Fitness prospects: effects of age, sex and recruitment age on reproductive value in a long‐lived seabird

Abstract

Summary 1.Reproductive value is an integrated measure of survival and reproduction fundamental to understanding life-history evolution and population dynamics, but little is known about intraspecific variation in reproductive value and factors explaining such variation, if any. 2. By applying generalized additive mixed models to longitudinal individual-based data of the common tern Sterna hirundo, we estimated age-specific annual survival probability, breeding probability and reproductive performance, based on which we calculated age-specific reproductive values. We investigated effects of sex and recruitment age (RA) on each trait. 3. We found age effects on all traits, with survival and breeding probability declining with age, while reproductive performance first improved with age before levelling off. We only found a very small, marginally significant, sex effect on survival probability, but evidence for decreasing age-specific breeding probability and reproductive performance with RA. 4. As a result, males had slightly lower age-specific reproductive values than females, while birds of both sexes that recruited at the earliest ages of 2 and 3 years (i.e. 54% of the tern population) had somewhat higher fitness prospects than birds recruiting at later ages. While the RA effects on breeding probability and reproductive performance were statistically significant, these effects were not large enough to translate to significant effects on reproductive value. 5. Age-specific reproductive values provided evidence for senescence, which came with fitness costs in a range of 17-21% for the sex-RA groups. 6. Our study suggests that intraspecific variation in reproductive value may exist, but that, in the common tern, the differences are small.

Reproductive costs in terrestrial male vertebrates: insights from bird studies

“…Accounting for age effects may also be recommended while investigating direct reproductive costs. Indeed, reproductive performances may be age-specific, with for example lower reproductive output at old ages compared to younger ages due to senescence [73,74], or at the opposite lower reproductive output at young ages due to inexperience [75], possibly preventing the detection of reproductive costs. Carefully disentangling the age effects from the costs of previous reproduction appears crucial.…”

Survival and local recruitment are driven by environmental carry-over effects from the wintering area in a migratory seabird

“…Although studies on demography in this species are extensive (e.g. Nisbet and Cam 2002;Ezard et al 2006;Becker et al 2008a, b;Szostek and Becker 2012;Zhang et al 2015a), little is known as yet about how environmental conditions in their year-round habitat affect demographic rates.…”

“…They usually make their first breeding attempt between the ages of 2 and 5 years (Ludwigs and Becker 2002;Szostek and Becker 2012). Recruitment age strongly affects breeding performance: older recruits have higher initial success, but younger recruits improve more between breeding attempts and have a higher overall fitness (Limmer and Becker 2010;Zhang et al 2015a), even though early and successful reproduction can result in a survival cost (Zhang et al 2015b). With increased breeding experience, parental provisioning skills improve (Limmer and Becker 2009).…”

“…With increased breeding experience, parental provisioning skills improve (Limmer and Becker 2009). The oldest breeding individuals tend to have the highest breeding success , showing reproductive senescence only after a long period of increased success (Rebke et al 2010;Zhang et al 2015a). Skipped breeding happens most often after the first breeding attempt (ca.…”

“…We assumed no difference in survival between the sexes (Nisbet and Cam 2002;Ezard et al 2006;Szostek et al 2014b;Zhang et al 2015a). The covariates were tested for inter-correlation (Appendix Table B.2).…”