Bachelor of Science (Honours)
School of Earth, Atmospheric and Life Sciences
Mulley, Brooke Phillipa, Viability of an Endangered Population of Greater Gliders, Bachelor of Science (Honours), School of Earth, Atmospheric and Life Sciences, University of Wollongong, 2022.
Greater gliders are experiencing widespread decline across their distribution. They are obligate cavity dependent folivores with poor thermotolerance and high susceptibility to fragmentation and fire. These characteristics put greater gliders at high risk of further decline and extinction. Conservation of all populations are crucial to the species’ persistence. One of these populations of greater gliders is found at Seven Mile Beach National Park (SMBNP), on the South Coast of New South Wales. This population is heavily isolated and is known to occur at low densities, which has resulted in their state listing as an endangered population. The viability of this population is currently unknown. Therefore, the aim of this thesis was to evaluate the status and viability of the SMBNP population of greater gliders to inform targeted conservation management strategies. A tool used to guide the conversation of native fauna is population viability analysis. However, the quality of a population viability analysis model is influenced by the accuracy of input parameters, particularly initial population size. The first part of this thesis was a study on the use of double observer distance sampling method, as it has been recommended as the most robust method for estimating greater glider population size. Thus, this methodology was first used to generate a more accurate population estimate of greater gliders compared to a past strip transect survey conducted in 2019. This thesis then also investigated the effectiveness of double observer distance sampling to guide future population viability modelling. Population estimates using the double observer method found 347 greater gliders at SMBNP at a density of 0.46 gliders per ha. This equated to 0.05 more gliders per ha than previous estimates. We also found that key assumptions would be violated if strip transects, or single observer distance sampling were to be used. Therefore, these results reinforced double observer distance sampling as the most appropriate survey method for greater gliders. Additionally, this study investigated the effect of number of repeats on the calculated density by creating precision 4 estimates for different combinations of transect repeats. Precision increased with number of transect repeats, indicating double observer distance sampling could benefit from repeated visits of transects. While this study found more gliders than previously estimated, this population still exists at low densities. Following this, the second part of this thesis used the calculated double observer distance sampling estimate as the input data for population viability modelling using VORTEX. Additional parameters were incorporated into the model, where parameters on species reproduction and life history (i.e. mating system and mortality rates) were sourced from literature and known effective population size was sourced from previous field data. Using these parameters, the SMBNP population trajectory could be modelled. Population viability analysis modelling found that the greater glider population had poor viability and high extinction risk, exhibting minimal chance (1%) of persistence for the next fifty years. Sensitivity testing was then conducted to investigate which threatening processes have the largest effect on population viability. This was done by examining the effect of systematic perturbation of base assumption on extinction parameters. It was found that fire caused the greatest negative impact on extinction parameters, consistent with other publications suggesting populations suffer significant decline after severe fire. Given the isolation of the population and the predicted changes in climate, it was found that wildfires were the biggest identified threat to the population. Low effective population size and inbreeding effects were ranked as second most important factors that could impact extinction outcomes for the population. This is due to the current isolation of SMBNP increasing the risk of these factors. Thus, this study reinforces the need to continue with the creation of an effective wildlife corridor to reconnect SMBNP with the Illawarra escarpment. As the current wildlife corridor (the Berry Bush Links project) is unlikely to facilitate greater gliders, nor be functional for up to 100 years, the population will need short-term management strategies to increase its chance 5 of persistence until this time. The relative effectiveness of management strategies was evaluated by modelling the effect of different amounts of nest box placement and reinforcement (population supplementation) on extinction parameters under likely catastrophe scenarios (heatwave, fire and altered regime). The management strategy with the highest relative effectiveness over three likely catastrophe scenarios is an ongoing reinforcement program to boost effective population size combined with the placement of 50 nest boxes to assist with hollow supplementation. Thus, this study recommends nest box placement at Seven Mile Beach National Park and further investigation into the feasibility of a long-term translocation program.
FoR codes (2020)
410203 Ecosystem function, 410407 Wildlife and habitat management, 410401 Conservation and biodiversity
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.