Dissertations / Theses on the topic 'Common brushtail possum'

The common brushtail possum (Trichosurus vulpecula) is the most significant vertebrate pest in New Zealand as an ecological threat to the indigenous biodiversity and an economic threat as a vector for bovine tuberculosis. Biological control is considered to be the most accepted management strategy to reduce the population, specifically by impairing fertility. Successful development of a biocontrol agent (most likely a protein or peptide macromolecule) requires identification of a compound that is species-specific and potent. The challenge is also to deliver the bioactive to this free-ranging, widespread, feral animal and ensure sufficient bioavailability. Macromolecules have low oral bioavailability, thus new formulation strategies are required to enhance stability and absorption in the gastrointestinal tract (GIT) of T. vulpecula. Oral administration of the bioactive contained within a non-toxic bait is the most practical delivery strategy. Essential to designing an oral delivery system is to quantify the transit time of different sized delivery systems. The gastrointestinal transit in T. vulpecula was investigated (n = 72) by gamma scintigraphy. Technetium-labelled (99mTc) anion exchange resin particles (75 - 125 (mu)m or 500 - 700 (mu)m) or solution (99mTc-DTPA) was administered orally. After 3, 6, 12, 24 or 32 h, distribution of radioactivity in excised GITs was determined. Transit profiles were similar for each formulation. For delivery to the hindgut, bioactives need protection for 12 h though the upper GIT. Particulate formulations may be retained in the caecum for up to 32 h. Transit time was not different between animals dosed in the evening or the morning. Furthermore, GIT morphology is different between specimens in this study from southern New Zealand and Australian specimens. This may reflect improved diet quality in New Zealand. A model protein (insulin) was incorporated into poly(ethyl 2-cyanoacrylate) (PECA) nanoparticles prepared by interfacial polymerisation of water-in-oil microemulsions. The mean size of nanoparticles was 220 nm with a mean entrapment efficiency of 78%, determined using reverse phase HPLC. In vitro release of insulin from PECA nanoparticles in phosphate buffer (0.067 M, pH 7.4) at 37°C was triphasic and not all entrapped insulin was released. Following in vitro incubation of nanoparticles with enzyme solutions prepared from the GIT of T. vulpecula, lumen enzymes were more aggressive towards insulin compared to mucosal enzymes and the hindgut lumen was the GIT region with the lowest degradation. For the first time in a marsupial species, the in vivo pharmacokinetics of insulin-loaded, PECA nanoparticles were investigated following i.v. and intra-caecal administration and measured by radioimmunoassay. The low cross reactivity of human and endogenous brushtail possum insulin means that T. vulpecula is a suitable non-diabetic model to study pharmacokinetics of insulin. The i.v. pharmacokinetics of insulin solution and insulin-loaded nanoparticles were similar. On intracaecal dosing, co-administration of a permeation enhancer (EDTA) resulted in a small increase in plasma insulin concentration compared to insulin-loaded nanoparticles alone. In conclusion, transit time to the caecum of T. vulpecula following oral delivery was 12 h for fluid and particulate formulations < 1 mm diameter and was independent of the time of day the dose was given. T. vulpecula is a potential non-diabetic model for the study of insulin pharmacokinetics. This thesis demonstrates the potential application of oral peptide and protein delivery technology in the area of wildlife management.

Thesis by publication -- 8 co-authored articles.
Thesis (PhD)--Macquarie University, Division of Environmental and Life Sciences, Department of Biological Sciences.
Includes bibliographical references.
Preface -- Management issues of urban common brushtail possums (Trichosurus vulpecula): a loved or hated neighbour -- Effects of deslorelin implants on reproduction in the common brushtail possum (Trichosurus vulpecula) -- Brushtail possums (Trichosurus vulpecula) in metropolotan Sydney: population biology and response to contraceptive implants -- Strategic survey for Toxoplasma gondii and Neospora caninum in the common brushtail possum (Trichosurus vulpecula) from urban Sydney, Australia -- Leptospirosis serology in the common brushtail possum (Trichosurus vulpecula) from urban Sydney, Australia -- Conclusions.
The common brushtail possum (Trichosurus vulpecula) is indeed a common inhabitant of many Australian citites, and one of the few marsupials that has adapted well to the urban environment. Their close proximity to people provides a great opportunity to experience native wildlife in the backyard, however, their utilization of house roofs, bold behaviour and appetite for garden plants often leads to conflict with householders. Population numbers are sufficiently high to require ongoing management to minimise negative impacts for humans and brushtail possums alike in a socially acceptable manner. The aim of this thesis was to identify current management issues and address the need for improved and novel management strategies. The potential of slow-release implants, containing the GnRH agonist deslorelin, as a contraceptive agent for brushtail possums was tested on a captive population. Males appeared resistant to treatment, but deslorelin was found to inhibit reproduction in female brushtail possums for at least one breeding season, making it a promising tool to control fertility in some wild populations. A further aim was to trial deslorelin implants on a wild urban population, to collect more information about the urban biology of this species and to point out issues which have previously not been addressed. Close proximity and interaction of urban brushtail possums with humans and their domestic animals can increase the risk of disease exposure and transmission and influence the health of wild populations. Serosurveys showed that animals were readily exposed to Leptospira spp. and Toxoplasma gondii. This thesis also provides the first data on brushtail possum dispersal in urban areas, knowledge which is highly relevant to the development of management strategies such as fertility control. The findings from this research broaden our knowledge about urban brushtail possums and should assist wildlife authorities in developing alternative or improved management procedures.
Mode of access: World Wide Web.
xxv, 287 p. ill., maps

This study investigates the ecology of one of the best known Australian marsupials, the Common Brushtail Possum Trichosurus vulpecula, in central Australia. Trichosurus vulpecula is one of few medium-sized mammal species that persist in arid Australia today. Its distribution within the arid zone has declined markedly since European settlement. Two populations, one within the East MacDonnell Ranges along the Hale River and the other on Irving Creek, a River Red Gum creek in the Petermann Ranges, were studied in the southern Northern Territory. Others locations in the region were visited opportunistically. Trie central Australian Trichosurus is not distinct genetically from populations elsewhere in Australia. The diet of T. vulpecula consisted of a range of leaves, flowers and fruits of perennial dicotyledonous species as well as some ephemeral herbs. Grasses were absent from the diet. Variation in the diet reflected seasonal availability in flowers and fruits. The species preferentially consumed at each site had significantly higher moisture content and dry matter digestibility than species not consumed. Preferred species included Amyema maidenii leaves (a mistletoe), Acacia spp. flowers and fruits, Santalum lanceolatum leaves (a shrub), Marsdenia australis leaves (a vine), Solarium quadriloculatum fruit (shrub) and Euphorbia spp. leaves (herb). Small amounts of invertebrate material were consumed throughout the year. Other non-plant material consumed included honeycomb and unfledged birds eg. Budgerigars. There were no significant differences in the diet between the sexes. Trichosurus vulpecula were found in six main habitats: Acacia aneura/Callitris glaucophylla on rocky hills; E. camaldulensis sandy creek-lines; mixed Acacia rocky hills, Rocky Eucalyptus creek-lines; Degraded drainage lines; and Wet gullies. Logistic regression modelling revealed a significant correlation between mistletoe species richness, higher levels of soil nitrogen and the presence of T. vulpecula. In habitats occupied by T. vulpecula species richness of mistletoes was associated with the absence of fire and the presence of reliable ground water supplies. Trichosurus vulpecula were highly mobile with mean home ranges at Hale River of 44.21 � 22.76 ha and considerably higher than those recorded in previous studies in Australia. Mean home ranges at Irving Creek were much smaller, at 4.99 � 1.46 ha and VII similar to that recorded in other studies in Australia. At both sites, males had larger home ranges and there was a high degree of overlap with other males and females. At the Hale River study site, T. vulpecula predominantly denned in caves or cavities in rocks, whereas at Irving Creek all den sites were in large Eucalyptus camaldulensis on the drainage line. Adult and pouch young sex ratios were at parity. During this study, T. vulpecula was found to breed continuously, with births recorded in almost all months. Growth of the young were more rapid than previously recorded for Trichosurus in Australia. This is interpreted as an adaptation for living in an arid environment, enabling the young to achieve independence before quality food supplies diminish. No single exotic predator or competitor was solely responsible for the decline of T. vulpecula in arid Australia, implying an interactive impact. Prey switching by dingoes from rabbits to T. vulpecula, macropods and echidnas followed the crash of rabbit populations at Hale River. Predation by dingoes on T. vulpecula was only recorded once, at the Irving Creek study site, where numbers of rabbits remained stable throughout the study. The impact of exotic herbivores occurred through habitat degradation rather than competition. Evaluation of the ecological data collected during this study generally supports current models of decline and extinction in medium-sized mammals in arid Australia, integrating the effects of predators, competitors, drought and fire. However, the importance of each factor on populations of T. vulpecula was found to vary depending on their location in the landscape. This study suggests two separate models to explain the decline of T. vulpecula in arid Australia after the arrival of Europeans. The first operates in the riparian lowlands and the second on the rocky ranges. In both models, prior to European settlement, T. vulpecula occupied refuge habitats characterised by readily available moisture for plant growth (run on areas and/or shallow water tables) and soils with higher soil nutrient concentrations. The impact of fires on these refugia was minimal, as Aboriginal burning practices protected them with mosaic burning generally preventing large-scale fires from developing. Following European settlement, the forces impacting on populations were different in the riparian lowlands from those affecting rocky ranges. In the riparian lowlands, the effects of rabbits and livestock together with predation were found to have the major impact on T. vulpecula populations. Fire was not a significant factor in these areas. In the rocky ranges, fire was the most significant factor affecting T. vulpecula populations. Introduced herbivores did not degrade these habitats as they did in the riparian lowlands because the rugged and steep nature of the ranges acted as a physical barrier. Similarly, predator numbers were lower because of the relative difficulty in moving over rough ground and the generally lower relative abundance of preferred prey such as rabbits. An adaptive management strategy needs to be implemented to determine the effects of different management regimes on T. vulpecula population viability. The key elements of a management strategy in the riparian lowlands involves the manipulation and monitoring of predators, rabbits and livestock numbers. In the rocky ranges, the key management strategy involves the implementation of a patch burning to prevent fires entering habitats occupied by T. vulpecula. Importantly, any management strategies should involve Aboriginal people. Trichosurus vulpecula is an important part of Aboriginal culture. Its decline is of great concern to many people and several of the remaining populations and potential reintroduction locations are on Aboriginal land. Because of their relationship with the land and the animals, people have both the knowledge of the animal and the skills (such as patch burning) to provide information to managers which will assist with management. To achieve these management directions a coordinated national education programme is required to inform and convince the Australian community that conservation of T. vulpecula is deserving of attention in arid and semi-arid Australia. This is particularly important given the perception that T. vulpecula is a common species throughout Australia, despite its massive decline in arid Australia since European settlement.

Predators and plant toxins which act as chemical defences, represent two different but proximate constraints for foraging herbivores, limiting food intake and influencing behaviour. Consequently, foraging herbivores respond to spatial and temporal variation in food resources and danger, making foraging decisions based on their nutrient requirements, while trying to avoid predators. Not all individuals within a population, however, will deal with this trade-off in the same way. One driver of this variation should be individual consistent behavioural differences, defined as ‘personality’. The immediate consequence of the existence of personality in a population is that different individuals will perceive their own personal landscape of food and fear. This, in turn, may alter how each decides to forage throughout the landscape. I have investigated aspects of predation risk, foraging strategies and individual consistency in behaviour of a model generalist herbivore, the common brushtail possum (Trichosurus vulpecula), to ultimately understand how personality influences foraging decisions of herbivores in the wild. I provided evidence of how personality affects decision-making by individuals in a natural context, showing that boldness influences foraging in response to food toxins and predation risk. I demonstrated that these two costs are perceived differently by individuals with different personalities. As a consequence, different individuals altered foraging behaviour in different ways resulting in different foraging outcomes between bold and shy animals. Foraging behaviour of possums at risky feeders in the field was related to the level of boldness they showed in captivity. This study provides an insight into the interactions between plants, predators and herbivores and the role of personality in influencing foraging behaviour.

The western ringtail possum, Pseudocheirus occidentalis, is classified as threatened, both nationally and internationally. Land clearing for building development threatens the last major coastal population stronghold in and around the town of Busselton in the south-west of Western Australia (WA). Translocation of displaced P. occidentalis from this locality into nearby conservation estates commenced in 1991, in the presence of fox control, with the aim of re-establishing populations of the species within suitable habitat outside its current range. Initial successes (1991-1998) were followed by a major population decline at one site for unclear reasons. The aim of this project was to determine which factors presently limit translocation success for P. occidentalis and thereby provide direction for future management of the species. Displaced and rehabilitated P. occidentalis were translocated into three sites, two of which were baited for fox control. Survival was monitored weekly, causes of mortality were ascertained and attributes of habitat use were mapped and analysed. Each individual P. occidentalis underwent comprehensive health and disease screening under isoflurane anaesthesia prior to translocation and whenever recaptured for re-collaring. Health, survivorship and habitat use of resident common brushtail possums, Trichosurus vulpecula, were similarly studied at each site. Pilot spotlight surveys using line transect methods were performed at the end of the study to provide provisional data on population densities. Health screening revealed no evidence that infectious disease currently limits translocation success for P. occidentalis. Possums of both species were negative for toxoplasmosis, leptospirosis, salmonellosis and chlamydiosis. Cryptococcal antigen was detected in one individual T. vulpecula but was not of pathological significance. Endoparasite levels were negatively correlated with body condition. Differences between pre- and post-translocation haematological values were found, suggesting that habitat quality or nutrient intake were lower at the translocation sites than at the sites of origin. Mortality rates of translocated P. occidentalis were high. The majority of P. occidentalis deaths were attributed to predation, with foxes, cats, pythons and raptors all implicated. Some P. occidentalis died in poor body condition from apparent hypothermia/hypoglycaemia, with moderate to heavy parasite burdens present at necropsy. Most T. vulpecula mortality was attributable to fox predation. Survivorship analyses were carried out using information-theoretic techniques to investigate which, if any, of a suite of hypothesised factors most influenced post-translocation survival of P. occidentalis. The most highly ranked models were those that included pre-release white blood cell counts and/or numbers of T. vulpecula at the release site. Survivorship of P. occidentalis was negatively correlated with each of these factors, and the two together acted in a synergistic fashion. Effects of fox control on P. occidentalis survivorship were equivocal. The average annual survival rate of established P. occidentalis was less than half that of resident T. vulpecula. Post-translocation dispersal distances varied among individual P. occidentalis. Mean home range sizes of translocated P. occidentalis were larger than those reported for other coastal populations. Individual home ranges overlapped one another, both within and between possum species. Vegetation dominated by peppermint (Agonis flexuosa) was utilised by translocated P. occidentalis where available, and habitat partitioning between the two possum species was observed in some areas. A greater range of diurnal rest site types were utilised by P. occidentalis than T. vulpecula. Spotlight surveys revealed presence of low density P. occidentalis populations, including juveniles, at two sites but numbers remained negligible in the site at which the post-1998 decline had occurred. Complex interactions involving health, predation, habitat quality and inter-specific competition influence the success or otherwise of wildlife translocation programs. The results of this project suggest that all these factors, particularly predation, affected translocation outcomes for P. occidentalis during the period of study. Complete exclusion of exotic predators (foxes and cats) from the translocation sites may be necessary in future, especially given the numbers of native predators (pythons and raptors) present. In addition to heavy predation pressure, the small size and apparently low carrying capacity of the translocation sites for P. occidentalis, along with high numbers of resident T. vulpecula, currently appears to limit P. occidentalis survival and population growth. While, in the short term, the most efficient use of funds and the best option for the species in its current coastal strongholds might be to put greater effort into conserving P. occidentalis in its natural environment, there could also be value in carrying out further experiments to determine whether or not translocation success can be improved through use of particular management actions. The principles of adaptive management apply both to management of P. occidentalis in its natural environment and to conduction of translocation programs. Possible experimental approaches are outlined and recommendations for further research proposed.

Electrolyte transport in the intestine of the common brushtail possum (Trichosurus vulpecula) differs from that observed in eutherian mammals. This study has used molecular physiology to identify and characterise the expression and distribution of membrane transporters potentially responsible for these differences in electrolyte transport in the possum intestine. In the possum ileum, secretagogues stimulate an electrogenic Cl⁻-independent HCO₃⁻ secretory response but secretagogue-stimulated Cl⁻ secretion does not occur in this tissue. Based on the ion dependence and pharmacology of the stimulated secretory response, the expression of the cystic fibrosis transmembrane conductance regulator (CFTR), pancreatic Na⁺ HCO₃⁻ cotransporter (pNBC) and Na⁺ K⁺ 2Cl⁻ cotransporter (NKCC1) were investigated in the ileum. Reverse transcription PCR experiments showed that CFTR, pNBC and NKCC1 mRNA transcripts were expressed in the ileal epithelium. It was then demonstrated by in situ hybridisation that both CFTR and pNBC were localised predominantly in the crypts and the levels of expression decreased along the crypt-villous axis towards the lumen. Significantly, the in situ hybridisation results showed that there were low levels of NKCC1 transcript in the ileal epithelium. Western blot studies confirmed that mature CFTR and pNBC proteins were expressed in the ileum, while NKCC1 protein was not detected. The findings of the present study suggest that the absence of Cl⁻ secretion in the ileum is because NKCC1 expression is not elevated in the epithelium. The expression of mature CFTR and pNBC protein suggest that these membrane transporters are involved in the stimulated electrogenic HCO₃⁻ secretory response. The evidence also suggests that CFTR may mediate HCO₃⁻ efflux in the ileum. In contrast, secretagogues do not stimulate an electrogenic secretory response in the proximal and distal colon. This study has shown that CFTR, NKCC1 and pNBC proteins are expressed in the proximal and distal colon. Both NKCC1 and pNBC transcripts were localised to the crypt base in the proximal colon. However, it was shown that CFTR has a punctate distribution and the transcript was predominantly observed in the upper crypt and surface cell region. This study indicated that NKCC1 and pNBC were distributed in a different region of the epithelium compared to CFTR. It was concluded that the distribution of these membrane transporters in different regions of the epithelium accounts for the absence of a stimulated electrogenic secretory response in the possum colon. Given that no stimulated electrogenic secretory response is observed in the colon, it is suggested that HCO₃⁻ secretion by the ileum may have an important physiological role in maintaining an appropriate fluid and pH composition for fermentation in the colonic lumen.

Intraspecific variation in traits, such as animal behaviour, has important ecological consequences. This variation may affect an animal’s diet, space use and the risks they face from predators and parasites. Individual dietary specialisation recognises the intraspecific variation in realised dietary niche. Whether individual specialists and generalists consume diets differing in quality as well as breadth is unclear. Animal personality (consistent individual variation in behaviour) may influence dietary specialisation by altering how individuals perceive and react to external stimuli. Animal personality and personality-driven urban space use may affect variation in parasite occurrence among animals at the human-wildlife interface. I tested the association between behavioural and dietary phenotypes by quantifying animal personality, and diet in multiple dimensions, using free-ranging common brushtail possums (Trichosurus vulpecula). I also tested variation in parasite (protozoan Cryptosporidium) occurrence as linked to animal personality and space use of possums at the urban-natural interface. I found that dietary specialists ate a narrow set of low-quality resources while generalists consumed a broad, high-quality diet. My study demonstrates the important link between animal personality and individual dietary specialization for the first time. I identified three Cryptosporidium species — C. hominis, C. muris and C. parvum — in possums. Personality and urban space use affected the likelihood of individual possums carrying Cryptosporidium. My results highlight the importance of individual variation in behaviour to identify individual phenotypes that may disproportionately affect both food-web and disease dynamics: proactive – generalists likely to be pests and proactive – greater users of urban space likely to carry pathogens. Understanding these relationships provides a key basis for improving biodiversity conservation, pest, and disease management.

Biodiversity conservation throughout the world is challenged by the impacts of a changing climate on fragmented landscapes. To mitigate these threats, conservation managers require models which can demonstrate the consequences of both negative impacts and management actions. This need can be addressed through spatial modelling applications. Unfortunately, throughout much of the world, spatial modelling is forgone, being seen as requiring skills and resources beyond the means of many conservation planners and managers. This thesis seeks to address this dilemma by delivering criteria for a successful modelling application and by providing case studies which demonstrate how appropriate modelling can be undertaken without highly specialised skills or prohibitively expensive software and equipment. In this way it facilitates the delivery of better targeted and, consequently more effective, management actions. For my case studies I have used the south-western corner of Australia as a demonstration landscape. This region is recognised internationally as a “biodiversity hotspot,” not only for the biological richness and uniqueness of species but also for the level of threat to which they are subject. Like many landscapes throughout the world, much or this region’s natural biota exists in fragmented, fragile and degraded patches and is therefore highly vulnerable to the anticipated impacts of anthropogenic global warming. In this thesis I have: 1) examined the principles of spatial modelling and reviewed how spatial modelling has been applied to conservation management in this region, 2) conducted examples of different forms of spatial modelling using actual regional conservation management issues, and 3) demonstrated how these examples can be incorporated into conservation management planning. My key findings are: Spatial modelling provides users with an opportunity to effectively test hypotheses, thereby informing the planning process and improving conservation outcomes. Where spatial modelling is omitted from the process, knowledge gaps are often addressed by the axiomatic and by assumption. This is contrary to the principles of effective adaptive management. Modelling tools are inherently more effective when selected for their capacity to meet a planning objective rather than where projects are tailored to meet a model’s capacity. The coordinated use of multiple tools can often provide a more robust understanding of the consequences impacts and mitigating actions. All tools and data sets used should be utilised with a clear and acknowledged understanding of their suitability, strengths and limitations. A wide range of spatial modelling tools (and data sets) are freely and readily available to conservation managers. Most of these come with excellent tutorials and support services. Data gaps can often be addressed through targeted field observations, obtained through complimentary planning processes, or synthesised from accessible data sets. There is a very large body of peer reviewed literature demonstrating means by which others have applied existing modelling tools, or developed tools themselves, to meet a wide range of applications. Accessing this literature is an excellent means of building spatial modelling capacity. New and improved tools, methodologies and data sets are constantly being developed. A failure to implement effective spatial modelling is becoming increasing difficult to justify.

Research into the diversity and evolution of mammalian colour vision has become even more exciting with the recent discovery of both trichromatic and dichromatic colour vision in the Australian marsupials. Our knowledge about these colour vision systems is limited, with a number of discrepancies in the research. Methodology issues with some of the anatomical and behavioural studies may have falsely indicated trichromacy. It is also uncertain whether only the tammar wallaby (Macropus eugenii) has dichromatic colour vision, or if dichromacy is represented in a number of marsupials. It is believed that most marsupials can perceive ultraviolet light, yet the transmission properties of ocular media have not yet been measured. In this thesis, I use anatomical and behavioural methods to examine colour vision in the Common Brushtail Possum (Trichosurus vulpecula). I firstly present a detailed analysis of the spectral transmission of light through the ocular media. Here, I demonstrated the variability of ocular media for three marsupial species: the ultraviolet light sensitive fat-tailed dunnart (Sminthopsis crassicaudata), non-ultraviolet light sensitive tammar wallaby, and common brushtail possum. I then examine the topographical arrangement and spectral sensitivities of photoreceptors in the common brushtail possum. Using opsin antibodies known to label photoreceptors, I show that brushtail possums have an anatomical basis for at least dichromatic colour vision, with both M/LWS ({u03BB}max = 545nm) and SWS cones present in the retina. There is also a small population of unlabelled cones, which may form a third cone population. Their extremely low densities,however, would hardly contribute to visual processing. By tracking cone densities across the retina, I provide the first evidence for regionalisation in both opsin and cell morphology types in an Australian mammal. Finally, I showed functioning dichromatic colour vision with behavioural operant conditioning techniques. Brushtail possums have an innate preference to using brightness rather than colour vision. By introducing spatial information which faded over time, I was able to encourage subjects to choose between colours irrespective of brightness. Both increment-threshold spectral sensitivity and wavelength discrimination experiments indicate their perception of colours is based on dichromatic colour vision. By comparing behavioural and microspectrophotometry results, I conclude that SWS cones peak in sensitivity around 435 nm. This is the first non-macropod known to have a violet, rather than an ultraviolet visual pigment. This thesis confirms a diversity of both trichromatic and dichromatic colour vision in marsupials, with the tammar wallaby not the only marsupial with dichromatic colour vision. I propose that brushtail possums have selectively reduced spectral sensitivity to dichromacy, evidenced by the presence of three cone types, yet perception of colours based on two cone types. The study of marsupial colour vision provides a rich resource for examining the diversity and use of dichromatic and trichromatic colour vision in mammals other than primates.

Life history theory aims to describe and explain patterns in the life cycles of organisms and relate these patterns to intrinsic and extrinsic influences. The life history of an organism is commonly defined as a set of co-evolved strategies that relate directly to an individuals genetic fitness, lifetime reproductive success (LRS) and survival. The great majority of research on life history variation in mammals has concentrated on placental mammals, while marsupials have been largely overlooked. This thesis investigates life history variation, and the influence of this variation on reproductive strategy and success, among individuals in an arboreal marsupial, the common brushtail possum (Trichosurus vulpecula). A population of T. vulpecula was studied from 2001-2004 on Magnetic Island, north Queensland; the population was censused each month by live-trapping. Demographic changes in the population were modelled using capture-mark-recapture data. The population size remained stable over the study period and there was little temporal variation in recruitment or survival. T. vulpecula on Magnetic Island displayed life history traits similar to those reported for other populations of the species. The majority (>80%) of females began to reproduce at the age of two and the main birth period occurred in the autumn months of April and May. Some females went on to produce a second young in the spring, after successfully raising a first. Males became sexually mature at the age of three. Survival, body mass and body condition declined in both males and females after the age of six, although the declines were more pronounced in males. Variation in life history was strongly related to differences in female reproductive strategy and success. In terms of somatic investment, older females invested significantly more into individual offspring than younger females; older females also gave birth earlier in the season and were more likely to produce a second offspring in the spring birth cohort. Maternal age also influenced the birth sex ratio; young, primiparous females gave birth to significantly more male offspring than older females, regardless of their condition while older, multiparous females were more likely to give birth to a male offspring when in good condition. The extent of male biased sexual dimorphism in T. vulpecula was extremely variable among 11 populations in northern Australia. Dimorphism was related to seasonality of breeding, being greatest in populations where births occurred all year round. Mean body mass of male possums also decreased with increasing population density, while there was no effect of density on female mass. There was also some evidence that population density influenced the degree of breeding synchrony within populations, particularly in locations with a more seasonal climate. In the Magnetic Island population, mating effort also varied considerably among male possums and young males lost more mass during the mating period than did older males. There was also some indication that males demonstrated age-specific variation in mating behaviour, which may be related to their size and experience. The results of my study show that life history traits in both male and female T. vulpecula are phenotypically plastic. Age-specific variation in reproductive strategy was found in both male and female possums and is likely associated with the trade-off between current and future reproduction. Increased reproductive effort in older females also appears to entail significant costs in terms of an associated decline in survival, condition and body mass. Variation in body condition also influenced offspring sex allocation in females and is most probably an adaptation to maximise LRS. Male possums displayed a more pronounced decline in survival and condition after the age of five compared to females and this may be a direct cost of increasing mating effort as a young adult.

Life history theory aims to describe and explain patterns in the life cycles of organisms and relate these patterns to intrinsic and extrinsic influences. The life history of an organism is commonly defined as a set of co-evolved strategies that relate directly to an individuals genetic fitness, lifetime reproductive success (LRS) and survival. The great majority of research on life history variation in mammals has concentrated on placental mammals, while marsupials have been largely overlooked. This thesis investigates life history variation, and the influence of this variation on reproductive strategy and success, among individuals in an arboreal marsupial, the common brushtail possum (Trichosurus vulpecula). A population of T. vulpecula was studied from 2001-2004 on Magnetic Island, north Queensland; the population was censused each month by live-trapping. Demographic changes in the population were modelled using capture-mark-recapture data. The population size remained stable over the study period and there was little temporal variation in recruitment or survival. T. vulpecula on Magnetic Island displayed life history traits similar to those reported for other populations of the species. The majority (>80%) of females began to reproduce at the age of two and the main birth period occurred in the autumn months of April and May. Some females went on to produce a second young in the spring, after successfully raising a first. Males became sexually mature at the age of three. Survival, body mass and body condition declined in both males and females after the age of six, although the declines were more pronounced in males. Variation in life history was strongly related to differences in female reproductive strategy and success. In terms of somatic investment, older females invested significantly more into individual offspring than younger females; older females also gave birth earlier in the season and were more likely to produce a second offspring in the spring birth cohort. Maternal age also influenced the birth sex ratio; young, primiparous females gave birth to significantly more male offspring than older females, regardless of their condition while older, multiparous females were more likely to give birth to a male offspring when in good condition. The extent of male biased sexual dimorphism in T. vulpecula was extremely variable among 11 populations in northern Australia. Dimorphism was related to seasonality of breeding, being greatest in populations where births occurred all year round. Mean body mass of male possums also decreased with increasing population density, while there was no effect of density on female mass. There was also some evidence that population density influenced the degree of breeding synchrony within populations, particularly in locations with a more seasonal climate. In the Magnetic Island population, mating effort also varied considerably among male possums and young males lost more mass during the mating period than did older males. There was also some indication that males demonstrated age-specific variation in mating behaviour, which may be related to their size and experience. The results of my study show that life history traits in both male and female T. vulpecula are phenotypically plastic. Age-specific variation in reproductive strategy was found in both male and female possums and is likely associated with the trade-off between current and future reproduction. Increased reproductive effort in older females also appears to entail significant costs in terms of an associated decline in survival, condition and body mass. Variation in body condition also influenced offspring sex allocation in females and is most probably an adaptation to maximise LRS. Male possums displayed a more pronounced decline in survival and condition after the age of five compared to females and this may be a direct cost of increasing mating effort as a young adult.

The level of impact of forest disturbance on mammal communities depends on a species’ degree of forest-dependence as well as the intensity and scale (temporal and spatial) of the disturbance. Where land-use practices such as logging, agriculture, and urbanisation alter the habitat characteristics of a forest, a wide range of effects may lead to a reduction in species diversity or the decline of a population. Arboreal marsupials are the faunal group considered to be most at risk from habitat disturbance in Australian forests. Despite this, there have been relatively few studies examining the influence of forest disturbance on arboreal marsupials, particularly in Tasmania. The overall aim of this thesis is to determine whether habitat disturbance (as a result of harvest and associated activities (and wildlife in one site)) and forest type influence the physiology and population biology of an arboreal marsupial, the common brushtail possum (Trichosurus vulpecula), in Tasmanian forests. A multi-dimensional approach integrating physiological, genetic, and ecological studies was employed to address this aim at both the individual and population levels. In particular, this thesis examines potential impacts of habitat disturbance and forest type on physiological parameters of well-being, reproductive parameters, and population parameters (demographic and genetic) in the brushtail possum. Trapping was conducted in spring/summer and autumn/winter during 2007–2008 at six dry Eucalyptus forest sites (three regenerating after harvest and three in relatively undisturbed forest) in southeast Tasmania and four wet Eucalyptus forest sites (two regenerating after harvest and two in relatively undisturbed forest) in northeast Tasmania. Disturbed sites were 4–11 years post harvest. All sites were embedded within a matrix of mature or older-aged regenerating forest. Vegetation and structural attributes of the study site and the land immediately surrounding it were assessed. At each site, data were collected on the characteristics of the faunal community (community composition and biodiversity, species abundance, body mass, sex, and breeding success), which included the brushtail possum. Blood samples, tissue biopsies, and late lactation milk samples were collected from brushtail possums to assess physiological well-being, population genetics, and reproductive parameters. Plasma cortisol concentration was assessed via radioimmunoassay as a proxy for adrenal status, white blood cell differential was performed on blood smears as a proxy for generalised immune response, and haematocrit was measured as a proxy for body condition. DNA was extracted from tissue for genetic analyses using microsatellites to explore mating system, genetic diversity, and implications of gene flow between brushtail possum populations. Brushtail possum milk was analysed for lipid, solid, carbohydrate, and protein concentrations. Analysis showed that, in general, habitat structural complexity within sites and age structure of the forest in the surrounding landscape did not vary significantly, indicating that broad resource availability (food and refuge) was equivalent across sites. However, basal area, the number of hollow-bearing trees, and the percentage of mature forest, young forest, and overstorey cover varied with disturbance, while understorey cover and numbers of both tree hollows and hollow-bearing trees varied by forest type. Faunal distribution was dictated by forest type. While most species showed little influence of habitat disturbance, brushtail possums exhibited lower abundance, decreased breeding frequency, and a male-biased adult sex ratio at the disturbed sites. Comparison of physiological parameters across sites suggest that the brushtail possum is physiologically resilient, with no clear influence of habitat disturbance or forest type on adrenal status, generalised immune response, or body condition. There was a subtle difference in fat content of brushtail possum milk, driven primarily by milk composition at one site; this probably reflects site level differences in maternal diet. However, there were no differences in breeding success, distribution of births, and timing of developmental features, survival, or body condition of young across sites. Genetic analysis suggests that there are two populations of brushtail possums influenced by geographic distance, with near-random mating and moderate genetic diversity, across eastern Tasmania. There were no effects of disturbance, as examined in this study, on genetic diversity or mating system. However, disturbance resulted in an altered landscape with decreased female-specific resources (e.g., tree hollows which are necessary for reproduction). Results suggest that the male-biased adult sex ratio observed in brushtail possum populations living in disturbed sites was due to a lower abundance of adult females at these sites, rather than maternal sex allocation, retention of subadult males (e.g., lack of dispersal), or increased immigration of adult males. The outcomes of this study demonstrate the value of using a multi-dimensional approach that integrates physiological, genetic, and ecological investigations of the potential influences of habitat disturbance and forest type on animal species. Such an approach reduces uncertainty about the relationship between disturbance and the response and subsequent recovery of fauna, which is important for the development of effective forest management strategies. Brushtail possums are resilient and able to cope with habitat disturbance at the individual level. However, subtle population-level responses may have implications for population growth and long-term viability of brushtail possums in areas subject to intensive and extensive forest harvesting. These results also illustrate the importance of retaining mature habitat elements in the landscape to allow forest-dependent fauna to recolonise harvested areas and persist into the long term.

The global extirpation of the world’s apex predator fauna is consistently highlighting their important functional role in preserving biodiversity and maintaining ecosystem resilience. Apex predator declines and extinctions are promoting more invasive and homogenised ecosystem states, linked with secondary species extinctions, changes to community composition, and redefined carnivore guilds. In taxonomically and geographically diverse ecosystems devoid of apex predators similar general patterns expressed in community dynamics are emerging, such as mesopredator release, yet the magnitude and significance of the effects are driven by their context. The Tasmanian devil (Sarcophilus harrisii) is the largest extant marsupial carnivore and is facing the real threat of disease induced extinction in the wild from a consistently fatal transmissible cancer, devil facial tumour disease (DFTD). The devil is now effectively the apex mammalian predator in Tasmanian ecosystems following the extinction of the thylacine (Thylacinus cynocephalus) but DFTD is threatening its ecological role in the environment. Since the disease arose in the early to mid 1990s devil populations have suffered declines in excess of 95% in long-term disease areas, and it has infected more that 75% of their current geographic range. Tasmania retains the most intact guild of marsupial carnivores in Australia and maintains healthy populations of many native mammal and bird species that are extinct or threatened on mainland Australia. The loss of Tasmanian devils over large tracts of Tasmania is of tremendous conservation concern for native biodiversity and community resilience. This study provides the first assessment of the ecosystem effects of Tasmanian devil decline and aims to determine overarching effects of the loss of an ecologically functional devil population on terrestrial mammalian fauna. Within the scope of this thesis, broad concepts encompassing abundance, behaviour and disease ecology of native and introduced species are assessed within four discrete projects. I utilised complimentary approaches with the benefit of this unique large scale natural experiment to assess common theories as well as considering less widely examined concepts which may be pertinent to global apex predator demise. First, using a state-wide spotlighting database which pre-dates DFTD by more than a decade, I evaluated the mesopredator release hypothesis (MRH) and the extent to which mesopredators are regulated by top-down or bottom-up environmental processes. Second, I conducted a rapid snapshot survey across a large spatial extent encompassing different devil densities to assess changes to community composition, invasive system states and the cascading effects of mesopredator release on populations of their prey. Third, I measured risk-sensitive behaviour of the common brushtail possum, a species regularly preyed upon by Tasmanian devils, employing a ‘giving up densities’ approach across a DFTD arrival gradient, which represents a proxy for devil population decline over time. Finally, following the evidence for mesopredator release of feral cats, I assessed whether there was potential for increased disease transmission of Toxoplasma gondii, a parasite whose only known definitive hosts are members of the Felid family but that can infect all warm-blooded mammals. This study provided several lines of evidence for a shifting ecosystem state and increasing threats to the persistence of native biodiversity in response to declining devil populations. Less diverse communities and a strong tendency towards more invasive system states were characteristic of areas with long-term devil decline. Native and introduced mammals responded differently to devil decline, and the direction of the response for species of each origin was consistent across different trophic levels. I found strong evidence for mesopredator release of the invasive feral cat (Felis catus) in response to devil decline and a concomitant decline and changing activity times in the much smaller native eastern quoll (Dasyurus viverrinus), suggesting that they may be indirectly protected by devils. Despite the comparable size and prey range of native spotted-tailed quolls (Dasyurus maculatus) to feral cats, there was no evidence of a similar response, notwithstanding some evidence for different activity times across different devil densities. The magnitude of the responses of mesopredators to declining devil populations was significantly affected by environmental variables. In anthropogenically dominated landscapes bottom-up control appears to be the principal regulating force, and in less disturbed areas top-down control is stronger. There was evidence for an increasingly invasive state, represented by a significantly higher proportion of activity of feral cats and introduced small mammals, which appeared to be affecting native prey species. Small- and medium-sized native species within the prey size range of large mesopredators showed population declines analogous to the declines observed in devil populations and also evidence for increased predation pressure, indicating that apex predator loss in Tasmania is threatening native biodiversity. There was evidence of behavioural responses in prey species to the decline in devil numbers. Using the giving up densities approach, I found evidence that the predominantly arboreal brushtail possum (Trichosurus vulpecula), a common prey item of devils, has changed its anti-predator behaviours and has increased its ground foraging activity in response to declining devil populations, whilst maintaining vigilant behaviours appropriate for the avoidance of other predator species. Behavioural responses have the potential to initiate a trophic cascade if changes in behaviour translate into increased fitness and reproductive output. Some native species are at risk from higher feral cat densities not only from increasing predation pressure but also from potentially amplified transmission of the Toxoplasma parasite. Australian native marsupials may be particularly susceptible to acute Toxoplasma, a consequence likely attributable to a lack of co-evolution. I found tentative support for higher prevalence rates in areas with higher cat densities and also a strong link to increased susceptibility in native species at higher trophic levels. There was also some suggestion for reduced behavioural reactions in infected individuals, with the potential to increase predation rates. This was among the first research that has investigated changing disease dynamics in response to mesopredator release, and represents an important and novel step towards more wide-ranging research of the effects of apex predator loss on biodiversity. The combined results, derived from empirical approaches, provide compelling evidence that diverse and complex changes are occurring in Tasmania’s fauna communities following apex predator decline. The evidence is indicative of extensive and far-reaching consequences in the Tasmanian ecosystem, threatening native biodiversity and promoting alternative ecosystem states. The lessons learned from applying existing community ecology theories and approaches to this unique large scale natural experiment are applicable to other ecosystems confronted with apex predator loss and highlight the importance of a multifaceted and comprehensive approach to apex predator studies.