Collective detection based on visual information in animal groups.

Jacob D Davidson,Iain D Couzin,Simon P Leblanc,Colin R Twomey,Vivek H Sridhar,Matthew M G Sosna

doi:10.1098/rsif.2021.0142

Abstract

We investigate key principles underlying individual, and collective, visual detection of stimuli, and how this relates to the internal structure of groups. While the individual and collective detection principles are generally applicable, we employ a model experimental system of schooling golden shiner fish (Notemigonus crysoleucas) to relate theory directly to empirical data, using computational reconstruction of the visual fields of all individuals. This reveals how the external visual information available to each group member depends on the number of individuals in the group, the position within the group, and the location of the external visually detectable stimulus. We find that in small groups, individuals have detection capability in nearly all directions, while in large groups, occlusion by neighbours causes detection capability to vary with position within the group. To understand the principles that drive detection in groups, we formulate a simple, and generally applicable, model that captures how visual detection properties emerge due to geometric scaling of the space occupied by the group and occlusion caused by neighbours. We employ these insights to discuss principles that extend beyond our specific system, such as how collective detection depends on individual body shape, and the size and structure of the group.

Highlights

Being part of a group is an effective strategy for avoiding predation threats [1,2,3,4] and locating promising resources [5,6]
Since our tracking is only in two dimensions, we investigate how detection results may be sensitive to out-of-plane effects by using an approximate procedure, where we randomly choose certain neighbours as out of the plane of visual detection, and as not blocking detection in associated directions
For our study system, we find that meaningful distinctions in available visual information emerge when groups contain between 30 and 70 fish; at these sizes and larger, some individuals may detect an object while others do not

Summary

Introduction

Being part of a group is an effective strategy for avoiding predation threats [1,2,3,4] and locating promising resources [5,6]. Enhanced detection of external objects (for example a predator, or a source of food) is a key aspect of being part of a group, with the benefits referred to as the ‘many eyes’ effect [7,8]. The structure within a group influences how individuals interact with one another and the surrounding environment. Groups tend to have more individuals and an increased density under heightened predation risk [9,10,11,12,13,14,15] (but see [16,17]). An individual’s position within the group can determine both its possible risk to predation [18], as well as the extent of its social interactions [19,20]. Despite the importance of social grouping for gathering information about the external environment [21,22], there has been little quantification of how withingroup structure and the size of the group influence the group’s interactions with their environment

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Conclusion