On the (In)stability of Dominance Hierarchies in the Cichlid Fish Oreochromis mossambicus.

Dominance hierarchies were studied during 8 weeks in eight heterosexual captive groups of Oreochromis mossambicus at the onset of sexual maturity. Linearity was assessed for each group on a weekly basis based on the Landau's index (b) and on the procedure described by Appleby [Appleby MC (1983): Animal Behaviour 31:600-608]. Week-to- week stability of the hierarchical structures was measured using the Burk's stability index (b) and Spearman rank correlation coefficients for the ranks of fishes in consecutive weeks. The two measures of stability showed a high level of concordance but the Spearman rank correlations were more conservative in detecting cases of stability. Although most dominance structures were linear they were unstable from week to week. Dominant individuals were less likely to experience rank reversals than subordinates. Rank reversals were especially likely among hierarchical neighbors. Dominance hierarchies did not stabilize in the time span of this study. [ABSTRACT FROM AUTHOR]