The devastation of the UK’s red squirrel population is well known. The breakthrough discovery that squirrelpox carried by invasive grey squirrels accelerates this decline has also received much attention. Less well known, perhaps, is that a Heriot-Watt mathematician played a key role in uncovering this important new knowledge.

Since its introduction into the UK, the grey squirrel has ‘replaced’ the native red squirrel throughout most of England and Wales, and in parts of Scotland and Ireland. Maintaining the surviving populations is a conservation priority: the red squirrel was one of the first species targeted in the UK Biodiversity Action Plan (2007).

Dr Andrew White is a theoretical ecologist in the Maxwell Institute for the Mathematical Sciences. His interest in red squirrel replacement began during a multi-disciplinary project with ecologists at Stirling University a decade ago, when he devised a mathematical model to assess how different factors affected the replacement of reds by greys. The scientific view at that time was that competition for resources was the key problem. But that theory did not square well with Dr White’s data. Scientists already knew that grey squirrels carry a pox that is vastly more deadly to their red cousins, but could not judge how much impact it had. Dr White built a model incorporating both factors, and got a good fit with the data.

Fast-forward a few years and Dr White’s work has had notable impact on environmental policy and practice. In Scotland, targeted control of greys aimed at containing the spread of squirrelpox began in 2008, together with the country-wide establishment of red squirrel strongholds covering 100,000 hectares.

With squirrelpox still a potent threat, Dr White’s modelling expertise continues to be called upon. Recently, for example, he has helped Scottish National Heritage and Forestry Commission Scotland assess strategic options to limit current and potential squirrelpox outbreaks.