School of BioSciences - Theses
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ItemA genetic approach to the conservation of holly leaf grevilleas (Proteaceae)( 2016)The holly leaf grevilleas consist of an informal aggregate of 15 species found in south-eastern Australia. The group exhibits high levels of morphological variation and the most widespread species, Grevillea aquifoilum Lindl., is also the most variable. Most species are restricted endemics and their geographic limits make them vulnerable to the effects of fragmentation and environmental change. In some species, production of viable seed is unknown or has not been confirmed. Identifying factors that contribute to the persistence of species when fecundity is low is of critical importance to their conservation. Here, a phylogenetic analysis is used to clarify the evolutionary relationships among lineages within the holly leaf grevilleas. The lineages identified are then the basis of chapters 4 – 6 that address questions of what constitutes the units of conservation and how clonal plants should be assessed. Analysis of 12 cpDNA regions strongly supported the more southerly distributed holly leaf grevilleas as a monophyletic group comprising four clades (‘G. aquifolium’, ‘G. dryophylla’, ‘G. repens’, ‘G. ilicifolia’). The two northern holly leaf grevillea species, G. renwickiana and G. scortechinii, found in New South Wales and southern Queensland, were not positioned with the southern species but their relationship with outgroup species G. willisii from northeastern Victoria and G. acanthifolia and G. laurifolia from New South Wales could not be ascertained with confidence. Two nuclear regions, PHYA and waxy1, were less variable and not analysed in combination with cpDNA. PHYA was largely uninformative with most species forming a polytomy. Two major variants were identified in waxy1 and consisted of one functional and one non-functional copy based on DNA translation. Minor alleles of functional and non-functional copies were present in some accessions. Using only the functional copy (including multiple alleles when present), the southern ‘G. ilicifolia’ clade, as identified from cpDNA, was clearly differentiated from the northern clade and the remaining species. Within the southern species, those not belonging to the ‘G. ilicifolia’ clade were grouped together but clades identified in the cpDNA phylogeny were not recovered in the waxy1 analysis. Incongruence between the phylogenetic placement of some taxa and current species assignment based on morphology, including apparent paraphyly of G. aquifolium, may indicate an evolutionary history of hybridisation, introgression and incomplete lineage sorting and/or the use of morphological characters that are not lineage-specific. For example, the two subspecies of G. montis-cole differentiated morphologically on the basis of style-length are positioned in different clades and warrant specific rank if supported with nuclear data, and G. steiglitziana is split between two lineages within the southern ‘G. dryophylla’ clade. The phylogenetic placement of G. ‘williamsonii’, a taxon no longer recognised, with sympatric G. aquifolium, coupled with microsatellite analysis supports the current taxonomic view of its synonymy with G. aquifolium. The cpDNA phylogeney also raises questions about the taxonomy of G. microstegia and G. bedggoodiana, taxa that are also positioned with G. aquifolium in the ‘G. aquifolium’ clade. Population genetic analyses of G. infecunda and G. renwickiana found both species to be comprised of a small number of clonal lineages with no evidence of contemporary sexual reproduction. Within species, no clones were found at multiple locations and cpDNA haplotypes were derived from single lineages. In G. infecunda, 38 clonal lineages were identified from a microsatellite analysis of 280 samples from 11 populations. The number of clones present per population ranged from 1 to 11 and clone size varied from a single stem to several hectares. In G. renwickiana, analysis of 197 samples revealed that all but one of seven populations were monoclonal. Clones were distributed over a minimum area of one hectare. Sequencing of microsatellite alleles showed that variation in allele size profiles among clonemates could be interpreted as somatic mutation. The genetic patterns evident in the two species are likely to be the result of a loss of sexual reproduction, due to pollen sterility in G. infecunda and the effects of triploidy in G. renwickiana. For the clonal taxa, G. infecunda and G. renwickiana, lack of sexual reproduction leaves little opportunity for adaptation or migration in response to changing conditions. However, to facilitate the adaptive responses of ecological communities rather than individual species, conservation should encompass obligately clonal species because of their role, albeit finite, in mitigating ecological instability as floras respond to rapidly changing environments.
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ItemRobust prediction and decision strategies for managing extinction risks under climate change( 2016)Effective management of biodiversity requires decision strategies that are robust to the uncertainty embodied in predictions of habitat suitability and environmental change. This is particularly relevant in the context of climate change, which may interact with existing threats in unexpected ways. Predictive modelling has become important for addressing questions about climate change impacts. In particular, correlative species distribution models (SDMs) are popular for predicting species' fates, and have been noted as effective tools for guiding conservation decisions. However, SDM predictions are uncertain due to our imperfect understanding of the processes underlying species-environment associations, and, crucially, imprecision in predictions of regional climate change. While this is widely recognised, SDM prediction uncertainty is frequently overlooked, and practical approaches to handling this uncertainty are rare. When SDMs are used to investigate questions of species' persistence during times of environmental change, failure to consider uncertainty about the arrangement and quality of habitat may lead to flawed inferences and ineffective management. It is therefore essential that we improve our understanding of key uncertainties, and develop methods that explicitly handle uncertainty in a way that promotes sensible management decisions. In this thesis, I explore these issues through case studies of the mountain pygmy-possum, Burramys parvus, in the alpine region of south-eastern Australia. I draw on a range of quantitative tools and classical decision theory to: (1) determine the magnitude of uncertainty about habitat suitability due to SDM predictor choice, and how this varies under climate change; (2) develop a framework for identifying the optimal spatial allocation of resources for species' conservation under climate change, given uncertain predictions of habitat suitability; (3) explore the utility of abundance time series for improving our understanding of environmental dynamics influencing populations; (4) combine SDMs and models of population dynamics with decision theory to assess the extent to which predictions are refined by explicitly including population processes; and (5) develop a suite of open source software tools that facilitate common ecological modelling tasks, making rigorous investigation of climate change questions more computationally efficient and feasible. I found that standard approaches to model evaluation obscure key differences amongst competing SDMs, suggesting that consideration of ecological relevance during model construction is essential. I showed that despite extensive uncertainty about future habitat, conservation actions can be prioritised in a way that reflects managers' appetites for risk and reward. I demonstrated that for spatially-structured populations, hierarchical models can reveal the spatial scales at which environmental processes control population growth. Regional synchrony in population dynamics is evident for B. parvus, but local, density-independent environmental forces are more important in determining abundance trajectories. Finally, I demonstrated that habitat change is an unreliable surrogate for a species' response to climate change. Predictions about the distribution and quality of future habitat for B. parvus are uncertain. However, this is an inevitable challenge when forecasting species' fates. Importantly, it does not preclude effective management. The way forward is to recognise and account for uncertainty in ecological models, thereby enabling sensible conservation decisions for species impacted by climate change.
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ItemParasitism by Trichogramma wasp: potential and reality under climate change scenario, with focus species attacking Asian corn borer( 2016)Climate change may directly influence the distribution of parasitoids, lead to phenological asynchrony with their hosts, and/or lead to other disruptions of multitrophic interactions. By determining the impacts of global warming effects which may influence Trichogramma populations, researchers and land users can be provided with ways to further enhance the efficiency of biocontrol. First, I identified common Trichogramma species emerging from Asian corn borer Ostrinia furnacalis egg masses (based on morphology and internal transcribed spacer 2- ITS-2) throughout southwestern Taiwan. I then compared their life history characteristics and thermal limits and determined the Wolbachia infection status of field-collected parasitoids. Although T. ostriniae and T. sp. y appear to be morphologically similar, the ITS-2 identity between these two taxa is only 89%. A commercially released Trichogramma colony thought to be T. chilonis possessed 99% identity with the field T. sp. y individuals. The current study provides a baseline for future work, and also highlights the importance of accurately identifying species when establishing colonies of natural enemies for biocontrol. Next, I evaluated the distributions of Trichogramma ostriniae and its native host, Ostrinia furnacalis (in southeastern Asia), and target host, Ostrinia nubilalis (in North America), using a combination of MAXENT and CLIMEX modelling approaches. Trichogramma ostriniae was predicted to occur in the summer corn region of China, with distribution limits linked to its sensitivity to cold, and the seasonality of radiation and precipitation. The stepwise modelling approach used here proved useful for assessing environmental factors linked to an egg parasitoid and its lepidopteran host and for identifying areas potentially suitable for inundative releases. Finally, integrating meta-analysis results and reviewing related literature, indicated that both top-down and bottom-up factors could moderate the effect size of egg parasitoids over a range of Extreme High Temperature (EHT) values. These patterns suggest a complex response to climate change, mediated by temperature factors, precipitation seasonality, crop type and perhaps other factors related to latitude. Trichogramma biocontrol efficiency is hampered by extreme climate change as they are more senstive to environmental factors than their hosts. The work presented here highlights effects of precipitation and radiation seasonality on parasitism, life history traits, and distributions of Trichogramma species, which could act to either improve or optimise the execution of lepidopteran biocontrol projects. Results of this study will be useful to managers for successful use of Trichogramma in biocontrol under a climate change future.
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ItemGeographic range and the mountain niche: ecology, adaptation and environmental change( 2015)The geographic range is one of the most fundamental traits of a species. For this reason, understanding the ecological and evolutionary drivers of the size, position, and structure of the range is a key research challenge. The geographic range also has an overriding influence on the environments to which a species is exposed and their spatial and temporal variation. This study addresses four questions relevant to understanding interactions between the environment and individuals, populations, species and communities, with a focus on mountain regions where environmental variation is particularly pronounced. First, using meta-analysis and a single-genus case study, I explore the relationship between geographic range size and characteristics of the ecological niche. Range size can vary by several orders of magnitude among closely related species, but is strongly and consistently associated with both niche breadth and niche position: the most widespread species tend to be those with a broader niche and/or those that utilise resources that are common across the landscape. Second, I investigate the relationship between niche and range limits by testing variation in physiological tolerance across environmental gradients in two mountain systems: beetles (Carabidae: Nebria Latreille) from the North American Cascade Range and grasshoppers (Acrididae: Kosciuscola Sjösted) from the Australian Alps. Whereas the Nebria, distributed across a 2000 m elevational gradient, showed almost no variation in thermal tolerance, the Kosciuscola showed significant interspecific variation in cold tolerance, consistent with the decrease in average temperature with elevation. I suggest that cold tolerance limits might constrain the upper range edge of at least one species. Third, I explore how past climate cycles and Australia’s dissected mountain landscape have influenced the population structure of an alpine-endemic grasshopper (Kosciuscola tristis) using a combination of genetic methods. Despite continuity of alpine habitat during Pleistocene glacial cycles and, by global standards, small-scale disjunctions in the present distribution of these environments, K. tristis showed deep lineage divergence associated with geographic breaks in alpine conditions. Fine-scale structure in the absence of clear geographic barriers suggests that habitat heterogeneity might structure populations at a regional scale. The last component of this work tests the response of alpine invertebrate species and communities to reduced winter snow cover. This is a likely future scenario in the Australian high country, where the winter snowpack is already marginal. I show that Australia has a diverse subnivean arthropod fauna, characterised by the high relative abundance of springtails (Collembola), mites (Acari), spiders (Araneae) and beetles (Coleoptera). Experimental reduction of the winter snowpack caused shifts in community composition, driven by a small number of abundant arthropod taxa. These effects were apparent at a small spatial and temporal scale, with rapid recovery from experimental perturbation in spring. Mountain ecosystems are threatened by climate change as they are already rare at a landscape scale, are typically fragmented and have limited scope for climate tracking. The work presented here highlights effects of small-scale environmental variation on species traits, genetic structure and communities, which could act to either buffer or exacerbate landscape-scale climatic changes.