Identifying differences in the rules of interaction between individuals in moving animal groups

TL;DR

This study investigates how individual differences in social responsiveness influence leadership and movement patterns in pairs of fish, revealing that spatial positioning and behavioral responses shape collective movement dynamics.

Contribution

It uncovers the rules of interaction and individual differences that lead to leadership and spatial organization in moving animal groups.

Findings

Individuals at the front exhibit greater speed changes.

Front-positioned individuals are less likely to turn towards their partner.

Groups move faster when led by the front-positioned individual.

Abstract

Collective movement can be achieved when individuals respond to the local movements and positions of their neighbours. Some individuals may disproportionately influence group movement if they occupy particular spatial positions in the group, for example, positions at the front of the group. We asked, therefore, what led individuals in moving pairs of fish (Gambusia holbrooki) to occupy a position in front of their partner. Individuals adjusted their speed and direction differently in response to their partner's position, resulting in individuals occupying different positions in the group. Individuals that were found most often at the front of the pair had greater mean changes in speed than their partner, and were less likely to turn towards their partner, compared to those individuals most often found at the back of the pair. The pair moved faster when led by the individual that was usually at the front. Our results highlight how differences in the social responsiveness between individuals can give rise to leadership in free moving groups. They also demonstrate how the movement characteristics of groups depend on the spatial configuration of individuals within them.