Detecting Density Dependence in Recovering Seal Populations
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Time series of abundance estimates are commonly used for analyses of population trends and possible shifts in growth rate. We investigate if trends in age composition can be used as an alternative to abundance estimates for detection of decelerated population growth. Both methods were tested under two forms of density dependence and different levels of environmental variation in simulated time series of growth in Baltic gray seals. Under logistic growth, decelerating growth could be statistically confirmed after 16 years based on population counts and 14 years based on age composition. When density dependence sets in first at larger population sizes, the age composition method performed dramatically better than population counts, and a decline could be detected after 4 years (versus 10 years). Consequently, age composition analysis provides a complementary method to detect density dependence, particularly in populations where density dependence sets in late.
KeywordsDensity-dependent population growth Age-structured populations Population management Detecting population trends Environmental stochasticity
Financial support was provided by the Swedish Environmental Protection Agency, the Royal Society of Arts and Sciences in Göteborg, and the Centre of Theoretical Biology at the University of Göteborg. Many thanks to Ailsa J. Hall for useful comments on earlier drafts.
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