1. Community and Conservation Ecology Group, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands
2. Institute of Biology / Geobotany and Botanical Garden, Martin Luther University Halle‐Wittenberg, Am Kirchtor 1, 06108 Halle, Germany
3. Natural Sciences, Bennington College, Bennington VT 05201, USA;