Group decision-making in meerkats ( Suricata suricatta)

Abstract

Groups of social animals are common in nature and often remain cohesive despite variation in each member’s needs and optimal activity. How and why individuals coordinate themselves within groups has long been a puzzle for behavioural ecologists. Recently, theories on group decision-making have greatly advanced but there is still a lack of empirical evidence about the applicability and the generality of such theories in animals. Within my PhD project, I addressed questions on group decision-making in wild groups of meerkats (Suricata suricatta), cooperatively breeding mongooses with high reproductive skew, foraging as cohesive units. I tried to fill the gap between theory and empirical evidence by quantifying naturally occurring transitions of activities and conducting experiments. Groups mainly risk losing their cohesiveness when individuals change activity. Such activity transitions are initiated by some group members, but complete transitions are only fulfilled when all members follow the initiator in its change of activity. Only then the initiator can be regarded as a leader. Changes of group activity result from various group decision-making mechanisms, yet, the differences between them are still not clear. In meerkats, I investigated initiation of activity change in two contexts (the emergence order from the burrow and the leaving order from the burrow area) and how this could be linked to leadership. I addressed how meerkat groups were renovating their sleeping burrow. I investigated who was involved in deciding when to move from one foraging patch to another and the underlying decision mechanism. Furthermore, I analysed several factors influencing spatial positioning within groups and the likely advantages and drawbacks of them. Finally, I elicited conflicts of interest between two individuals within a group to assess how individuals with divergent incentives are still able to remain in a cohesive group. The initiation of activity changes in meerkats in two temporarily close contexts depended on different factors: individual identity was important for the emergence order, while foraging success explained the leaving order. Burrow renovation, a cooperative behaviour in meerkats, resulted from social facilitation. However, meerkats also used consensus decisions, particularly when they moved from one foraging patch to another. I demonstrated that a quorum of two to three individuals emitting moving calls was necessary before the group increased speed and changed to a new foraging location. Analysing the geometry of the group revealed that meerkats associated with some group members more often than with others, indicating some social preferences. In conflict situations, the first individual to move was usually followed, even by the individual who had a divergent incentive, emphasizing the importance of group cohesion for meerkats. My thesis shows that within the same species a wide range of group decision-making mechanisms is used. Some activity changes are initiated by specific obvious signals and decisions are found by a quorum of the group. In other situations, the first individual to show an activity change is followed without any obvious decision periods to find a consensus between individual preferences. These observations indicate that not only initiators of an activity change, but also the followers with their decision to join or not, play an important role in the outcome of group decisions. Individuals appear highly responsive to each other at any time, which is likely to be crucial for animals living in an environment where group cohesion has high fitness benefits.