Generation time determines the pace of key demographic and evolutionary
processes. Quantified as the weighted mean age at reproduction, it can
be studied as a trait that varies within and among populations and may
evolve in response to ecological conditions. We combined quantitative
genetic analyses with age- and density-dependent models to study
generation time variation in a bird metapopulation. Generation time was
heritable, and males had longer generation times compared with females.
Individuals with longer generation times had a higher lifetime
reproductive success but not a higher expected population growth rate.
Density regulation acted on recruit production, suggesting that longer
generation times should be favored when populations are closer to
carrying capacity. Furthermore, generation times were shorter when
populations were growing, and longer when populations were closer to
equilibrium or declining. These results support classic theory
predicting that density regulation is an important driver of the pace of
life-history strategies.