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What regulates population dynamics in marine fish?

New ConEvolHer article: Although population regulation is a central concept in ecology, it is surprisingly difficult to detect it empirically. In marine fish populations, it is commonly assumed that the main source of regulation is density-dependent recruitment, which is based on a decreasing number of recruits per capita with increasing population size. Other sources of density dependence such as growth are known, however it is often no clear whether they are of importance.

A new study  published in the Journal of Animal Ecology by ConEvolHer members Fabian Zimmermann and Mikko Heino explores this question for the first time on a broad scale by quantifying and comparing directly density dependence in growth and recruitment over a large set of fish populations. The results show that marine fish are indeed mostly regulated by density-dependent recruitment, yet density-dependent growth was found to be also common.

 The conclusion of the study is that population regulation through density-dependent recruitment is indeed typical for marine fish populations and has stronger effects on population biomass, supporting common assumption that density-dependent recruitment tends to be most important source of population regulation. The results, however, also underline that density-dependent growth is not uncommon and often co-occurs with density-dependent recruitment. Consequently, this challenges the prevailing paradigm of supremacy of population regulation though density-dependent recruitment, with important theoretical and practical implications, suggesting that density-dependent growth should receive more attention in predicting dynamics of fish populations. Ultimately, this could help to improve sustainability and productivity of fisheries.

The full article is available free of charge 

Comparison of the effects of density dependence on population biomass: the ratio between density-dependent growth and recruitment indicates which source of density dependence has stronger effects on biomass in 70 fish populations from the Northeast Atlantic Ocean. Recruitment tends to be more important in almost all populations (values smaller than one), independent of statistical significance.