The Past, Present, and Future of Large Reptiles: Rewilding, Climate Change, and Conservation Palaeobiology

Species extinctions reduce the diversity of functions that an ecosystem can provide, with negative effects for both natural habitats and society. Rewilding is the restoration of these ecosystem functions by returning locally extinct species or their ecological analogues to an environment. Rewilding also has the potential to limit the impact of future climate change on species and ecosystems by introducing or reintroducing species to areas that will be climatologically suitable in the future. The interplay between rewilding and climate change is particularly relevant to the conservation of reptiles. Reptiles respond rapidly to climate change and support important ecosystem functions. As such, climate change is likely to cause local extinctions and range shifts of reptile species, disrupting the ecosystem functions they provide. Despite this, rewilding projects and related research have largely overlooked reptile species. In this thesis I took an interdisciplinary approach, drawing on neontological and palaeontological data and techniques, to examine the interplay between climate change and rewilding in the context of the conservation of reptiles and the ecosystem functions they support. I used the genus *Varanus* as a model taxon to understand how reptiles contribute to ecosystem functions and respond to climate change. To study the contribution of reptiles to ecosystem functions in the context of rewilding, I investigated the response of heath goannas (*Varanus rosenbergi*) of the Yorke Peninsula, South Australia to rewilding interventions as part of the Marna Banggara Rewilding Project (Chapter 2) and quantified their contribution to scavenging services within the landscape (Chapter 3). I found that goanna populations were increasing slowly in response to the control of invasive European mammals as part of the rewilding project. However, I suggested further action must be taken beyond merely controlling invasive species to support the recovery of reptile populations and reinstate the ecosystem functions they support. I went on to quantify the ecosystem services supported by heath goannas as scavengers and found that they play an important role in removing carcasses and reducing agriculturally harmful blowfly populations and therefore are a good candidate for rewilding to expand the range of the population and the services it supports. I used a variety of ecological modelling approaches to study the responses of *Varanus* species to climate change. Using species distribution models, I identified climatic variables as the major determinant of *Varanus* species distributions out of a suite of abiotic, biotic, and anthropogenic variables (Chapter 4). This suggested that climate change will have major and direct effects on the distributions of *Varanus* species. I went on to develop a novel ecometric modelling approach, utilising machine learning technology and fossil data to predict the responses of *Varanus* species to climate change (Chapter 5). My models predicted major range shifts in large species of *Varanus* over the next 100 years. Therefore, any rewilding projects including reptiles should integrate forecasted range shifts into their planning. This could include introducing species that have not lived in a region in recent history but are predicted to have suitable habitat there in the future, rather than reintroducing those that have recently gone extinct from an area but will not retain suitable habitat due to climate change. I brought my study of ecosystem functions and responses to climate change together to investigate the response of heath goannas to climate change and suggest appropriate conservation management responses to maintain the ecosystem functions supported by the species in the face of these changes (Chapter 6). I found that climate change is likely to drive local extinction of heath goannas from much of their current range. However, I also identified that protected areas will act as refuges from the effects of climate change. I suggested that action to expand protected areas may be the best approach to minimise the risk of local extinction of this functionally important species. My research demonstrates that large reptiles, such as members of the genus *Varanus*, provide important roles in ecosystems and should be active targets for rewilding projects. Climate change is likely to cause major and rapid shifts in reptile ranges; conservation planning needs to account for these shifts by taking forecasted range shifts into account. My findings highlight the need for conservation planning and action at large spatial and temporal scales to protect reptiles and the functions they provide for ecosystems worldwide.

Direct funding was provided by the NERC C-CLEAR DTP (grant number NE/S007164/1) and from a Chester Zoo Conservation Scholarship. Non-monetary support by access to organisational resources was provided by the Northern and Yorke Landscape Board, South Australia.