1. Boucher, D.H., James, S. & Keeler, K. Am. Rev. ecol. Syst. 13 (in the press).
2. May, R.M. (ed.) Theoretical Ecology: Principles and Applications, Ch.5 (Blackwell, Oxford, 1976).
3. Taylor, L.R. & Elliott, J.M. J. Anim. Ecol. 50, 951 (1981).
4. Vandermeer, J.H. & Boucher, D.H. J. theor. Biol. 74, 549 (1978).
5. Goh, B.S. Am. Nat. 113, 261 (1979).