Intruding male red swamp crayfish,Procambarus clarkii,immediately dominate members of established communities of smaller,mixed-sex conspecifics

The effects of competing asymmetries (intruder size advantage vs. prior residence) on dominance relationships were investigated in a laboratory setting. Sexually mature (Form I) male red swamp crayfish, 25%-27% larger than the average member of several mixedsex communities of 20-25 sexually mature conspecifics, individually intruded upon these communities on successive days. Each community was invaded once a day, with each of these large intruders invading every community once during the experiment. Five days after the last large intruder invasion, novel intruder group males, approximately the same size as the average community member, individually invaded the same communities, all communities being invaded once during a single day of testing. These novel intruders were used to differentiate the effects of intruder size from those effects of being put into a novel environment. During each intrusion, the frequencies of dominance, submission, aggressive standoffs, and nonaggressive interactions between the intruder and members of the community were recorded. The large intruders on each day immediately and virtually completely dominated all encountered community members, and the large intruders were significantly more dominant than the novel, smaller-sized intruders. The size advantage of the large intruders overwhelmed prior residence in influencing dominance outcomes, even in these well established communities. © 1995 Wiley-Liss, Inc.