Thesis
Factors that influence the persistence and decline of threatened small macropods: An ecological investigation at multiple spatial scales (Citation and Abstract only)
Southern Cross University, School of Environment Science and Engineering
Doctor of Philosophy (PhD), Southern Cross University
2020
DOI:
https://doi.org/10.25918/thesis.496
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Abstract
Ecological inquiry at multiple spatial scales enables us to discern factors that promote persistence of species and also, the presence or absence of threatening processes, all of which have implications for threatened species conservation and management. In this thesis, I discuss mammal extinctions in Australia and place such events within a global context. It is apparent that mesic high rainfall and forested ecosystems in south-east Australia provide refugia for several threatened small macropod species where congener species have dramatically declined and become extinct in arid and semi-arid regions of Australia. Multiple spatial resolutions offer opportunities to examine how large-scale landscape factors and fine-scale habitat factors influence threatened small macropods, their predators and allows us to investigate how predator prey interactions may be mediated by such factors. Mesic ecosystems display large variation in factors that promote persistence of threatened species including ecosystem productivity, landscape connectivity and habitat structural complexity. Likewise, threatening processes such as introduced predators, deforestation/ cleared vegetation and altered elements of the fire regime are heterogeneous over large spatial scales. These factors form a theme of enquiry in this thesis.
The research in this thesis commences in Chapter 2, which was conducted over a large spatial scale (~1500 km) in eastern Australia. I examine how landscape factors such as rainfall, elevation, fire frequency, vegetation type and landscape clearing influence the endemic mammal assemblage and introduced predators in south-east Australia. I also examine the spatial and temporal associations between predators and the endemic mammal assemblage. I employed three overarching hypotheses to help explain the occupancy of target species: i) a physical environment hypothesis, ii) a disturbance hypothesis and iii) the mesopredator release hypothesis.
I found that i) rainfall was a strong driver of mammal occupancy with a general trend being that small macropods were positively influenced by increasing rainfall and large macropods and the red fox (Vulpes vulpes) were negatively influenced by increasing rainfall. In addition, the feral cat (Felis catus) was positively influenced by elevation. ii) I found that the long-nosed potoroo (Potorous tridactylus) and the red-necked pademelon (Thylogale thetis) were negatively influenced by fire frequency, the red-necked pademelon (Thylogale stigmatica) was also negatively influenced by vegetation clearing and the red fox and feral cat (Felis catus) were positively influenced by factors associated with vegetation clearing and habitat fragmentation. iii) Support for the mesopredator release hypothesis was equivocal. However, I found no evidence of mesopredator suppression with both the occupancy of the red fox and feral cat being high and dingo (Canis familiaris) occupancy being low across the eastern portion of the state of New South Wales (NSW). In addition, I found a negative temporal relationship between the red fox and the dingo. In Chapter 2, I conclude that the high rainfall regions of north-east NSW provide important refugia for threatened small macropods due to supportive environmental factors (productivity and habitat structure) and the relatively low occupancy of the red fox. I also conclude that careful consideration of fire regimes will be an important component for the conservation of species such as the long-nosed potoroo. The threat of the feral cat in high elevation reserves was a novel finding and this too will need further consideration for threatened species conservation within such reserves.
Chapter 3 was conducted at the bioregional scale, across nine high-rainfall conservation reserves in sub-tropical north-east NSW. In this chapter, I employed the landscape of fear hypothesis to help explain fine scale habitat preferences for threatened macropods. I also examined co-occurrence patterns between predators and prey species. I predicted that habitat selection for the long-nosed potoroo and red-legged pademelon would reflect risky verses safe areas by account of the presence and ubiquity of predators within the ecosystem. A key result of Chapter 3 was that despite suitable habitat being found across the nine conservation reserves, the long-nosed-potoroo was distributed through just five reserves with their stronghold of high occupancy in the Border Ranges National Park (NP) and the red-legged pademelon maintained a high occupancy in Richmond Range NP. The red fox was near to absent which was congruent with the findings of an inverse relationship between annual rainfall and red fox occupancy in Chapter 2. The feral cat had a very high occupancy in the Border Ranges (a high elevation rainforest reserve) which was also congruent with my findings in Chapter 2.
In alignment with my predictions, the potoroo was strongly influenced by dense ground layer habitat and the red-legged pademelon preferred open areas of understory habitat that I presume aids rapid bounding to escape predation. I suspect these micro-habitat preferences provide these species with optimal opportunities to avoid predators via either concealment or open areas to move through when predators approach. I found a positive site-based interaction between the dingo and the long-nosed potoroo which was highest in areas of open ground cover. Given the findings that the potoroo preferred dense ground cover and the dingo preferred open ground cover, this result suggests that open areas of ground level habitat provide dingoes with opportunities to exploit potoroos, however, dietary studies from the conservation reserves examined in this chapter have not identified the potoroo as a dingo prey species to date. My results from Chapter 3 demonstrate that complex mesic habitats are important refugia for the threatened long-nosed potoroo and red-legged pademelon. These findings proceeded to guide the survey design of Chapter 4.
The aim of Chapter 4 was to conduct baseline monitoring of the long-nosed potoroo and red- legged pademelon populations in Border Ranges NP and Richmond Range NP and to conduct power analyses to determine the optimal number of detection sites and survey nights to be able to detect a population decline of a given magnitude with the power of a given certainty in future sampling. Border Ranges NP and Richmond Range NP were selected for this study because these reserves conserve populations of long-nosed potoroo and red-legged pademelon in relatively higher abundance when compared to other reserves in the bioregion (Chapter 3). In this study, I established a large number of detection sites with seasonal replication of monitoring periods to capture temporal and spatial heterogeneity across the sites. Without considering spatial heterogeneity in habitat preference and seasonal fluctuations in detection, such baseline data may contain biases. Without considering these factors, baselines may not reflect ecological realities, resulting in inaccurate population estimates and ultimately, poor conservation outcomes.
The results of Chapter 4 revealed seasonal differences in the detection of the long-nosed potoroo and red-legged pademelon. Long-nosed potoroos had the highest detection in winter compared to all other seasons and the red-legged pademelon had low detection during summer compared to all other seasons. These findings have implications for the most important seasons in which to conduct future monitoring of these species. In Chapter 4, power analyses suggested that a survey design that implements 120 camera trap locations across both reserves, surveyed for 8 weeks during winter would yield 90% power to detect a decline of 0.5 for both macropod species. The development of this prescribed survey design, underpinned by robust baseline data, will enable accurate population monitoring of these threatened macropod species.
In Chapter 5, I implemented a before-after control-impact experiment to examine the short- term response of the long-nosed potoroo, red-legged pademelon and their predators to small scale prescribed burns. I hypothesised that predator activity would increase following the implementation of prescribed burns and small macropods would decrease in activity. I found that long-nosed potoroo, red-legged pademelon and dingo activity remained unchanged following prescribed burns despite reductions in shrub and ground layer vegetation, which refuted my hypotheses. Although the feral cat and red fox were present, their activity was negligible. I attribute the lack of change in activity of small macropods to the small and patchy nature of the prescribed burns which allowed for fine scale refugia and also the very low density of foxes at my study sites. I conclude that the impacts faced by small macropods in temperate regions of Australia following prescribed burns and wildfires, where fox densities are high, may not be generalised to high rainfall mesic habitats of subtropical Australia where fox densities are low.
The threatened small macropods of south-eastern Australia ultimately persist due to the environmental qualities afforded by high rainfall and structurally complex habitats within protected conservation areas. Heterogeneity in the distribution of the red fox has also allowed threatened small macropods to persist where fox numbers are low. In arid and semi-arid regions of Australia, small macropods are reliant on feral free enclosures to ‘rewild’ populations and such enclosures have been proposed for mesic eastern Australia however we must continue to understand the best ways to menage and conserve wild populations of threatened small macropods. This thesis has demonstrated the importance of the factors associated with high rainfall mesic ecosystems in providing refugia for threatened small macropods. However, these factors alone may not provide a panacea to long-term trends of range contractions and declines. Small macropods have persisted within remaining refugia through historic large scale land clearing, the demands placed on them from changing environmental conditions, the pressures placed on them from changed fire regimes and the introduction of novel predators. All factors of which are a legacy of anthropogenic influences which must be managed for the conservation of these species.
Details
- Title
- Factors that influence the persistence and decline of threatened small macropods: An ecological investigation at multiple spatial scales (Citation and Abstract only)
- Creators
- Darren McHugh
- Contributors
- Ross Goldingay (Supervisor) - Southern Cross UniversityMike Letnic (Supervisor) - University of New South WalesDavid A Newell (Advisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University, School of Environment Science and Engineering
- Number of pages
- 163
- Identifiers
- 991013291354802368
- Copyright
- © Darren McHugh 2020
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis