1. Department of Mathematics and Mathematical Statistics, Umeå University, Umeå, Sweden
2. Evolution & Ecology Research Centre, and School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney NSW, Australia
3. Forest Ecology and Forest Management Group, Wageningen University, Droevendaalsesteeg 3a, PB Wageningen, The Netherlands
4. Evolution and Ecology Program, International Institute for Applied Systems Analysis, Schlossplatz 1, Laxenburg, Austria