Office for Environmental Programs - Theses
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ItemPersistence of the Eastern Dwarf Tree Frog (Litoria fallax) in Melbourne: habitat characteristics and climatic niche( 2014)Human activities are increasingly leading to the movement of species into areas outside their natural range. The Eastern Dwarf Tree Frog (Litoria fallax) has been translocated from its original range in Queensland and New South Wales, Australia to the city of Melbourne, 600 km south of its previous range. Individuals of this species are known to travel on transportation trucks in fresh food and agricultural produce, and they are known as a 'banana box frogs' for their penchant for hiding in banana boxes. Litoria fallax has now been recorded at 28 sites around greater Melbourne and is known to be persisting at 7; however, with many gaps in the wildlife databases, this figure is likely to be higher. With Local habitat features known to significantly influence the presence of frog populations I conducted habitat surveys at sites throughout Melbourne where L. fallax is known to have and have not persisted. Its ongoing presence at a site was most closely correlated with a higher cover of submerged and riparian vegetation. With L. fallax being so far to the south of its original range, climate was an important factor to explore, so I ran a climate-suitability model for L. fallax using the software package Maxent. The model included five climatic variables-temperature seasonality, minimum temperature of the coldest quarter, mean temperature of warmest quarter, precipitation of warmest quarter and minimum relative humidity-chosen for their relevance to the biology and behaviour of L. fallax, such as the association between breeding and rainfall events. Results of the modelling showed that not only does Melbourne fall within the suitable climatic range of L. fallax, but that this range extends along most of the east and south coast of Australia. This suggests that a substantial range expansion of this species is possible. Whilst greater Melbourne does fall within the climatic niche of L. fallax, the predicted climate suitability varies throughout the region with a lower relative probability of occurrence in the northern suburbs where most of the populations are persisting. Thus, my research demonstrates that climate modelling alone is not sufficient to assess the potential niche of an invasive species
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ItemThe distribution of Eucalypts in north-western Victoria: modeling the influence of functional traits along environmental gradients( 2013)Understanding how functional traits influence species distributions along environmental gradients provides insight into plant ecological strategies for survival and reproduction. Here I examine how traits influence eucalypt distributions along environmental gradients. I use a species distribution model that incorporates Eucalyptus plant traits to understand their distributions in the mallee region of north-western Victoria. I examined the trait-environment interactions using the leaf-height-seed plant ecology strategy scheme (specific leaf area, height at maturity and seed mass) with 15 Eucalyptus taxa. The results show that all three traits influence species responses to environmental variables. Generally, traits influenced species responses to variables that are surrogates for water availability. Species with high specific leaf area increased in predicted occurrence along water availability gradients (rainfall in July, topographic wetness index, vertical distance to streams and soil properties). Tall species respond positively to soil nutrient gradients (soil radiometric Potassium measures and topographic wetness index) and water availability gradients (vertical distance to streams, topographic wetness index) except rainfall. Species with large seeds respond positively to sandy soils, which may reflect a response to either soil water or nutrient availability. Some of the trait-environment interactions in the mallee stay consistent with those of previous regional and global studies of traits (e.g. species responses of SLA to rainfall) and some turn out to be different (e.g. tall species' lack of response to rainfall). The trends that differ from other studies may highlight the particular properties of the ecosystem of the study area or result from use of different environmental variables. These results may have implications such as informing conservation efforts aimed at preserving functional diversity or assessing suitability for new plantation sites.
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ItemIntegrating species distribution modelling and cost-efficiency analysis to prioritise Platypus habitat management activities in the greater Melbourne region( 2012)Conservation activities are restricted by budget. This fact calls for an efficient use of resources for management activities that are expected to improve the condition of conservation targets. Prioritisation of management activities based on cost-efficiency has been advocated as a means to increase efficiency and achieve larger conservation benefits at a lower cost. Cost-efficiency assessments require estimation of costs and expected benefits of management activities. If the conservation target is a particular species or a group of species, benefits can be predicted from species distribution models (SDM) which relate species' records to environmental variables. Platypus (Ornithorhynchus anatinus) distribution models were developed and embedded in a conservation investment prioritisation protocol to demonstrate how financial costs and benefits to platypus of riparian vegetation restoration could be efficiently balanced. The platypus is a unique, charismatic focal species for conservation efforts in the case study region of greater Melbourne (south-east Australia). Platypus habitat is increasingly threatened in the case study area, mostly due to urbanisation and its impacts on habitat and water quality. Development of platypus SDMs was guided by selection of predictor variables that balance ecological relevance and possibility of change via management actions (i.e. riparian vegetation cover, catchment imperviousness), with the aim of using these models to predict platypus habitat benefits from management activities, in addition to current habitat suitability. Potential locations for vegetation management activities were prioritised based on expected platypus habitat benefits which were traded against the financial costs of achieving those benefits using a benefit-cost ratio analysis. Cost-efficiency analysis was undertaken between and within catchments to identify locations in which greatest habitat benefits can be achieved at the lowest cost. Predictions from SDMs show low platypus habitat suitability for most of the study area, with the exception of the middle and upper reaches of the Yarra catchment and upper reaches of the Bunyip River. High platypus habitat suitability is restricted to non-urban areas in streams with high riparian tree cover, relatively high precipitation during dry periods and low topographic wetness index. Results of the cost-efficiency analysis show greatest habitat benefits can be achieved at the lowest cost in locations with a medium current vegetation condition (riparian tree cover between 40 and 60%) and low to medium expected vegetation change from management activities (10-20% addition to riparian tree cover). These features are found in the middle sections of the main Yarra River and in the lower sections of the Tarago River. Budget allocation based on cost-efficiency prioritisation achieves up to 26 times more habitat benefits than prioritisation based only on benefits. This effect is more pronounced for a small budget ($1 million) but makes little difference for larger budgets (>$20 million). Highest cost-efficiency of vegetation management actions is concentrated in locations within the Yarra and Westernport systems, which are between 6 and 100 times more cost-efficient than locations in the Werribee and Dandenong catchments. These results show the importance of integrating cost and benefit information when prioritising management actions, especially when costs and benefits are variable and heterogeneous across the landscape.