Abstract
The collective behaviour of social groups is often strongly influenced by one or few individuals, termed here ‘keystone individuals’. We examined whether the influence of keystone individuals on collective behaviour lingers after their departure and whether these lingering effects scale with their tenure in the group. In the social spider, Stegodyphus dumicola, colonies' boldest individuals wield a disproportionately large influence over colony behaviour. We experimentally manipulated keystones' tenure in laboratory-housed colonies and tracked their legacy effects on collective prey capture following their removal. We found that bolder keystones caused more aggressive collective foraging behaviour and catalysed greater inter-individual variation in boldness within their colonies. The longer keystones remained in a colony, the longer both of these effects lingered after their departure. Our data demonstrate that, long after their disappearance, keystones have large and lasting effects on social dynamics at both the individual and colony levels.
Highlights
The ability to execute effective collective behaviour is vital for social groups
While most behavioural ecologists are familiar with examples of how innovative behaviours emerge and spread culturally within a population [69,70,71], our findings differ from such studies in several important ways: (i) we provide evidence that individuals’ tendency to become keystone individuals and to initiate legacy effects are associated with their personality type, which is a semi-stable endogenous trait of an individual
We demonstrate that the legacy effects of keystone individuals have the potential to buffer their societies from radical shifts in collective behaviour associated with their sudden disappearance
Summary
The coordinated gliding of fish schools when evading predators or the emergent nest structures of social insects represent collective adaptations that afford groups advantages that are not achievable for solitary individuals [1]. Such collective traits have captured the imagination of scientists including ecologists [2,3], behaviourists [4,5], mathematicians [6] and engineers [7,8], perhaps, more than anything else, because these collective traits are thought to emerge without central control [9]. We consider here an extreme case of how individual variation can impact collective behaviour, where the behavioural traits of just one or a few highly influential individuals shape the behaviour of entire societies
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