1School of Biological Sciences, University of Aberdeen, Cruickshank Building, St. Machar Drive, Aberdeen, AB24 3UU, UK
2NERC Centre for Ecology and Hydrology, Hill of Brathens, Banchory, Aberdeenshire AB31 4BW, UK
3National Centre for Advanced Bio-Protection Technologies, P.O. Box 84, Lincoln University, Canterbury, New Zealand