Acknowledgements
We thank C. Godin for having provided the Figure 2*a. We warmly thank A. Cambien, A. Banos, J. Baudry, P. Couteron, and D. Lo Seen for their advice during the process of writing this paper. This synthesis was developed in the course of several projects funded by the Agence Nationale de la Recherche (projects “BiodivAgriM” and “INC”, ANR-biodiversité 2007, project “STAMP”, ANR-blanc 2007). We are thankful to anonymous reviewers for their helpful comments and suggestions on an earlier draft.