SELECTING DOMINANTS AND SUBORDINATES AT CONFLICT OUTCOME CAN CONFOUNDTHE EFFECTS OF PRIOR DOMINANCE OR SUBORDINATION EXPERIENCE

Individuals with a previous experience of dominance are likely to be d ominants in further encounters. To test this effect, individuals with a previous experience of dominance are used for the experiments. One w ay to obtain such individuals is to let opponents 'self-select': encou nters between pairs of more or less equivalent opponents are staged an d one selects ex post facto the dominant and subordinate from the ensu ing conflict, This paper formally shows that the selection of dominant and subordinate animals modifies the dominance probability functions of the two corresponding sub-samples of animals. As a result, the prop ensity of previous winners to win again and of previous losers to repe at their loss can be attributed to this artefact rather than to prior social experience. This result has serious methodological implications . When one relies solely on selection to obtain winners and losers, eq uiprobability is no longer the appropriate null hypothesis against whi ch prior social experience effects have to be tested, To clearly demon strate the effect of dominance experience, one must show that prior wi nners defeat neutral opponents in at least two-thirds of all cases; re ciprocally, to show that prior subordinate experience plays a role, pr ior losers must win in less than one-third of all fights against neutr al opponents; finally, to conclude that a combined effect of the two k inds of prior experience is in operation, one must obtain that prior w inners defeat prior losers in more than 83% of all planned conflicts. The present result does not imply that experience effects are not at w ork when the selection procedure is used, but that the procedure used to show their effects is inadequate because effects of experience on a subsequent encounter are confounded with those introduced by statisti cal selection.