The conservation biology of endangered heath frogs and the ecological costs of longwall mining

Conservation science seeks to develop effective strategies to limit species’ extinctions, with constantly evolving challenges intrinsic to the discipline. Amphibians are arguably the most imperilled group of all vertebrates; however, conservation efforts are often hampered by incomplete knowledge of amphibian ecology and biology. This scarcity of ecological information is particularly apparent for Littlejohn’s tree frog (Litoria littlejohni) and Watson’s tree frog (Litoria watsoni), two behaviourally cryptic species commonly referred to as ‘heath frogs’. Litoria littlejohni and L. watsoni remain relatively unknown to science, occupying small, isolated patches of habitat along the east coast of Australia from Newcastle (north of Sydney, New South Wales) to north-east Victoria. The distribution of L. littlejohni also overlaps with longwall mining – a form of underground coal extraction that often triggers the cracking and shifting of the surrounding rock strata (a process referred to as ‘subsidence’). The impact of longwall mining on stream-breeding fauna is very uncertain, with few experimental studies dedicated to exploring the potential influence of this form of habitat disturbance. Despite their Endangered conservation statuses and evidence of population decline (likely driven by the amphibian chytrid fungus, Batrachochytrium dendrobatidis, and the impacts of drought and bushfires), the ecology and basic biology of heath frogs remain poorly understood because of their inherently low detection rates and inconsistent breeding behaviours. Without an informed understanding of L. littlejohni and L. watsoni’s ecological requirements, effective conservation of heath frogs will be extremely challenging – especially in areas subject to longwall mining. This PhD thesis aimed to build a knowledge base on the ecological requirements of L. littlejohni and L. watsoni, with a view of informing the conservation management of heath frogs into the future. Complementary to this overarching aim, I also set out to investigate the potential role of longwall mining in impacting L. littlejohni and the wider anuran community as a whole. First, I place this PhD thesis into the broader context of threatened species management prioritisation through an analysis of the current approaches to assessing extinction risk (including the IUCN Red List assessment method), with focus on relevance to amphibian species. The remainder of this thesis is comprised of research chapters that explore the conservation ecology of L. littlejohni and L. watsoni, each with its own set of research objectives and hypotheses. These studies collectively present the first comprehensive evidence of the detrimental impact of longwall mining on L. littlejohni and the quality, availability, and persistence of its habitats. However, these findings could not have been uncovered without first investigating the basic ecological requirements and breeding habitat selection by heath frogs. With this new knowledge, the results of these studies pave the way for the development of tailored, scientifically-supported conservation strategies for L. littlejohni and L. watsoni. The impacts of drought, disease, mining, and bushfires have all contributed to the disappearance of L. littlejohni and L. watsoni from considerable portions of their distributions. These compounding threats mean that heath frogs face an uncertain future. However, the exploration of breeding habitat use, reproduction, and recruitment elucidated here provide conservation managers with critical information needed to inform the mitigation of threats and to secure the future of the charismatic heath frogs, Litoria littlejohni and Litoria watsoni.