Abstract
Several studies of marine top predators, above all of seabirds, have analysed the effects of either individual age or environmental fluctuations on reproduction; nevertheless, little is known about the age patterns in breeding performance in a variable environment. To investigate the simultaneous influence of age and environmental conditions on laying dates and egg volumes, we tested different climate and food availability indices in a transequatorial migratory seabird using female data from a 23-year study. Our results show an initial improvement in breeding parameters with age (i.e. earlier laying dates and greater egg volumes) but no pattern of senescence in older age groups. The best models showed an interaction of time and age in breeding performance, i.e. the age pattern of breeding performance changed each year likely as a result of environmental variability. Nevertheless, climatic indexes used here explained part of that annual variability: NAO and SOI index accounted for 24% and 20% of deviances in laying dates and egg volume respectively. Part of that unexplained variability might be related to other processes such as intermittent breeding and the individual quality of breeders, which were not assessed in our study.
Highlights
In marine ecosystems, climatic fluctuations and other physical oceanographic variables affect the population dynamics of organisms by exerting an influence on their vital rates
Environmental covariates were negatively associated with the parameters considered, but this association was statistically significant, the covariates explained a relatively small part of the total temporal variability (NAO winter index explained about 24% of variance in laying date and Southern Oscillation Index (SOI) index 20% in egg volume; Table 2)
Fishing discards taken as a proxy of food availability had a positive effect on both parameters, but the variance explained was low and this effect cannot be considered an important predictor of laying dates and egg volume
Summary
Climatic fluctuations and other physical oceanographic variables affect the population dynamics of organisms by exerting an influence on their vital rates. Large-scale climatic phenomena and oceanographic processes produce changes in water temperatures and currents that generate spatio-temporal variation in the production, distribution, and abundance of the prey consumed by marine predators such as seabirds (Durant et al, 2004). These processes may affect the foraging ecology of seabirds (Navarro and Gonzalez-Solís, 2009; Weimerskirch et al, 2012) and influence their survival, reproduction and population dynamics (Jenouvrier et al, 2005; Genovart et al, 2013).
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