The spatial scale of density-dependent growth and implications for dispersal from nests in juvenile Atlantic salmon

Journal Oecologia
05 October 2010 19:05

Abstract
By dispersing from localized aggregations of recruits, individuals may obtain energetic benefits due to reduced experienced density. However, this will depend on the spatial scale over which individuals compete. Here, we quantify this scale for juvenile Atlantic salmon (Salmo salar) following emergence and dispersal from nests. A single nest was placed in each of ten replicate streams during winter, and information on the individual positions (±1 m) and the body sizes of the resulting young-of-the-year (YOY) juveniles was obtained by sampling during the summer.

In six of the ten streams, model comparisons suggested that individual body size was most closely related to the density within a mean distance of 11 m (range 2–26 m). A link between body size and density on such a restricted spatial scale suggests that dispersal from nests confers energetic benefits that can counterbalance any survival costs. For the four remaining streams, which had a high abundance of trout and older salmon cohorts, no single spatial scale could best describe the relation between YOY density and body size. Energetic benefits of dispersal associated with reduced local density therefore appear to depend on the abundance of competing cohorts or species, which have spatial distributions that are less predictable in terms of distance from nests. Thus, given a trade-off between costs and benefits associated with dispersal, and variation in benefits among environments, we predict an evolving and/or phenotypically plastic growth rate threshold which determines when an individual decides to disperse from areas of high local density.


  • Sigurd Einum, Department of Biology, Centre for Conservation Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
  • Grethe Robertsen, Department of Biology, Centre for Conservation Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
  • Keith H. Nislow, USDA Forest Service Northern Research Station, 201 Holdsworth NRC, 160 Holdsworth Way, Amherst, MA 01003, USA
  • Simon McKelvey, Cromarty Firth District Salmon Fisheries Board, c/o C.K.D. Falbraith, 17 Old Edinburgh Road, Inverness, IV2 3HF UK
  • John D. Armstrong, Fisheries Research Services Freshwater Laboratory, Faskally, Pitlochry, Perthshire PH16 5LB, UK

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