Partitioning variance in reproductive success, within years and across lifetimes

Variance in reproductive success (![Graphic][1], with k =number of offspring) plays a large role in determining the rate of genetic drift and the scope within which selection acts. Various frameworks have been proposed to parse factors that contribute to ![Graphic][2], but none has focused on age-specific values of ![Graphic][3], which indicate the degree to which reproductive skew is overdispersed (compared to the random Poisson expectation) among individuals of the same age and sex. Here, an ANOVA sums-of-squares framework is used to partition variance in annual and lifetime reproductive success into between-group and within-group components. For annual reproduction, the between-age effect depends on age-specific fecundity ( b x ), but relatively few empirical data are available on the within-age effect, which depends on ϕ x . By defining groups by age-at-death rather than age, the same ANOVA framework can be used to partition variance in lifetime reproductive success into between-group, within-group, and longevity components. Analyses of simulated data and worked examples for black bears and great tits illustrate the methods and show that the largely-neglected within-age effect a) typically represents a substantial component of the overall variance (even under a null model of random reproductive success), and b) can dominate the overall variance when ϕ x >1. ### Competing Interest Statement The authors have declared no competing interest. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif