Filters
Availability
Publication Year
Resource Type
Faculty
School/Institute
Publication Search Results
Sort
Results per page
1 - 9 of 9
-
(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.
-
(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.
-
(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.
-
(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.
-
(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.
-
(2024)ThesisProlonged droughts and high temperatures throughout the 21st century have driven extreme fire risk weather around the world, resulting in widespread and extreme severity wildfires. In Australia, this was highlighted throughout the Black Summer fire season, which lasted a total of 8 months from July 2019 to April 2020. The fire season was and still is referred to as unprecedented and devastating, and for good reason. The fires killed people and wildlife, destroyed property and habitat, caused widespread atmospheric and aquatic pollution, destabilized and eroded soils, and left the government, scientists, and the public wondering how Australian ecosystems would recover. However, fire impacts, even of extreme severity fires, are never homogeneous, and fire interactions with Australian native ecosystems are complex, with many Australian species depending on fire for their survival. This PhD thesis provides a window into the complexities of how the 2019-20 fire season impacted people and the vegetation and soils in their surrounding environment. The first section of this thesis contains a qualitative assessment, i.e., surveys and interviews, of the public’s observations and perceptions of the 2019-20 fire season in New South Wales. Survey results showed that residents were motivated to take actions, including fire preparation and post-fire restoration efforts, because of the 2019-20 fires (Chapter 2), and public behaviours and their influence on government policy are known to influence fire outcomes. Furthermore, the 2019-20 fires increased perceived risk of fires on soil health (Chapter 2), yet few residents in the study were aware of the condition of their soils before or after the fire (Chapter 3). The work in Chapters 2 and 3 revealed a knowledge gap regarding the impacts of fire, and in particular, high severity fire on soil. To address this gap, the second section of this PhD thesis comprises a quantitative assessment of a high severity fire from the 2019-20 fire season and its impact on physicochemical and biological soil quality indicators of soils with different pre-fire management. Soil analyses showed that the high severity reached by fires unexpectedly reduced soil carbon and nitrogen levels (Chapter 4). Furthermore, an analysis of microbial communities showed fire reduced the abundance of symbiotic bacteria and fungi (Chapter 5) posing a risk to orchids and other threatened plant species on Kangaroo Island that depend on microbial plant symbionts. My research provides a rare empirical assessment of fire impacts on soils, particularly regarding high severity fire impacts on soil fungal and bacterial community composition and implications for post-fire soil microbial function. Furthermore, it highlights the limited knowledge but potential interest that the public has in understanding the importance of soils and the ecosystems services they provide. This work shows a need for more expansive soil monitoring after fire events such as the 2019-20 fire season, and I propose that engaging the public in soil monitoring efforts could address this need.
-
(2024)ThesisDrylands are extreme environments with <600 mm of annual rainfall and frequent high temperatures (>30°C). Like many ecosystems changing conditions, as a result of climate change, are threatening species’ survival, diversity and habitat persistence. Dryland lakes provide critical habitat for many aquatic organisms including zooplankton, birds, fish and frogs. Zooplankton are a vital component of dryland lake food webs contributing to the basal food source that enables the boom-and-bust ecological response of these ecosystems. Zooplankton persist in these environments via a range of adaptations including the production of resting eggs which sit in dry lakebed sediments and hatch when rainfall fills lakes. Ecosystems and organisms that currently experience extreme climatic conditions are ideal for studying the impacts of climate change because biota here may be already close to their physiological limits. Zooplankton in dryland lakes are an example of this. I used a range of methods to comprehensively investigate the potential impact of climate change on zooplankton in dryland lakes. This was done by investigating several factors including: changes in hydrology, increased heatwave temperatures and duration, and the implications of how spatial distribution of resting zooplankton eggs, both horizontal and vertical, may leave them vulnerable to environmental change. My study site included a suite of nine hydrologically isolated dryland lakes in Australia’s semi-arid zone, each chapter focused on all or a subset of these lakes. The lakes have highly variable and aseasonal filling and drying regimes, reflected in a variable salinity, depth and area. Significant fills (> 75%) are rare with ten observed by local land holders over 52 years (1965 - 2016). I modelled the effects of increased air temperatures and changes in rainfall on filling and drying patterns to understand changes in zooplankton habitat availability under projected climate change. Temperature influenced lake drying through increased evaporation, reducing suitable zooplankton habitat. Given the already infrequent filling of lakes, and zooplankton adaptations, their persistence is unlikely to be adversely impacted by conditions expected under current climate change projections. I tested the effects of longer and hotter heatwaves on resting zooplankton eggs by measuring hatching abundances. Overall abundances of zooplankton were not significantly impacted by tested heatwave scenarios (6- and 14- day; ground temperatures of 55°C, 62°C and 66°C). However, some salt lake species appeared to be more sensitive than freshwater species and in some cases hotter heatwaves appeared to accelerate growth responses resulting in distorted morphology. This finding suggested that the sub-lethal effects may impact zooplankton growth and long-term persistence. I explored the vertical distribution of resting zooplankton eggs at a range of sediment depths down to 68 cm (~2,900 years). I considered the impacts of current sediment temperature, sedimentation rates, age and historic hydrology on the vertical distribution of resting eggs. Despite vastly different sedimentation rates little to no hatching occurred below 3 cm across all sample sites. The lack of resting zooplankton eggs at depth may have implications for zooplankton persistence where surface egg banks are impacted by anthropomorphic processes such as climate change. I also explored the impacts of wind dispersal on the spatial distribution of resting zooplankton eggs. I found that resting egg abundances were impacted by wind dispersal with greatest abundances downwind. The effects of wind may be important with climate change where filling and drying patterns are altered, reducing hatching opportunities for resting eggs at the edges of dryland lakes. My work indicated that zooplankton are for the most part resilient to protracted dry periods and increased heatwaves under current climate change projections. My work also highlighted the importance of a greater research focus to understand and conserve zooplankton in dryland lakes.
-
(2024)ThesisFuture circulation changes in the tropical Pacific Ocean may have wide-ranging impacts on global climate and biogeochemistry. The Equatorial Undercurrent (EUC) is a conveyor belt of cool, nutrient-rich waters that sustain high surface biological productivity. In a future of continued anthropogenic warming, climate models project a strengthening of the EUC in the western Pacific, however, there is considerable uncertainty on the validity, cause, and biogeochemical implications of the projected change. In this study, we examine the historical representation and future changes of tropical Pacific circulation in the latest generations of the Coupled Model Intercomparison Project (CMIP6 and CMIP5) and a dynamically downscaled eddy-permitting ocean model. The circulation transport and seasonality across models are broadly consistent with observations and ocean reanalysis products. Despite an overall increase in model resolution, we only find minor improvements in systematic biases between CMIP ensembles. The magnitude of EUC changes is larger in the eddy-permitting model than in CMIP ensembles, but the change in CMIP6 is less prominent than CMIP5. Consistent across most models, the EUC change is likely driven by anti-correlated southern interior and boundary convergence changes that strengthen the EUC in the west, with little or reduced overall change further east. By back-tracking particles in the eddy-permitting ocean model, we find the EUC is projected to receive more water from the southwest low-latitude western boundary currents (LLWBCs), particularly the New Ireland Coastal Undercurrent. Despite weak changes in overall transport, the makeup of the EUC changes significantly in the central and eastern Pacific. In particular, the EUC receives less water from the Mindanao Current and interior convergence in both hemispheres. Using a semi-Lagrangian iron model combined with observational estimates of iron, we find that increased transport from the southern LLWBCs drives increased EUC dissolved iron concentration and flux in the western Pacific. However, the increase in mean iron concentration does not persist further east without large assumed LLWBC iron inputs in the future. Irrespective of the changes in iron concentration, the total EUC iron flux in the eastern Pacific is diminished further east due to the weakened EUC volume transport. The projected redistribution of EUC source waters may affect air-sea feedbacks, oxygen ventilation and primary production in the tropical Pacific.
-
(2024)ThesisThe success of translocations is underpinned by careful planning, but a lack of research addressing a priori hypotheses or experimentally comparing management strategies often prevents planning decisions from being evidence-based. Translocations of the greater bilby (Macrotis lagotis), a nationally threatened Australian marsupial and ecosystem engineer, are recommended to aid the species’ recovery and restore ecosystems. I used a series of experimental approaches to address key knowledge gaps pertaining to the establishment, persistence and ecosystem impacts of translocated greater bilby populations. I explored the role translocations are playing in threatened species conservation and ecosystem restoration, including the greater bilby, and the ways applied translocation research may improve translocation outcomes (Chapter 1). I examined factors influencing post-translocation behaviour and health. I found animals sourced from a familiar environment gained more weight and were less active than those sourced from an unfamiliar environment, whereas the presence of established conspecifics had no impact (Chapter 2). I assessed parentage skews and the effectiveness of admixture across three translocated bilby populations during their establishment and found genetic diversity was negatively impacted by skewed paternal offspring contributions but positively affected by admixture (Chapter 3). I also tested the impact of a population supplementation on the behaviour of resident conspecifics and subsequent integration of the new animals (Chapter 4). I found the new arrivals had little influence on the resident’s behaviours and they successfully integrated, but this success may be related to the population growth stage. Using a before-after-control-impact methodology I also examined how bilby translocation influenced the density and occupancy of ground-dwelling arthropods, a common dietary item (Chapter 5). I found no short-term impact and instead detected significant climate related declines closely preceding the translocation. Overall, my findings are directly applicable to translocation practitioners in the selection of source sites (Chapter 2), and alternative strategies to admixture to maximise genetic diversity (Chapter 3). My findings also highlight the importance of considering conspecific population growth stage and boom-bust cycles when planning supplementations to aid population persistence (Chapter 4) and ecosystem restoration (Chapter 5).