1. Alterra, Animal Ecology Team; PO Box 47, 6700 AA; Wageningen; The Netherlands
2. Department of Animal Ecology and Tropical Biology; Biocenter, University of Würzburg; Am Hubland, 97074; Würzburg; Germany
3. Finnish Environment Institute; Natural Environment Centre; Ecosystem Change Unit; P.O. Box 140; FI-00251; Helsinki; Finland
4. School of Agriculture, Policy and Development; University of Reading; Reading; RG6 6AR; UK
5. Department of Biology & Centre of Environmental and Climate Research; Lund University; S-223 62; Lund; Sweden