1. Division of Zoology, Department of Biology, POBox 1050 Blindern, N–0316 Oslo, Norway
2. Centre forAdvanced Study, The Norwegian Academy of Science and Letters, Drammensveien 78, N– 0271 Oslo, Norway
3. Department of Statistics and Actuarial Science, University of Iowa, Iowa City, IA 52242, USA
4. Norwegian Institute for Nature Research (NINA), POBox 736 Sentrum, N–0105 Oslo, Norway
5. Institute of Mathematics and Statistics, Cornwallis Building,The University of Kent at Canterbury, Canterbury, Kent CT2 7NF, UK
6. Department of Statistics, University of Hong Kong, Hong Kong