School of BioSciences - Theses
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ItemSpeciation and secondary contact in a colourful agamid, Ctenophorus decresii( 2019)Colour polymorphism, the co-existence of multiple heritable colour morphs within an interbreeding population, is thought to promote rapid phenotypic evolution and speciation. This is based on the importance of colour signals in reproductive isolation in combination with the underlying genetic architecture of polymorphism, where morphs are predicted to be governed by few genes of major effect. This prediction is supported by empirical data and stems from how colour morphs often differ in suites of co-adapted traits. During secondary contact between populations that differ in morphs, there is expected to be a high probability of genetic incompatibilities between morphs due to a breakdown of adaptive genetic correlations. Furthermore, colour signal divergence may also be accompanied by changes in behaviour and/or mating preferences leading to incompatibilities between populations which differ in morphs. These factors together may facilitate the formation of reproductive isolation and ultimately lead to speciation. In this thesis, I investigated divergence and the outcome of secondary contact between lineages of the tawny dragon, Ctenophorus decresii, which differ in morph number and type. Ctenophorus decresii is a sexually dimorphic agamid lizard endemic to South Australia, and comprises two genetically distinct and geographically structured lineages: northern and southern. I tested for differences in colour vision between the lineages, which differ in a sexual signal, male throat coloration, particularly in the absence or presence of ultraviolet (UV) reflectance. The northern lineage is colour polymorphic with four discrete throat morphs which lack significant UV reflectance: orange, yellow, orange-yellow (orange centre surrounded by yellow), and grey. Southern lineage males are monomorphic with blue throats and a strong UV reflectance peak. Male throat coloration is an important intraspecific sexual signal, as it is emphasised in territorial and courtship displays. I investigated whether lineages differ in visual sensitivity to UV wavelengths by measuring retinal opsin protein expression of four cone opsin genes (SWS1, SWS2, RH2, LWS) using droplet digital PCR. I found that lineages did not differ in gene expression of the four opsins and discussed this in the context of conserved visual sensitives in terrestrial systems. The lineages meet in a contact zone where multi-locus genetic data suggested the presence of hybrids and potential barriers to gene flow. Using extensive field surveys, male phenotype data, genomic single nucleotide polymorphisms (SNPs), and a mitochondrial (mtDNA) marker, I investigated the outcome of secondary contact between the lineages. Furthermore, I captive-bred pure and first generation (F1) hybrid offspring to characterise colour traits independent of exogenous selection. I found that the contact zone is narrow and several generations old with no parental forms or F1 hybrids present. The northern mtDNA haplotype was prevalent in hybrids, and there were high frequencies of backcrossing to the northern lineage but not to the southern lineage, indicating genetic incompatibilities. The northern throat polymorphism was maintained, without any loss of morphs, whereas the southern throat morph was absent. This contrasted with the more intermediate throat phenotype of captive-bred F1 hybrids, particularly in ultraviolet reflectance, suggesting strong selection for the northern throat phenotype within the contact zone. The viability and fitness of F1 hybrids have consequences for contact zone dynamics, and ultimately whether species boundaries are eroded or maintained. I performed pure and reciprocal cross F1 hybrids in a laboratory setting and measured parental reproductive traits and offspring fitness traits. I found that northern females have a higher reproductive output with more, larger clutches per breeding season and lower embryonic mortality. Although pure and hybrid offspring did not differ in individual fitness traits, hybrids produced from a combination of northern females and southern males exhibited higher fitness in more categories (i.e. growth rate, bite force, sprint speed). These factors in combination may contribute to the prevalence of northern lineage mtDNA haplotypes in the contact zone. Finally, I taxonomically separated the northern and southern lineages of C. decresii sensu lato on the basis of differentiation in morphology and male coloration, genetic divergence with restricted gene flow, and geographic structuring. This revision results in C. decresii sensu stricto (previously southern lineage) and C. modestus (previously northern lineage). I evaluated morphological traits of the type specimen of Amphibolurus modestus (Ahl 1926), previously a synonym of C. decresii sensu lato, and determined that it represented a specimen of the northern lineage. Therefore, I formally re-instated and re-described Ctenophorus modestus (Ahl 1926). The addition of this species to the C. decresii species group, which now comprises six species, supports the notion that geographic divergence in male coloration is an important component to speciation in this group.
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ItemImpacts of streetlights on sleep in urban birds( 2019)Over the past century, artificial light has dramatically transformed our environment. Light at night is increasing globally, to the extent that in many places, true darkness no longer exists. As the timing of light can influence almost all aspects of biology, the alteration of natural light cycles could pose a severe threat to wildlife. One particularly harmful impact could be the disruption of sleep. In this dissertation, I investigate the impacts of artificial light at night on sleep. Despite the importance and prevalence of sleep across the animal kingdom, sleep is arguably underappreciated in studies of ecology and conservation. After providing a general introduction (Chapter 1), I begin by giving a broad perspective of sleep research, including current methods, opportunities, and the significance of sleep for issues such as artificial light at night (Chapter 2). I then provide a review of the evidence for impacts of artificial light at night, in both humans and wildlife (Chapter 3). Finally, I explore the effects of artificial light at night on two diurnal bird species: pigeons (Columba livia) and black swans (Cygnus atratus). I focus on the effects of one of the most common sources of outdoor lighting: streetlights. Light at night from LED streetlights caused pigeons to have less rapid eye movement (REM) sleep and non-REM sleep, have more fragmented sleep, and sleep less intensely than during darkness (Chapter 4). Some of these effects persisted for more than a day after exposure to light at night. In black swans, light at night in a naturalistic environment reduced night-time rest, which we demonstrate reflects reduced sleep (Chapter 5). This research provides the first direct evidence that exposure to environmentally-realistic artificial light at night can disrupt sleep in birds. One possible strategy for reducing disruption of sleep could be to alter the colour of lighting. To test this idea, I compare the effects of two different lighting colours: white (blue-rich) and amber (blue-reduced) light. Previous research has shown that blue wavelengths of light have the greatest effect on melatonin, a hormone important for sleep regulation. However, contrary to my predictions, amber and white light had very similar effects on sleep in both pigeons (Chapter 4) and swans (Chapter 5). Together, these findings will help councils and other land managers to make more informed decisions about lighting, particularly for areas that might offer important refuges for wildlife.
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ItemHeterozostera resilience( 2019)Seagrass perform critical provisioning, regulating, cultural and supporting ecological functions and services humans rely on worldwide. Unfortunately, many seagrass ecosystems are vulnerable to disturbance and are being lost at alarming rates. Some seagrass species have been listed by the International Union for the Conservation of Nature as threatened and endangered where population sizes are small or are highly restricted in geographic distribution. For several other species, there is not enough data to determine whether a species is at risk or not. When ecological resilience thresholds for species survival and reproduction are exceeded, declines in seagrass may occur. Declines over time and space may be episodic or ongoing and occur as a result of impacts from both natural and anthropogenic stressors, such as turbidity, eutrophication, hypersalinity and urbanization. Increasing global change phenomena are expected to exacerbate declines of seagrass in many parts of the world, and vast losses of seagrass have functional implications for other ecosystems and organisms. Heterozostera are unique seagrass broadly distributed throughout coastal southern latitudes especially in Australia. Only three populations of Heterozostera are found outside of Australia, in a small region of the eastern Pacific in Chile. The populations are made up of 2 nonflowering clones. Therefore, Heterozostera of Australia may be functionally endemic to southern Australia, including Tasmania. Substantial loss of Heterozostera has been reported from the middle of Heterozostera's range in several locations of Victoria, Australia. Subsequent recovery of diminished populations has been slow in some sites, especially in Western Port, Victoria. Few published accounts related to resilience, including seagrass population monitoring for conservation and restoration of Heterozostera in the southern hemisphere have been completed. The aim of this thesis is to advance basic botanical research on Heterozostera in support of taxonomic resolution and the development of conservation strategies, especially those focused on modeling and applied seagrass resilience and restoration in Australia. More studies are needed to contribute to the development of restoration and resilience management strategies for lesser studied southern hemisphere seagrass ecosystems, and this work supports the generation of additional discoveries. Specifically, the objective of this dissertation is to identify and examine the autoecology and resilience Heterozostera, including sexual and clonal reproductive success under variable environmental cues. In all, five comprehensive studies of Heterozostera biogeography and biology are included in this dissertation, along with a theoretical framework and summary exploring the roles of environmental parameters in the autoecology of resilience for temperate Australian Heterozostera. Chapter 1 presents a review of research in support of Australian Zosteraceae, including trends and gaps in our understanding of seagrass resilience mechanisms, including both resistance and recovery pathways in Heterozostera. Chapter 2 details the results of an extensive survey of existing sediment and nutrient conditions for Heterozostera populations across 15 seagrass meadows located in southeastern Australia's Port Phillip Bay. Chapter 3 summarizes a series of experiments aimed at discovering effective Heterozostera seed storage and collection protocols for use in land based aquaculture, and specifically examining the potential roles of seed colour, sterilisation and refrigeration with the goal of improving long term seed viability. Chapter 4 contains a fully factorial germination assay undertaken to identify potential cues to Heterozostera germination, including sediment type and sterilization, nutrient loads, and refrigeration. Chapter 5 details a germination experiment using a 2 ppm copper sulphate (CuSO4) solution to cue germination of Heterozostera seed. Lastly, Chapter 6 explores the rates of asexual growth and survival of three types of clonal reproductive Heterozostera propagules (rhizome, plantlet and shoot). This work provides novel information about several topics of research with regard to the autoecology of Heterozostera including: (1) species identification, (2) species ecology and biogeography, (3) reproductive material collection and storage, (4) seed germination, and (5) clonal transplanting. This research demonstrates Heterozostera is capable of widespread recovery across a range of sediment and nutrient conditions. Continued work on lesser known Heterozostera species (H. tasmanica and H. polychlamys), and other rarer seagrasses world-wide are critical for understanding the potential loss of resilience and increased vulnerability (or conversely, the potential for recovery, adaptation and survival) of threatened and endangered seagrass populations with limited global dispersal. Collectively these studies details methods to support future Heterozostera research in both laboratory and field settings where culture of reproductive materials are required. In addition, the outcomes from this research provides novel information in support of progressing insitu seeding and transplanting efforts aimed to improve operation of land based seagrass nurseries and research studies. Novel evidence builds support that Heterozostera nigricaulis as a functionally resilient species of seagrass, largely due to its ability to inhabit variable ecological conditions and to utilize multiple sexual and asexual reproductive strategies to recover populations following disturbances.
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ItemPredicting ectotherm life cycles under a variable climate: physiological diversity of matchstick grasshopper eggs and their ecological and evolutionary implications( 2019)Understanding the processes underlying the phenology and distribution of species is a key problem in ecology. These relationships are important for predicting the responses to species to environmental change. Phenology and distribution are closely linked to climate and weather through the thermal dependence of life cycles. However, for many biodiverse taxa, like insects, we have a poor understanding of the mechanistic links between adaptive traits and how life cycles are adapted to seasonal and variable temperature patterns. Insect life cycles are synchronised with suitable climatic conditions at critical life stages, such as the egg stage. Variation in thermal sensitivity of development and dormancy are two mechanisms by which insects can generate adaptive life cycle phenotypes. Eggs, therefore, present a unique opportunity to link adaptive variation in traits with corresponding variation in life cycles and thermal environments to examine how life cycles are adapted to variable climates. To understand the adaptation of insect life cycles to variable climates, we require a mechanistic understanding of the interactions between adaptive developmental traits of eggs and variation in the thermal environment on adaptations. Our ability to test thermal adaptation in ectotherms is also limited by our ability to efficiently characterise thermal responses. In this thesis, I described how thermocyclers are an efficient means of characterising the thermal response of small ectotherms with enough precision and sample size. I then used the widely distributed, endemic and flightless Australian matchstick grasshopper genera Warramaba (Orthoptera: Morabidae) as a model system to examine the significance of variation in thermal responses at the egg stage for life cycles under a variable climate. I used a mechanistic modelling framework to tease apart developmental and environmental sources of variation in life cycles at the egg stage and simulate their consequences for phenology and distribution in the field. Matchstick grasshoppers showed remarkable diversity in developmental responses to temperature at the egg stage, primarily in the expression of dormancy. I found that diverse Warramaba life cycles are shaped by the interactions between such developmental variation and local environmental temperatures. I demonstrated that we can achieve a mechanistic understanding of life cycle adaptation by considering the evolution of temperature-dependent traits and the evolution of life history within the context of seasonal temperature cycles. Mechanistic models are powerful tools to investigate the sources of life cycle variation and their consequences for insect distribution and phenology. Such frameworks are directly transferrable to other socio-economically important or threatened species to understand how insects are adapted to local climatic conditions and predict responses to a changing climate.
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ItemWho to trust? Assessing and improving expert judgement in ecological domains( 2019)Managing ecosystems and species involves estimation and prediction of complex ecological interactions and their response to management intervention. While data are invaluable for informing management decisions, often the data required are unavailable, incomplete or uninformative. In these contexts, expert judgement is routinely utilised to inform critically important decisions. It is important that these judgements represent the best possible foundation for decisions and assessments. The application of structured expert elicitation protocols has been advocated as a means by which expert judgement may be improved. While these protocols have been substantially discussed in the ecological literature, their widespread application in ecological domains has remained limited. It is suggested that a lack of prescriptive guidance, supported by evidence that structured protocols can be applied within the practical and financial constraints of most ecological contexts, may be impeding the widespread adoption of these protocols. This thesis explores how barriers to the implementation of structured elicitation protocols may be overcome, and the extent to which their application improves judgements. It provides prescriptive guidance on the application of the IDEA protocol for structured expert elicitation, and presents evidence that the application of the entire protocol is both practical and improves judgements. It examines how judgements derived from the IDEA protocol may be further improved through performance weighted aggregations of the Classical Model, and the extent to which performance weighting may be practically applied.
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ItemTaxonomy, ecology and conservation genomics of North-Eastern Australian Earless Dragons (Agamidae: Tympanocryptis spp.)( 2018)Land clearing and modification of natural habitats is threatening biodiversity globally. In Australia, most native grassland habitats have been heavily modified for agriculture, including cropping and grazing. Grassland specialist species, including earless dragon lizards (Tympanocryptis spp.) in north-eastern Australia, are of conservation concern due to this continued habitat loss and fragmentation. However, the north-eastern Australian group of earless dragons (including the recently described T. condaminensis, T. wilsoni and T. pentalineata) are at significant risk, due to the presence of multiple undescribed cryptic Tympanocryptis lineages within this region. It is imperative that the taxonomy is resolved for these cryptic lineages of conservation concern, so conservation of these species may occur. One of the major challenges for taxonomists in recent times has been the species delimitation of morphologically cryptic taxa. The detection of distinct molecular lineages within cryptic genera has increased exponentially over the past decades with advances in genetic techniques. However, there are discrepancies in the rate and success of detection of cryptic taxa between studies using genetic methods and those using classic external morphology analyses. Therefore, novel integrative methods for species delimitation of cryptic taxa provide an avenue to incorporate multiple lines of evidence, including the application of osteological variation assessment where external morphological assessment fails to distinguish species. I develop a new pipeline integrating genomic data using single nucleotide polymorphisms (SNPs) and osteological geometric morphometric evidence from micro X-ray computed tomography (CT) imagery to assess variation between cryptic lineages for confident species delimitation. Here, I use this novel integrative pipeline to delimit cryptic lineages of earless dragons in north-eastern Australia. Prior to this study, there was evidence of three undescribed species of Tympanocryptis in this region. Using single mitochondrial and nuclear genes along with >8500 SNPs, I assess the evolutionary independence of the three target lineages and several closely related species. I then integrate these phylogenomic data with osteological cranial variation from CT imagery between lineages. I find that the very high levels of genomic differentiation between the three target lineages is also supported by significant osteological differences between lineages. By incorporating multiple lines of evidence for species delimitation, I provide strong support that the three cryptic lineages of Tympanocryptis in north-eastern Australia warrant taxonomic review. Earless dragons are found in most environments across the Australian continent, including a variety of ecological niches, from stony desert to tropical woodland or cracking clay savannah, although each species is often restricted to s certain habitat-type. I investigate the phylogenetic relationships among currently described earless dragons and newly delimited putative species with an assessment of broad biogeographic divisions, focussing on the north-eastern Australian Tympanocryptis group. I found significant structure across the north-eastern Australian lineages, with deep divergence between lineages occurring in the inland Great Artesian Basin region and more coastal Great Dividing Range. Regional diversification is estimated to have occurred in the late Miocene with subsequent Plio-Pleistocene speciations, and divergence and distributions of these species may therefore be reflective of the climate induced grassland-rainforest oscillations during this time. Based on these phylogenetic geographic relationships and the species delimitation from the integrative taxonomy approach, I describe three new species of Tympanocryptis from the cracking clay grasslands of the Darling Riverine Basin (T. darlingensis sp. nov.) and Queensland Central Highlands (T. hobsoni sp. nov.), and the stony open eucalypt woodlands on the Einasleigh Uplands (T. einasleighensis sp. nov.). The revision of these species provides further taxonomic clarity within the Tympanocryptis genus, and is an imperative step in the conservation of the north-eastern Australian earless dragons. These three putative Tympanocryptis species and the other three recently described earless dragons in north-eastern Australia inhabit restricted niches and areas with varying levels of habitat fragmentation and modification, and are therefore of significant conservation concern. However, little is known about these six north-eastern Australian earless dragon species. I utilise genomic methods to investigate population connectivity and genetic structure to determine management units. I then use species distribution modelling (SDM) to assess habitat suitability and fragmentation of each species. I integrate results of these analyses to form conclusions on the distribution and population structure of these earless dragons. I then discuss the major threatening processes and potential conservation strategies. This thesis uses several integrative approaches in resolving the taxonomy and forming conclusions on the conservation management of the north-eastern Australian Tympanocryptis species. This study successfully delimits cryptic lineages, explores the phylogenetic and geographic relationships between species, and provides baseline population genomics and ecological data to be used for conservation assessments and management decisions of earless dragons in north-eastern Australia.
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ItemFrom little things big things grow - savanna burning, suppressed trees and escape from the fire trap in Australian mesic savannas( 2017)This thesis explores growth responses and strategies of fire-suppressed trees in mesic savannas. Frequent fires are common to savannas globally, and cause most savanna trees to remain trapped as resprouts in the understorey by a cycle of topkill, where all above-ground parts of the plant are killed, followed by resprouting. Escape of suppressed resprouts from this fire trap is reflected in savanna tree community structure and composition. In this thesis, I contribute to the growing body of work from across the savanna biome that seeks to unravel the different effects of fire, competition and species growth strategies as mechanisms driving savanna tree communities. This question is fundamental to understanding what limits tree biomass in savannas and to predicting effects of different fire regimes in both the short term and in future climate scenarios. Despite much argument and modelling, mechanistic drivers of mesic savannas remain topics of conjecture, in part due to historical, environmental and species trait differences between continents. I collected the data used throughout this thesis within the Tiwi Carbon Study, a nine-year long fire experiment that aimed to provide accounts of carbon stored in soils, live vegetation and dead biomass under different fire regimes. The carbon economy is becoming a significant economic contributor to Aboriginal communities across remote northern Australia, with associated human benefits of social empowerment, wellbeing and connection to traditional practices. The increased focus on active management of northern Australian savannas for carbon sequestration and emissions abatement within a carbon market provides a human perspective to the ecological focus of my thesis. Within this context, there is a renewed imperative to understand what limits trees in savannas to anticipate effects of changes to fire regimes on carbon stocks and biodiversity. Using individual-level data I collected for 11 common resprouting savanna tree species subjected to different fire regimes on the Tiwi Islands in monsoonal northern Australia, I: (1) develop a theoretic framework that describes persistence and escape of suppressed resprouts subjected to frequent fire; (2) develop novel methods for estimating species and fire-specific escape heights; (3) model resprout growth and escape from the fire trap as mediated by fire and competition; (4) define sapling growth strategies based on functional and architectural traits that may influence escape potential; and, (5) demonstrate the effects of varying fire frequencies on savanna structure and composition. I found that the likelihood of escape from the fire trap is context-specific and related to differences in fire intensity, species traits and topkill-avoidance. Fire promotes fast growth of trees compared to fire exclusion, which may promote higher escape rates over shorter timeframes. However, less frequent fire leads to increased midstorey densities overall, thus affecting stand structure. In Australian savannas, eucalypts receive particular attention because of their canopy dominance, but I found minimal evidence of distinctly different growth responses between eucalypt and non-eucalypt resprouts that might explain this. Fine-scale environmental variation and individual species characteristics must be considered for robust estimates of escape from the fire trap. My research further implicates non-fire disturbances and different reproductive strategies as potentially illuminating drivers of different species responses – important topics for future research.
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ItemThe ecological costs and benefits of urban stormwater wetlands to frogs( 2018)The speed and scale at which humans are altering natural systems creates novel challenges for many species. Some species can cope with human-induced rapid environmental change by exhibiting adaptive behavioural or phenotypic plasticity. Many others, however, respond maladaptively in ways that can impact individual fitness. When rapid environmental change triggers mismatches between perceived and actual habitat quality, animals can prefer inferior habitats, that are known as ecological traps. Using a meta-analysis, I show that ecological traps are an unexplored but potentially important conservation risk to animals within wetland habitats (Chapter 2). Focusing on urbanisation and stormwater wetlands as a case study, I assess how anthropogenic environmental change affects frogs, in terms of the environmental variables influencing species occurrence (Chapter 3), the capacity of individuals to make adaptive habitat selection decisions (Chapter 4), and the fitness and behavioural consequences of these decisions (Chapter 4 and 5). I show that frogs occupied wetlands across a broad spectrum of pollution levels, including even the most contaminated, and that pollution exposure reduced survival and impaired predator avoidance behaviours. Breeding frogs did not avoid wetlands where these fitness reductions occurred, demonstrating that stormwater wetlands can function as ecological traps. Collectively, my results highlight the need for a greater focus on individual-level metrics (e.g. fitness and habitat preferences) in addition to the more commonly measured population- and community-level metrics (e.g. richness and abundance). Based on my research, I propose three key recommendations to maximise biodiversity at wetlands within urban landscapes. Firstly, appreciate that poor water quality at stormwater wetlands may impact resident wildlife, and attempt to reduce the causal factors. Second, despite this, do not ignore the potential value of stormwater wetlands in providing habitat and enhancing connectivity amongst aquatic habitats, particularly when they are appropriately designed and managed. Finally, it is important to design and construct wetlands for wildlife that are not connected to stormwater networks, with their placement within the landscape carefully considered.
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ItemTriple jeopardy in the tropics: assessing extinction risk in Australia's freshwater biodiversity hotspot( 2017)Freshwaters are the most degraded and imperiled ecosystem globally. Despite this high vulnerability, conservation efforts in freshwaters often lag behind those in terrestrial and marine ecosystems. In Australia this is particularly evident; despite high levels of river degradation, few freshwater fishes have had their conservation status assessed and only 14% of fishes are listed. Most listed species are restricted to southern Australia where rivers are particularly degraded. Northern Australia’s rivers are very diverse with many highly range restricted fishes. Yet almost no species are listed, despite potential vulnerability and an increasing number of threats across the north. Nowhere is this more evident than the Kimberley region in the north-west, where 49% of species are restricted to three or fewer rivers, and 10% are restricted to an area of <20 km2. Very little is known about the ecology of the region’s endemic fishes, so their vulnerability cannot be assessed. In my thesis I assess extinction risk in the freshwater fishes of the Kimberley using the triple jeopardy framework, that is whether they have small geographic ranges, low abundances and/or narrow ecological niches. Specifically I aim to (1) determine the relationships between range size, body size and abundance in all Australian freshwater fishes and (2) whether these relationships can be used to identify species at risk of extinction. I then determine whether (3) small ranged Kimberley endemics have narrow habitat, dietary or thermal niches compared to closely related widespread species and (4) synthesize these results to identify the fishes most at risk of extinction in the Kimberley. First, I test for a relationship between geographic range size and body size in all Australian freshwater fishes. I then investigate how this relationship varies with conservation status. I identify currently unlisted freshwater fishes that share traits with listed species and map their distribution, along with freshwater fish research effort, across Australia. I found a positive relationship between range size and body size. For a given body size, conservation listed species have a range less than one tenth the size of unlisted species. Based on this relationship, I identified 55 additional species that may be vulnerable to extinction. Most of these species are restricted to northern Australia where freshwater fishes are poorly known due to low research effort. Second, I test for abundance-geographic range size and abundance-body size relationships in Australian freshwater fishes and investigate how these relationships vary with conservation status. I identify and map currently unlisted freshwater fishes that are numerically rare, and combined with the results outlined above, map species with a double jeopardy risk of extinction. I found a negative body size-abundance relationship and no correlation between range size and abundance. Although relative abundance was a poor predictor of current conservation listing, I identified 59 consistently rare species. Twenty of these species (34%) currently suffer a double jeopardy risk of extinction and all were restricted to northern Australia. Third, using closely related widespread and endemic congeneric pairings of Kimberley freshwater fishes, I investigate whether endemic species have narrow dietary niches at any stage during their development. Using qualitative measures of habitat and presence/absence data, I also assess habitat specialization. Most range-restricted species have narrower ecological niches making them more vulnerable to extinction. Fourth I test the thermal performance of two pairs of congeneric species that are sympatric in the Drysdale River, with one widely distributed species and one range restricted species in each pair. In the Syncomistes pair, resting metabolic rate (RMR) was similar between species at low temperature but at higher temperatures the RMR of the widespread species was lower due to the onset of anaerobiosis. The range-restricted Syncomistes also has a higher critical thermal limit (CTL). In the Melanotaenia pair, the results were the opposite, with the widespread species having a higher CTL and RMR. The thermal performance of each species was related to their distribution within the catchment rather than their geographic range size, with the thermally sensitive species dominating the cooler, perennial downstream reaches, and the hardier species being more abundant in the hotter, more ephemeral upper catchment. Finally, I use the above information to assess the triple jeopardy extinction risk in the fishes of the Kimberley. Seventy-nine per cent of Kimberley endemic fishes are vulnerable on one or more axis, and two species had a triple jeopardy risk of extinction. The majority of vulnerable species are found in the remote rivers of the north-western Kimberley, but the most imperiled species (Hypseleotris kimberleyensis) is restricted to the heavily degraded Fitzroy River. My thesis shows that, despite fundamentally different environments, life histories and dispersal capacity, Australian freshwater fishes exhibit range size, body size and abundance relationships largely similar to terrestrial fauna. By identifying northern Australia as a hotspot of unrecognized vulnerable species, I provide an important context for guiding targeted research and informing future conservation management of Australia’s freshwater fishes. Combined with their small ranges and/or low abundance, the narrower niches of most Kimberley endemic species makes the region’s fishes particularly extinction prone. By identifying which endemic species are most vulnerable, my study provides specific information for targeting conservation efforts in the region. As the Kimberley and northern Australia more broadly are earmarked for major development, substantial effort is needed to effectively manage fish populations, design and manage developments with the environment as a major stakeholder and preserve remote rivers with high endemism and extinction risk. However, as northern Australia’s rivers are in good condition, with planning and research there is an excellent opportunity for proactive, properly informed freshwater conservation across the region.
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ItemAssessing and managing interacting species at risk of coextinction( 2016)Interactions between organisms are ubiquitous: predators hunt prey, plants compete for light, and pollinators visit flowers to forage on nectar. Through their interactions species influence each other's population dynamics and ultimately their persistence: Darwin was already convinced that if bumblebees became extinct their food plants would follow quickly. Despite their importance, interactions are commonly ignored when we assess species' extinction risk or plan for their conservation management. My thesis is divided into six chapters, addressing two important components of conserving interdependent species. First, I assess if and how we can use a common type of data - observed interaction networks - to assess the coextinction risk of interacting species in networks, and to predict how interactions influence cascading extinctions when interdependent species are lost. Secondly, I investigate how interacting species can be protected in combined management approaches, focussing on the increasingly common method of translocating species for conservation. To answer this questions, I develop a range of statistical and mathematical modelling approaches and apply these to theoretical simulations and empirical data. In chapter 2, I investigate how quantitative methods can help to identify those species in interaction networks that are at risk of coextinction, while incorporating important factors such as uncertainty and imperfect detection of species in the field. I develop a hierarchical $N$-mixture model that accounts for imperfect detection and allows one to disentangle two factors that influence interaction frequencies between species: the probability that two species interact, and the abundances of species. This enables one to estimate with uncertainty the number of interaction partners of a species and the community size of dependents. I fit the model to data that from simulations of different parameter scenarios and to empirical networks of flower-visiting insects found on a threatened ecological community of plants from the Stirling Ranges National Park in Western Australia. In chapter 3, I extend this modelling approach to investigate how imperfect detection and uncertainty influence the progression of extinction through mutualistic networks. Therefore, I apply the modelling approach from chapter 2 to observed networks to correct these networks for sampling bias. Then, I sequentially remove plant species from the networks to investigate how extinction cascades differ between observed and corrected networks. I show that networks corrected for sampling bias, are more densely connected and the interactions between species are more diffusely distributed throughout the networks. This causes corrected networks to be less specialised, and plant species to be more redundant, leading to increased network robustness. The results of chapter 2 and 3 indicate that imperfect detection strongly affects observed interaction networks and suggests that it is unwise to draw strong inferences for the conservation status of species and the robustness of ecosystems without acknowledging imperfect detection and uncertainty. In the second part of this thesis, I investigate management actions for improving the persistence of cothreatened interacting species, with a particular focus on conservation translocations. The fourth chapter investigates how useful current single-species translocation guidelines are for conserving cothreatened species and the interactions between them. I first classify potential systems of cothreatened species and devise appropriate management options for each system. Secondly, I extend current single-species guidelines to incorporate interactions in the assessment, planning and implementation phase for the conservation of multiple interacting species. For each phase of a translocation, I present case studies of threatened interacting species where a combined translocation could save the species. In chapter 5, I examine in detail how different types of interactions influence the optimal size of founder populations and the order in which interacting species should be translocated. I use mathematical models for coupled two-species systems, in which species interact in consumer-resource, competitive or mutualistic interactions. While some common rules in translocating interacting species emerge, most decisions about necessary founder sizes and translocation order are interaction-type specific. In the two chapters about combined translocations of cothreatened species, I show that interspecific interactions are important processes that shape population dynamics, and should therefore be incorporated into the quantitative planning of multi-species translocations. Finally in chapter 6, I synthesise the findings of my work and highlight future research avenues.