Author: Rupert Mathwin
Mathwin, Rupert, 2024 Modelling a threatened species (Litoria raniformis) to guide conservation, Flinders University, College of Science and Engineering
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Southern bell frogs (Litoria raniformis) were once common throughout south-eastern Australia but have declined substantially since the 1970s, notably within Australia's second-largest catchment, the Murray-Darling Basin. In the 1990s and 2000s, the Basin experienced a major drought and southern bell frog populations in the catchment collapsed. This included a large range reduction when the species disappeared from the lowest 320 km of the river. In response to the drought’s widespread ecological degradation, the Australian Government introduced sweeping water reforms in the Basin and enacted The Water Act 2008. These reforms included a water allocation that is owned by the Environment and delivered to recover water-dependent ecosystems (environmental water). Environmental watering has stabilised some populations of southern bell frogs; however, challenges persist in the lower catchment where southern bell frog populations remain unstable and have not re-established in the lowest 320 km of their former range. In this thesis I explore the decline, persistence, and recovery of southern bell frogs. The core narrative follows an adaptive modelling process whereby I develop an aspatial stochastic population model, and then use each subsequent chapter to adapt and improve the preceding models. The final iteration combines a genetic algorithm with a stochastic, agent-based, hydro-ecological metapopulation model of a 70 km reach of the Murray River to refine an optimal environmental watering policy in a multi-user system.
I demonstrate that the primary driver of southern bell frog declines in this reach is the impoundment and abstraction of flow that has reduced the frequency of wetland inundation, and thus breeding opportunities. This highlights the critical role of environmental water delivery in recovering this species. I calculate the relative risk associated with each watering frequency and recommend watering four out of every five years to maximise the population viability of remnant southern bell frog populations. I demonstrate the importance of metapopulation structure in species persistence and model the reach-wide benefits of modifying the spatial and temporal orientation of environmental water deliveries. Spreading delivery sites along the reach increases the average probability of persistence at each wetland by 16% compared to grouping the sites together. I show that without prioritised environmental water delivery during drought conditions, the average probability of persistence per wetland is < 4%. I highlight opportunities to generate environmental watering efficiencies by refining a near-optimal policy that meets the existing management targets for river redgum (Eucalyptus camaldulensis) and lignum (Duma florulenta), but also maximises the metapopulation viability of southern bell frogs (and requires no additional water). I provide context for these findings with a global review of amphibian conservation initiatives that manipulate water, showing that drying wetlands to remove predators, and maintaining hydroperiod until the completion of metamorphosis are well supported, but many promising strategies remain poorly
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studied and underreported. I include a sustainable harvest strategy to support ex situ conservation programs for southern bell frogs.
Keywords: amphibian, captive assurance colony, conservation, environmental, environmental water provision, flow, frog, hydroperiod, pump, salamander, spray, toad, water, Litoria raniformis, population viability analysis, river regulation, stochastic population model, sustainable harvest, translocation, conservation trade-offs, environmental water, genetic algorithm, multi-objective optimisation, predictive modelling, stochastic metapopulation model, threatened species, climate change, conservation policy, drought, ex situ conservation, water management, water scarcity
Subject: Environmental Science thesis
Thesis type: Doctor of Philosophy
Completed: 2024
School: College of Science and Engineering
Supervisor: Professor Corey J. A. Bradshaw