Malthusian Relativityι**=7/3ψ
Life history evolution - traits & transitions

Lack's clutch size

Fig. 1 Left: Relative fitness (total reproductive value) as a function of brood size for great tit. Data from Tinbergen and Daan (1990). Right: Relative fitness (total reproductive value) as a function of brood size for kestrel. Data from Daan et al. (1990). Filled circles are natural brood sizes, and open circles manipulated brood sizes, showing that both species have brood sizes close to the fitness optimum.

Lack’s fitness trade-off between current reproduction and future survival has been documented in a number of species (e.g., Lack, 1954; Boyce and Perrins, 1987; Tinbergen and Daan, 1990; Daan et al., 1990). It is illustrated in Fig. 1 for the great tit and the kestrel. Both species have a natural brood size with a higher fitness than could be obtained from manipulated broods that were either larger or smaller than the natural brood size.


  • Boyce, M.S., and C.M. Perrins 1987. Optimizing great tit clutch size in a fluctuating environment. Ecology 68:142--153.
  • Daan, S., C.Dikstra and J.M. Tinbergen 1990. Family planning in the kestrel ( Falco tinnunculus): The ultimate control of covariation of laying data and clutch size. Behavior 114:83--116.
  • Lack, D. 1954. The natural regulation of animal numbers. Oxford University Press, Oxford.
  • Tinbergen, J.M., and S.Daan 1990. Family planning in the great tit ( Parus major): Optimal clutch size as integration of parent and offspring fitness. Behavior 114:161--190.