Science Collected Works - Theses
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ItemSevere weather forecasting in coastal East Antarctica(University of Melbourne, 1999)
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ItemFire and soil interactions in a Mallee heathland : the generation of heterogeneity in an homogeneous landscape(University of Melbourne, 1999)The soils of Australian heathlands are considered to be markedly nutrient-deficient, with some of the lowest concentrations of nitrogen, phosphorus and other essential nutrients ever recorded. The flora is strongly adapted to nutrient conservation and efficiency of use. Yet these same heathlands are often subject to invasion by tall woody shrubs that eventually come to dominance, at the expense of the presumably �better-adapted� typical heathland species. In an attempt to understand and characterize this change in dominance and species composition, the changes in soil nutrient supply and storage were tracked thru a semi-arid heathland in north-western Victoria. Different species used the available nutrients differently, and their impacts on the soil nutrient pool varied with size and age. Some (such as the dominant Casuarina pusilla) augmented the meagre soil nitrogen supply by nitrogen fixation, particularly when younger. Such fixation decreased or even disappeared as the shrubs aged (�senesced�). In August-September 1992 the �available� ammonium concentration in soil from under C. pusilla canopies (at 4.4 ppm) was over double that from under canopies of Callitris verrucosa (at 1.7 ppm) or from the inter-canopy gaps (1.4 ppm). Available ammonium also varied seasonally (with peaks in the moist soils of early spring, August-September, and troughs in desiccated soils early in autumn, April-May), and with stand age. Vigorous N fixation of young C. pusilla and others contributed to relatively high soil ammonium concentrations in 11-year old regrowth when compared with much lower concentrations in 34-year old regrowth, or older. Other species, notably the deep-rooted C. verrucosa, added to the low capital of circulating phosphorus by accessing supplies deep in the profile and bringing some of this to the surface. The litter of some species was richer in these limiting nutrients than the litter of others - again affecting the nutrient return to the surface soil pool and differential accumulation of nutrients under different species. In particular, long-term nutrient enrichment in surface soils enabled annuals formerly absent from these heathlands to establish and grow, in very old stands only (at least greater than 35 years post-fire). Individual species characteristics affected nutrient use and supply to the soils. The markedly sclerophyllous and nutrient deficient leaf litter from Banksia ornata added little of these nutrient s to the soil in the first few years after fire, in contrast with the nitrogen-rich litter from Casuarina pusilla. There was a post-fire flush of nutrients to the surface soil - assisting regrowth and establishment of seedlings. Nitrogen availability and transformations in the soil soon returned to the pre-bum situation, probably within a year. However, the increased soil concentrations of mineral phosphorus immediately after fire, declined much sooner and there was evidence of a subsequent decline in phosphorus availability, to significantly below that of soils in unburnt heathland. The soil nutrient availability in the community is characterized by relative stasis punctuated by short-term flushes deriving from rainfall events, seasonal changes in ambient temperature and occasional fires. Variability in nutrient availability also has a spatial component, deriving from the different architecture, tissue nutrient concentrations, growth stage and internal recycling capacities of the various dominant species present. The landscape was apparently remarkably uniform. Nevertheless, significant habitat heterogeneity was generated by these differences in nutrient use. There was a variety of regeneration strategies adopted by the component species. Some regenerated successfully in the absence of fire - some by seed and others by vegetative means. Small epacrids and myrtles (such as Astroloma and Brachyloma, Baeckea and Calytrix) successfully established from seed in unburnt heathland. Regeneration of many other shrubs and sclerophyllous monocots appeared to require fire and they were unable to regenerate successfully without the opportunities presented by the post-fire environment. The regeneration strategies adopted by four prominent dominants, Banksia ornata, Callitris verrucosa, Casuarina pusilla and Hakea mitchellii (all serotinous shrubs) were investigated. In spite of this apparent similarity, each had a unique response to fire and the opportunities it provided for seed regeneration. The variability of growth and nutrient responses of the many component species, and their interactive effects with the habitat, produced a far more heterogeneous landscape than might have been expected from the remarkably uniform soils and landscape profile. This heterogeneity enabled many species to co-exist, each exploiting a particular, site- specific combination of features and, in turn, producing a site-specific (even �unique�) set of habitat features. The biological components of the ecosystem generated habitat heterogeneity, permitting many species to co-exist. In return, this biodiversity enabled further micro-habitat specialization and habitat heterogeneity. The heathlands did not reach a �steady state� or climax, but continued to change in the continued absence of fire. Species gradually disappeared from the community (either �retreated� to the soil seed bank or truly disappeared as the few remnant adults, with their elevated seed bank, died without replacement). Other species entered the community as the formerly subordinate and then co-dominant C. verrucosa assumed complete dominance - mimicking the invasion and establishment of woody shrubs in heathlands elsewhere. By this stage, the successional change was irreversible. Whether the change is described as �senescence� or �maturation� is subjective. It depends on the perceptions of the particular observer. Although land management has recently come to recognize the importance of heterogeneity in biodiversity maintenance, it has traditionally had difficulty with managing for heterogeneity in time and space. The problems of managing for habitat heterogeneity are considered and a practical conceptual context is provided for future land management.
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ItemTerritorial behaviour and mating success in male New Zealand fur seals, Arctocephalus Forsteri(University of Melbourne, 1997)Fur seals are polygynous marine mammals that breed in high densities in terrestrial colonies. Female fur seals deliver and nurse their pups within the breeding colony and male fur seals fight vigorously to acquire and defend territories in the areas of breeding colony that are used by females. The breeding season is extended over 6-8 weeks and some males retain a territory within the breeding colony throughout the season, during which time they fast. Male fur seals are thought to have highly variable reproductive success relative to that of females; some males mate up to 30 times within one season and may hold a territory for several seasons, while others never mate. In contrast, females may produce a maximum of approximately 20 offspring in their lifetime. The factors underlying the mating success of adult male New Zealand fur seals, Arctocephalus forsteri, were examined at Cape Gantheaume, Kangaroo Island, South Australia. Individually marked adult male fur seals were observed whilst ashore during three annual breeding seasons and during the intervening non-breeding seasons. The territorial behaviour and mating success of individually marked adult male fur seals were measured over three successive breeding seasons (1992-1994) and terrestrial behaviour was also measured during the intervening non-breeding seasons. Data on morphology and age were also collected for each male. Larger males gained territories during the breeding seasons and male mass correlated with the duration of territorial tenure, but mass was not correlated with mating frequency among males that mated within their territories. The maximum mass of adult males was 160 kg. The age range of adult male seals was 7 - 15 years. The males that held territories following the birth of the first pup were older than the males that did not, but age was only correlated with mating success in one of the three breeding seasons. The youngest of these males was eight years old. All of the marked males visited the colony outside the breeding season. Some males simply hauled-out in the haul-out areas of the colony while some visited the territories that they had held during the previous breeding season that were within the sections of the colony used by females and pups (breeding areas). The males that visited their territories spent more time in social behaviour than those that were in the haul-out areas and also tended to spend less time resting. The behaviour of these males was also compared to that in their territories during the breeding season: outside the breeding season they spent more time resting overall but were significantly more alert during the mornings than they were during the breeding season. Males were more reluctant to leave their territories when threatened than they were to leave the haul-out areas. The terrestrial behaviour of males outside the breeding season was associated with mating success because males that visited their territories in the non-breeding season were more likely to hold a territory the following season than those that did not.
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ItemMean curvature evolution of graphs in Riemannian manifolds(University of Melbourne, 1999)
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ItemThe variability of atmosperic carbon dioxide and its surface sources(University of Melbourne, 1999)Mass balance inversions are useful tools for determining surface sources and sinks of CO2, based on the atmospheric observations and a transport model of the atmosphere. These inversions require CO2 concentrations for the whole surface layer of the model domain. Hence, previously only two dimensional inversions of the CO2 observations have been performed, as observations have been too sparse to determine the longitudinal variability of this Greenhouse gas. In this thesis we review the mass balance inversion and perform some simple two dimensional experiments. There is important information about the longitudinal variability in the observations which is ignored in the two dimensional study, so we have developed a way of estimating the global surface CO2 concentrations. This is done by using a method of assimilating CO2 observations into a forward run with a transport model using the constraint of a best guess initial source field. This is then used to constrain the mass balance inversion to estimate surface sources including longitudinal variability. We use data from 1980 to 1993, and obtain an estimate of the temporal variability of the sources over this period. Principal Component Analysis is used to find modes of variability in the observations and the sources, and the key mode of variability is shown to be related to the El Nino-Southern Oscillation phenomenon.
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ItemFloral form and ontogenetic process in Winteraceae(University of Melbourne, 1999)The flowers of Winteraceae show great diversity and variation in organ number and phyllotaxis. The morphology and development of selected species were investigated and changes in ontogenetic processes needed to account for diversity and variation in floral form were identified. Terminal flowers in the uniflorescences of Drimys winteri have a significantly greater number of organs than lateral flowers. This increase is due to extended growth of the meristem of the terminal flower during stamen primordium initiation and determination. The shape of the meristem in terminal flowers is more or less circular in cross-section, but that in the lateral flowers is initially narrow elliptic before gradually becoming more or less circular. The change in the shape of the meristem in lateral flowers is interpreted as due to the lessening pressure exerted on the bud by the tightly fitting floral bracts as the floral primordium grows out of the cleft between the floral bract and the uniflorescence axis in which it is inserted. The shape of the meristem influences the position of the first few primordia to be initiated as primordia appear to initiate preferentially towards the poles of the ellipse of elliptical meristems. The sides of the meristems also gradually initiate primordia as the bud develops so that at maturity the sequence of initiation is no longer discernible. A diversity of phyllotactic patterns in flowers of D. winteri results from unconstrained initiation of petal primordia by the large floral meristem following a delay between sepal and petal initiation. These phyllotactic patterns are most often of whorled or Fibonacci-type phyllotaxies, but rarely true Fibonacci spirals. Within the phyllotactic pattern of individual flowers there are substantial deviations in divergence angle and plastochrone ratio. These deviations are related to the shape of the floral meristem; the level of deviation increasing as the meristem becomes more eccentric. In unisexual flowers of Tasmannia xerophila and T. lanceolata the petals are initiated after the sepals without any significant delay. The sepals influence the positions of the petals on the meristem, and the form of the flower is more constrained than D. winteri. The basic phyllotaxis is whorled, but the two species of Tasmannia differ in the strict sequence of organ orientation and identity: typically T. xerophila has a pair of medially placed sepals, followed by a pair of lateral petals, and then an alternate tetramerous whorl of stamens or carpels, whereas T. lanceolata has both a lateral and medial pair of sepals followed by an alternate tetramerous whorl of petals, and then by stamens or a single carpel. The identity of each organ in the sequence differs between the two species but the pattern of organ position is very similar. The phyllotaxis is also similar for pistillate and staminate flowers, further emphasising that the pattern is a inaction solely of primordium positioning on the meristem and is independent of the subsequent developmental fate of those primordia. The flowers of Zygogynum bailloni are much more regular than the flowers of A winteri, although they have a similar number of organs. The outer petals are confluent from an early stage and the rigid structure created by this fusion defines the shape of the meristem and constrains the positions where further organs will initiate. Typically there are three alternating tetramerous whorls of petals followed by alternating octamerous whorls of stamens. The last whorl initiated on the flower contains both stamens and carpels; the carpels enlarge and become connate as the bud develops. The outer petals and the carpels become connate because the expansion of their primordia outpaces that of the meristem, leaving insufficient space for the primordia to develop as free structures. Bubbia howeana, Exospermum stipitatum and Zygogynum bicolor have flowers with organs in whorls in a similar manner to Z baillonU although there are differences in the degree of connation of the outer petals and carpels, and in the overall size of the flowers. A developmental model was constructed to explain the diversity and variation in Winteraceous flowers using ontogenetic parameters. These parameters involved timing of initiation and duration of growth of primordia, and the shape and size of the meristem. The parameters were plotted on a phylogenetic tree to assess their implications for character evolution. Despite the potentially labile and changeable nature of these processes, most transitions appeared to be single events. The lack of reversals suggests that the underlying causes of the diversity and variation in the flowers of Winteraceae are simple in nature. It is possible to partition the structure of the variation in the flowers and to understand the developmental causes of the variation. The patterns observed in Winteraceae are an epiphenomenon of the processes of growth and development, and an understanding of ontogenetic process is the key to understanding the evolution of floral form in this family.
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ItemNerve mediated inhibitory responses in the guinea-pig taenia caecum(University of Melbourne, 1999)
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ItemResource allocation in cyanogenic Eucalyptus cladocalyx(University of Melbourne, 1999)Cyanogenesis is the production of hydrogen cyanide (HCN) by plants and other organisms from endogenous cyanide containing compounds, typically cyanogenic glycosides. This thesis presents a coordinated ecological and physiological analysis of the cyanogenic process in a single species for the first time. Eucalyptus cladocalyx F. Muell. was used as a model to study the allocation of resources to a cyanogenic glycoside under controlled conditions and in the field. This particular species was chosen because it is highly cyanogenic and, as such, allocates similar proportions of nitrogen to the defence and photosynthetic systems. The aim of the study was to characterise the cyanogenesic system and interpret the results in the light of current theories of plant defence. Defence theories can be categorised into those that emphasise either the acquisition or the allocation of a plant�s resources. To date, defence theories have emphasised carbon-based systems. Data presented here shed new light on how such theories can be applied to constitutive nitrogen- based defence systems. The cyanogenic compound was identified as prunasin and the presence of an enzyme with some similarities to other cyanogenic (?-glucosidases was detected. Several important characteristics of spatial and temporal variation in the distribution of prunasin in E. cladocalyx are described for the first time. Prunasin concentration was measured in all parts of six-month-old E. cladocalyx seedlings grown at high (6 mol m-3) and low (2 mol m-3) nitrogen. In addition, leaves and reproductive organs from a plantation of six-year-old trees were sampled over a 12 month period. The highest concentrations of prunasin were in young, developing vegetative and reproductive organs but it was absent from the roots. Up to 20% of leaf nitrogen was allocated to the cyanogenic glycoside, although this proportion varied with leaf age, position and growth conditions. Prunasin synthesis was not induced by wounding leaves, and the concentration did not fluctuate diurnally. A two-dimensional analysis of individual leaves showed no variation in prunasin or nitrogen concentration. However, samples from four different sides of the crown of an adult tree showed that leaves with a westerly aspect allocated significantly more nitrogen to cyanide than those from the other aspects. Seasonal studies showed a decrease in prunasin concentration of young, adult leaves during February, coinciding with the peak flowering period. Leaf nitrogen was positively correlated with prunasin concentration in both fully-expanded and young leaves, although the actual stoichiometry of the relationship altered with age. Herbivory in E. cladocalyx showed a modest, negative correlation with cyanide concentration of young leaf tips, implying an important defensive role for prunasin. The effect of elevated CO2 and different levels of nitrogen on the partitioning of nitrogen between photosynthesis and prunasin was examined. It was expected that the frequently observed increase in photosynthetic nitrogen-use-efficiency of plants grown at elevated CO2 would lead to an effective reallocation of available nitrogen from photosynthesis to prunasin. Seedlings were grown at two concentrations of CO2 (ambient and twice ambient) and nitrogen (as above), and the proportion of leaf nitrogen allocated to photosynthesis, Rubisco, protein and prunasin compared. Leaf prunasin concentration was strongly affected by nitrogen supply, but did not increase, on a dry weight basis, in the leaves from the elevated CO2 treatments. However, the proportion of nitrogen allocated to prunasin increased significantly in the elevated-CO2 grown plants. There was less protein in leaves of plants grown at elevated CO2 in both nitrogen treatments but the concentration of active sites of Rubisco only decreased in plants from the low nitrogen treatment. In addition, leaves of plants grown at elevated CO2 contained a higher concentration of phenolics than those grown at ambient CO2. The last part of the project examined cyanogenic polymorphism. The aim was firstly, to identify acyanogenic forms (if any) of E. cladocalyx and, secondly, to estimate the degree of variability in the cyanogenic potential (ie. prunasin concentration) of a naturally occurring population. Kangaroo Island, South Australia was chosen for the study. No acyanogenic plants were detected, but plants varied enormously in the concentration of prunasin in leaf tissue. There was no clear association between cyanogenic potential and environmental factors such as rainfall, soil type or proximity to the coast Nitrogen also varied widely between individuals. Unlike the results from controlled experiments, nitrogen and cyanide appeared to vary independently of one another in the natural population. While there appears to be a strong genetic basis to the cyanogenic potential of an individual plant, the concentration of prunasin expressed in the leaves varies with both the nitrogen supply and the nitrogen use efficiency of the plant. The latter observations conform to the resource-acquisition theories of plant defence. The variation in distribution within a plant, however, is more in keeping with predictions arising from resource-allocation theories. A theory describing how nitrogen allocation could be optimised with respect to defence has been proposed which attempts to accommodate the apparently contradictory approaches of the different defence theories. In addition, a model linking the glucose-mediated regulation of genes and the amino acid diversion model of secondary metabolism is used to speculate on a possible physiological mechanism controlling the synthesis and allocation of cyanogenic glycosides.
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ItemThe value of zoos : a quantitative assessment of the prevailing paradigm(University of Melbourne, 1998)The roles of zoological gardens in modem society is controversial. Zoos or 'menageries' of the past were for human entertainment. Animals did not behave like those in the wild and thus portrayed distorted images of wildlife. Under increasing pressure from welfare organisations (hereafter referred to as animal liberationists) and conservationists, the role of zoos is evolving. The release of 'The World Zoo Conservation Strategy' (WZCS) (International Union for Directors of Zoological Gardens (lUDZG) / Captive Breeding Specialist Group of lUCN/SSC (CBSG), 1993) articulated the commitment of modem zoos to play a role in species and habitat conservation, education, research, and recreation. Education is an essential role of modem zoos (lUDZG/CBSG, 1993) and it relies on zoos displaying animals that represent those in the wild. This study aimed to examine the status of zoos in Australia and New Zealand, with an emphasis on the modem zoos' aim of education (lUDZG/CBSG, 1993; Appendix A). It assessed a range of captive environments. These included 'typical' metropolitan zoos and the more modem approach to animal management represented at Victoria's Open Range Zoo at Werribee (VORZ). Visitors to the latter view savanna animals in more 'natural' surroundings during a safari tour which takes them amongst the animals. The educational value of exhibits was assessed by measuring animal behaviour and school students' perceptions of the animals. This employed a model zoo species from a savanna habitat; the Plains or Burchell's Zebra Equus burchelli. More general visitor attitudes to zoos and conservation were also investigated. The low intensive management of animals at VORZ allowed a large degree of 'natural' behaviour to be displayed, evident through the social organisation and behaviour, group dynamics, time budgets, and night behaviour of the animals. Hence this population potentially provided a valuable educational resource. In contrast, the behaviour of zebras in most metropolitan settings was characterised by unnatural time budgets (particularly feeding times), high levels of aggression, unnatural mare / stallion relationships, and restricted behavioural repertoires of stallions. These settings provided the animals with little control over their behaviour, which was largely influenced by a number of exhibit and husbandry characteristics. This indicated little potential educational value of the metropolitan animals and poor animal welfare. The VORZ exhibit, while more successful than Royal Melbourne Zoo (RMZ) at representing the 'real' animal and simulating an African savanna for students, did little to promote positive attitudes towards wild animals and their conservation, and to provide accurate knowledge of wild animals. A number of factors potentially limiting the educational value of the VORZ exhibit were discussed, including students holding traditional preconceptions of captivity, and the age of students. Zoo exhibits, irrespective of how 'natural' they are, may have limited educational impact if not complemented by appropriate educational aids. The RMZ exhibit did little to enhance student knowledge. It played a more traditional role, with evidence of students perceiving the animals as the 'exhibit', and the animals and their surroundings as 'unnatural'. Hence the RMZ exhibit did not play an educational role. Visitors to VORZ and RMZ largely supported the roles of zoos in educating visitors, helping conserve threatened animals, and providing a modern approach to animal management. VORZ was more successful than RMZ at promoting positive attitudes towards conservation and the role of zoos in conservation. Additionally, VORZ was perceived as a more appropriate environment for practicing conservation, through education and breeding threatened animals. Traditional attitudes towards zoos were also evident by visitors to both zoos. The present study suggested that open-range zoos, such as VORZ, are a positive step towards meeting the standards set by both the world zoo community (lUDZG/CBSG, 1993) and animal liberationists (World society for the protection of animals (WSPA) / The Born Free Foundation (BFF), 1994). However appropriate educational aids, such as the tour guide commentary at VORZ, may be essential to the value of 'naturalistic' exhibits. The contribution that metropolitan zoos can make to conservation, through exhibiting non territorial equids such as Plains zebras, is negligible. Typical' metropolitan zoos of today may have little potential to be education facilities, and must accept their current role as primarily entertainment. Zoos committed to increasing their conservation roles need to do more than simply develop more 'natural' exhibits. This study supports the need for specialisation of exhibits (lUDZG/CBSG, 1993; Chapter 1), such as sanctuaries for threatened species, native wildlife parks and open-range zoos. Metropolitan zoos need to improve educational tools for visitors, and to re-assess the purpose of exhibited species with respect to education. They must present an environment that evokes learning in an entertaining way. Recommended animal management and educational aids for all zoos committed to playing a role in conservation education are detailed, with particular emphasis on enhancing the educational value of exhibiting non-territorial equids.