1. Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
2. Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, P.O. Box 5003, Ås 1432, Norway
3. Natural Resources Institute of Finland (Luke), Ecosystems and Ecology, Saarikoskentie 99910, Finland
4. Department of Production Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki, Paroninkuja 20, 04920 Saarentaus, Finland