Ecology, 95(2), 2014, pp. 446–457 Ó 2014 by the Ecological Society of America From recruitment to senescence: food shapes the age-dependent pattern of breeding performance in a long-lived bird DANIEL ORO, 1,3 NOELIA HERNA ´ NDEZ, 1 LLUIS JOVER, 2 AND MERITXELL GENOVART 1 1 Population Ecology Group, Institut Mediterrani d’Estudis Avanc ¸ ats (IMEDEA), CSIC-UIB, Miquel Marque `s 21, Esporles, Mallorca 07190 Spain 2 Departamento de Salut Pu ´blica, Unitat de Bioestadı´stica, Universitat de Barcelona, Barcelona 08036 Spain Abstract. We used a long-term data set (26 years) from Audouin’s Gull (Larus audouinii ), a long-lived seabird, to address the relationship between the age-dependent pattern of reproductive performance and environmental conditions during breeding. Although theoretical models predict that the youngest and oldest breeders (due to inexperience and senescence, respectively) will perform less well than intermediate age classes, few empirical data exist regarding how this expected pattern varies with food availability. To assess the influence of age and food availability (corrected by population size of the main consumers to take into account density dependence) on a number of breeding parameters (laying dates, egg volume, clutch size, and hatching success), we modeled mean and variances of these parameters by incorporating heterogeneity into generalized linear models. All parameters varied with age and to different degrees, depending on food availability. As expected, performance improved with increased food supply, and the observed age pattern was quadratic, with poorer breeding performances occurring in extreme ages. For most parameters (except for laying dates, for which age and food did not interact), the pattern changed with food somewhat unexpectedly; the differences in performance between age classes were higher (i.e., the quadratic pattern was more noticeable) when food was more readily available than when food availability was lower. We suggest that, under poor environmental conditions, only high-quality individuals of the younger and older birds bred and that the differences in breeding performance between age classes were smaller. Although variances for egg volume were constant, variances for laying dates were highest for the youngest breeders and tended to decrease with age, either due to the selection of higher-quality individuals or to a greater frequency of birds skipping breeding with age, especially when food was in low supply. Our results show that mean and variances of breeding parameters changed with age, but that this pattern was different for each parameter and also varied according to food availability. It is likely that, other than food, certain additional factors (e.g., sex, cohort effects, density dependence) also influence changes in breeding performance with age, and this may preclude the finding of a common pattern among traits and among studies on different taxa. Key words: age pattern; Audouin’s Gull; breeding performance; Ebro Delta, western Mediterranean; food availability; Larus audouinii; long-lived birds; selection hypothesis; variance analysis. INTRODUCTION It is a well-known phenomenon in nature that the reproductive performance of individuals improves with age (Forslund and Pa¨rt 1995, Coulson et al. 2001, Bowen et al. 2006, Trumbo 2009). Younger breeders often perform badly and have lower reproductive capacity, which is related to their lack of experience in acquiring sufficient quality and quantity of resources, such as food, mates, and territories (Reid et al. 2003, Sanz-Aguilar et al. 2008). This lack of skills in first-time breeders compared to older individuals commonly translates into costs in successive breeding frequency or even in future survival (i.e., the survival–reproduction trade-off; see Stearns 2000). In many long-lived animals, a similar pattern of lower breeding performance has been found in the oldest individuals, a phenomenon known as reproductive senescence (e.g., Jones et al. 2008, Aubry et al. 2009, Rebke et al. 2010). Three nonexclusive hypotheses exist to explain the poorer performance of younger breeders. The first is the constraint hypothesis (Curio 1983), which states that individuals gain experience and skills over the years (e.g., Nol and Smith 1987, Desrochers 1992, De Forest and Gaston 1996). On the other hand, the restraint hypothesis (Curio 1983) suggests that younger breeders that have higher residual reproductive value than older individuals should reduce their reproductive effort to avoid incurring high survival costs (e.g., Ericsson et al. 2001, Velando et al. 2006). Finally, the selection hypothesis advocates the existence of a selection filter, Manuscript received 21 February 2013; revised 6 June 2013; accepted 26 June 2013; final version received 28 July 2013. Corresponding Editor: G. Nevitt. 3 E-mail: d.oro@uib.es 446