Probable exaptations within the « distributed » herd (original) (raw)

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.

The temporal selfish herd: predation risk while aggregations form

Proceedings of The Royal Society B: Biological Sciences, 2010

The hypothesis of the selfish herd has been highly influential to our understanding of animal aggregation. Various movement strategies have been proposed by which individuals might aggregate to form a selfish herd as a defence against predation, but although the spatial benefits of these strategies have been extensively studied, little attention has been paid to the importance of predator attacks that occur while the aggregation is forming. We investigate the success of mutant aggregation strategies invading populations of individuals using alternative strategies and find that the invasion dynamics depend critically on the time scale of movement. If predation occurs early in the movement sequence, simpler strategies are likely to prevail. If predators attack later, more complex strategies invade. If there is variation in the timing of predator attacks (through variation within or between individual predators), we hypothesize that groups will consist of a mixture of strategies, dependent upon the distribution of predator attack times. Thus, behavioural diversity can evolve and be maintained in populations of animals experiencing a diverse range of predators differing solely in their attack behaviour. This has implications for our understanding of predator -prey dynamics, as the timing of predator attacks will exert selection pressure on prey behavioural responses, to which predators must respond.

Asymmetrical individual return herding

El efecto manada ocurre cuando los individuos privilegian la opinión de consenso y las transacciones pasadas por sobre los fundamentos de los precios. En este estudio analizamos 101 acciones chilenas transadas durante el período1990 a 2009. Contrariamente a la evidencia empírica para los Estados Unidos y los mercados internacionales (véase, Christie y Huang, 1995; Demirer y Kutan, 2006; Gleason, Lee & Mathur 2003; Gleason, Mathur & Peterson, 2004), el efecto manada es más probable cuando el mercado accionario se encuentra deprimido, una vez que se considera el volumen transado. Nuestros resultados también sugieren una relación inversa entre volatilidad y volumen, lo que contradice la hipótesis de distribución de un factor (MDH). Esta asociación resulta particularmente significativa cuando se escogen umbrales más extremos para los retornos. El efecto manada ocurre cuando los individuos privilegian la opinión de consenso y las transacciones pasadas por sobre los fundamentos de los pre...

Collective Motion as an Ultimate Effect in Crowded Selfish Herds

Scientific Reports, 2019

The selfish herd hypothesis explains how social prey can assemble cohesive groups for maximising individual fitness. However, previous models often abstracted away the physical manifestation of the focal animals such that the influence of getting stuck in a crowded herd on individual adaptation was less intensively investigated. Here, we propose an evolutionary model to simulate the adaptation of egoistic social prey to predation given that individual mobility is strictly restrained by the presence of other conspecifics. In our simulated evolutionary races, agents were set to either be confined by neighbours or move to empty cells on the lattice, and the behavioural traits of those less exposed were selected and inherited. Our analyses show that under this crowded environment, cohesive and steady herds were consistently replaced by morphing and moving aggregates via the attempt of border agents to share predation risk with the inner members. This kind of collective motion emerges pu...

Collective behavior and evolutionary games - An introduction

2013

This is an introduction to the special issue titled "Collective behavior and evolutionary games" that is in the making at Chaos, Solitons & Fractals. The term collective behavior covers many different phenomena in nature and society. From bird flocks and fish swarms to social movements and herding effects, it is the lack of a central planner that makes the spontaneous emergence of sometimes beautifully ordered and seemingly meticulously designed behavior all the more sensational and intriguing. The goal of the special issue is to attract submissions that identify unifying principles that describe the essential aspects of collective behavior, and which thus allow for a better interpretation and foster the understanding of the complexity arising in such systems. As the title of the special issue suggests, the later may come from the realm of evolutionary games, but this is certainly not a necessity, neither for this special issue, and certainly not in general. Interdisciplin...

Decision-making Processes in Group Departures of Cattle

Ethology, 2009

To keep social cohesiveness, group-living animals have to reach consensus decisions through recruitment processes. This implies that decisionmaking depends on the behaviours and social relationships of several group members at different stages of movements. We tested these assumptions in a group of fifteen 18-mo-old Charolais heifers (Bos taurus) at pasture, in which two observers continuously videotaped social interactions and group departures after resting periods. These departures were preceded by a phase of preparation characterized by an increase in activity. The number of heifers participating to a movement increased with the number of group members oriented in the direction of the movement before departure. The first moving animal also recruited a higher number of mates when it had a greater number of close neighbours, the first individuals to follow being mainly its preferential partners. Coercive interactions such as pressing behaviours were observed within the 5 min preceding or following departure. After departure, the numbers of walks and restarts of the first two movers were still operative in recruiting others. The frequency of pauses of the first mover was significantly higher when it was not followed, meaning that it adjusted its behaviour to that of other group members. Decision-making was distributed among group members, with any individual being liable to move first. The behaviour of cows and their spatial distribution before departure, at departure and after departure significantly affected the number of participants in the movement, demonstrating that decisionmaking was time-distributed in the studied cattle group. A. Ramseyer et al. Decision-making in Cattle