| Summary: | The selective costs and benefits affecting the evolution of group living have long interested behavioural ecologists because knowledge of these selective forces can enhance our understanding not only of why organisms live in groups, but also why species exhibit particular patterns of social organisation. Tamarins form stable and permanent mixed-species troops providing an excellent model for examining the costs and benefits hypothesised for group living. However, testing hypotheses in the wild is difficult, not least because participating species are rarely found out of association. In contrast, in captivity it is possible to compare matched single- and mixed-species troops and also to study the same individuals in single and mixed-species troops to see what effect the presence of a congener has on behaviour. In this way, captive work can help us confirm, reject, or refine the hypotheses, and aids in the generation of new ones, for relating back to the wild. The utility of this approach is demonstrated in this thesis which explored some of the foraging benefit hypotheses and, in particular, the underlying notion that individuals in tamarind mixed-species troops can increase their foraging efficiency through social earning. Single and mixed-species troops of Saguinus fuscicollis and S. labiatus were studied at Belfast Zoological Gardens. It was found that social interaction with conspecifics and congeners facilitated learning by individuals of various types of food-related information (food palatability, location, and method of access). However, although social learning operated in mixed-species troops, it did so under the shadow of inter-specific dominance. The results were used, in conjunction with field observations in Bolivia, to make inferences about the adaptive function of social learning in the wild. These findings strengthen the hypotheses which suggest that increased opportunity for social learning, through an increase in troop size and as a result of species divergence in behaviour, is an adaptive advantage of mixed-species troop formation in tamarins.
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