1. Centre d’Ecologie Fonctionnelle et Evolutive, CNRS, UMR 5175, 1919 route de Mende, 34293 Montpellier Cedex 5, France;
2. INRA, Agronomy Research Unit, Grassland Ecosystem Research Team, 234 Avenue du Brézet, 63100 Clermont‐Ferrand, France;
3. The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK;
4. Biomathematics and Statistics Scotland, The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK