Consensus or deadlock? Consequences of simple behavioral rules for coordination in group decisions

Coordinated collective behaviors often emerge from simple rules governing the interactions of individuals in groups. We model mechanisms of coordination among ants during cooperative transport, a challenging task that requires a consensus on travel direction. Decisions required for cooperative transport differ from other, well-studied consensus decisions because groups often deadlock, with individuals trying to move in opposing directions, and cooperative transport groups are often relatively small. Small groups may be more affected by individual nonconformity. Using deterministic and stochastic models, we investigate behavioral factors that affect deadlock duration. Our goal is to determine whether groups following simple behavioral rules can reach a consensus using minimal information. We define and investigate multiple types of behavioral rules that govern individual behavior and also differ in the information available. We find that if individuals more readily give up when they are going against the majority, groups rapidly break deadlocks. This occurs through positive and negative feedbacks that are implemented in our model via a single mechanism. We also find that to quickly reach a consensus, groups must have either a shared bias, high sensitivity to group behavior, or finely tuned persistence. While inspired by ants, our results are generalizable to other collective decisions with deadlocks, and demonstrate that groups of behaviorally simple individuals with no memory and extremely limited information can break symmetry and reach a consensus in a decision between two equal options