Speed-mediated properties of schooling

Abstract

Collectively moving animals often display a high degree of synchronization and cohesive group-level formations, such as elongated schools of fish. These global patterns emerge as the result of localized rules of interactions. However, the exact relationship between speed, polarization, neighbour positioning and group structure has produced conflicting results and is largely limited to modelling approaches. This hinders our ability to understand how information spreads between individuals, which may determine the collective functioning of groups. We tested how speed interacts with polarization and positional composition to produce the elongation observed in moving groups of fish as well as how this impacts information flow between individuals. At the local level, we found that increases in speed led to increases in alignment and shifts from lateral to linear neighbour positioning. At the global level, these increases in linear neighbour positioning resulted in elongation of the group. Furthermore, mean pairwise transfer entropy increased with speed and alignment, implying an adaptive value to forming faster, more polarized and linear groups. Ultimately, this research provides vital insight into the mechanisms underlying the elongation of moving animal groups and highlights the functional significance of cohesive and coordinated movement.

Group-level patterns emerge from individual speed as revealed by an extremely social robotic fish

“…[28,29]). Individual speed also strongly drove the alignment and temporal coordination of the pairs, in line with previous empirical studies that found fast moving groups tend to be polarised and slow moving groups to be disordered [12,13,30]. As in our study the robotic partner completely lacked any alignment rules, our findings provide novel empirical evidence that individual speed is a key factor facilitating group alignment and coordination.…”

“…Although speed-mediated changes in local interaction rules may help to explain these effects [6,10], groups may be more likely to become disordered at lower speeds because of larger potential angular fluctuations at lower speeds, as is predicted from theoretical analysis [8]. Our finding that faster groups showed better coordination of movement changes and information flow being higher in faster groups, as shown by previous work [13], can thereby be directly explained by the higher (local) order that arises with higher individual speeds.…”

“…Live guppies paired with an extremely social robotic fish showed large and repeatable individual differences in movement speeds that in turn strongly explained leadership, group cohesion, alignment, and movement coordination. By testing all fish with a robot that used identical interaction rules and lacked any preferred movement speed and directionality, these results provide novel experimental evidence that suggests individual speed is a fundamental factor in the emergence of collective behavioural patterns, in line with existing theoretical and empirical work [4,8,12,13,23]. As individual differences in speed are associated with a broad range of phenotypic traits observed among grouping animals, this may also help provide a mechanistic explanation for the effect of phenotypic heterogeneity for group-level patterns [3], such as has been shown for size, hunger, and parasitism [24,25].…”

“…Hence, individual speed may be an additional fundamental factor that underlies the emergence of the global properties of groups. Indeed, both short-term changes and heterogeneity in speed have been linked to a range of group-level properties, such as group cohesion, structure, shape, coordination, and leadership by both theoretical analyses [8], simulations [1,4,9], and empirical work [6,[10][11][12][13][14]. Importantly, grouping individuals may differ in their preferred and optimal movement speeds yet must also coordinate and adjust their behaviour to successfully group together [3,15].…”

Local interactions and their group-level consequences in flocking jackdaws

“…Finally, we demonstrate that the local side-by-side structure scales up to the global level, making the entire flock elongated in the direction perpendicular to the movement. This is similar to the way in which fish schools are elongated in the movement direction as a result of the frontto-back local configuration of neighbours [42,[62][63][64]. We note, however, that the elongated group shape was observed here for birds traveling together in a particular direction (in this case, towards evening roosts).…”