Ian A N Dublon1, David J T Sumpter2. 1. Biodiversity Research Centre, Earth and Life Institute, Université Catholique de Louvain (UCL), 1348 Louvain-la-Neuve, Belgium. 2. Mathematics Department, Uppsala University, Box 480 751 06, Uppsala, Sweden. Electronic address: david.sumpter@math.uu.se.