Mathematical modelling for red squirrel conservation

Abstract

In this thesis we develop mathematical models to understand the impact of forest management and pine marten predation on red and grey squirrel disease-mediated competitive dynamics. Our work extends a well-tested, spatially-explicit, stochastic model framework to assess the impact of forest management plans undertaken in designated red squirrel stronghold forests in Scotland. We determine the impact of the forest management on the population viability of red squirrels, when threatened by grey squirrel invasion. The model framework is further extended to identify natural strongholds - forest sites that act as red squirrel strongholds without the need for specific forest composition plans or grey squirrel control. The results have direct implications for forest management practice and will inform an upcoming review of red squirrel conservation policy on the future of designated strongholds. The stochastic model framework was modified to include pine marten dynamics in order to assess the impact of pine marten predation on red and grey squirrel interactions. Over the last few decades pine marten have seen a recovery in their density and range in Scotland and Ireland, and this has coincided with a reduction in grey squirrel density and the recovery of red squirrels. We use the model to assess the impact of pine marten trans-locations into North Wales, with particular attention paid to the red squirrels resident on Anglesey and in Clocaenog (a forest site in North Wales). The thesis also develops a deterministic model framework to understand how a temporal refuge from predation can mediate the interactions of competing prey species. This deterministic framework is extended to consider the red and grey squirrel and pine marten system, where a temporal refuge can occur when pine marten predation is focussed on the peak phase of vole density cycles. The refuge from predation has the potential to reverse the beneficial advantage of pine marten for red squirrels, and provides a necessary note of caution for the role of pine marten as grey squirrel control agents. The work in this thesis highlights how important mathematical models are in understanding the potential impact of conservation policy on focal species in Scotland and Wales.