1. Wilson, E. O. (1989) Threats to biodiversity, Sci. Amer.
Sept., 108–116.
2. Daily, G. C., Matson, P. A., and Vitousek, P. M. (1997) Ecosystem services supplied by soil, in G. C. Daly (ed.), Nature’s Services: Societal Dependence on Natural Ecosystems, Island Press, Washington, D.C., pp. 113–132.
3. Costanza, R. and Folke, C. (1997) Valuing ecosystem services and efficiency, fairness, and sustainability as goals, in G. C. Daly (ed.), Nature’s Services: Societal Dependence on Natural Ecosystems, Island Press, Washington, D.C., pp. 49–68.
4. van Kooten, G. C. (1998) Economics of conservation biology: a critical review, Env. Sci. Pol. 1, 13–25.
5. Schmitz, O. J. (1993) Trophic exploitation in grassland food chains: simple models and a field experiment, Oecologia
93, 327–335.