Abstract: Agonistic intervention behavior was observed in captive groups of chimpanzees (Pan troglodytes), rhesus monkeys (Macaca mulatta), and stumptail monkeys (M. arctoides). Reciprocity correlations of interventions were determined while removing from the data the effects of several symmetrical relationship characteristics, that is, matrillineal kinship, proximity relations, and same-sex combination. It was considered likely that if significant reciprocity persisted after controlling for these characteristics, the reciprocity was based on cognitive mechanisms. Statistical significance was tested by means of recently developed matrix permutation procedures. All three species exhibited significant reciprocity with regard to beneficial interventions, even after controlling for symmetrical traits. Harmful interventions were, however, reciprocal among chimpanzees only. This species showed a “revenge system”, that is, if A often intervened against B, B did the same to A. In contrast, both macaque species showed significantly inversed reciprocity in their harmful interventions: if A often intervened against B, B rarely intervened against A. Further analysis indicates that the strict hierarchy of macaques prevents them from achieving complete reciprocity. Compared to chimpanzees, macaques rarely intervene against higher ranking group members. The observed contrast can be partially explained on the basis of differences in available space, as indicated by a comparison of indoor and outdoor living conditions for the chimpanzee colony. Yet, even when such spatial factors are taken into account, substantial behavior differences between chimpanzees and macaques remain.

Abstract: Abstract  The influence of individual factors on dominance rank and the relationship between rank distance and patterns of aggression predicted by models of evolutionarily stable strategies (ESS) of animal conflict were investigated in a managed bachelor group of Sorraia horses, Equus caballus. The group was composed of four to six stallions 3- to 12-years-old during the study period. The dominance hierarchy was significantly linear and rank was not related to age, weight, height or aggressiveness. Frequency and intensity of agonistic interactions were low, but higher-ranking stallions did not receive lower aggressiveness than lower-ranking stallions. There was some evidence that dominance relationships were more contested among close-ranking stallions, as predicted. Agonistic-related interactions among close-ranking stallions served similar functions to those among distant-ranking stallions, but the latter interacted more frequently than expected for access to resting sites and/or resting partners. Therefore, we found some evidence that agonistic-related interactions among distant-ranking stallions play a larger role in providing access to valuable and defendable resources than those among close-ranking stallions. Nevertheless, the fact that space to escape from aggression was limited and breeding access was independent from dominance rank may have reduced the benefits relative to costs of aggression and therefore limited the occurrence of contests over dominance and resources.

Abstract: Theoreticians propose that trained winning and losing are important processes in creating linear animal dominance hierarchies, and experiments have shown that both processes can occur in animals, but their actual roles in creating natural hierarchies are unknown. We described agonism in 18 broods of three blue-footed boobies, Sula nebouxii, a species for which trained winning and losing have been demonstrated, to infer how these processes generate and maintain a natural hierarchy. Ranks in the linear hierarchy that emerged in every brood were initially assigned by asymmetries in age, size and maturity, which led to differences between broodmates in levels of expressed and received aggression and, consequently, to differences in the training of their aggressiveness and submissiveness. Later, ranks appeared to be maintained by the chicks' acquired aggressive and submissive tendencies combined with ongoing effects of persisting differences in size and maturity. Our results suggest that trained winning and trained losing are important in the construction of booby hierarchies but that these two axes of learning are largely independent. Increase in submissiveness occurs over a period of about 10-20 days, and the level of submissiveness reached varies with the amount of aggression received. After training, submissiveness is apparently maintained by a lower level of aggression and increasing use of threats. Threats become increasingly effective as chicks age, but are never as effective as attacks.

Abstract: This simulation study explores some conditions leading to transitivity within dominance orders. Combinations of three parameters were varied to study their consequences upon hierarchy formation and upon the degree of linearity of resultant structures. The factors studied were: (1) the importance of initial resource holding potentials (RHPs); (2) changes brought in RHPs by successive victories and defeats; and (3) accuracy of RHP assessment made by opponents. Results show that initial differences in RHP always lead to perfectly transitive chains whose rank order reflects the importance of initial differences. Even when simulated animals make important errors while assessing each other during round robin tournaments, emerging dominance structures are perfectly linear and ranks obtained in the structure are highly correlated with initial values in RHPs. Moreover, accumulated experiences of victory and/or defeat alone always lead to perfectly linear hierarchies. Their combination with initial individual differences in RHP led to the same conclusion. Even when assessment was far from being perfect, not only perfect chains were formed but initial values in RHPs significantly influenced rank order when the contribution of victory and defeat to RHP was relatively unimportant. The higher the importance of victory and defeat to RHP as compared to that of initial RHP values, the lower was the correlation between initial RHP values and the ranks order reached by individuals in the resultant hierarchies. In general also, the lower the variation within initial RHPs, the lower was the correlation between initial RHPs and ranks in the hierarchy. At a given level of initial RHP dispersion, increasing the contribution of victory and defeat to RHP diminished the correlation between initial RHP values and obtained ranks. In addition, inaccurate assessment reduced the overall correlation, especially when dispersion of initial RHP values was low and the contribution of victory and defeat relatively unimportant. These results shed some light on the controversy about the respective roles of initial individual attributes and that of patterns of resolution in the formation of animal hierarchies. We present the emergence of social order within closed systems as those simulated here as a case of self-organization.

Abstract: Although many Malagasy lemurs are thought to be female dominant and to have female feeding priority, to date the relationship between these behaviors has been rigorously established only in Lemur catta, and other ways that females might achieve feeding priority have not been examined closely. Erhart and Overdorff [International Journal of Primatology 20:927-940, 1999] suggested that one way female primates achieve feeding priority is to initiate and lead groups to food, thereby gaining access to the food first and positively influencing their food intake compared to other group members. Here we describe female dominance patterns and potential measures of feeding priority in two groups of black-and-white ruffed lemurs (Varecia variegata) that were observed over a 15-month period in southeastern Madagascar. We predicted that the females would 1) be consistently dominant to males, 2) lead groups to food sources more often than males, and 3) have higher feeding rates compared to males when they arrived at food sources first. The results were dissimilar between the study groups. During the study, the oldest adult female in group 1 died. There was no evidence for female dominance in this group, and the remaining (likely natal) female did not lead the group more often, nor did she have a higher food intake than males. Group 1 dispersed shortly after the time frame reported here. In contrast, the resident female in group 2 was dominant to group males (based on agonistic interactions), led the group to food sources more often, and experienced a higher food intake when she arrived first at a food source. How these patterns vary over time and are influenced by the number of females in groups, group stability, food quality, and reproductive condition will be examined in future analyses.