Flexibility of collective decision making during house hunting in Temnothorax ants

Individual animals routinely face decisions that are crucial to their fitness. In social species, however, many of these decisions need to be made jointly with other group members because the group will split apart unless a consensus is reached. Here, we review empirical and theoretical studies of consensus decision making, and place them in a coherent framework. In particular, we classify consensus decisions according to the degree to which they involve conflict of interest between group members, and whether they involve either local or global communication; we ask, for different categories of consensus decision, who makes the decision, what are the underlying mechanisms, and what are the functional consequences. We conclude that consensus decision making is common in non-human animals, and that cooperation between group members in the decision-making process is likely to be the norm, even when the decision involves significant conflict of interest.

The traditional emphasis when measuring performance in animal cognition has been overwhelmingly on accuracy, independent of decision time. However, more recently, it has become clear that tradeoffs exist between decision speed and accuracy in many ecologically relevant tasks, for example, prey and predator detection and identification; pollinators choosing between flower species; and spatial exploration strategies. Obtaining high-quality information often increases sampling time, especially under noisy conditions. Here we discuss the mechanisms generating such speed-accuracy tradeoffs, their implications for animal decision making (including signalling, communication and mate choice) and the significance of differences in decision strategies among species, populations and individuals. The ecological relevance of such tradeoffs can be better understood by considering the neuronal mechanisms underlying decision-making processes.

The acquisition and use of socially acquired information is commonly assumed to be profitable. We challenge this assumption by exploring hypothetical scenarios where the use of such information either provides no benefit or can actually be costly. First, we show that the level of incompatibility between the acquisition of personal and socially acquired information will directly affect the extent to which the use of socially acquired information can be profitable. When these two sources of information cannot be acquired simultaneously, there may be no benefit to socially acquired information. Second, we assume that a solitary individual's behavioural decisions will be based on cues revealed by its own interactions with the environment. However, in many cases, for social animals the only socially acquired information available to individuals is the behavioural actions of others that expose their decisions, rather than the cues on which these decisions were based. We argue that in such a situation the use of socially acquired information can lead to informational cascades that sometimes result in sub-optimal behaviour. From this theory of informational cascades, we predict that when erroneous cascades are costly, individuals should pay attention only to socially generated cues and not behavioural decisions. We suggest three scenarios that might be examples of informational cascades in nature.