Selfish fish Animal Behaviour 2013 printed version.pdf
Robert J Young
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Abstract
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This research investigates the behavior of two-spot astyanax (Astyanax bimaculatus) in response to various predatory stimuli, focusing on the concept of active selfishness within groups. The study reveals that individuals are more likely to attack fellow group members when faced with an 'active search' predator, which increases the attacked individual's risk of predation. Such behavior highlights an innate response shaped by natural selection, exposing a complex cost of group living where individuals may exploit their conspecifics to enhance their own survival.
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Prey synchronize their vigilant behaviour with other group members
Proceedings of The Royal Society B: Biological Sciences, 2007
It is generally assumed that an individual of a prey species can benefit from an increase in the number of its group's members by reducing its own investment in vigilance. But what behaviour should group members adopt in relation to both the risk of being preyed upon and the individual investment in vigilance? Most models assume that individuals scan independently of one another. It is generally argued that it is more profitable for each group member owing to the cost that coordination of individual scans in nonoverlapping bouts of vigilance would require. We studied the relationships between both individual and collective vigilance and group size in Defassa waterbuck, Kobus ellipsiprymnus defassa, in a population living under a predation risk. Our results confirmed that the proportion of time an individual spent in vigilance decreased with group size. However, the time during which at least one individual in the group scanned the environment (collective vigilance) increased. Analyses showed that individuals neither coordinated their scanning in an asynchronous way nor scanned independently of one another. On the contrary, scanning and non-scanning bouts were synchronized between group members, producing waves of collective vigilance. We claim that these waves are triggered by allelomimetic effects i.e. they are a phenomenon produced by an individual copying its neighbour's behaviour.
Spatial positioning in the selfish herd
Behavioral Ecology, 2010
The antipredator benefits of grouping are relatively well understood; however, predation risk often differs for individuals that occupy different positions within a group. The selfish herd hypothesis describes how individuals can reduce risk of predation by moving to specific positions within the group. In existing theory, this movement occurs through the adoption of possible ''movement rules'' that differ in their cognitive complexity. Here, we investigate the effectiveness of different previously suggested rules in reducing risk for central and peripheral individuals within a group. We demonstrate that initial spatial position is important in determining the success of different risk-reducing movement rules, as initially centrally positioned individuals are likely to be more successful than peripheral ones at reducing their risk relative to other group members, regardless of the movement rules used. Simpler strategies are effective in low-density populations; but at high density, more complex rules are more effective. We also find that complex rules that consider the position of multiple neighbors are the only rules that successfully allow individuals to move from peripheral to central positions or maintain central positions, thus avoiding predators that attack from outside the group. Our results suggest that the attack strategy of a predator should be critically important in determining prey escape strategies in a selfish herd context and that prey should modify their behavioral responses to impending attack in response to their position within a group.
Social deprivation affects cooperative predator inspection in a cichlid fish
Royal Society Open Science, 2015
A Sensory-Driven Trade-Off between Coordinated Motion in Social Prey and a Predator’s Visual Confusion
PLOS Computational Biology, 2016
Social animals are capable of enhancing their awareness by paying attention to their neighbors, and prey found in groups can also confuse their predators. Both sides of these sensory benefits have long been appreciated, yet less is known of how the perception of events from the perspectives of both prey and predator can interact to influence their encounters. Here we examined how a visual sensory mechanism impacts the collective motion of prey and, subsequently, how their resulting movements influenced predator confusion and capture ability. We presented virtual prey to human players in a targeting game and measured the speed and accuracy with which participants caught designated prey. As prey paid more attention to neighbor movements their collective coordination increased, yet increases in prey coordination were positively associated with increases in the speed and accuracy of attacks. However, while attack speed was unaffected by the initial state of the prey, accuracy dropped significantly if the prey were already organized at the start of the attack, rather than in the process of self-organizing. By repeating attack scenarios and masking the targeted prey's neighbors we were able to visually isolate them and conclusively demonstrate how visual confusion impacted capture ability. Delays in capture caused by decreased coordination amongst the prey depended upon the collection motion of neighboring prey, while it was primarily the motion of the targets themselves that determined capture accuracy. Interestingly, while a complete loss of coordination in the prey (e.g., a flash expansion) caused the greatest delay in capture, such behavior had little effect on capture accuracy. Lastly, while increases in collective coordination in prey enhanced personal risk, traveling in coordinated groups was still better than appearing alone. These findings demonstrate a trade-off between the sensory mechanisms that can enhance the collective properties that emerge in social animals and the individual group member's predation risk during an attack.
The Evolution of Different Forms of Sociality: Behavioral Mechanisms and Eco-Evolutionary Feedback
PLOS ONE, 2015
Different forms of sociality have evolved via unique evolutionary trajectories. However, it remains unknown to what extent trajectories of social evolution depend on the specific characteristics of different species. Our approach to studying such trajectories is to use evolutionary case-studies, so that we can investigate how grouping co-evolves with a multitude of individual characteristics. Here we focus on anti-predator vigilance and foraging. We use an individual-based model, where behavioral mechanisms are specified, and costs and benefits are not predefined. We show that evolutionary changes in grouping alter selection pressures on vigilance, and vice versa. This eco-evolutionary feedback generates an evolutionary progression from "leader-follower" societies to "fission-fusion" societies, where cooperative vigilance in groups is maintained via a balance between within-and betweengroup selection. Group-level selection is generated from an assortment that arises spontaneously when vigilant and non-vigilant foragers have different grouping tendencies. The evolutionary maintenance of small groups, and cooperative vigilance in those groups, is therefore achieved simultaneously. The evolutionary phases, and the transitions between them, depend strongly on behavioral mechanisms. Thus, integrating behavioral mechanisms and eco-evolutionary feedback is critical for understanding what kinds of intermediate stages are involved during the evolution of particular forms of sociality.
Groups confuse predators by exploiting perceptual bottlenecks: a connectionist model of the confusion effect
Behavioral Ecology and Sociobiology, 1995
Aggregation is a well documented behaviour in a number of animal groups. The "confusion effect" is one mechanism thought to mitigate the success of predators feeding on gregarious prey and hence favour aggregation. An artificial neural network model of prey targeting is developed to explore the advantages prey species might derive through a tendency to group. The network illustrates how an abstract model of the computational mechanisms mediating the perception of prey position is able to show a degradation in performance as group size increases. The relationship between group size and predator confusion has a characteristic decreasing decelerating shape. Prey "oddity" is shown to reduce the impact of the confusion effect, thereby allowing predators to target prey more accurately. Hence shoaling behaviour is most profitable to the prey when prey phenotypes are visually indistinguishable to a predator. Futhermore it is shown that prey "oddity" is relatively more costly in large groups than in small groups and the implications for assortative schooling are discussed. Both the model and the results are intended to make the general point that cognitive constraints will limit the information that a nervous system can process at a number of different levels of neural organization.
Grouping increases the ability of the social rodent, Octodon degus, to detect predators when using exposed microhabitats
Oikos, 2002
Grouping increases the ability of the social rodent, Octodon degus, to detect predators when using exposed microhabitats. -Oikos 98: 491-497.
When are two heads better than one? Visual perception and information transfer affect vigilance coordination in foraging groups
Behavioral Ecology, 2004
Animals frequently raise their heads to check for danger. In a group, individuals generally raise their heads independently. Earlier models suggest that all group members could gain by coordinating their vigilance, i.e., each member raising its head when others are not. We re-examine these suggestions, considering groups of different sizes, in light of empirical findings that:
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Grouping increases the ability of the social rodent, <i>Octodon degus</i> , to detect predators when using exposed microhabitats
Oikos, 2002
Grouping increases the ability of the social rodent, Octodon degus, to detect predators when using exposed microhabitats.-Oikos 98: 491-497. We examined the hypothesis that a main benefit of group-living in the hystricognath rodent, Octodon degus (common degu), is to decrease individual risk of predation. During a first series of field observations, we contrasted group size of degus when using covered microhabitats with that of degus using exposed patches. During a second set of field observations, we assessed how distance to detection and to escape by degus varied with group size upon the approach of a potential human predator. Degus in exposed patches formed larger groups than degus in covered microhabitats. After excluding the influence of nearest burrow to focal subjects, we found that degus of larger groups detected an approaching human predator at a greater distance than degus of smaller groups. Likewise, degus of larger groups escaped to nearby burrows at a greater distance from the approaching predator than degus of smaller groups. All these pieces of evidence support the predatory risk hypothesis according to which group-living in degus functions to reduce the risk of predation.
Modelling non-attentional visual information transmission in groups under predation
Ecological Modelling, 2020
Group living is of benefit to foraging individuals by improving their survival, through passive risk dilution by sheer numbers and through increasingly more active processes, ranging from cue transmission to alarm calling. Cue transmission of information within a group cannot easily be tracked in the field, but can be studied by modelling. An unintentional visual cue can be given by a fleeing action, and when it occurs in the visual field of an individual, can by contagion incite it to flee as well, making such a cue functional in anti-predator warning. The visual field is limited not only by morphology, causing a blind angle at the back, but also by behaviour. For instance, foraging with the head down can cause an extra "blind" angle in front for cues from other individuals, changing an unobstructed frontal visual field to a split lateral shape. The questions of the present study are: how do visual fields, in terms of their size and blind angles, influence survival of individuals in a group through their effect on non-attentional reception of cues to danger among group members after attentional detection of a predator, and how can we quantify this? We use an agent-based spatially explicit model to investigate the effect of contagious fleeing after detection of predators on survival rate. This model is a bottom-up model of foraging agents in a simple environment, where only assumptions about basic competences are made. We vary the size and the shape of the visual field (lateral, with the additional frontal "blind" angle, versus a frontal continuous view), the group size, the movement probability, and the style of movement (regular movement or start-stop movement) in residential groups. We devise a measure for the transmission rate and we measure the length of the transmission chains. We find that, as expected, in a residential group, a larger visual field enhances survival rate. Moreover, a lateral field is more effective than a frontal field of the same total size because it increases the field of vision and therefore the non-attentional reception of visual cues about danger during, for instance, foraging, for all but the largest visual fields. This is demonstrated by the higher transmission rates and longer chains of transmission for lateral fields. Better transmission for lateral visual fields results in more synchronized fleeing behaviour. As long as the visual field is large enough, having a blind angle in front does not detract from sufficiently effective transmission. These findings should be taken into account in empirical studies of vigilance in groups of foraging animals.
Behavioral Ecology-2006-Webster-959-64
Familiarity is thought to stabilize dominance hierarchies and reduce aggressive interactions within groups of socially living animals. Though familiarity has been widely studied in shoaling fish, few studies have investigated changes in prey competition as a function of time spent together within groups of initially unfamiliar individuals. In this study, we created shoals of threespined stickleback (Gasterosteus aculeatus) and monitored changes in foraging rates and related competitive behaviors within shoals over a 4-week period in experimental series where prey was spatially and temporally concentrated or dispersed. Prey share was unequal under both prey distribution modes, and disparity in prey share was not seen to change as trials progressed. Interestingly, the contest rate for prey items fell over time when individuals were competing for dispersed prey but not when prey were concentrated. We found no evidence that fish showed association preferences for either group members that had consumed a greater or lesser proportion of prey during trials. Though the intensity of competition may be reduced by increased group stability in nature, this is likely to be strongly dependent on the way prey resources are distributed through space and time.
Animal Group Forces Resulting from Predator Avoidance and Competition Minimization
Journal of Theoretical Biology, 1999
A new model to explain animal spacing, based on a trade-o! between foraging e$ciency and predation risk, is derived from biological principles. The model is able to explain not only the general tendency for animal groups to form, but some of the attributes of real groups. These include the independence of mean animal spacing from group population, the observed variation of animal spacing with resource availability and also with the probability of predation, and the decline in group stability with group size. The appearance of &&neutral zones'' within which animals are not motivated to adjust their relative positions is also explained. The model assumes that animals try to minimize a cost potential combining the loss of intake rate due to foraging interference and the risk from exposure to predators. The cost potential describes a hypothetical "eld giving rise to apparent attractive and repulsive forces between animals. Biologically based functions are given for the decline in interference cost and increase in the cost of predation risk with increasing animal separation. Predation risk is calculated from the probabilities of predator attack and predator detection as they vary with distance. Using example functions for these probabilities and foraging interference, we calculate the minimum cost potential for regular lattice arrangements of animals before generalizing to "nite-sized groups and random arrangements of animals, showing optimal geometries in each case and describing how potentials vary with animal spacing.
Collective predator evasion: Putting the criticality hypothesis to the test
PLOS Computational Biology, 2021
According to the criticality hypothesis, collective biological systems should operate in a special parameter region, close to so-called critical points, where the collective behavior undergoes a qualitative change between different dynamical regimes. Critical systems exhibit unique properties, which may benefit collective information processing such as maximal responsiveness to external stimuli. Besides neuronal and gene-regulatory networks, recent empirical data suggests that also animal collectives may be examples of self-organized critical systems. However, open questions about self-organization mechanisms in animal groups remain: Evolutionary adaptation towards a group-level optimum (group-level selection), implicitly assumed in the “criticality hypothesis”, appears in general not reasonable for fission-fusion groups composed of non-related individuals. Furthermore, previous theoretical work relies on non-spatial models, which ignore potentially important self-organization and s...
The effects of external cues on individual and collective behavior of shoaling fish
Science Advances
Collective animal behavior is an emergent phenomenon arising from the local interactions of the members of animal groups. Considerable progress has been made in characterizing these interactions, particularly inferring rules that shape and guide the responses of animals to their near neighbors. To date, experimental work has focused on collective behavior within a single, stable context. We examine the individual and collective behavior of a schooling fish species, the x-ray tetra (Pristella maxillaris), identifying their response to changes in context produced by food cues or conspecific alarm cues. Fish exposed to alarm cues show pronounced, broad-ranging changes of behavior, including reducing speed and predictability in their movements. Alarmed fish also alter their responses to other group members, including enacting a smaller zone of repulsion and increasing their frequency of observation of, and responsiveness to, near neighbors. Fish subject to food cues increased speed as a function of neighbor positions and reduced encounter frequency with near neighbors. Overall, changes in individual behavior and the interactions among individuals in response to external cues coincide with changes in group-level patterns, providing insight into the adaptability of behavior to changes in context and interrelationship between local interactions and global patterns in collective behavior.
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