1. Instituto Gulbenkian de Ciência, Apartado 14, 2781-901 Oeiras, Portugal
2. Departamento de Biologia Vegetal & CMAF, Faculdade de Ciências de Lisboa, Bloco C2, Piso 4, Campo Grande, 1749-016 Lisboa, Portugal
3. Ecology and Epidemiology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK