Author(s): Bjrn Sderbck
Interspecific and intraspecific aggressive interactions in the coexisting crayfish species Astacus astacus and Pacifastacus leniusculus were experimentally studied in the laboratory. Pacifastacus leniusculus strongly dominated aggressive interactions with similar-sized A. astacus in heterospecific pairs of juveniles and adults. Pairs of young-of-the-year were considerably less aggressive than the larger body-size groups, and in this size group neither species was aggressively dominant. The two species showed substantial differences in patterns of aggressive behaviour. A higher frequency of unilateral aggressive acts and much lower frequency and shorter duration of fights in P. leniusculus pairs indicate that this species is more inclined to establish a dominance order than A. astacus. The aggressive dominance of P. leniusculus over A. astacus indicates that P. leniusculus might be able to competitively exclude A. astacus when the species are competing for a limited resource.