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(2023)ThesisConservation translocations are becoming an increasingly necessary tool to stem the decline of threatened species globally. The greater bilby (Macrotis lagotis) is a nationally threatened species in Australia. While bilby translocations are expected to contribute to the species’ persistence, the scarcity of information on their behaviour and ecology prevents informed-management. By intensively studying a population of bilbies both prior to, and following reintroduction, and subsequent reinforcements to a fenced sanctuary, I aimed to (1) advance knowledge of bilby behaviour and examine behaviours potentially relevant to fitness (i.e. survival and breeding success), (2) improve ecological knowledge of bilbies within understudied (temperate) climates, and (3) use this knowledge to suggest and develop effective tools for their conservation. Chapter 1 describes the current state of research in applied conservation research, and how increased behavioural data could help address some of the current knowledge gaps for bilby conservation. In Chapter 2, I examined patterns in bilby resource selection, finding that selection changed between seasons and years due to the environmental conditions and resources available. I also found that resource requirements are likely to be behavioural-state dependent and sex-specific. In Chapter 3, I constructed social networks to examine nocturnal proximity of bilbies and concurrent burrow sharing and found that associations were non-random. Expanding on this, in Chapter 4, I found that burrow sharing was likely to help describe breeding strategies, as males strongly avoided other males, and mixed-sex dyads exhibited kin-avoidance when mate choice was more limited. In Chapter 5, I developed a test to screen personality traits in bilbies, finding links between male response to handling and relative breeding success post-release. Lastly, in Chapter 6, I described a method to collect detailed movement data on the bilby, and discussed some of the practical and animal welfare constraints for its application. My thesis provides new insights into the behavioural ecology of the bilby with potential implications for future management of the species. With further translocations necessary for long-term persistence of the bilby, this research is highly relevant to current and future management of this ecologically important species, with potential applications to other similarly at-risk species.
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(2023)ThesisRising atmospheric CO2 concentration is one of the major drivers of climate change. To provide effective mitigation policies to curb these emissions, a thorough understanding of past changes in the carbon cycle is required. Decades of research on understanding carbon cycle changes during the last glacial cycle have put forward several processes impacting the concentration of atmospheric CO2. One of these processes is changes in aeolian iron flux into the Southern Ocean. Marine plankton fix dissolved inorganic carbon (DIC) during photosynthesis and transfer the fixed carbon to the deep ocean. DIC removal from the surface lowers the surface ocean partial pressure of CO2, which leads to carbon drawdown from the atmosphere. As the Southern Ocean is a high-nutrient-low-chlorophyll region, the increase in iron input can impact Southern Ocean marine ecosystems, by increasing export production, and therefore decreasing surface DIC. This thesis aims to investigate the responses of Southern Ocean marine ecosystems to changes in iron flux, and their impact on ocean biogeochemistry and atmospheric CO2 during the last glacial period. For this, I use a recently developed complex ecosystem model, which includes four different classes of phytoplankton functional types. Chapter 2 of this thesis is the first study to use this complex ecosystem model and document the competitive dynamics between different plankton species for light and nutrient availability under Last Glacial Maximum (LGM) climate boundary conditions (∼21 thousand years ago, 21 ka). Chapter 2 further assesses the impact of enhanced aeolian iron input on ecosystems. This study shows that lower sea surface temperatures and greater sea ice cover during the LGM causes a 2.4% reduction in Southern Ocean export production. However, a 78% increase in iron supply with a weaker ventilation in the Weddell Sea, increases diatoms and coccolithophores in the Southern Ocean, leading to a 4.4% higher carbon export at the LGM compared to pre-industrial (PI). Proxy records indicate a ∼32 ppm decrease in CO2 around ∼70 ka. Previous modelling studies have indicated a possible decline of 5 to 28 ppm in atmospheric CO2 driven by enhanced iron fertilization under PI and LGM boundary conditions. I constrain this contribution in chapter 3, by performing a series of sensitivity experiments under 70 ka climate boundary conditions taking into account the uncertainty associated with iron solubility in the ocean. I find that the CO2 change follows an exponential decay relationship with increasing iron flux due to saturation of biological pump at high iron values. Based on this, I suggest that enhanced iron input at 70 ka most likely led to a 9 to 11 ppm CO2 decrease with a maximum decrease of 21 ppm. Iron fertilisation could thus provide a 28 to 34% contribution to the total observed CO2 decline at 70 ka. Finally, in chapter 4, I include a unique approach to understand the processes leading to the abrupt 15 to 20 ppm increase in atmospheric CO2 during Heinrich Stadials, which are associated with a near collapse of the Atlantic Meridional Overturning Circulation (AMOC), a sudden decrease in Greenland temperature and warming in the Southern Ocean. Previous modelling studies have investigated the role of the ocean circulation in driving changes in atmospheric CO2 concentration during these abrupt events, while the role of reduced aeolian iron input during Heinrich stadials remained poorly constrained. I find that reduced iron fertilization combined with an AMOC shutdown could lead to a 7 ppm CO2 increase, 6 ppm of which is due to iron fertilisation. The research presented in this thesis improves our understanding of the impact of iron fertilization on Southern Ocean ecosystems, and on the global carbon cycle, particularly in the context of the last glacial period. This work also elucidates the importance of including changes in iron input to the ocean when investigating changes in atmospheric CO2 during abrupt climate change.
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(2023)ThesisBiodiversity loss is occurring globally with intensifying human-driven land-use change. Effective conservation planning with increasing anthropogenic pressure requires knowledge of: (1) species’ responses to habitat modification, including their ability to persist in, and their relative susceptibility to, human modified environments, and (2) species’ traits that facilitate persistence in these landscapes. This information is critical for predicting extinction risk and mitigating species declines. As one of the most threatened yet understudied vertebrate taxa, amphibians are promising candidates to broaden understanding of biodiversity responses to habitat change and identify conservation options. This thesis examines species’ responses to anthropogenic habitat modification and explores how species’ ecology, behaviour and life history may influence persistence in these environments, with a focus on frogs. I use a multi-scale approach, combining taxonomically broad analyses of citizen science data (landscape scale) with targeted species-specific fieldwork (local and regional scale). Chapter 1 reviews current knowledge of species’ responses to habitat modification, highlights research priorities and outlines my research approach. Chapter 2 integrates continental citizen science data with a global human modification index to quantify frog species’ tolerance of habitat modification and to identify broad trait-based associations. Chapter 3 uses this data to assess if and how habitat modification influences frog breeding phenology and call acoustics. Chapter 4 explores underexamined genetic threats to species in modified landscapes, with evidence from two sympatric frog species, the threatened Booroolong frog (Litoria booroolongensis) and the non-declining eastern stony creek frog (L. wilcoxii). Chapter 5 considers how species’ behaviours may influence vulnerability to habitat modification, drawing on movement and habitat use data gained from radiotracking these two species. Chapter 6 synthesises these findings, discusses implications for conservation management and outlines future research avenues. Overall, this thesis offers insight into why some species persist whilst others decline in modified landscapes, and the capacity of frogs to cope with habitat modification. I show how integrating big data with field studies can improve knowledge of species’ traits and species-environment relationships at multiple scales, with broad conservation implications.
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(2023)ThesisThe Tasmanian devil is one of few mammalian species to have developed physiological and behavioural specialisations for scavenging. Yet until recently, the devil has largely been omitted from scavenger theory. In this thesis, I propose the devil as a model for studying the foraging behaviour of a scavenger unencumbered by the pressures of surviving within a large predator community. I utilised analysis of nitrogen (δ15N) and carbon (δ13C) stable isotopes in devil whiskers and the tissue of potential food items, allowing evaluation of individual diet composition that is more precise and on a longer timescale than has been previously feasible. I firstly tested whether devils were capable of dietary specialisation, finding that the majority of individuals fed within a narrow dietary niche, despite feeding broadly as a population. I then investigated the factors that may drive this specialisation and found that generalist feeding behaviour only occurred among small devils in highly competitive populations. Next, I characterised the dietary composition of devils across a habitat gradient of human influence from cleared pasture to undisturbed rainforest. I found that populations in areas of greater disturbance showed restricted dietary niches, suggesting that all individuals fed on similar food items, even within native forest regenerated after clearfell logging. Old-growth rainforest populations had comparatively diverse diets, showing evidence of niche partitioning by body size. Finally, I looked at how devil diets varied between four seasons which may differ in resource availability, nutritional requirements, and population dynamics. I found that the population dietary niche of devils remains relatively stable year-round. The only seasonal shift in diet was a marginal difference in nitrogen isotope values between summer and winter in rainforest populations, suggesting that devils are highly resistant to natural environmental pressures. My research indicates that mammalian scavengers may have specialised diets and even scavenge more frequently in the absence of competition for resources. Anthropogenic disturbance likely contributes to this, providing greater access to high-quality carrion and removing potential competitors. However, dietary niches that are limited to large, human-supplied carcasses could indicate the elimination of smaller food resources and the alteration of foraging behaviours. They could also lead to an increase in interactions between individuals all feeding on the same food items, something of particular concern for an endangered species threatened by the transmission of a deadly infectious cancer.
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(2023)ThesisTracking global changes in biodiversity requires an enormous amount of data across both time and space. The increasing popularity of citizen science projects, driven in part by mobile device applications, can help provide that data in ways that have been historically impossible with commissioned scientific studies. With an ability to sample over a large area simultaneously, data from citizen science projects provide an excellent opportunity to study spatio-temporal patterns in nature with potentially low centralized cost. For example, accurate information on the drivers of phenology (the timing of biological events such as reproduction) is critical to inform conservation measures and priorities, such as well-timed, cost-effective population monitoring. The overall aim of this research is to advance the use of biodiversity citizen science data for ecology and conservation, using frogs as an exemplar taxonomic group. I investigate how citizen science can answer essential questions about biodiversity, and what motivates participants to collect biodiversity data. Specifically, I use citizen science data to (1) understand the meteorological determinants of frog calling behaviour, (2) quantify core calling periods and likelihood of detection for Australian frogs, and (3) assess ecological correlates of frog co-occurrence patterns. I complement this biodiversity-focused research with a social science approach by (4) surveying citizen science participants to understand how their motivations and behaviour relate to their data collection. I found that day-of-year was a strong, but not isolated cue to breed for most Australian frog species. In detailing the strength of the relationship between meteorological drivers and each frog species, I produced information vital to both planning surveys and interpreting the significance of those results. In surveying participants, I found that citizen science fills an important niche in their lives, holds significant promise for increasing participant wellbeing, thus increasing the number of interested participants and the power to collectively achieve biodiversity monitoring and conservation aims. This interdisciplinary consideration of both the human and wildlife aspects of citizen science can reveal valuable knowledge, solutions, and synchronicities in a diverse conservation landscape.