1. Center for Ecological Research, Kyoto University, Otsu, 520–2113 Japan;
2. Graduate School of Environmental Earth Sciences, Hokkaido University, Sapporo, 060 Japan;
3. Department of Geography, University of Cambridge, Downing Place, Cambridge, CB2 3EN UK;
4. The Arnold Arboretum, 22 Divinity Avenue, Cambridge, MA 02138, USA;