Reintroductions through the lens of the refugee species concept, with case studies of Australian rodents

Abstract

Species reintroductions are a challenge that typically require significant resources to achieve success. In this thesis I argue that, for the special case of refugee species, conventional guidelines for reintroductions may contribute to the inefficient use of conservation and management resources. A refugee species is one that has become restricted to the subset of their formerly occupied habitats that are of suboptimal quality. As such, they may suffer poor conservation outcomes if only maintained in their currently occupied 'refuge' habitats. My overarching objective was to showcase how practitioners can reassess and approach the steps in a long-term reintroduction strategy in a way that could improve the conservation of these special cases.

Chapter 2 tests the application of a Mini Safe Haven (MSH) approach in a trial reintroduction of a potential refugee species to inferred formerly occupied habitat. I hypothesised that providing a MSH would help a species to persist where it was naive to a key predation threat. I found that a MSH was more successful for supporting the persistence of released individuals than a more traditional soft-release approach. I highlight the broad applicability of MSHs as a complementary tool for wildlife conservation and pest impact-mitigation efforts, and recommend avenues for further refinement of the approach.

In Chapter 3, I inform the design of reintroductions for a species through analysis of the hypothesis that its reproductive output in captivity was influenced by behavioural, demographic, experiential, pedigree, health, and physiological variables. This is a novel approach to formulating hypotheses to be tested in reintroduction trials and experiments. Although this method would be useful in a range of reintroduction contexts, it will be of particular benefit in cases where the focal species is a confirmed, or potential, refugee, because there is likely to be a high level of uncertainty around their post-release survival and reproduction.

Chapter 4 tests a strategic translocation and assessment of microhabitat use, which included a biological interpretation of the null hypothesis that there is no difference in the focal species' microhabitat use between current refuge and inferred former habitats. I inferred insights to address ecological misconceptions and revise recommended restoration works and other release tactics for the focal species, as appropriate for the habitats assessed. Systematic implementation of this approach may help to reverse the impacts of shifting baseline syndrome (i.e., misconceptions of the norm that can arise when the knowledge of previous human generations is forgotten or ignored) that may pose an obstacle to the effective conservation of a refugee species.

Finally, in the culmination of my thinking on refugee species throughout my candidature, Chapter 5 details a framework I developed to aid the identification and prioritisation of potential refugee species, which includes maps that could reduce the risk of ecological misconceptions attributable to shifting baseline syndrome. I found that approximately 60% of Australia's extant native rodents are potential refugee species; unrelated to their threatened status. I discuss the global applicability of this framework for complementing existing threatened species frameworks, and supporting ambitious (and potentially controversial) reintroductions.