1. Department of Mathematics and Statistics; Maynooth University; Maynooth Co. Kildare Ireland
2. Department of Ecology, Evolution, and Behavior; University of Minnesota; St Paul Minnesota 55108 USA
3. Waterford Institute of Technology; Cork Road Waterford Ireland
4. School of Mathematical Sciences; Ecological and Environmental Modelling Group; University College Dublin; Dublin 4 Ireland
5. Teagasc, Environment Research Centre; Johnstown Castle; Wexford Ireland