Data from: Heterogeneity in individual quality in birds: overall patterns and insights from a study on common terns

While life-history theory predicts a trade-off between reproduction and
survival, positive covariance, indicative of heterogeneity in individual
quality, is often reported among individuals from natural populations. We
review longitudinal studies of wild bird populations that test the
relationship between annual reproductive success and lifespan and find the
majority to report a positive correlation, while none reports a negative
correlation. Heterogeneity in individual quality in resource acquisition,
masking resource-based trade-offs, therefore appears to be common in
birds. Considering that there is little evidence for heritable variation
in fitness, heterogeneity in individual quality among adults may be due to
life-long effects of developmental conditions. In a 20-year case study on
common terns (Sterna hirundo), we test for life-long effects of cohort
quality and within-cohort nest quality, but find no significant effects on
long-term proxies of quality. Since other studies do find strong life-long
effects of developmental conditions, we suggest that the brood reduction
strategy adopted by common terns, causing the majority of offspring to die
rapidly after hatching, efficiently reduces variation in offspring quality
at independence. As such, a brood reduction strategy may contribute to
reduced heterogeneity in adult survival in stochastic environments, both
suggested to be more common and adaptive in long-lived species. Further
study is required to assess heterogeneity in individual reproduction,
especially in relation to environmental stochasticity and species’
life-history strategies, in order to assess whether the relative strength
of selection in early and late life may indeed affect the magnitude of
heterogeneity in individual quality over life, and how this is mediated by
parent-offspring conflict.