Abstracts (first author)
Indicators of selection pressure, and changes in vital rates at multiple ages: a general method
Hamilton's (1966) indicators of selection pressure on age-specific additive changes in mortality and fecundity have provided evolutionary biology with the key to study evolutionary effects of age-specific changes in vital rates. However, other indicators of ‘selection pressure’, the sensitivity of fitness to some standardized perturbation of a vital rate, have been proposed and advocated, involving non-additive changes in vital rates (Baudisch 2005), or changes that involve multiple ages (Hamilton 1966, Abrams 1991). In addition, it may be wearisome to obtain an indicator of selection pressure on more complex patterns of change across ages. Realizing that any eventual effect on fitness results not only from selection pressure, but also from the force of perturbation of the vital rates, we develop the calculus to evaluate the effect on fitness of the combination of selection pressure with a perturbation function. We apply this calculus to: 1) show that other indicators of selection pressure can be derived from Hamilton’s ‘elementary’ indicators on additive perturbations; 2) show that choosing an indicator of selection pressure and the appropriate perturbation function is merely a matter of parameterization, rather than a true conceptual difference; 3) propose to use Hamilton’s indicators of additive change for all analyses, since in this way all the biological variation is contained in the perturbation function; and 4) investigate in what direction a resident phenotype may evolve under some given life-history trade-off that produces change in age-patterns of fecundity and/or mortality. Under 4), the central idea is that life-history trade-offs can be presented as perturbation functions that lead to a different perturbation (different magnitude and direction) at different ages. Implications for the evolutionary theory of aging are discussed.