Although numerous studies have reported reproductive senescence in wild animal populations, we still know very little on inter-individual differences in rates of ageing and on the factors accounting for these differences. To investigate age-related variation in breeding success in a natural population of Alpine chamois (Rupicapra rupicapra), we used 15 years of data obtained by monitoring individual ear-tagged females. Analyses at the population level confirmed the occurrence of a decline in female breeding success, which is most noticeable from 9 years of age onward. Using an age-reverse approach, we showed that senescence in female breeding success occurs at the same age, since only very old individuals (older than 16 years) showed a decline in breeding success in the years preceding death. Interestingly, we also found evidence that 'success comes from success', as females that gave birth in a given year were more likely to procreate again in the following year. Moreover, results showed that discrepancies between successful and unsuccessful individuals tend to become more relevant in the oldest age classes. There was no evidence of a terminal allocation. These results emphasize the importance of age-dependent effects and individual quality in shaping reproductive senescence in a wild long-lived ungulate.
We are grateful to all the park rangers of the Swiss National Park, especially Fadri Bott, for their work on marking and re-sighting chamois. This project was partially supported by the Italian Ministry of Education, University and Research (PRIN 2010-2011, 20108 TZKHC). F. T. was the recipient of a PhD fellowship from the University of Sassari. S. G. had the support of the P.O.R. F.S.E. 2007-2013—Obiettivo competitività regionale e occupazione. Asse IV Capitale umano—Linea di attività 1.3.1 fund. We are grateful to Jean-Michel Gaillard, Marco Festa-Bianchet and an anonymous referee for their helpful suggestions on the paper. The English version was edited by G. Falceri.
- age dependency
- individual quality