1Macaulay Institute, Craigiebuckler, Aberdeen, Scotland, AB15 8QH, UK
2Universiteit Hasselt, Environmental Biology, Centre for Environmental Sciences, Limburgs Universitair Centrum, B-3590 Diepenbeek, Belgium
3Vlaamse Instelling voor Technology Onderzoek, B-2400 Mol, Belgium
4Brookhaven National laboratory, Biology Department, Upton, NY 11973, USA