The role of individuality in collective group movement

Abstract

How different levels of biological organization interact to shape each other's function is a central question in biology. One particularly important topic in this context is how individuals' variation in behaviour shapes group-level characteristics. We investigated how fish that express different locomotory behaviour in an asocial context move collectively when in groups. First, we established that individual fish have characteristic, repeatable locomotion behaviours (i.e. median speeds, variance in speeds and median turning speeds) when tested on their own. When tested in groups of two, four or eight fish, we found individuals partly maintained their asocial median speed and median turning speed preferences, while their variance in speed preference was lost. The strength of this individuality decreased as group size increased, with individuals conforming to the speed of the group, while also decreasing the variability in their own speed. Further, individuals adopted movement characteristics that were dependent on what group size they were in. This study therefore shows the influence of social context on individual behaviour. If the results found here can be generalized across species and contexts, then although individuality is not entirely lost in groups, social conformity and group-size-dependent effects drive how individuals will adjust their behaviour in groups.

Ants work harder during consensus decision-making in small groups

“…In shared decisions, empirical data indicate that the contribution of individuals can be shared equally among all individuals or reside predominantly in a subset of the group [5,[33][34][35][36]. The strength of individual influence may also vary with group size, with individuals having a greater potential influence in smaller groups [37]. This scope for variation in the proportion of individuals involved in decisions, and the magnitude of the contribution that individuals make to the decision process, may give smaller groups some capacity to ameliorate the limitations of group size.…”

Determining asymptotically large population sizes in insect swarms

“…When the group is very large, the idea that the group behaviour represents some kind of universal state is reasonable, as is the assumption that all the individuals in the group can be treated as interchangeable, uniform agents. But for small groups, these assumptions become more suspect [12], and the group may behave differently [13,14]. One must ask, then, how large an animal aggregation must be before the asymptotic state is reached and the addition of more individuals does not change the dynamics.…”

Leadership emergence in a data-driven model of zebrafish shoals with speed modulation

“…Building on recent efforts to infer details of the specific interactions among teleost fish [18][19][20][21], we extend the individual zebrafish model formulated in [34] to study their social behaviour in small shoals. Specifically, the model we describe incorporates speed regulation, which is both fundamental to the locomotory patterns of individuals [35,36] and has been recently proposed as a central mechanism for explaining collective behaviour of similar teleosts [17,20,21,37,38].…”