Jean-Yves Monnat

Individual Covariation in Life‐History Traits: Seeing the Trees Despite the Forest

We investigated the influence of age on survival and breeding rates in a long‐lived species Rissa tridactyla using models with individual random effects permitting variation and covariation in fitness components among individuals. Differences in survival or breeding probabilities among individuals are substantial, and there was positive covariation between survival and breeding probability; birds that were more likely to survive were also more likely to breed, given that they survived. The pattern of age‐related variation in these rates detected at the individual level differed from that observed at the population level. Our results provided confirmation of what has been suggested by other investigators: within‐cohort phenotypic selection can mask senescence. Although this phenomenon has been extensively studied in humans and captive animals, conclusive evidence of the discrepancy between population‐level and individual‐level patterns of age‐related variation in life‐history traits is extremely rare in wild animal populations. Evolutionary studies of the influence of age on life‐history traits should use approaches differentiating population level from the genuine influence of age: only the latter is relevant to theories of life‐history evolution. The development of models permitting access to individual variation in fitness is a promising advance for the study of senescence and evolutionary processes.

ARE ADULT NONBREEDERS PRUDENT PARENTS? THE KITTIWAKE MODEL

Understanding evolutionary consequences of intermittent breeding (non- breeding in individuals that previously bred) requires investigation of the relationships between adult breeding state and two demographic parameters: survival probability and subsequent breeding probability. One major difficulty raised by comparing the demographic features of breeders and nonbreeders as estimated from capture-recapture data is that breed- ing state is often suspected to influence recapture or resighting probability. We used mul- tistate capture-recapture models to test the hypothesis of equal recapture probabilities for breeding and nonbreeding Kittiwakes and found no evidence of an effect of breeding state on this parameter. The same method was used to test whether reproductive state affects survival probability. Nonbreeding individuals have lower survival rates than breeders. Moreover, nonbreeders have a higher probability of being nonbreeders the following year than do breeders. State-specific survival rates and transition probabilities vary from year to year, but temporal variations of survival and transition probabilities of breeders and nonbreeders are in parallel (on a logit scale). These inferences led us to conclude that nonbreeders tend to be lower quality individuals. The effect of sex was also investigated: males and females do not differ with respect to survival probabilities when reproductive state is taken into account. Similarly, there is no effect of sex on transition probabilities between reproductive states.

Timing of prospecting and the value of information in a colonial breeding bird

We investigated if one category of birds, prospectors, i.e. those likely to seek future breeding sites, attempt to gather information on the local reproductive success of their conspecifics. If prospecting is an important information-gathering process, it should occur when reliable estimation of the local reproductive success can be made. We tested this prediction in a colonial seabird, the Kittiwake Rissa tridactyla, by monitoring the number of prospectors and the value of the information available on local reproductive success in a series of breeding cliffs during two breeding seasons. We found that the bulk of prospecting occurred when the best information on local reproductive success was available. The pattern was very similar in the two study years (1985 and 1992); prospecting occurred late in the season, as reported for most bird species. This result is consistent with the potential use of conspecific reproductive success as a proximate cue for habitat selection.

Now you see him, now you don't: experience, not age, is related to reproduction in kittiwakes.

In long-lived species, individuals can skip reproduction. The proportion of breeders affects population growth rate and viability, there is a need to investigate the factors influencing intermittent breeding. The theory predicts that if lack of experience is an important constraint, breeding probabilities should increase with experience for individuals of the same age, whereas under the so-called restraint hypothesis, breeding probabilities should increase with age regardless of experience. However, because the probability of detecting individuals in the wild is generally less than 1, it is difficult to know exactly the number of previous breeding episodes (breeding experience). To cope with this issue, we developed a hidden process model to incorporate experience as a latent state possibly influencing the probability of breeding. Using a 22-year mark-recapture dataset involving 9970 individuals, we analysed simultaneously experience and age effects on breeding probabilities in the kittiwake (Rissa tridactyla). We did not detect an influence of age on adult breeding probabilities. We found that inexperienced birds breed less frequently than experienced birds. Our approach enables us to highlight the key role of experience on adults breeding probabilities and can be used for a wide range of organisms for which detection is less than 1.

Habitat Selection, Age-Specific Recruitment and Reproductive Success in a Long-Lived Seabird

Delayed recruitment (i.e. first reproduction) is a key feature of the demography of long-lived species such as seabirds. If physiological, behavioral, and environmental factors are thought to influence age at first breeding, knowledge of the fitness prospects corresponding to different recruitment tactics is needed to get insight into the evolution of delayed recruitment.