1. Section of Ecology; Department of Biology; University of Turku; FIN-20014 Turku Finland
2. Biogeco; INRA; Univ. Bordeaux; F-33610 Cestas France
3. Irstea; UR EFNO; F-45290 Nogent-sur-Vernisson France
4. Dynafor; INPT; EI Purpan; INRA; Univ. Toulouse; F-31320 Auzeville France