Know when you’re beaten: Efficient cooperative transport requires either a directional bias or that outnumbered individuals give up more quickly

Ants are excellent examples of self-organized systems capable of remarkable coordination. Here, I model some proximate mechanisms that may lead to this coordination in the context of cooperative transport, which occurs when a group of ants work together to move a large object intact. Using a deterministic model in continuous time with one implicit spatial dimension, I examine the initial phase of transport, or how individuals agree on a direction to move the object. Key parameters of the model are the extent of bias in individuals’ preferred direction of movement, and persistence, or the reluctance of individuals to give up their preferred direction. In this deterministic system at least a small directional bias is necessary for movement. When directional bias is small, efficiency is maximized when individuals give up more readily if the transport is slow and they are outnumbered (more individuals pulling the opposite direction). In this situation high persistence reduces efficiency. However, high persistence increases efficiency if individuals either 1) give up more readily when transport is slow regardless of whether they are outnumbered or 2) give up at the same rate regardless of transport success. This model provides new insight into behavioral parameters that may modulate the cooperative transport efficiency of ant species in nature.