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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ItemHabitat preference and distribution of the Powerful Owl (Ninox strenua) on the Mornington Peninsula, Victoria( 2013)Identifying the distribution of threatened fauna is fundamental to allocating scant resources for conservation purposes. Predictive habitat modelling based on environmental data from species records is currently used to inform conservation management but research is needed to verify the reliability of those Species Distribution Models (SDMs). This study focused on the threatened Powerful Owl Ninox strenua, in a region that lacked historical records but where SDMs predicted suitable habitat was available. This study was aimed at ground truthing the existing habitat suitability model for the Powerful Owl while providing new data to improve the spatial comprehensiveness of the model. The Victorian state-wide habitat suitability model for the Powerful Owl was used to stratify the study area (Momington Peninsula) into three classifications of habitat suitability (Low, Low- Medium and Medium). Forty sites were randomly selected comprising 13 low suitability, 13 low-medium habitat suitability, and 14 medium habitat suitability sites. Powerful Owl call-playback was undertaken a total of 112 times with each site surveyed at least once. A subset of 6 sites per habitat suitability class were surveyed 5 times to provide an estimate of detection probability. Repeat surveys at the same site were important to improve the probability of determining if Powerful Owls were present at a site (one to four visits increased overall detection from 33 per cent to 80 per cent). A Bayesian state-space modelling approach was used to estimate the occupancy of Powerful Owls as a function of habitat suitability class and prey abundance. Detectability was modelled using survey conditions (wind speed). This study shows that existing state-wide models of Powerful Owl habitat suitability reliably predict the occupancy of this species on the Momington Peninsula. Powerful Owls were found at a higher proportion of Medium (72%) and Low-Medium sites (66%), with lower levels of occupancy in Low habitat suitability sites (24%). This study provides new information regarding the distribution and habitat preference of the Powerful Owl on the Momington Peninsula, while highlighting the value of predictive species distribution modelling for wildlife conservation and management
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ItemAssessment of threats to the Mekong River Irrawaddy dolphin (Orcaella brevirostris)( 2010)The Mekong dolphin is a highly threatened freshwater population of Irrawaddy dolphin, Orcaella brevirostris, inhabiting the Mekong River in the Lao People's Democratic Republic and Cambodia. Despite the Mekong dolphin's low population size and rapid decline, there has thus far been no rigourous investigation of threats to the population, a gap this risk assessment aims to fill. A wide variety of threats are discussed including small population issues, boat traffic, fishing, tourism, environmental contamination, hydropower development and disease. Dolphin bycatch and disease are found to be the greatest threats, but competing mutually exclusive hypotheses prevent any definitive conclusions being drawn. It is imperative that this dichotomy be addressed as soon as possible and appropriate action taken to eliminate the threat. The development of hydropower dams, particularly on the mainstream of the Mekong River within dolphin habitat loom as the greatest future threat that may spell the end for this beleaguered dolphin population. Further indepth stochastic modelling is recommended to better understand the interactions and implications of some threats and guide conservation management of the population
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ItemEffects of experimental flooding on egg survival of Krefft's River Turtle: implications for freshwater turtle conservation( 2012)Anthropogenic changes to river catchments via changes to flow rate and volume can dramatically influence biodiversity. Most of Australia's major rivers are now impounded from the construction of dams and weirs causing the loss and significant alteration to habitat due to modified flow regimes. Such changes can negatively impact biodiversity, particularly specialist species. For example, anthropogenically altered flow regimes expose freshwater turtle to a seasonal inundation events that are assumed to exacerbate egg mortality during the incubation phase. Thus flooding of freshwater turtle eggs has been identified as an additional threatening process that could further impact both listed and non-listed freshwater turtles. Consequently, understanding the degree of mortality imposed on turtle eggs during incubation is a crucial step to ascertaining management implications from altered flow regimes on turtle populations. Here I conducted experiments to specifically identify the effects of 1) duration and 2) timing of inundation on Emydura macquarii krefftii egg hatching success and hatchling phenotypes. This was done in order to measure both direct and potentially indirect mortality costs associated with altered river flow regimes. Four treatments of eggs; control, 30 minutes submersion, one hour submersion and 6 hours submersion were flooded at nine periods during incubation (within the first 24 hours then every week following). Analysis revealed that inundation for any length of time caused a significant increase in egg mortality compared to control eggs. The developmental age at which inundation treatments were applied also had a significant impact on hatching success, with age 0 exhibiting the highest mortality rate and other developmental ages displaying fairly similar but increased mortality relative to controls. These results suggest that E. m. krefftii eggs are very sensitive to even brief episodes of inundation, especially within the first 24 hours of incubation. Moreover, if other turtle species are proven to exhibit similar sensitivities to inundation during egg incubation from altered river flow regimes these results suggests additional and potentially high mortality to all terrestrial nesting freshwater turtles. Ultimately these results support the need to prioritise informed management of anthropogenically altered flow regimes in order to prevent potential loss of an entire guild of vertebrates and their ensuing ecological function
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ItemDesign for persistence: graph-based connectivity, habitat reserves and species persistence( 2007)Connectivity is widely thought to play a key role in the persistence of metapopulations. However, there is no generally accepted approach to measuring connectivity in landscapes. Current reserve selection algorithms tend to focus on clustering habitat sites as an approach to maximising connectivity. An alternative approach to understanding connectivity is, however, to focus on the spatial configuration of habitat patches in a landscape. In this study, graph methods are used to represent habitat networks and investigate the relationship between spatial configuration and the flow of species moving across the network. Betweenness Centrality, a graph metric designed to measure the proportion of traffic passing through any node in a network, is applied in modified form as a reserve selection algorithm. The performance of reserves selected using Betweenness Centrality is assessed against species persistence measures from the metapopulation model RAMAS and compared to equivalent reserve selections for other well known reserve selection algorithms. Within the limited set of cases considered, this study found that Betweenness Centrality has a high degree of success in designing reserves for species with high dispersal characteristics, but is unable to predict appropriate reserve sites for low or non-dispersing species. Further directions for research in the field are suggested, with an emphasis on rigorously validating this type of approach to understanding connectivity.
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ItemA population viability analysis (PVA) for Eastern Sarus Crane, Grus antigone sharpii( 2005)The Sarus Crane Grus antigone (Linnaeus, 1758), a wetland bird species in South East Asia and Northern Australia, is currently listed as a globally vulnerable species. A subspecies of this bird, the Eastern Sarus Crane G. a. sharpii is distributed in the lower Mekong basin, South East Asia and is considered endangered due to its small population size, about 500-1000 individuals, inappropriate reserve management, and the intense development pressures in the region. A population viability analysis (PVA) of the birds may help managers to comprehend the processes governing the population dynamics and then highlight needs for future conservation, management, and research activities. Part 1 of this paper provides requisite data for the Eastern Sarus Cranes' PVA, including estimates of population abundance, survival and fecundity rates, and the carrying capacity of the area supporting the population. These data were obtained from fieldwork between the years 2001 and 2004 by the author and from a review of the literature. Part 2 is the description and simulations of the PVA models. Three stage-based demographic models of the population were run in RAMAS/Metapop 4.0 (Akcakaya 2002) to understand structural sensitivities of the models. Different scenarios were then run on the complete model to investigate the effects that each of them has on the model outcomes. The compiled data were also parameterised and simulated in VORTEX 9.5 (Lacy et al. 2005) to compare the risk estimates made by the two modelling packages. Part 3 involves discussions and conclusions of the results from the PVA models and proposals of management and conservation actions for the population. Although habitat loss has been considered the most threatening process to the population, the models were particularly sensitive to changes of poaching activities on the population. It is therefore suggested that improved population management is the most cost-effective option for the conservation of the endangered subspecies in the near future.
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ItemDistribution and abundance of five threatened marsupials at Mount Rothwell( 2005)The conservation and management of Australia's threatened marsupials must be based on a sound knowledge of their biology and ecology. Two aspects of ecology, distribution and abundance, are of particular importance. This study examined the distribution and abundance of five species reintroduced at Mt Rothwell. A brief examination was also made of each species' sex ratio and general condition. Data was collected via a markrecapture survey, and analysed using the MARK computer program and Arcview mapping software. An estimated 164 +-28 Rufous Bettong (Aepyprymnus rufescens) inhabit Mt Rothwell and were trapped predominantly in grassland habitat. Although the population size of Eastern Quoll (Dasyurus viverrinus) could not be reliably estimated, it is assumed to consist of 20 individuals, almost all found in the grasslands. Southern Brown Bandicoot (Isoodon obesulus) were the most populous species, with 289 +- 82 individuals inhabiting both woodland and grassland habitats. There was insufficient data to estimate the population size of the Eastern Barred Bandicoot (Perameles gunnii), but fourteen individuals were released one year ago, and all trapped individuals were in the grasslands. Conversely, Long-nosed Potoroo (Potorous tridactylus), estimated at 30 +- 12 individuals, were found exclusively in woodland habitat. The results of this study will provide baseline information necessary for future management decisions, and will be of great benefit to the conservation of these species at Mt Rothwell.