“Leading According to Need” in Self‐Organizing Groups

Abstract

Self-organizing-system approaches have shed significant light on the mechanisms underlying synchronized movements by large groups of animals, such as shoals of fish, flocks of birds, or herds of ungulates. However, these approaches rarely consider conflicts of interest between group members, although there is reason to suppose that such conflicts are commonplace. Here, we demonstrate that, where conflicts exist, individual members of self-organizing groups can, in principle, increase their influence on group movement destination by strategically changing simple behavioral parameters (namely, movement speed, assertiveness, and social attraction range). However, they do so at the expense of an increased risk of group fragmentation and a decrease in movement efficiency. We argue that the resulting trade-offs faced by each group member render it likely that group movements are led by those members for which reaching a particular destination is most crucial or group cohesion is least important. We term this phenomenon leading according to "need" or "social indifference," respectively. Both kinds of leading can occur in the absence of knowledge of or communication about the needs of other group members and without the assumption of altruistic cooperation. We discuss our findings in the light of observations on fish and other vertebrates.

Context-dependent hierarchies in pigeons

“…However, the relationship between social structure and leadership is still unknown in some of the most rapid, large-scale, and impressive examples of collective motion: bird flocks and fish shoals. Initial simulations of these groups posed anonymous, homogeneous interaction rules (12, 13), but individual differences are now the focus of both theoretical and empirical investigations (3,(14)(15)(16)(17)(18)(19). Elucidating how social structure and individual differences affect group decision-making across a range of taxonomic groups will put the study of collective behavior into a broader biological context.…”

Leaders benefit followers in the collective movement of a social sawfly

“…Significantly, foraging was initiated by the heaviest larvae only when identified leaders were removed (in the followers treatment), which may reflect a difference in the resource requirements between follower individuals. The resource requirements of animals are linked with body size, and can strongly influence foraging decisions: differing resource requirements motivating an individual's choice to lead are supported by both theoretical [1,14,27] and empirical studies [15,[28][29][30]. In bees, larger workers are not only more likely to forage, they also start to forage earlier in life [31].…”

“…Such individual information can be crucial for a group when relocating or foraging, with informed individuals leading, or guiding, the uninformed [13]. Alternatively, individuals that are more highly motivated may be more likely to initiate movement and become leaders [1,14]. For example, fish that occupy the front positions of shoals may be nutritionally challenged and are thus more motivated to forage [15], whereas females in energetically demanding reproductive states tend to lead foraging movements in several group-living mammals [16,17].…”

Distinguishing Social from Nonsocial Navigation in Moving Animal Groups

“…It has been suggested that animals alter the strength of their social interactions on the basis of, for example, their individual needs to maintain nutrient levels (Conradt et al 2009). Our method is ideally suited to assess the impacts of factors such as food deprivation, predation, or social composition of groups on the sociality of groups or of individuals within groups.…”

“…For example, fish larvae settling on a reef (Codling et al 2004 and references therein), migrating birds (Bajec and Heppner 2009), swarming locusts (Buhl et al 2006), and possibly even humans walking toward similar targets (see Faria et al 2009 for experiments) may interact with different levels of sociality. It has also been suggested that different levels of motivation (e.g., hunger) can significantly alter the outcome of group navigation (Conradt et al 2009). Such variations in behavioral state could result in varying levels of sociality even between groups from a single species.…”