Variation in probability of first reproduction of Weddell seals
Article first published online: 27 JUN 2006
Journal of Animal Ecology
Volume 75, Issue 5, pages 1058–1070, September 2006
How to Cite
HADLEY, G. L., ROTELLA, J. J., GARROTT, R. A. and NICHOLS, J. D. (2006), Variation in probability of first reproduction of Weddell seals. Journal of Animal Ecology, 75: 1058–1070. doi: 10.1111/j.1365-2656.2006.01118.x
- Issue published online: 27 JUN 2006
- Article first published online: 27 JUN 2006
- Received 8 November 2005; accepted 28 March 2006
- age-specific recruitment;
- life-history traits;
- multistate model;
- 1For many species, when to begin reproduction is an important life-history decision that varies by individual and can have substantial implications for lifetime reproductive success and fitness.
- 2We estimated age-specific probabilities of first-time breeding and modelled variation in these rates to determine age at first reproduction and understand why it varies in a population of Weddell seals in Erebus Bay, Antarctica. We used multistate mark–recapture modelling methods and encounter histories of 4965 known-age female seals to test predictions about age-related variation in probability of first reproduction and the effects of annual variation, cohort and population density.
- 3Mean age at first reproduction in this southerly located study population (7·62 years of age, SD = 1·71) was greater than age at first reproduction for a Weddell seal population at a more northerly and typical latitude for breeding Weddell seals (mean = 4–5 years of age). This difference suggests that age at first reproduction may be influenced by whether a population inhabits the core or periphery of its range.
- 4Age at first reproduction varied from 4 to 14 years, but there was no age by which all seals recruited to the breeding population, suggesting that individual heterogeneity exists among females in this population.
- 5In the best model, the probability of breeding for the first time varied by age and year, and the amount of annual variation varied with age (average variance ratio for age-specific rates = 4·3%).
- 6Our results affirmed the predictions of life-history theory that age at first reproduction in long-lived mammals will be sensitive to environmental variation. In terms of life-history evolution, this variability suggests that Weddell seals display flexibility in age at first reproduction in order to maximize reproductive output under varying environmental conditions. Future analyses will attempt to test predictions regarding relationships between environmental covariates and annual variation in age at first reproduction and evaluate the relationship between age at first reproduction and lifetime reproductive success.