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Detecting density dependence in recovering seal populations

Journal article
Authors Carl Johan Svensson
Anders Eriksson
Tero Harkonen
Karin C. Harding
Published in Ambio
Volume 40
Issue 1
Pages 52-59
ISSN 0044-7447
Publication year 2011
Published at Linnaeus Centre for Marine Evolutionary Biology (CEMEB)
Department of Marine Ecology
Pages 52-59
Language en
Keywords Density-dependent population growth, Age-structured populations, Population management, Detecting population trends, Environmental stochasticity
Subject categories Marine ecology


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.

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