Highly dynamic fission–fusion species can exhibit leadership when traveling

Abstract

Leadership by specific individuals is thought to enhance the fitness of followers by allowing them to take advantage of the knowledge or skills of key individuals. In general, consistent leadership is expected to occur primarily in stable groups of related individuals where the benefits enhance the inclusive fitness of a leader. Societies with less stability in group composition (i.e., fission–fusion groups) are less likely to feature unshared decision making. However, in situations where frequent interactions among individuals occur (e.g., small population size and small range of movement) and/or the complexity of the environment requires substantial experience and knowledge, consistent leadership might be expected. We tested if a highly dynamic fission–fusion population of bottlenose dolphins (Tursiops truncatus), inhabiting a complex environment, exhibited leadership when traveling. A small number of specific individuals led group travel more often than expected by chance, and were more likely to initiate successful direction changes of groups than following individuals. The number of leaders in a group remained relatively constant across a wide range of group sizes and was not affected by the number of potential leaders (i.e., those that had led previously) present in the group. Together, these results suggest that leadership can occur in species with high rates of group fission and fusion. Therefore, the loss of key individuals could have disproportionate effects on population dynamics.