises the importance of maintaining and/or restoring structurally complex landscape elements, so that these can act as dispersal conduits for different species with differing mobility. This approach is an important tool to mitigate the effects of habitat fragmentation on native wildlife.
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ItemIndividual variation in reproductive success in the sacred ibis( 1988)Factors affecting the reproductive success of individually colour-banded sacred ibis, Threskiornis aethiopicus stricitpennis (Gould), at Healesville Sanctuary, Victoria, were studied from November, 1983, to March, 1987. Although the majority of clutches were of three eggs, the modal fledging success was two young, due to starvation of the third chick. The likely adaptive value of brood reduction is discussed. Characteristics of individuals (e.g. weight, body condition, culmen length, estimated age and dominance status) had no discernible effect on the number of chicks raised to fledging from one attempt (fledging success). The structure of the dominance hierarchy among male sacred ibis at Healesville is described. Dominance relationships among females were not consistent and, therefore, analysis of dominance status was restricted to males. Weight was the major trait contributing to a male's dominance status. High-status males achieved a higher seasonal reproductive success than did low-status males in two seasons when resources were apparently at low levels. Reproductive success over five consecutive years was largely dependent on survival, but, no significant relationships between individual traits and survival were found. Male sacred ibis achieving high seasonal reproductive success tended to survive better than did less successful males. Thus, variation in success measured over a short term (one season) underestimated the variation between males in success measured over a long term (five years). Variation in success of females also increased with the longer sampling period, but not at as fast a rate as variation in male success. Variation in success is therefore significantly greater in males than females, even though the sacred ibis is a monogamous species. Variability in reproductive success and number of attempts among individuals is facilitated by the changes of mate frequently observed in individuals breeding more than once in a season. Female sacred ibis were found to invest more in any one attempt than were male ibis. Consequently, individual females averaged fewer nesting attempts per season than did males and, with the sex-ratio of unity, females were a limiting resource for males. The resulting opportunity for selection on males is apparently fulfilled to some degree, with high-status, heavy and old males being particularly successful in competition for mates.
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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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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.
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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)
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ItemThe Australian freshwater malacostraca and their epizoic fauna( 1964)Because of their disjunctive distribution, the Parastacidae (Crustacea, Decapoda) and the Phreatoicoidea (Crustacea, Isopoda) have long been of considerable zoogeographic interest. The Phreatoicoidea are known from South Africa, India, Australia and New Zealand; the Parastacidae from Madagascar, New Guinea, Australia, New Zealand and South America. Of potentially great value, then, is a study of the epizoic fauna found closely associated with these fresh-water crustacea, and in some cases, sharing the disjunctive distribution. When new species of the peritrichous ciliate Lagenophrys were discovered on the cuticle of those crustacea, the opportunity was taken to initiate an investigation into zoogeographical implication of the distribution of a host-epizooid complex. The hosts were of established interest. Lagenophrys was of presumed interest because of low vagility during its dispersal phase, and because of the apparently high specificity of northern hemisphere members of the genus. In this thesis attention has been concentrated on the peritrichous epizooids. Although ideally a study should ultimately analyse the whole complex, the difficulties involved in such disparate taxonomies allowed of brief notes only on the other groups. Observations of the genus Temnocephala are included in the systematic section below but the other groups will be merely mentioned. Half the thesis is devoted to problems directly concerning the Parastacidae. For maximum value from the data on the epizoic fauna, precise determinations of host species were essential. In the course of investigation, it became clear that a review of Parastacidae systematics would be a prerequisite. (It will be seen that the Parastacidae form the most important group of hosts for the peritrichs investigated.) This situation arose partly from the lack of facilities at present obtaining in Australia for identification of the Parastacidae, and partly from ambiguities in the currently accepted systematics. These problems are posted in the section on Parastacidae, and their influence on problems of specificity is discussed in the final section.