Tesi sul tema "Trichosurus vulpecula"

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

A total of 9 brushtail possums (Trichosurus vulpecula) were trained to perform a two-manipulanda, conditional discrimination task. The possums learned to press a right lever in the presence of a tone (80 dB(A)) during tone-on trials, and a left lever in the absence of the tone on tone-off trials. Overall sessions of 11 conditions contained tone frequency between 100 Hz and 35 kHz were tested. Each condition contained training and then probe sessions. In training sessions, the possums were presented with tone-on and tone-off trials, pseudo-randomly. Once the possums responded with over 90% accuracy for five consecutive sessions, then probe sessions were introduced. Probe sessions were similar to the training sessions, except that the tone intensity for tone-on trials was reduced by 8 dB(A) across blocks of 20 trials until their response accuracy in a block fall below 60% or reached 24 dB(A). Data were analysed using overall percentages correct and log d analysis. Both measures indicated that overall response accuracy decreased for all possum as tone intensity reduced. Based on these data analyses, threshold values were calculated using the criterions at 75% correct and a log d of 0.48. The threshold values for each possum and across all possums were plotted as a function of the tone frequency to produce an audiogram. A curvilinear regression was fitted for each threshold values. The functions of both measures were very similar. Both audiograms showed that the possums could hear the tones between 100 Hz and 35 kHz, and were most sensitive to tones between 15 and 20 kHz. This experiment involved many difficulties with producing and measuring tones especially outside of human hearing range. Due to these difficulties, several problems and concerns were raised during the experiment, these were discussed in this study and also recommendations for future research were then presented.

Aerial control using 1080 (sodium monofluoroacetate) baits is widely used in New Zealand for the control of introduced brushtail possums (Trichosurus vulpecula), with the aim of protecting national conservation and agricultural values from these damaging pests. This thesis integrates research, completed over 25 years, that was motivated by growing recognition in the 1970s of the extent of possum impacts and the need to improve the effectiveness and efficiency of the control operation. Field research assessed the palatability of three types of cereal-based pellet baits and carrot baits in different regions, habitat types and seasons. Palatability was assessed by the consumption of the different bait types presented independently of each other on 15-30 plots, with rotation of bait types at plots on successive nights to provide equal exposure to each bait type. There was regional variation in possums' bait preferences, possibly reflecting genotypic differences, whereas seasonal variation was less evident. Carrot bait was preferred or equally preferred to cereal bait in 14 out of 20 field trials. The proportion of possums eating baits was then investigated by, firstly, developing a technique for tracing bait acceptance using rhodamine B, a UV-fluorescent dye. In four field trials, more than 95% of possums accepted three types of dye-marked bait, eliminating bait refusal as a major reason for low kills in winter control operations. In a fifth trial, conducted in summer, only 68% of possums accepted bait suggesting that seasonal availability of favoured foods may influence bait acceptance. Since possums must encounter baits before deciding whether to eat them, field studies were undertaken to assess the coverage achieved in normal aerial baiting operations. Large gaps, up to 400 m in width, were often found between baiting swaths; these could allow some possums to survive. A controlled field experiment, using acceptance of rhodamine-dyed bait as a measure of effectiveness, showed that bait distribution was least accurate where flight paths were not marked. Where gaps of 100 m between flight paths were deliberately created, bait acceptance was slower and less than where coverage was complete. Sowing baits at 3 kg/ha was as effective as at 10 kg/ha, indicating the potential for substantially reducing operational costs by using machinery capable of faultlessly distributing baits at low rates. Navigational guidance systems were evaluated and found to improve the accuracy of bait distribution. During 1993-1997, when a lower sowing rate of 5 kg/ha was adopted operationally by regional managers, control effectiveness was unchanged but annual savings of around $9 million accrued. Because of the lack of suitable sowing machinery, a bucket was developed to permit faultless distribution of baits at lower rates, demonstrating the possibility of yet further cost-savings. The possibility of seasonal food availability affecting bait acceptance was investigated in three different forest habitats. Dyed baits were aerially distributed on 100 ha at each site in each season over two years. In each trial, fat-based condition indices of possums were calculated and the abundance of possum-preferred plant foods described. Bait acceptance was consistently high (85-100%) in the 24 trials, and was not influenced by either condition or availability of preferred foods. It seems likely that seasonal variation in operational effectiveness is caused by either the availability of sharply seasonal, scarce foods that possums may feed on intensively for brief periods, or by warmer temperatures that render 1080 less effective. The influence of 1080 on acceptance of (rhodamine-dyed) baits was investigated in a field trial. Examination of possums for dye-marking showed that 25% of possums refused to eat either a lethal quantity of bait or any bait at all, compared with 98% of possums eating non-toxic bait. This indicated that 1080 is aversive to possums, which is a potential major reason for their surviving control operations. Pen trials were therefore conducted to further examine the problem and to seek solutions. Toxic carrot baits were rejected by 27.5% of possums, equally by smell and taste aversion, whereas toxic cereal pellets were rejected by 34%, mainly by taste aversion. Orange and cinnamon were shown to be among the most preferred of 42 flavours tested and, when applied to toxic baits, 1080 was effectively masked. Bait refusal was reduced to ≤7%, the same as that recorded for possums presented with flavoured non-toxic baits. For long-term control of possum populations, aerial 1080 baiting can be used sequentially with other poisoning methods. However, the compatibility of these methods is dependent on the likelihood of possums developing bait shyness if sublethally dosed. Studies were therefore conducted to characterise and compare the four main toxicants used (1080, cyanide, cholecalciferol and brodifacoum) for induction and mitigation of bait shyness. Shyness was induced in approximately 80% of possums sublethally dosed with cyanide, 60% with 1080, 20% with cholecalciferol, and 0% with brodifacoum. Cyanide and 1080 shyness were found to persist in many possums for at least 12 and 24 months, respectively. Use of alternative bait types, and of baits containing an alternative slow-acting toxin (brodifacoum) were shown to be effective ways of overcoming shyness. This, and other related research, is reviewed to provide operational specifications that maximise the likelihood that all targeted possums will (i) encounter bait, (ii) eat it, and (iii) die. The likely future use of aerial 1080 baiting is described and the technological, economic, environmental and social constraints on its sustainability are discussed. Finally, the uptake of the research by possum managers is considered, and areas identified in the thesis where information is incomplete are summarised as prioritised topics for further research.

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.

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.

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.

The principal use of sodium monofluoroacetate (1080) in New Zealand is to control brushtail possums (Trichosurus vulpecula). Aerial application of baits containing 1080 is the most common method used for large-scale control of possums. The use of 1080 attracts a great deal of controversy, in particular the effects on the environmental, non-target species, and the potential chronic effects in humans associated with environmental exposures. Although the nature of the acute toxicity of 1080 has been known for more than fifty years, little is known of its effects on humans, in particular its chronic effects to environmental exposures. A benchmark dose (BMD) as an alternative to a no-observed-adverse-effect-level (NOAEL) approach was investigated as a means to improve current health risk assessment values of 1080. Both approaches were investigated for three critical toxicological end points, namely cardiomyopathy, testicular toxicity and teratogenic effects identified from the few available critical studies. The calculated BMDs and lower-bound confidence limits (BMDLs) for the three end points were estimated using the Weibull, probit and quanntal linear models. A benchmark response (BMR) of 10% (extra risk) was chosen and the Akaike�s information criterion (AIC) was used in selecting the appropriate model. The BMDL estimates derived were generally slightly higher but comparable to the corresponding NOAEL for those same endpoints. The computed BMD₁₀ and BMDL₁₀ for cardiomyopathy and testicular effects were 0.21 mg kg⁻�bw⁻� and 0.10 mg kg⁻�bw⁻�, respectively. Tolerable Daily Intakes (TDIs) were derived using the NOAEL approach and the BMD methodology and applying an uncertainty factor of 3000. The resulting TDI using the BMDL were generally consistently slightly higher than those derived using the NOAEL approach. Based on the best fit of modelled dose-response data, a TDI of 0.03 [mu]g kg⁻�bw⁻�day⁻� is proposed for human health risk assessment. Two sets of Provisional Maximum Acceptable Values (PMAV) were derived using the highest concentration of 4.0 [mu]g L⁻� 1080 found in water (N=1450), and using the maximum allowable concentration of 2.0 [mu]g L⁻� of 1080 in water for adults (0.58 [mu]g L⁻� and 0.94 [mu]g L⁻�, respectively) and children (0.23 [mu]g L⁻� and 0.4 [mu]g L⁻�, respectively). Parameters used in the derivation of PMAVs were average weight, average quantity of water consumed, and proportion of total intake allocated to drinking water. The derived adult PMAV of 0.60 [mu]g L⁻� is proposed in revising the PMAV for 1080 in the Drinking Water Standards New Zealand. This value is 6-fold lower than the current PMAV of 3.5 [mu]g L⁻�. Additional toxicology studies are recommended to meet the definition of a "complete database" and therefore estimating a more defensible TDI, and consequently a PMAV for 1080. Risk management approaches are consistent with the Ministry of Health�s current precautionary approach. A PMAV of 0.60 [mu]gL⁻� in drinking water is recommended to consider it suitable for human consumption and that continuous monitoring be carried if the level of 1080 exceeds 50% of the proposed PMAV as a requirement for Priority 2 determinands in the Drinking Water Standards. Precautionary approach appears to be warranted and this was supported by information provided by the Public Health Units (PHU) where 1080 was permitted to be dropped onto drinking water catchments. The PHUs exercised precautionary measures by imposing appropriate conditions to suit local circumstances. As 1080 may likely remain an essential tool to contain tuberculosis spread by possums and to reduce possum damage to forests and crops until better methods of control are developed, a number of recommendations were proposed to protect public health.

In Experiment one 7 Brushtail possums were trained, using food, to perform a Delayed-Matching-To-Sample procedure using still and flickering light stimuli, over a 0, 1 and 2 second delay. A criterion of 80 percent correct for 5 consecutive days was set for the requirement to probe test. Probe session delays were 0, 0.5, 1, 2, 4, and 8 seconds. Performance was analysed using the measure of discrimination log d. Log d = 1 at the possums training delay and dropped back to log d = 0 at the longer inexperienced delays. The possums performance at this task was only adequate, so in case the stimuli were causing discrimination difficulties they were changed for the following experiment to horizontal and vertical light stimuli. Experiment two used the horizontal and vertical light stimuli to further test DMTS in possums. The possum's responding stayed at 50 percent correct, or chance, so the task was changed to a Simultaneous-Choice procedure. However, this did not have any effect on improving their results with responding accuracy remaining at 50 percent correct. Experiment three involved a conditional discrimination procedure, which was implemented to find out whether the possums could in fact discriminate between a horizontal and vertical light. All the possums in this experiment reached 80 percent correct overall and at responding to either a horizontal or vertical light. These results are enough to conclude that it was not the stimuli used in the previous two experiments which that had been causing the difficulties but the task itself. It is not known exactly why the possums were so unsuccessful in performing a DMTS or MTS task. More research into DMTS in possums in greatly needed and would offer a better understanding of the results of this study.

The decline in range and density of frugivorous birds worldwide could have consequences for the functioning of ecosystem processes such as seed dispersal. I endeavoured to determine the effects of bird declines on seed dispersal and assess the current status of dispersal in New Zealand. My first aim was to determine whether decreased bird density can reduce competitive interactions between birds, leading to birds concentrating on higher-reward fruit species. I measured fruit removal rates and fruit preferences of birds in Canterbury forest remnants with high (Hay and Prices) and low (Lords and Kaituna) bird densities. Removal rates of Melicytus ramiflorus and Coprosma spp. were lower at low-bird sites, and the size of this effect was greater for low-reward plant species. Coprosma areolata (a low-sugar fruit) had limited dispersal at Kaituna (59% fruit removed by end of 2012 season), compared with 92% removal at Hay, whereas 99-100% of M. ramiflorus and C. robusta (higher-sugar) fruits were removed at both sites. My second aim was to determine whether seed dispersal by introduced possums (Trichosurus vulpecula) can compensate for bird declines. I analysed seeds present in possum and bird faecal samples collected at Kowhai Bush, Kaikoura. Possums dispersed <3% of the total seeds, much less than bellbirds (21%), silvereyes (16%), song thrushes (33%) and blackbirds (28%). Possums also destroyed approximately 15% of seeds found in faeces, reduced the germination of gut-passed C. robusta seed to half of that from bird faeces (30% vs. 60-70%), and did not swallow fruits any larger than those moved by the much smaller birds (c. 7 mm diameter). My third aim was to determine the relationship between percentage of fruits dispersed and distance from parent tree for three large-seeded trees; Beilschmiedia tawa, Elaeocarpus dentatus, and Prumnopitys ferruginea. I fitted dispersal kernels to the observed dispersal distances out to 50 m for both undispersed whole fruits and seeds consumed by a bird, and found that dispersal quantity below the parent tree strongly underestimates total dispersal quantity. The average percentage dispersed overall was 81% for B. tawa, 75% for E. dentatus and 91% for P. ferruginea, and for all species finding only 11-18% clean seeds under the parent tree would correspond to an overall percent dispersed of at least 50% of the whole seed crop. My final aim was to determine the consequences of dispersal failure for recruitment in three plant species; Elaeocarpus hookerianus, Ripogonum scandens, and C. robusta. I compared the fate of dispersed and undispersed seeds in a manipulative field experiment. Exclusion of mammals plus removal of fruit pulp had the greatest effect on survival, while the combined effects of dispersal failure (under parent, high density, whole fruit) and inclusion of mammals decreased the number of live seedlings present at the final count by 75-92%. Overall, most native plants were receiving adequate dispersal and there was little evidence for strong risks to plant regeneration from dispersal failure, despite the reduced bird densities and ongoing negative effects of introduced mammals in New Zealand.

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.

Resource selection by the brushtail possum (Trichosurus vulpecula) was studied in a beech (Nothofagus) forest in order to elucidate possum ecology in an extensive forest type lacking extensive possum research. The study was conducted in the Upper Grey Valley, north Westland, on a post-glacial terrace dominated by Nothofagus fusca and Nothofagus menziesii and dissected by a gravel road. Five principal research questions were posed for the study of possums within the site. These were: 1. What are the movement parameters of the resident possum population? 2. What are the patterns of vegetation heterogeneity? 3. What constitutes possum diet? 4. What are the relationships between possum diet and vegetation heterogeneity? 5. What are the relationships between possum movements and vegetation heterogeneity? Twelve possums were radio-collared and radio-tracked over a year. Home ranges calculated with the kernel method averaged 8.1 ± 1.0 ha (mean ± s.e.), which is large when compared to possum home ranges observed in other continuously forested sites. Range lengths were similarly large (456 ± 42 m). Bi-monthly variation was only displayed with significantly smaller home ranges in winter when compared to autumn. Despite the fact that the study site was generally dominated by N fusca and N menziesii, considerable heterogeneity existed with respect to the possum palatable species within the site. Many palatable species such as Aristotelia serrata, Fuchsia excorticata, Muehlenbeckia australis and Trifolium repens occurred predominately along the roadside, whilst Weinmannia racemosa occurred predominately on steep areas within the forest. TWINSPAN classification of the forest identified three vegetation communities. These were open sites, including the road and swamp areas, steep areas, including the hill and escarpments, and terrace areas. Resource selection by possums within the site was investigated with diet preference analysis, habitat selection analysis and modelling of use of space versus resource variables. Diet preference was analysed by comparing the level of consumption of food types with their level of availability within the site at multiple scales. The top five ranked preferred food types, calculated overall, were, in decreasing rank, Fuchsia excorticata foliage, Carpodetus serratus fruit, Rubus cissoides foliage, Muehlenbeckia australis foliage and Pseudopanax colensoi fruit. Habitat selection analysis indicated that although overall selection was not occurring, possums exhibited a degree of preference towards the terrace community. Modelling of resource variables against use of space indicated that although there was latent variability between individual possums, there was a trend for greater use of areas with high abundance of preferred species. Modelling of pooled possum use of space on an annual scale indicated that use was positively correlated with species richness and negatively correlated with N fusca, Quintinia acutifolia, and Coprosma rotundifolia abundance, which are all unpreferred species. Annual home ranges of possums were found to be negatively correlated with forage quality as defined by preferred species. A model of possum resource selection within the site was postulated to the effect that possums choose their home range location randomly, with respect to vegetation heterogeneity, and then modify the size of their home range to suit nutritional needs rather than modifying range location. The ranging behaviour and resource selection of possums observed in this study have implications for the management of possums in similar forest types. Efficiency of control and monitoring operations may be increased by using a spacing regime derived from possum home ranges. Inferences obtained from habitat selection analysis indicate that stratification of control and monitoring operations is not warranted in similar forest types. The development of extensive models with predictive capabilities for the distribution of possums within the environment has the ability to become a useful tool for possum managers. Further research of potential benefit could include investigation into resource quality and availability, the effect of home range size on residual trap catch (RTC) indices, improving diet assessment techniques and assessing possum preference for non-foliar food types.

The impacts of possum herbivory were assessed on 713 individual plants of the nationally endangered Pittosporum patulum and 115 individual plants of the threatened ('Gradual Decline') mistletoes (Alepis flavida & Peraxilla tetrapetala) over three years in the Temple and Huxley river valleys in the Ohau catchment, South Island New Zealand. Statistical models were used to test the influence of several explanatory variables on the probability of survival and growth rates of these rare palatable plants. Increasing defoliation levels were the most significant predictors of mortality for both P. patulum and mistletoe, and reduced growth rates in P. patulum. Mortality of P. patulum increased with plant size although smaller plants were also affected by mortality. P. patulum mortality was greater for non-forest habitats, and growth rates were greatest on warm aspects. Mistletoe mortality increased with warm aspect, steeper slopes and at lower altitudes. Plant survival and growth increased in the Temple valley following possum control. Although indicative of a positive treatment effect, other factors may have also influenced this result. Possums are the major herbivore responsible for the widespread decline of P. patulum and beech forest mistletoes throughout New Zealand, although the autecology of P. patulum predisposes it toward extinction more so than mistletoe. Monitoring in conjunction with possum control operations provide good opportunities for understanding the impacts of possums on palatable plants and ecosystems. Assessing defoliation levels on indicator species like P. patulum and mistletoes can serve as a guide for managers to assess ecosystem stress from herbivory.

The eco-epidemiology of bovine tuberculosis (Tb) in wild deer (mainly red deer Cervus elaphus) in New Zealand was investigated. Bovine Tb is caused by Mycobacterium bovis. Specific aims were to clarify the likely routes of infection in deer, and to determine the status of deer as hosts of Tb, the likely rates and routes of inter- and intra-species transmission between deer and other wildlife hosts, the role of deer in spreading Tb, and the likely utility of deer as sentinels of Tb presence in wildlife. As the possum (Trichosurus vulpecula) is the main wildlife host of Tb, the research also included some investigation of transmission routes in possums. Patterns of infection were measured in 994 deer killed between 1993 and 2003. Tb prevalence varied between areas (range 8–36%). Few deer had generalised infection, with 21–68% of infected deer having no visible lesions, depending on the area. The retropharyngeal lymph nodes and oropharyngeal tonsils were commonly infected. No dependent fawns less than 0.75 years old were infected, indicating intra-species transmission is rare in wild deer. Where possums were not controlled, the net (cumulative) force of infection in young (1–4 y) deer was 0.10–0.24 per year in males and 0.09–0.12 per year in females, but much lower in older deer (less than 0.05 per year). Possum control reduced the net force of infection quickly, and eventually to zero. However, Tb persisted in possum-controlled areas through immigration of infected deer and, for almost a decade, through the survival of resident deer infected before possum control. Tb was lost from infected deer at an exponential rate of 0.13 per year, mostly as a result of deer recovering from infection rather than dying from it. Wild deer do die of Tb, but there was no discernible effect on age structure. The occurrence of infection in deer was not linked to the local deer or possum density at their kill sites (i.e. in their home range), but the area-wide prevalence of Tb in deer was closely correlated with Tb levels in possums, which were in turn correlated with area-wide measures of possum density. For wild deer in New Zealand, Tb is a persistent but usually inconsequential disease of the lymphatic system. It is acquired mainly by young independent deer, usually orally via the tonsils, and probably as a result of licking infected possums. Many species fed on deer carrion, including possums. Most possums encountering carrion did not feed on it, but a few fed for long periods. Other scavengers such ferrets (Mustela furo), hawks (Circus approximans), and weka (a hen-sized flightless native bird; Gallirallus australis) fed in a way that probably increased the infectivity of carrion to possums. Commercial deer hunting may have facilitated the historical establishment of Tb in possums. Scavenging (including cannibalism) and interactions with dead and dying possums are identified for the first time as potentially important routes for transmission of Tb to possums, and I develop new hypotheses involving peri- and post-mortem transmission in possums that explain many of the epidemiological patterns that are characteristic of the disease in possum. In continuous native forest, deer home range size averaged 250 hectares for six young females, and over twice that for two males. Over 90% of infected deer are likely to die within 2 km (females) or 6 km (males) of where they acquired Tb, but deer could occasionally carry Tb up to 30 km. Deer will be useful as sentinels, but only where other sentinels are rare, because the force of infection for a deer with a single infected possum in its home range is only 0.004 per year, compared to greater than 0.2 per year for deliberately released pigs. Deer are occasionally capable of initiating new cycles of infection in wildlife, but deer control is not essential to eradicate Tb from wildlife.

Despite extensive international acceptance of the critical role of mammalian post-dispersal seed predation in many plant communities, in New Zealand we have limited knowledge of these predators’ influence on plant recruitment in our forests. The principle objective of my thesis was to determine the importance of exotic mammals as post-dispersal seed predators in a New Zealand conifer-broadleaf forest remnant. To address this goal, I used a series of field-based experiments where the actions of different post-dispersal seed predators were separated by wire-mesh exclosures. My study was conducted at Mount Peel Forest Park Scenic Reserve, South Canterbury, New Zealand. Being a human modified conifer forest currently dominated by broadleaf species, it is typical of forest remnants in New Zealand. This presented an opportunity to study a wide range of both potential post-dispersal seed predators and broadleaf tree species. My findings indicate that exotic mammals are not only post-dispersal seed predators at Peel Forest, but are responsible for the majority of post-dispersal predation events observed. Ship rats (Rattus rattus) were the dominant post-dispersal seed predators, while brushtail possums (Trichosurus vulpecula), house mice (Mus musculus) and native invertebrates were also important post-dispersal seed predators for several tree species. Through use of time-lapse video and cafeteria experiments I found that exotic mammalian seed predators, when compared to native invertebrate seed predators, preyed upon larger-seeded plant species and were responsible for considerable seed losses of several tree species. However, exotic mammalian seed predators do share several foraging characteristics with native invertebrate seed predators, as predators foraged in similar habitats and responded in a similar way to changes in seed density. In investigating if post-dispersal seed predation by mammals had a flow-on effect to plant recruitment, I observed natural seedling densities at Peel Forest were significantly higher in the absence of mammalian seed predators, but I found no evidence that the presence of mammals significantly altered the overall species richness. At the community level, I did not find an interaction between habitat and exotic mammals, however I present evidence that for individual plant species a significant mammal : habitat interaction occurred. Consequently, even though my cafeteria experiment implied there was no significant difference in the overall amount of seed preyed upon within different habitats, the less favourable microsite conditions for germination under an intact continuous canopy allows mammals to exacerbate habitat-related patterns of seed mortality and have a noticeable effect on seedling establishment. In an effort to validate the use of manipulative experiments to predict the long-term effect of post-dispersal seed predation on plant dynamics, I attempted to link results of my cafeteria experiment with observed seedling abundance at Peel Forest. Seven tree species were used in this comparison and a strong correlation was observed. This result shows that the level of post-dispersal seed predation determined in the cafeteria experiment provided a good predictor of the effect of mammalian post-dispersal seed predation on seedling establishment. To fully gauge the impact of mammalian post-dispersal seed predators on seedling establishment, the relationship between these seed predators and the type of recruitment limitation experienced by a plant species was also investigated. By using a combination of seed addition, plot manipulations and seed predator exclusion I was able to investigate this relationship. I found evidence that seed limitation at Peel Forest is positively correlated with seed size, and that while mammalian post-dispersal seed predators can further reduce plant recruitment of plant species experiencing seed limitation, the influence of mammals in determining plant recruitment was limited for plant species experiencing microsite limitation. My study has proven that exotic mammals are now the dominant post-dispersal seed predators at Peel Forest, the amount of seed preyed upon varies among plant species, and post-dispersal seed predation by mammalian species can lead to differences in seedling richness and abundance. I proved that the influence of exotic mammals on seedling establishment is also linked to habitat structure and recruitment limitations. When combined these observations suggest that exotic mammalian post-dispersal seed predators may play an important role in determining landscape abundance and distribution of plants at Peel Forest.

Odour plays an important role in many predator/prey interactions. In the northern hemisphere, many mammalian prey species have been shown to respond to predator odours. It is also widely assumed that mammalian predators utilise odours to locate their prey. This thesis explores the importance of odour in Australian mammalian predator/prey interactions. Responses of native Australian species to the faecal odour of two predators; the native tiger quoll Dasyurus maculatus and the introduced red fox Vulpes vulpes, were evaluated through live-trapping and focussed behavioural studies of captive animals. Tiger quoll responses to prey olfactory cues were investigated in a captive experiment. Native rodents (bush rats Rattus fuscipes, swamp rats R. lutreolus and eastern chestnut mice Pseudomys gracilicaudatus) equally avoided traps scented with either quoll or fox faeces, and in captive experiments, bush rats and swamp rats reduced their average speed in response to both predator odours. Of the marsupial species, northern brown bandicoots Isoodon macrourus and common brushtail possums Trichosurus vulpecula were captured more frequently in quoll-scented traps than unscented traps or foxscented traps, while captures of brown antechinus Antechinus stuarttii, long-nosed bandicoots Perameles nasuta and southern brown bandicoot I. obesulus were unaffected by the either predator odour. In captive experiments, brown antechinus, long-nosed and northern brown bandicoots decreased their foraging in response to both predator odours, and spent less time in areas scented with quoll faeces. Tiger quolls didn't appear to detect odour sources from a distance of >65 cm, but they did follow scent trails and spent more time in areas scented with the urine and faeces of potential prey. Chemical analysis revealed no common components in fox and quoll odour which prey species could be responding to. Therefore, these native species have evolved to respond to fox odour since foxes were introduced to Australia 130 years ago. The stronger response of native rodents to fox odour may be a legacy of their co-evolution with canid predators prior to entering Australia. A better understanding of how odour is utilised in Australian predator/prey interactions may lead to a greater ability to protect Australia's unique mammalian fauna from introduced predators.

A study of the population dynamics of four hunted populations of the•Brushtail Possum Trichosurus vulpecula in Tasmania was carried out. Efforts by the management authority, the National Parks and Wildlife Service to monitor and census the species have been hampered by a lack •of suitable methods of population assessment. The principal aim of the study was to describe a methodology for timely monitoring of changes in local populations. •The approach taken was distinctive in that the collection of the sample and the analysis were carried out by separate parties. The analysis of the populations was made from material salvaged from commercial hunters in the course of their normal operations. This division of labour reduced the field time required to virtually zero. The material salvaged from the four populations has been used to.give reliable estimates of some population parameters including age structure, sex ratios, natality and recruitment rates. Predictions of the rate and direction of change in the populations were made on the basis of these estimates. The secondary age ratio was used as an estimate of the rate of recruit-ment. The effects of hunting could be seen in the high rates of recruit-ment in these as compared to unhunted populations. The secondary age ratio gave a measure of the intensity of hunting. Where the estimated production of juveniles was in excess of that needed to maintain the population, characteristics observed in unhunted populations were displayed. These were an age dependent survival between year classes for adults and an adult sex ratio near unity. For populations where the production of juveniles is insufficient to maintain the population these characteristics are altered. Hunting is unselective with respect to age and sex and when this is intense survival between age classes is approximately constant. Social factors mediate dispersal in juveniles so that the bulk of dispersing individuals Are male. A population dependent on immigration to maintain numbers thus tends to recruit males, depressing the proportion of adult females and thus the capacity of the population to produce young. An excess of adult males was found where the production of juveniles was not sufficient to maintain numbers. The status of the populations can be examined in some rletail," Differ-ences between populations are readily apparent and the effects of hunting can be gauged. The results are compatible with those from other studies of the species. The method of assessment allows estimates of changes to be made and provides an appropriate means to spot check the status of local populations of T. vulpecula.

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 marsupial brushtail possum (Trichosurus vulpecula) possess a glandular area of skin over its sternum known as the "sternal gland". This region of the integument is composed of two layers: a superficial layer of holocrine sebaceous tissue and a deeper layer of sudoriferous apocrine tissue. Secretions produced by the glandular tissue are rubbed on objects by the possum as a form of scent mark. The secretions are visible as an orange to brown coloured stain on the fur covering the sternum. The structure is found in both males and females. A review of the literature reveals that olfactory communication in the brushtail possum has been studied in some detail. In a variety of observational and experimental studies using captive and free-ranging animals information has been collected on the location and structure of scent glands, the chemical composition of secretions, the role of hormones, the range of scent marking behaviours, the response of conspecifics to odours and the possible function of odours. Despite the broad range of information already collected there are a number of aspects of olfactory communication in the brushtail possum that have not been explored in any detail, and there are many questions about the function of odours that remain unanswered. This study aims to continue the investigation of olfactory communication in the brushtail possum by focusing on the sternal gland and examining differences between the sexes. Three main areas are explored: • An examination of the histology and gross morphology of the sternal gland. • Development of a method of recording sternal gland scent marking under natural conditions. • Investigation of the use and possible function(s) of the sternal gland in the brushtail possum under natural conditions. The first part the study is a histological examination of the sternal integument carried out using tissue from 119 males and 52 female roadkill possums collected over a period of twelve months. Canonical variate analysis was used to look for differences across gender, maturity, season and reproductive status. The histological parameters were: total glandular tissue depth, depth and percentage of holocrine sebaceous tissue and apocrine sudoriferous tissue, holocrine sebaceous and apocrine sudoriferous nuclear diameter, and apocrine sudoriferous cell height and lumen diameter. Information was also collected on changes in the amount of staining of the sternal fur during the year using roadkill animals and animals trapped in the field. A range of differences in the histology of the sternal gland between and within the sexes, between mature and immature animals, and between groups of possums over different seasons was found. Development of the sternal gland is related to the onset of sexual maturity. The tissue of immature males and females is not significantly different, but mature animals have significantly greater tissue development than immature animals. Among sexually mature animals, males show a higher degree of tissue development, having greater glandular tissue depths and a higher percentage of each tissue type, than females. A number of significant seasonal differences in the histology of the sternal gland exist between the sexes and within each sex. The greatest differences between the sexes are seen during the breeding, post-breeding and dispersion periods and are related to differences in the behaviour and activity of each sex at these times. The differences were only observed in the total depth of the glandular tissue and in the holocrine sebaceous tissue parameters. Among mature males differences in sternal gland histology are closely related to the breeding season. During the breeding season and the time leading up to breeding holocrine sebaceous glandular tissue development and activity are at their greatest. These findings are correlated with a number of physiological and behavioural changes observed in male brushtail possums during the breeding period, including increased scent marking activity, an increase in the number of chemical compounds in the secretion, increased prostate size and an increase in testosterone level. Although most of the differences among males appear to be associated with changes in holocrine sebaceous tissue there is some evidence that sudoriferous apocrine tissue parameters show increased development during the period when young are dispersing. Among mature females seasonal differences in the size of the holocrine sebaceous nuclei were observed, with the greatest development occurring during the pre-breeding period, when females are carrying pouch young. No clear trends in sudoriferous apocrine tissue were apparent. Mature females were also examined with respect to their reproductive state. Although no significant differences were apparent, some variation in the glandular parameters is evident. Holocrine sebaceous tissue shows its greatest development in anoestrus females and its lowest development in oestrus individuals, and the depth of the sudoriferous apocrine tissue is greatest in oestrus females. The second part of the investigation is a two-year field study conducted to examine sternal gland scent marking in the brushtail possum. This task was made difficult by the nocturnal, cryptic and partly arboreal behaviour of the species. A range of techniques (including: acoustic biotelemetry, direct observation, radio tracking, and implantable transmitters) were trialed to find a suitable method for collecting information on scent marking under natural conditions. The advantages and disadvantages, the success and limitations of each technique are discussed. The method developed and used in this study involved a combination of spool-and-line tracking and application of fluorescent pigments to the sternal region. The combination of these methods has a number of advantages. The materials required are cheap and easy to construct, and they are easily attached and do not appear to affect the behaviour of the animal. It is possible to collect data without an observer being present at the time of the activity, which has the added advantage that the behaviour of the animal is not influenced by the presence of an observer. The technique allows data to be collected on more than one animal at a time and for information on the location and size of the scent mark to be determined. Spool-and-line tracking and fluorescent pigments were used to investigate the use and possible functions of the sternal gland scent marking in the brushtail possum. Data on the home range, use of dens, the spatial distribution of scent marks within the home range, the types of objects marked, and the timing of scent marking during the year was collected. Seasonal and gender differences were found. Males had larger home ranges than females. Although the home ranges of males and females overlapped, within each gender there was very little overlap of home ranges. Spool-and-line tracking revealed that individuals cover large areas of their home range during one night and that most of the area within a home range is used, although some areas are used more frequently than others. The majority of dens sites in this study were located off the ground. Dens were used in at least two different ways by possums. Dens found in hollow logs, close to the ground and in trees were often used during the night, in some cases to shelter from inclement weather. During the day den sites in trees were preferred by resting animals, with sites on the ground being used by sick or injured individuals. Between 8 to 12 den sites were recorded per individual, with dens being spread throughout the home range. Scent marking by brushtail possums was recorded on a variety of objects including, tree trunks, branches of shrubs, clumps of grasses, fallen logs, fallen sticks, branches and bark on the ground, pieces of wood, rocks and traps. Most marks were made on objects on the ground or close to the ground. There is no evidence of boundary marking of the home range by either sex. Some evidence of marking as a method of resource protection is evident. Maturity, gender and seasonal differences were found in sternal gland marking. No scent marking was observed in sexually immature individuals of either sex. Among mature individuals males were observed to mark more often with the sternal gland than females. The majority of the marks made by males were deposited on or within two metres of a tree or a trap. Females made most of their marks on objects on the ground and only a third were found on or close to trees or traps. The size of scent marks on trees did not differ between sexes, although marks on all other objects were generally larger in males than females. Males performed most marking in the dispersal, pre-breeding and early part of the breeding season. Once mating had occurred and during the time females had young in the pouch sternal scent marking among males was infrequent. Rates of marking in males correlated with changes in the degree of staining of the sternal fur. Among females sternal scent marking was highest when they had young in the pouch, with a lower level occurring during the dispersal phase and during the pre-breeding and breeding seasons in oestrus females. The level of sternal staining was lower during the period of greatest sternal marking in females. The results of the study indicate that although both male and female brushtail possums posses sternal glands there is significant sexual dimorphism in the gross morphology and histology of the sternal gland and in the deposition of secretions produced by the gland. Reasons for these differences are discussed by examining the possible functions of sternal gland odours and scent marking in the brushtail possum. Among males there are three distinct periods of sternal gland development and scent marking behaviour. The first occurs during the pre-breeding and breeding periods and is characterised by a higher level of holocrine sebaceous tissue development and scent marking. At this time an increase in scent marking may function to familiarise females with potential mates and/or to deter rival males. The second period in males occurs during postbreeding when females have young in the pouch and is characterised by a low level of gland development and marking behaviour. If the function of odours is to attract a female or deter a rival it is reasonable to expect that marking and gland development would decrease during a period when neither of these functions is operating. The third period corresponds with the dispersal of young and is characterised by greater development of sudoriferous aporcrine elements and an increase in scent marking. Although there is no evidence that scent marks are concentrated around home range boundaries, odours deposited at this time are most likely related to protection of resources such as den trees and feeding trees. The pattern of sternal gland development and scent marking in mature female possums is most likely related to the protection of resources. During the winter months when females are carrying pouch young an increase in marking may serve to protect trees required for shelter and food. In both sexes resource protection appears to be the major role for olfactory communication in the brushtail possum. The mechanisms of odour function, however, are more difficult to ascertain. Possible mechanisms of odour function through the establishment of dominance hierarchies among adjacent and overlapping individuals, through "scent matching" and "competitor assessment" by potential intruders and rivals, and through "confidence boosting" and "reassurance" of a resident individual are discussed.

I investigated the role of habitat in shaping mammalian evolution by studying the divergence of two parapatric subspecies, the common brushtail possum, Trichosurus vulpecula vulpecula, and the coppery brushtail possum, T.v.johnsonii, which are found in close proximity on the Atherton Tablelands in North Queensland, Australia. Their reputed distribution and colour differences, then unquantified, suggested that these subspecies may be candidates for evolution through parapatric speciation. This has never before been demonstrated in a mammal. I discovered that along a habitat gradient from dry sclerophyll forest and mosaic ecotone to rainforest, brushtail possums differed significantly in fur colour. The two morphs were characterised by their fur colour saturation: its colour intensity. Possums with low colour saturation were grey and did not inhabit rainforest. Those with high fur colour saturation were a red-copper colour and did not occur in dry sclerophyll forest. There was a dichotomy in the shade of red expressed among coppery brushtails, which was either a red-orange or redpurple hue, with the different rainforest localities of brushtails significantly associated with this variation. Brushtails in ecotone were either coppery or grey. Fur colour did not vary with distance from the ecotone, nor did fur colour appear to change once established in early development. Ecotone habitats supported very few possums, which may suggest some potential for the ecotone to restrict gene flow along the habitat gradient. The population density in rainforest was 18.6 times that in ecotone, and dry sclerophyll forest supported 8.7 times more brushtails than ecotone habitat. Coppery and grey brushtail possums were also morphologically distinct in body size. On average, coppery brushtails had ears that were 8mm shorter and 3.4mm thinner, legs that were 3.6mm shorter from knee to heel, and tails 34mm longer than grey brushtail possums of the Atherton Tablelands. There was no sexual dimorphism among brushtail possums along a habitat gradient for body size or colour, suggesting that sexual selection is unlikely to be acting upon these traits to promote divergence. Comparing mitochondrial DNA control region sequences I found that the morphological distribution was not the result of secondary contact between reciprocally monophyletic populations: coppery and grey possums have evolved together in multiple, distantly related clades. Analyses of the morphology of these clades demonstrated that variation in body-shape morphology was not associated with genetic similarity but with fur colour. As such, possums with the same fur colour also shared body size morphology, whether they were from genetically distant clades or if they were genetically similar. These differences, together with the bimodal distribution of morphs along habitat gradients, indirectly suggested that selection is acting upon these morphological traits to produce the phenotypes and distribution observed. Examination of the population structure of Atherton Tablelands brushtail possums using mitochondrial DNA control region sequences demonstrated that grouping populations by colour morphology did not explain genetic variation. Genetic differences between populations were not explained by the latitudinal, longitudinal, straight-line or elevation distances between them. However 30.1% of variation could be explained through the identification and separate grouping of the four populations that were closest to rainforest habitat. Along a habitat gradient, grey and coppery populations were distinct. Investigation of population structure with microsatellite loci showed significant gene flow throughout the Tablelands. Along the habitat gradient, adjacent coppery and grey populations were genetically distinct despite this widespread gene flow. Indeed several geographically more distant populations were not distinct with these markers. This suggested that gene flow is restricted along the habitat gradient. However reproductive isolation was not complete: calculations revealed that gene are exchanged in both directions along the gradient. Both grey and coppery brushtail possums reproduced synchronously, suggesting that there was no temporal discontinuity to gene flow. However this reproductive synchronicity may limit the potential for polygyny. With selection acting on morphology and gene flow restricted along a habitat gradient, two possums separated by the same geographic distance should be less related if they are different morphs than if they are the same colour. However, while the pairwise relatedness between different brushtail colour morphs was significantly different to those among coppery brushtails, there was no difference to comparisons among greys. This may be a consequence of the higher population densities of coppery brushtails; relatives may possess smaller home ranges and be closer. However these genetic results did not match our theoretical expectations: possums of different colour morphs and habitats were not less related than possums of the same morph at the same distance of separation. My underlying assumption was that fur colour in the coppery brushtail possum, like so many other species, is a genetically determined trait. If true, then brushtail colour is inherited and determined via an unprecedented mechanism. While this can not be discounted, I questioned my underlying assumption. Fur colour can also be phenotypically plastic. Climate and diet can determine fur colour, though usually only temporarily. Fur colour did not appear to change once established in early development. The presence and fine-scale distribution of coppery and grey brushtails in rainforest fragments suggested that climatic effects are highly unlikely to be determining fur colour. There has been one previous demonstration of diet permanently determining fur colour via maternal diet acting in utero in laboratory mice. I found that determination of brushtail fur colour by maternal diet and selection upon this trait better explains the observed morphological distribution and genetic structure. Further experimental research is needed to conclusively demonstrate this effect, to explore how widespread this capacity for coppery brushtail colour is, and to discover which foods are involved in fur colour expression. Such an congenital change would be highly significant in evolutionary research as it allows, without mutation, the widespread single generation adaptation of offspring to the environmental conditions experienced by the parent.

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.