Selfish-herd behaviour of sheep under threat

King, Andrew J.; Wilson, Alan M.; Wilshin, Simon; Lowe, John C.; Haddadi, Hamed; Hailes, Stephen; Morton, A. Jennifer

doi:10.1016/j.cub.2012.05.008

Cited by 120 publications

(116 citation statements)

References 9 publications

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“…By using homogeneous pastures, we minimize as much as possible the effect of environment heterogeneity (44). Direct predation disturbances that may be invoked to explain increases in group density (12,13,45) are also ruled out in this context. Therefore, we are able to argue that this collective behavior mainly results from socially driven individual decisions.…”

Section: Discussionmentioning

confidence: 99%

“…sheep herds | collective behavior | self-organization | computational modeling | Allelomimetism T he social interactions and behavioral mechanisms involved in the coordination of collective movements in animal groups largely determine the animals' ability to display adapted responses when they face challenges, such as finding, efficiently, food sources (1)(2)(3)(4) or safe resting places (5-7) or avoiding predators (8)(9)(10)(11)(12)(13). Thus, the diversity of collective motion patterns observed in groupliving species reflects the multiple forms of interactions individuals use for coordinating their behavioral actions (14,15).…”

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confidence: 99%

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Intermittent collective dynamics emerge from conflicting imperatives in sheep herds

Ginelli

Peruani

Pillot

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

135

132

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Among the many fascinating examples of collective behavior exhibited by animal groups, some species are known to alternate slow group dispersion in space with rapid aggregation phenomena induced by a sudden behavioral shift at the individual level. We study this phenomenon quantitatively in large groups of grazing Merino sheep under controlled experimental conditions. Our analysis reveals strongly intermittent collective dynamics consisting of fast, avalanche-like regrouping events distributed on all experimentally accessible scales. As a proof of principle, we introduce an agent-based model with individual behavioral shifts, which we show to account faithfully for all collective properties observed. This offers, in turn, an insight on the individual stimulus/ response functions that can generate such intermittent behavior. In particular, the intensity of sheep allelomimetic behavior plays a key role in the group's ability to increase the per capita grazing surface while minimizing the time needed to regroup into a tightly packed configuration. We conclude that the emergent behavior reported probably arises from the necessity to balance two conflicting imperatives: (i) the exploration of foraging space by individuals and (ii) the protection from predators offered by being part of large, cohesive groups. We discuss our results in the context of the current debate about criticality in biology.sheep herds | collective behavior | self-organization | computational modeling | Allelomimetism T he social interactions and behavioral mechanisms involved in the coordination of collective movements in animal groups largely determine the animals' ability to display adapted responses when they face challenges, such as finding, efficiently, food sources (1-4) or safe resting places (5-7) or avoiding predators (8-13). Thus, the diversity of collective motion patterns observed in groupliving species reflects the multiple forms of interactions individuals use for coordinating their behavioral actions (14,15). Deciphering these interactions, their relation with the patterns emerging at the collective level, and their connections with the physiological and ecological constraints peculiar to each group-living species is crucial to understanding the evolution of collective phenomena in biological systems (16-18). So far, only a handful of quantitative datasets have been gathered for large animal groups (19-21). Most of them have focused on elementary cases where the prevailing biological imperative seems to be group cohesion, either to gain protection from potential predators, such as for the spontaneous collective motion exhibited by starling flocks (19,22) and some fish schools (23-25), or for reproductive purposes, as in swarms of midges (21,26).One important and, so far, often neglected aspect of collective motion is the existence of individual-level behavioral shifts, which, in turn, may trigger a transition at the collective level. For instance, in many species of fish, groups regularly alternate between a swarming state, in wh...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Intermittent collective dynamics emerge from conflicting imperatives in sheep herds

Ginelli

Peruani

Pillot

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

135

132

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“…Fur seals (Arctocephalus pusillus pusillus) moving through areas of high risk of predation from white sharks (Carcharodon carcharias) appear to move towards their nearest neighbour rather than evaluating the position of multiple neighbours [21]. On the other hand, domestic sheep move towards the centre of the group when herded by a sheep dog [22], and three-spined sticklebacks (Gasterosteus aculeatus) move towards an individual that can be reached more quickly rather than one that is spatially closer [23], although these two cases did not evaluate alternative rules.…”

Section: Introductionmentioning

confidence: 99%

‘Selfish herds’ of guppies follow complex movement rules, but not when information is limited

Kimbell¹,

Morrell²

2015

Proc. R. Soc. B.

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Under the threat of predation, animals can decrease their level of risk by moving towards other individuals to form compact groups. A significant body of theoretical work has proposed multiple movement rules, varying in complexity, which might underlie this process of aggregation. However, if and how animals use these rules to form compact groups is still not well understood, and how environmental factors affect the use of these rules even less so. Here, we evaluate the success of different movement rules, by comparing their predictions with the movement seen when shoals of guppies (Poecilia reticulata) form under the threat of predation. We repeated the experiment in a turbid environment to assess how the use of the movement rules changed when visual information is reduced. During a simulated predator attack, guppies in clear water used complex rules that took multiple neighbours into account, forming compact groups. In turbid water, the difference between all rule predictions and fish movement paths increased, particularly for complex rules, and the resulting shoals were more fragmented than in clear water. We conclude that guppies are able to use complex rules to form dense aggregations, but that environmental factors can limit their ability to do so.

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“…This phenomenon is well documented in groups of moving animals, which often form tighter groups in response to the detection of a predator [1][2][3][4][5][6]; but it also takes place in other adverse conditions, such as in the absence of food [7] or when animals are introduced into an unknown environment [8,9]. In humans, the occurrence of sudden bank runs [10][11][12] and human stampedes [13 -19] suggests increased aggregation in adversity, although data are insufficient to draw definitive conclusions.…”

Section: Introductionmentioning

confidence: 95%

“…For example, both theory and experiments show that belonging to a group may protect against predators [6,[20][21][22][23]. In humans, copying others' behaviour can help to deflect the responsibility for an anticipated failure [24,25].…”

Section: Introductionmentioning

confidence: 99%

Adversity magnifies the importance of social information in decision-making

Pérez‐Escudero

Polavieja

2016

Preprint

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Decision-making theories explain animal behaviour, including human behaviour, as a response to estimations about the environment. In the case of collective behaviour, they have given quantitative predictions of how animals follow the majority option. However, they have so far failed to explain that in some species and contexts social cohesion increases when conditions become more adverse (i.e. individuals choose the majority option with higher probability when the estimated quality of all available options decreases). We have found that this failure is due to modelling simplifications that aided analysis, like low levels of stochasticity or the assumption that only one choice is the correct one. We provide a more general but simple geometric framework to describe optimal or suboptimal decisions in collectives that gives insight into three different mechanisms behind this effect. The three mechanisms have in common that the private information acts as a gain factor to social information: a decrease in the privately estimated quality of all available options increases the impact of social information, even when social information itself remains unchanged. This increase in the importance of social information makes it more likely that agents will follow the majority option. We show that these results quantitatively explain collective behaviour in fish and experiments of social influence in humans.

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Selfish-herd behaviour of sheep under threat

Cited by 120 publications

References 9 publications

Intermittent collective dynamics emerge from conflicting imperatives in sheep herds

Intermittent collective dynamics emerge from conflicting imperatives in sheep herds

‘Selfish herds’ of guppies follow complex movement rules, but not when information is limited

Adversity magnifies the importance of social information in decision-making

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