Meeting Abstract
Breeding responses to environmental quality may be age-dependent, with implications for population dynamics under environmental change and our understanding of the ageing process. We investigated relationships between age, reproductive performance, and the El Niño Southern Oscillation (ENSO; the dominant mode of interannual climatic variation in the eastern tropical Pacific) in a long-lived Galapagos seabird, the Nazca booby (Sula granti) using 18 years of longitudinal data from known-age females. Breeding date, clutch size, and offspring production were modeled as a function of age, sea surface temperature (SST, an index of ENSO) and their interaction, among other predictors. All breeding traits varied with age. Performance first improving during early life then declining in late-life. Clutch size increased linearly with SST while the relationship between offspring production and SST was hump-shaped (warm and cool SST extremes each depressed fledging success relative to neutral conditions). Age interacted with sea surface temperature to explain variation in all breeding traits. Considering early life, SST values associated with poor average performance increased the performance discrepancy between young versus middle-aged individuals for clutch size and breeding date. Differences in the fledging success of middle-aged versus old females were also greatest in poor environmental conditions, although the opposite pattern (smaller age effects in poor breeding environments) occurred for breeding date. Age influenced the direction and magnitude of individuals’ responses to climatic variation; patterns were complex and trait-dependent and are discussed with respect to age and environment acting on the constraints individuals’ face and their optimal reproductive effort.
