1. Department of Geography and Biodiversity Research Centre; University of British Columbia; Vancouver BC V6T 1Z4 Canada
2. German Centre for Integrative Biodiversity Research and University of Leipzig; Leipzig 04103 Germany
3. National Ecological Observatory Network; Boulder CO 80301 USA
4. Department of Ecology and Evolutionary Biology; University of Colorado; Boulder CO 80309 USA
5. Periglacial Research Unit; Alfred Wegener Institute; Potsdam 14473 Germany
6. Département de biologie; Universitè de Sherbrooke; Sherbrooke QC J1K2R1 Canada