1. School of Geosciences; University of Edinburgh; Geography Building Drummond Street Edinburgh EH8 9XP UK
2. Centre for Research into Ecological and Environmental Modelling; University of St Andrews; Buchanan Gardens St Andrews KY16 9LZ UK
3. Department of Mathematical Sciences; Norwegian University of Science and Technology; 7491 Trondheim Norway
4. School of Biological Sciences; University of Aberdeen; Cruickshank Building St Machar Drive Aberdeen AB24 3UU UK