Abstract: Dominance rank in female chimpanzees correlates positively with reproductive success. Although a high rank obviously has an advantage for females, clear (linear) hierarchies in female chimpanzees have not been detected. Following the predictions of the socio-ecological model, the type of food competition should affect the dominance relationships among females. We investigated food competition and relationships among 11 adult female chimpanzees in the Ta National Park, C+ete d'Ivoire (West Africa). We detected a formal linear dominance hierarchy among the females based on greeting behaviour directed from the subordinate to the dominant female. Females faced contest competition over food, and it increased when either the food was monopolizable or the number of competitors increased. Winning contests over food, but not age, was related to the dominance rank. Affiliative relationships among the females did not help to explain the absence of greetings in some dyads. However comparison post hoc among chimpanzee study sites made differences in the dominance relationships apparent. We discuss them based on social relationships among females, contest competition and predation. The cross-site comparison indicates that the differences in female dominance hierarchies among the chimpanzee study sites are affected by food competition, predation risk and observation time.

Abstract: Functional stimulus equivalence has been demonstrated using a transfer of training design with matching-to-sample training in which two sample stimuli are associated with the same comparison stimulus (A-B, C-B; many-to-one matching). Equivalence is shown by training a new association (A-D) and demonstrating the presence of an emergent relation (C-D). In the present experiment, we show that symmetry training, in which a bidirectional association is trained between two stimuli (A-B, B-A, using successive stimulus presentations followed by reinforcement), can also produce functional equivalence using a transfer of training design (i.e., train B-C, test A-C). The results suggest that training pigeons in the substitutability of two stimuli may be sufficient to produce functional stimulus equivalence between them. The results also have implications for the development of an emergent transitive relation, because training on A-B and B-C relations results in the emergence of an untrained A-C relation, if B-A training also is provided.