Abstract
Even though grouping behaviour has been actively studied for over a century, the relative importance of the numerous proposed fitness benefits of grouping remain unclear. We use a digital model of evolving prey under simulated predation to directly explore the evolution of gregarious foraging behaviour according to one such benefit, the ‘many eyes’ hypothesis. According to this hypothesis, collective vigilance allows prey in large groups to detect predators more efficiently by making alarm signals or behavioural cues to each other, thereby allowing individuals within the group to spend more time foraging. Here, we find that collective vigilance is sufficient to select for gregarious foraging behaviour as long there is not a direct cost for grouping (e.g. competition for limited food resources), even when controlling for confounding factors such as the dilution effect. Furthermore, we explore the role of the genetic relatedness and reproductive strategy of the prey and find that highly related groups of prey with a semelparous reproductive strategy are the most likely to evolve gregarious foraging behaviour mediated by the benefit of vigilance. These findings, combined with earlier studies with evolving digital organisms, further sharpen our understanding of the factors favouring grouping behaviour.
Highlights
Many prey choose to live, forage and reproduce in groups—this is one of the most readily observed phenomena in2015 The Authors
5 10 25 50 group size that a prey will be vigilant at a given moment in time, averaged across all of the prey in the population. These treatments are repeated across a wide range of group sizes, allowing us to study whether the selection for vigilance can be generalized to groups of varying sizes, and whether we can observe the inverse relationship between group size and vigilance predicted by the many eyes hypothesis
We find that prey living in homogeneous groups consistently evolve higher levels of vigilance than their counterparts living in heterogeneous groups
Summary
A common adaptive explanation for grouping behaviour is that it aids in anti-predatory 2 defence. Starlings (Sturnus vulgaris) are well known to forage in flocks in the presence of predators [1]. E.g. the eastern mosquitofish (Gambusia holbrooki), have been documented to identify predators more accurately in larger groups [2]. Ostriches (Struthio camelus) have been reported to experience anti-predatory benefits when foraging in groups [3]. Even when there is a correlation between grouping behaviour and protection from predators, it is difficult to pin down what benefits select for the evolution of grouping behaviour
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