1. Pimm, S. L. The structure of food webs. Theor. Popul. Biol. 16, 144–158 (1979)
2. May, R. M. Stability and Complexity in Model Ecosystems (Princeton Univ. Press, 1973)
3. Simon, H. A. in General Systems: Yearbook of the Society for General Systems (eds von Bertalanffy, L. & Rapaport, A.) Vol. 10 63–76 (Society for General Systems, Ann Arbor, Michigan, 1965)
4. McNaughton, S. J. Stability and diversity of ecological communities. Nature 274, 251–252 (1978)
5. Simmel, G. The Sociology of Georg Simmel (transl. and ed. Wolff, K. H.) (Free Press, Glencoe, Illinois, 1950)