Background/Question/Methods Variations in the reproductive and survival abilities of individuals within a population are ubiquitous in nature, key to individual fitness, and affect population dynamics. Thus, there is great interest in understanding the patterns, causes, and consequences of vital-rate variation. For long-lived species, long-term studies of large samples of known-age individuals are required to evaluate how vital rates vary by age, reproductive history, and other individual characteristics across diverse extrinsic (environment) and intrinsic (population attributes) conditions. A population of Weddell seals in Erebus Bay, Antarctica with high site fidelity has been intensively studied each Austral spring since the 1960s. Since 1982, all newborns have been tagged each year, multiple mark-recapture surveys have been conducted during each pupping season, and a series of vital rate analyses have been conducted using mark-recapture modeling of data from many thousands of known-age females with known reproductive histories across diverse conditions.
Results/Conclusions Estimated female survival rates are modest in the first two years of life and then high until reproduction commences, typically at 7-8 years of age. Conditions experienced early in life are related to survival at young ages but not at older ages. Hierarchical analyses that considered age, reproductive state, year, and individual identity provide clear evidence of age-related changes in vital rates, costs of reproduction to survival and future reproduction, and survival and reproductive senescence. Although more work is needed regarding the drivers of annual variation in vital rates, demographic buffering has been demonstrated to occur such that age-specific survival rates for adults are quite stable, whereas reproduction is much more variable among years. Age-specific probabilities of reproduction also vary greatly among individual females such that some individuals have much greater lifetime reproductive output than others. Ongoing analyses with integral projection models are evaluating the importance of individual heterogeneity in vital rates to population growth rates and seek to improve our understanding of population dynamics and our ability to predict population responses to environmental variation.
