Affiliation: | (1) Department of Mathematics and Statistics, Agricultural University of Norway, 1432 Aas-NLH, Norway;(2) Zoological Institute, University of Oslo, P.O. Box 1050, Blindern, Oslo 3, Norway;(3) Norwegian Forest Research Institute, P.O. Box 61, 1432 Aas-NLH, Norway;(4) Department of Animal Ecology, University of Lund, Ecology Building, S-223 62 Helgonavägen 5, Lund, Sweden |