Ecology of translocated pine martens Martes martes and their impacts on grey squirrels Sciurus carolinensis
Date: 21 October 2019
University of Exeter
PhD in Biological Sciences
The rate of biodiversity loss has been increasing since the beginning of the Anthropocene, driven by climate change, human population expansion and environmental degradation. Consequently, ecosystems have become simplified through the loss of important processes and species. Ecological restoration aims to reverse such changes through ...
The rate of biodiversity loss has been increasing since the beginning of the Anthropocene, driven by climate change, human population expansion and environmental degradation. Consequently, ecosystems have become simplified through the loss of important processes and species. Ecological restoration aims to reverse such changes through reinstating habitats, native species and their associated relationships, as well as removing invasive, non-native species. One strategy to restore ecological function is through the re-establishment of top-down processes driven by predators. The cascading effects of these predators, through direct predation and the fear they induce in prey can restore predator-prey dynamics in a disrupted food web. In this thesis, I investigate the restoration of a native and recovering predator, the pine marten Martes martes, with particular focus on its ecology and behaviour after a translocation event from Scotland to Wales. Subsequently, I assess its impact on the behaviour of one of its prey species, the invasive, non-native grey squirrel Sciurus carolinensis to better understand the relationship between these two species. I first introduce predator restoration using translocation in a project that aims to reintroduce and restore the native pine marten. I demonstrate that the phases of post-translocation movement comprise a period of ‘exploration’ followed by ‘settlement’ in all individuals, however the extent and duration of these movements differ between release groups. I show that conspecific presence is important in site fidelity and the resulting habitat in which martens establish themselves. I then investigate the diet of translocated martens at a population and individual level, before and after translocation. I reveal that pine martens consume a more diverse diet post-translocation, which incorporates grey squirrels, a prey item not found in their source sites in Scotland. Furthermore I document a degree of dietary specialisation within individuals, which is maintained relative to others after translocation. This suggests pine martens are facultative specialists with dietary preferences that they are able to supplement with readily available prey groups, enhancing their probability of survival after translocation. 6 Next, I address the impact of translocated pine martens on grey squirrel space use and survival. Grey squirrel range size and daily distance travelled was found to increase with increasing marten exposure. However, an impact on grey squirrel survival and range location was not found within the timeframe of this study. I then investigated the role that fear plays in the relationship between pine martens and grey squirrels. Using feeding experiments, I document a reduced volume of food consumed by squirrels in woodlands containing pine martens, suggesting that squirrels ‘give-up’ foraging earlier under such conditions. This suggests that squirrels display a fear-mediated response to pine marten risk, which in time may be detrimental to grey squirrel fitness. I consider the role of predation and fear in predator-prey dynamics and its importance in species management. Finally I conclude the key findings of this thesis with regards to pine marten and grey squirrel management in the UK, as well as their contribution to carnivore restoration and species management strategies. This work identifies that social structure and dietary flexibility are key considerations for predator restoration projects. Furthermore, the cascading effects of predators can play a potential role in the management of invasive non-native species, which may be more economically and socially acceptable than current strategies. This work highlights the importance of studying ecological processes underlying landscape-scale patterns to better inform the management of native and non-native species alike.
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