Re–examining safety in numbers: interactions between risk dilution and collective detection depend upon predator targeting behaviour

Bednekoff, Peter A.; Lima, Steven L.

doi:10.1098/rspb.1998.0535

Cited by 170 publications

(111 citation statements)

References 34 publications

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“…This dilution of risk corresponds to the logic of an earlier verbal model (Grand & Dill 1999) and assumes early targeting by the predator and no information transfer between foragers (Bednekoff & Lima 1998). Collective detection is probably important for many animal groups.…”

Section: (A) Fixed Groups (I) Predation Decreases With Group Sizementioning

confidence: 99%

Risk allocation and competition in foraging groups: reversed effects of competition if group size varies under risk of predation

Bednekoff

Lima

2004

Proc. R. Soc. Lond. B

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Animals often feed more quickly when in larger groups. This group-size effect is often explained by safety advantages for groups but an alternative explanation is that animals feed faster in larger groups because of greater scramble competition for limited food. We show that predation risk enhances the group-size effect if groups vary in size. By contrast, competition leads to the group-size effect only when individuals feed in groups of constant size. When individuals feed in groups that vary in size, the best strategy for dealing with competition is to feed intensely when in smaller groups and feed little when in larger (more competitive) groups. In all situations, the effects of competition interact with the effects of predation risk in a simple multiplicative way. Our results suggest that scramble competition is not a general explanation for the group-size effect on vigilance in situations where group size changes relatively rapidly.

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Section: (A) Fixed Groups (I) Predation Decreases With Group Sizementioning

confidence: 99%

Risk allocation and competition in foraging groups: reversed effects of competition if group size varies under risk of predation

Bednekoff

Lima

2004

Proc. R. Soc. Lond. B

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“…Predator behaviour has often been omitted from models of vigilance or at least simplified into a single, fixed-risk entity (except see Packer & Abrams 1990;Bednekoff & Lima 1998;Scannell et al 2001). We have shown that although the broad predictions of vigilance theory still hold (decreasing vigilance with increasing group size), by adding a predator that has a choice to make as to which group to attack, some new interesting dynamics are brought to light.…”

Section: Discussionmentioning

confidence: 99%

“…This occurred because the effect of dilution is generally stronger than an incremental change in vigilance rates: i.e. switching to the other group is likely to have a more profound effect on an individual's fitness than altering the cooperative vigilance rate (Bednekoff & Lima 1998;Dehn 1990). The more sensitive the predator is to small differences in prey susceptibility, the greater the adopted vigilance rate tends to be for the prey-of course this only occurs when the prey split into two groups; else the optimal vigilance rate is the same.…”

Section: Discussionmentioning

confidence: 99%

“…By forming groups, animals can theoretically benefit from the many-eyes effect of having neighbours that might alert one another to a potential threat, even if a particular individual has not detected the threat for itself (Pulliam 1973;Roberts 1996;Beauchamp 2003). Forming groups also introduces a dilution effect whereby having more neighbours simply means that the chance of oneself being predated is lessened (Dehn 1990;Bednekoff & Lima 1998). There are also well-established costs of grouping: most notably these take the form of competition for resources (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Evolution of anti-predator traits in response to a flexible targeting strategy by predators

et al. 2006

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Anti-predator benefits increase with vigilance rate and group size in many species of animal, while simultaneously resource intake rates usually decrease. This implies that there is an optimal group size and vigilance rate that will maximize individual fitness. While this basic theory of vigilance has been modelled and tested extensively, it has often been assumed that the predator represents a 'fixed-risk' such that groups of prey are essentially independent entities that exert little or no effect on one another either directly or indirectly. We argue that this is an over-simplification, and propose that the behaviour of one group of prey will likely affect the fitness of another local group of prey if the predator preferentially attacks the most vulnerable group-rather than attack both with constant rates. Using a numerical simulation model, we make the first examination of this game and allow the prey to dynamically evolve both optimal group size distributions between two habitats and vigilance rates in response to a predator with a preference for whichever group is the more vulnerable. We show that the density of prey in the population and the sensitivity of a predator to differences in prey vulnerability are likely to drive the dynamics of such a game. This novel approach to vigilance theory opens the door to several challenging lines of future research, both experimental and theoretical.

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“…Furthermore, individuals that only benefit from indirect detection may, because of an inappropriate reaction, become preferential targets for the predator [13]. Scanning for predators then becomes a defecting attitude that exposes non-vigilant companions to a higher risk of being targeted [15,16]. Collective vigilance is thus a complex and polymorphous game.…”

Section: Introductionmentioning

confidence: 99%

Negotiation may lead selfish individuals to cooperate: the example of the collective vigilance game

Sirot

2012

Proc. R. Soc. B.

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Game-theoretical models have been highly influential in behavioural ecology. However, these models generally assume that animals choose their action before observing the behaviour of their opponents while, in many natural situations, individuals in fact continuously react to the actions of others. A negotiation process then takes place and this may fundamentally influence the individual attitudes and the tendency to cooperate. Here, I use the classical model system of vigilance behaviour to demonstrate the consequences of such behavioural negotiation among selfish individuals, by predicting patterns of vigilance in a pair of animals foraging under threat of predation. I show that the game played by the animals and the resulting vigilance strategies take radically different forms, according to the way predation risk is shared in the pair. In particular, if predators choose their target at random, the prey respond by displaying moderate vigilance and taking turns scanning. By contrast, if the individual that takes flight later in an attack endures a higher risk of being targeted, vigilance increases and there is always at least one sentinel in the pair. Finally, when lagging behind its companion in fleeing from an attacker becomes extremely risky, vigilance decreases again and the animals scan simultaneously.

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Re–examining safety in numbers: interactions between risk dilution and collective detection depend upon predator targeting behaviour

Cited by 170 publications

References 34 publications

Risk allocation and competition in foraging groups: reversed effects of competition if group size varies under risk of predation

Risk allocation and competition in foraging groups: reversed effects of competition if group size varies under risk of predation

Evolution of anti-predator traits in response to a flexible targeting strategy by predators

Negotiation may lead selfish individuals to cooperate: the example of the collective vigilance game

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