Age-related reproduction: Conceptual revisions and empirical tests

Improvement in reproductive performance with age, up to a point of senescence, is a predominant pattern among vertebrates. The proximate underpinnings of such patterns are of increasing interest to evolutionary biologists, although they are not well characterized in the literature. To facilitate greater understanding of this topic, I (1) derived a hypothesis-testing framework to delineate six social and ecological factors thought to underlie within- individual improvements in age-related reproduction (ARR), organized the current literature on this topic to summarize the support for each factor and suggested future experimental and statistical approaches. I next (2) applied this framework to identify both patterns of ARR and covariates of ARR, utilizing a longitudinal data set from North American barn swallows. I conclude that within-individual analyses yield the most informative results in ARR, and underscore the crucial role that life history theory plays in shaping ARR and its proximate underpinnings.