The effects of group size, rate of turnover and disruption to demonstration on the stability of foraging traditions in fish

There is considerable laboratory-based evidence that social learning plays a role in the behaviour of many animals, including fish. However, a weakness of such studies in fish, is that in virtually all to date, the behaviour showed could be learned asocially, with the social influence merely accelerating the rate of learning. Lefebvre & Palameta (1988. Social Learning: Psychological and Biological Perspectives. pp. 141–164) argued that the most compelling evidence for social learning comes from studies where inexperienced animals are unlikely to learn the target behaviour by themselves. The present study is designed to address this concern, by employing a feeding tube task in which fish gain access to food by swimming in a manner that they would not normally show. Employing a transmission chain design, we show foraging traditions in guppies, Poecilia reticulata, and southern platyfish, Xiphophorus maculatus, in which shoal members continue to exploit the food available in the feeding tube, in spite of changes in the composition of the shoal due to the gradual removal of demonstrators. Two experiments provide strong evidence for social learning underlying traditional behaviour, such as migratory routes, in fish, and reveal how the stability of such traditions (duration within a population) is affected by group size (2, 4 or 6 fish) and rate of turnover (16.5%, 25% or 50% per day). While larger shoals of fish showed more stable traditions than smaller shoals, this was found to be related to their slower rate of turnover rather than a direct effect of group size.