• density dependence;
  • dispersal;
  • environmental heterogeneity;
  • genotypic selection;
  • intraspecific competition;
  • salmonids

Effects of intraspecific competition intensities on the relative performance (growth and movement) of juvenile brown trout Salmo trutta originating from nine different families were tested in tank experiments and in semi-natural streams. Both growth and movement differed consistently among families, indicating genetic variation in these traits. There were no significant interaction effects, however, between the intensity of competition and family origin on performance in either of the two experimental systems. Thus, genetic variation in response to competition intensity appeared to be limited in the population from which the juveniles used in this experiment originate.