The ecological context of life history evolution.

There is now a good theoretical understanding of life history evolution, and detailed explicit optimality models have been constructed. These present a challenge for empirical work examining some of the assumptions, such as the extent and mechanisms of the costs of growth and reproduction. In addition, there is an obvious need for comparative tests of the models. These tests, properly applied, may be particularly informative because they can deal with multiple independent variables, including ecological variables, and can reveal broad trends against a background of constraints on optima and the rate of evolutionary approach to them. Life histories are the probabilities of survival and the rates of reproduction at each age in the life-span. Reproduction is costly, so that fertility at all ages cannot simultaneously be maximized by natural selection. Allocation of reproductive effort has evolved in response to the demographic impact of different environments but is constrained by genetic variance and evolutionary history.