The use of Spatially Explicit Population Dynamics Models (SEPMs) as a tool for red squirrel conservation
Peter Lurz and Steve Rushton
Introduction
The future of red squirrels and many other threatened species in Britain will depend on an understanding of their ecology and their interactions with the landscape (Gurnell & Lurz 1997). Red squirrel conservation will require appropriate habitat management in selected, suitable areas in order to ensure long-term population viability. Forest ecosystems managed for timber production are constantly changing environments. They are subject to human interventions in the shape of harvesting and planting operations as well as recreational and other activities. Safeguarding endangered species in these environments is therefore a balancing act and requires multipurpose management strategies. Population dynamics models linked to a Geographic Information System (GIS) provide tools that allows predictions on the future distribution and viability of red squirrels or other species to be made under different ‘what if’ scenarios. They offer the opportunity to explore the impact of different forest design plans, management regimes (Rushton et al. 1997, 1999)or the impact of disease outbreaks on red squirrel population viability (Rushton et al. in press).
Definitions
Process-based models for modelling species distributions are based on the premise that the distribution of a species in the landscape arises from interactions between individual behavioural processes such as home-range behaviour, territoriality and dispersal and the life-history processes of births and deaths. In these models the habitat data act as templates on which the populations processes occur and the distribution of organisms in the landscape emerges as the model is run. The models are spatially referenced which means that they are linked to a map of a ‘real’ landscape, which generally includes information on the location of woodlands, habitat type (e.g. coniferous or deciduous), tree species and age. This is usually stored in a igitised format within a Geographical Information System (GIS) which allows map manipulations and data extraction. The models can be run for single species under different fecundity, mortality, dispersal and forest management regimes (e.g. control, changes in forest design) or for several species (e.g. red and grey squirrels) together. In these cases, species interactions such as competition, disease transmission or predation (e.g. mink, water vole) can be included in the model.
Examples of recent model applications
We have used models to predict red squirrel distributions and population dynamics in several different projects. We investigated the effect of woodland size and landscape connectivity on the Isle of Wight on red squirrel population viability for English Nature. The results (Rushton et al. 1999) suggested that dispersal on the Isle of Wight is restricted and stressed that some large interconnected woodlands should be maintained if red squirrels are to be conserved for the future. Corridors between woodlands will encourage dispersal and recolonisation of smaller fragments, but may also facilitate the spread of disease.
Other ongoing projects in collaboration with John Gurnell and supported by the Forestry Commission, CCW and JNCC, investigate:
- immunocontraception as a method for grey squirrel control to save red squirrels
- the impact of grey squirrels as vectors for disease (parapoxvirus)
- the utility of SEPM to identify potential conservation areas for red squirrels
The modelling work at CLUWRR has been linked to field projects on cone crop monitoring and red squirrel habitat use in spruce plantations (Lurz et al. 1995, 1997, 1998, 2000), red and grey squirrel competition (Wauters et al. in press) and a project by Amanda Lloyd on red squirrel population viability in Kielder Forest in relation to forest design, management and potential grey squirrel colonisation (see other project information).
Acknowledgements
We would like to thank the Forestry Commission, JNCC, CCW, English Nature and the People’s Trust for Endangered Species for their support. We are also grateful to Forest Enterprise Kielder Forest District, Royal Airforce at Spadeadam, Harry Pepper, Bill Burlton, Neville Geddes, John Gilbert and Roy Sanderson for their help and assistance.
Literature is listed on the Publications webpage