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, Wageningen, The Netherlands.
4 Evolution and Ecology Program, International Institute for Applied Systems Analysis, Schlossplatz 1, Laxenburg, Austria.