The Western Ringtail Possum (Pseudocheirus Occidentalis)
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A major road and an artificial waterway are barriers to the rapidly declining western ringtail possum, Pseudocheirus occidentalis Kaori Yokochi BSc. (Hons.) This thesis is presented for the degree of Doctor of Philosophy of The University of Western Australia School of Animal Biology Faculty of Science October 2015 Abstract Roads are known to pose negative impacts on wildlife by causing direct mortality, habitat destruction and habitat fragmentation. Other kinds of artificial linear structures, such as railways, powerline corridors and artificial waterways, have the potential to cause similar negative impacts. However, their impacts have been rarely studied, especially on arboreal species even though these animals are thought to be highly vulnerable to the effects of habitat fragmentation due to their fidelity to canopies. In this thesis, I studied the effects of a major road and an artificial waterway on movements and genetics of an endangered arboreal species, the western ringtail possum (Pseudocheirus occidentalis). Despite their endangered status and recent dramatic decline, not a lot is known about this species mainly because of the difficulties in capturing them. Using a specially designed dart gun, I captured and radio tracked possums over three consecutive years to study their movement and survival along Caves Road and an artificial waterway near Busselton, Western Australia. I studied the home ranges, dispersal pattern, genetic diversity and survival, and performed population viability analyses on a population with one of the highest known densities of P. occidentalis. I also carried out simulations to investigate the consequences of removing the main causes of mortality in radio collared adults, fox predation and road mortality, in order to identify effective management options. A rope bridge was built to provide this species with a safe passage across Caves Road in July 2013, and I present the results from 270 days of monitoring of the rope bridge and factors influencing the numbers of crossings. No radio collared possums crossed the road successfully during my study, while two were killed on the road. No collared possums crossed the waterway, except for one accidentally falling into the waterway during a severe storm. None of the home ranges included the road or waterway, suggesting that they both act as physical barriers for possums. Even a 5 m wide firebreak was enough to limit the movements of some possums where canopy connection was not available. Individuals in partially cleared campsites mostly remained within groups of trees with continuous canopy connections. Home ranges were small (males: 0.31 ± 0.044 ha, females: 0.16 ± 0.017 ha), and their sizes were affected by sex and proximity to the waterway. These results highlight the exceptionally sedentary and arboreal nature of this species. i I used 12 species-specific microsatellite DNA loci to investigate the fine-scale spatial genetic structure and the effects of a road and an artificial waterway on the population of P. occidentalis. Spatial autocorrelation analyses identified positive genetic structure over distances up to 600 m in continuous habitat. The artificial waterway was associated with significant genetic divergence, while no significant genetic divergence was detected across the road. However, this increasingly busy road may cause future divergence, and road mortality can still contribute to loss of genetic diversity. Therefore, providing safe passages to reconnect habitat is suggested to maximise genetic diversity and prevent isolation of subpopulations. Predation by red foxes (Vulpes vulpes) was the most common cause of mortality in adult radio collared possums contributing to 70 % of all confirmed mortalities. Road mortality also contributed to about 10 % of mortalities. A population viability analysis revealed that the probability of this important population going extinct in 20 years was alarmingly high (P = 0.921 with 95 % lower confidence interval of 0.903 and upper confidence interval of 0.937 ). Removal of the effects of road mortality and fox predation on adult and pouch young survival rates dramatically reduced the extinction probability (P = 0.318 without road mortality and P = 0. 004 without fox predation), indicating that reducing both road mortality and fox predation is essential to ensure the survival of this important population. We monitored the rope bridge using motion sensor cameras and microchip readers for 270 days. Western ringtail possums started crossing the bridge 36 days after its installation, which was remarkably sooner than expected or previously reported. It took other possums and glider species in the eastern states of Australia seven to 17 months to start crossing rope bridges across roads. After a period of habituation, multiple individuals were found crossing the bridge every night at a rate of 8.87 0.59 complete crossings per night, which was at least double of those reported on bridges built in eastern Australia. The number of crossings increased over time and decreased on windy or warm nights. Brightness of the moon also slightly reduced the crossings by the possums. Longer monitoring and genetic analyses to test whether crossings result in gene flow are necessary to assess the true conservation value of this bridge. However, these early monitoring results suggest that rope bridges have the potential to be safe crossing structures for this species. ii This study provides an example of an artificial linear structure other than a road having similar or even greater impacts on wildlife than a road. It therefore highlights the need for more research into the impacts of artificial structures such as waterways. The population of P. occidentalis I studied has a high probability of extinction in the near future and more effective management strategies, especially against the effects of fox predation and road mortality, are urgently needed in order to ensure its survival. iii Table of contents Abstract ………………………………………………………………………...……… i Acknowledgement ………………………………......………………………………. .. vi Declaration and publications ……………………………………………..………... viii 1. General introduction……………………………….……………………………. .... 1 1.1. Impacts of artificial linear structures ………………………...…….……….… 2 1.1.1. Impacts of roads ……………………………………………………….. 2 1.1.1.1. Habitat alteration, degradation and destruction .............................................. 2 1.1.1.2. Direct mortality ............................................................................................... 3 1.1.1.3. Habitat fragmentation ..................................................................................... 5 1.1.2. Impacts of artificial linear structures other than roads .............................. 7 1.2. Mitigation measures ............................................................................................. 8 1.2.1. Common measures ..................................................................................... 8 1.2.2. Wildlife crossing structures ....................................................................... 9 1.3. The western ringtail possum .............................................................................. 11 1.3.1. Biology and ecology ................................................................................ 11 1.3.2. Decline and management ......................................................................... 12 1.3.3. Locke Nature Reserve and surrounding campsites .................................. 14 1.4. Gaps in the knowledge ....................................................................................... 16 1.5. Research aims .................................................................................................... 17 1.6. Structure of the thesis ......................................................................................... 18 1.7. References .......................................................................................................... 19 2. An artificial waterway and a road restrict movements and alter home ranges of the western ringtail possum ................................................................................... 33 Abstract ..................................................................................................................... 34 Introduction ............................................................................................................... 35 Materials and methods .............................................................................................. 36 Results ....................................................................................................................... 44 Discussion ................................................................................................................. 49 References ................................................................................................................. 55 Supplementary results ....………………………………………………………........62 iv 3. The western ringtail possum shows fine-scale population structure and limited gene flow across an artificial waterway ................................................................ 63 Abstract ..................................................................................................................... 64 Introduction ............................................................................................................... 65 Materials and methods .............................................................................................