Can migrants escape from density dependence?
Article first published online: 26 JUN 2013
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Ecology and Evolution
Volume 3, Issue 8, pages 2524–2534, August 2013
How to Cite
Ecology and Evolution 2013; 3(8): 2524–2534
- Issue published online: 12 AUG 2013
- Article first published online: 26 JUN 2013
- Manuscript Accepted: 23 MAY 2013
- Manuscript Revised: 22 MAY 2013
- Manuscript Received: 11 FEB 2013
- Ministerio de Ciencia y Tecnología. Grant Numbers: CGL2007-60572, CGL2010-14964
- Fondos FEDER. Grant Number: PGIDIT03PXIC30102PN
- Spanish Government. Grant Number: BES-2008-001973
- Brown trout;
- individual approach;
- statistical modeling
Migration is thought to maximize growth by enabling individuals to escape from density dependence, but this has rarely been tested at the individual level in natural populations. We employed linear mixed modeling of the spacing between consecutive scale growth rings to reconstruct individual growth profiles of a paradigmatic fish migrant, the sea trout (Salmo trutta) and related these to estimates of year class strength over a 13-year period. Variation in scale growth was 1.3 times greater among individuals than within individuals in freshwater and 10 times greater at sea. Scale growth was inversely related to year class strength, both in freshwater (before migration) and at sea (after migration). Competition for patchily distributed resources is the most plausible explanation of the negative density-dependent growth observed in freshwater and, to a lesser extent, in the marine environment. Our study provides some of the strongest evidence for a role of density dependence in determining partial migrations because although migrants can maximize growth by moving into the sea, they do not appear to become free from density dependence constraints completely. This has implications for conservation and suggests that sea trout and other anadromous fish displaying partial migrations may not be best managed on a river by river basis, but rather from a broader, coastal perspective.