1. Harvey, P. H. & Zammuto, R. M. Nature 315, 319–320 (1985).
2. Harper, J. L. Population Biology of Plants (Academic, London, 1977).
3. Stearns, S. C. Q. Rev. Biol. 51, 3–47 (1976).
4. Tinkle, D. W. Am. Nat. 103, 501–516 (1979).
5. O'Connor, R. J. in Behavioural Ecology, Ecological Consequences of Adaptive Behaviour (eds Sibley, R. M. & Smith, R. H.) 105–142 (Blackwell, Oxford, 1985).