Evolution of aging in wild populations: Dynamic heterogeneity explains positive relationships between reproduction and survival

The evolutionary theory of life histories is heavily based on the tradeoff between reproduction and survival. However, evidence for this tradeoff in wild populations is scarce. In contrast to predictions, positive relationships between breeding effort in a given year and survival to the next year are commonly reported in natural populations. Such positive relationships have been argued to arise from differences in quality between individuals. We show, for a number of species, that dynamic --rather than static --differences in individual quality explain the observed positive relationships between the amount of reproduction in a given year and survival to the next year. For most species, differences in individual quality are not maintained across the whole lifetime and can therefore not explain positive relationships as argued in the classical approach. Positive or negative relationships between survival and reproduction are experienced only for relatively short periods of times in relation to the lifetime reproductive period. We also show that most of the variation in survival between individuals can not be explained by differences in respect to reproductive histories, which has considerable implications for the evolution of life-histories.