No abstract

An individual's age at first reproduction and investment in successive reproductive attempts are involved in mechanisms that can impede somatic repair, resulting in a decline in reproductive abilities with age (reproductive senescence). We used long-term data from the Black-legged Kittiwake, a long-lived seabird, to address the relationship between recruitment age, age-specific breeding success (BS), and reproductive senescence, while accounting for breeding experience and temporal variation in BS. We first detected late-life improvement in BS across all recruitment groups, which we recognized as "within-generation selection" or the selective disappearance of "frail" phenotypes. When such heterogeneity was accurately accounted for, we showed that all individuals suffered reproductive senescence. We first highlighted how different combinations of pre- and post-recruitment experience across recruitment groups resulted in maximal BS at intermediate ages. BS increased in early recruits as they gained post-recruitment experience, whereas late recruits gained pre-recruitment experience that led to high BS at recruitment. Only individuals recruiting at intermediate ages balanced their pre- and post-recruitment experience. Consistent with the "cumulative reproductive cost hypothesis," we also observed a faster decline in BS in early recruits at advanced ages, whereas individuals delaying recruitment experienced the slowest decline in BS with age. Early recruits, however, reached the highest levels of BS at intermediate ages, sensus stricto (10-13 years old), whereas individuals delaying recruitment experienced the lowest at similar ages. These divergent trajectories may reflect a "delayed trade-off" balancing a maximization of midlife BS against reproductive senescence at advanced ages. Additionally, annual variation in BS had a greater effect on individuals early in life, suggesting that experienced individuals were able to buffer out the effects of temporal variation on BS, which can ultimately improve fitness in stochastic environments. Our findings stress that (1) both observed and unobserved heterogeneity are important in detecting within-individual senescence, and (2) short-term trade-offs may be rare in long-lived species; thus, cumulated reproductive costs should be invoked as an alternative mechanism underlying reproductive senescence.

Heterogeneity in individual quality can be a major obstacle when interpreting age‐specific variation in life‐history traits. Heterogeneity is likely to lead to within‐generation selection, and patterns observed at the population level may result from the combination of hidden patterns specific to subpopulations. Population‐level patterns are not relevant to hypotheses concerning the evolution of age‐specific reproductive strategies if they differ from patterns at the individual level. We addressed the influence of age and a variable used as a surrogate of quality (yearly reproductive state) on survival and breeding probability in the kittiwake. We found evidence of an effect of age and quality on both demographic parameters. Patterns observed in breeders are consistent with the selection hypothesis, which predicts age‐related increases in survival and traits positively correlated with survival. Our results also reveal unexpected age effects specific to subgroups: the influence of age on survival and future breeding probability is not the same in nonbreeders and breeders. These patterns are observed in higher‐quality breeding habitats, where the influence of extrinsic factors on breeding state is the weakest. Moreover, there is slight evidence of an influence of sex on breeding probability (not on survival), but the same overall pattern is observed in both sexes. Our results support the hypothesis that age‐related variation in demographic parameters observed at the population level is partly shaped by heterogeneity among individuals. They also suggest processes specific to subpopulations. Recent theoretical developments lay emphasis on integration of sources of heterogeneity in optimization models to account for apparently “sub‐optimal” empirical patterns. Incorporation of sources of heterogeneity is also the key to investigation of age‐related reproductive strategies in heterogeneous populations. Thwarting “heterogeneity's ruses” has become a major challenge: for detecting and understanding natural processes, and a constructive confrontation between empirical and theoretical studies.

Naves, L. C., Monnat, J. Y. and Cam, E. 2006. Breeding performance, mate fidelity, and nest site fidelity in a long-lived seabird: behaving against the current? Á Oikos 115: 263 Á276.There is evidence that breeding failure is associated with divorce and dispersal in many bird species. However, deviations from the general pattern ''success-stay/failure-leave'' seem to be common, suggesting that factors other than breeding performance may importantly influence mate and habitat selection. Moreover, variability in response to performance suggests coexistence of different evolutionary strategies of mate and site selection within a population. In this study, we assessed how individuals conform to the success-stay/failure-leave pattern in kittiwakes (Rissa tridactyla ), and aimed to identify categories of individuals presenting different behavioural patterns. We considered individual attributes (experience, prior residence at the nest site, performance in multiple breeding attempts), pair attributes (arrival asynchrony, timing of failure, pair duration), and productivity in habitat patches. Timing of failure was an important factor. Pair reunion probability was close to 0.5 in failed pairs, but it was consistently higher in early failed than in late failed pairs. Prior residence better explained variability in probability of reunion in failed pairs than pair duration. However, the positive influence of prior residence on the probability of reunion was perceptible only in early failed pairs. Divorce probability in successful pairs increased with arrival asynchrony, and was higher in first-time than in experienced breeders. Local productivity positively influenced site fidelity probability in early failed birds, but not in late failed ones. Using memory models, we found that dispersal decisions integrate information on individual breeding performance in a temporal scale longer than one year. This study contributed to the identification of relevant states to be considered when addressing mate and nest site choice. Natural selection may operate on slight fitness differences that cannot be detected without high levels of stratification according to the appropriate individual and habitat attributes. L. C. Naves (liliananaves@yahoo.com), Univ. Pierre et Marie Curie, Laboratoire d'É cologie, Bât A7 case 237. 7, quai St Bernard, FR-75252 Paris cedex 05,

Many studies have provided evidence that, in birds, inexperienced breeders have a lower probability of breeding successfully. This is often explained by lack of skills and knowledge, and sometimes late laying dates in the first breeding attempt. There is growing evidence that in many species with deferred reproduction, some prebreeders attend breeding places, acquire territories and form pairs. Several behavioural tactics assumed to be associated with territory acquisition have been described in different species. These tactics may influence the probability of recruiting in the breeding segment of the population, age of first breeding, and reproductive success in the first breeding attempt. Here we addressed the influence of behaviour ('squatting') during the prebreeding period on demographic parameters (survival and recruitment probability) in a long-lived colonial seabird species: the kittiwake. We also investigated the influence of behaviour on reproductive trajectory. Squatters have a higher survival and recruitment probability, and a higher probability of breeding successfully in the first breeding attempt in all age-classes where this category is represented. The influence of behaviour is mainly expressed in the first reproduction. However, there is a relationship between breeding success in the first occasion and subsequent occasions. The influence of breeding success in the first breeding attempt on the rest of the trajectory may indirectly reflect the influence of behaviour on breeding success in the first occasion. The shape of the reproductive trajectory is influenced by behaviour and age of first breeding. There is substantial individual variation from the mean reproductive trajectory, which is accounted for by heterogeneity in performance among individuals in the first attempt, but there is no evidence of individual heterogeneity in the rate of change over time in performance in subsequent breeding occasions