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Rands, S. A., Cowlishaw, G., Pettifor, R. A., Rowcliffe, J. M., & Johnstone, R. A. (2003). Spontaneous emergence of leaders and followers in foraging pairs. Nature, 423(6938), 432–434.
Abstract: Animals that forage socially often stand to gain from coordination of their behaviour. Yet it is not known how group members reach a consensus on the timing of foraging bouts. Here we demonstrate a simple process by which this may occur. We develop a state-dependent, dynamic game model of foraging by a pair of animals, in which each individual chooses between resting or foraging during a series of consecutive periods, so as to maximize its own individual chances of survival. We find that, if there is an advantage to foraging together, the equilibrium behaviour of both individuals becomes highly synchronized. As a result of this synchronization, differences in the energetic reserves of the two players spontaneously develop, leading them to adopt different behavioural roles. The individual with lower reserves emerges as the 'pace-maker' who determines when the pair should forage, providing a straightforward resolution to the problem of group coordination. Moreover, the strategy that gives rise to this behaviour can be implemented by a simple 'rule of thumb' that requires no detailed knowledge of the state of other individuals.
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Newman, M. E. J. (2003). Mixing patterns in networks. Phys Rev E Stat Nonlin Soft Matter Phys, 67(2 Pt 2), 026126.
Abstract: We study assortative mixing in networks, the tendency for vertices in networks to be connected to other vertices that are like (or unlike) them in some way. We consider mixing according to discrete characteristics such as language or race in social networks and scalar characteristics such as age. As a special example of the latter we consider mixing according to vertex degree, i.e., according to the number of connections vertices have to other vertices: do gregarious people tend to associate with other gregarious people? We propose a number of measures of assortative mixing appropriate to the various mixing types, and apply them to a variety of real-world networks, showing that assortative mixing is a pervasive phenomenon found in many networks. We also propose several models of assortatively mixed networks, both analytic ones based on generating function methods, and numerical ones based on Monte Carlo graph generation techniques. We use these models to probe the properties of networks as their level of assortativity is varied. In the particular case of mixing by degree, we find strong variation with assortativity in the connectivity of the network and in the resilience of the network to the removal of vertices.
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Adolphs, R. (2003). Cognitive neuroscience of human social behaviour. Nat Rev Neurosci, 4(3), 165–178.
Abstract: We are an intensely social species--it has been argued that our social nature defines what makes us human, what makes us conscious or what gave us our large brains. As a new field, the social brain sciences are probing the neural underpinnings of social behaviour and have produced a banquet of data that are both tantalizing and deeply puzzling. We are finding new links between emotion and reason, between action and perception, and between representations of other people and ourselves. No less important are the links that are also being established across disciplines to understand social behaviour, as neuroscientists, social psychologists, anthropologists, ethologists and philosophers forge new collaborations.
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Conradt, L., & Roper, T. J. (2003). Group decision-making in animals. Nature, 421(6919), 155–158.
Abstract: Groups of animals often need to make communal decisions, for example about which activities to perform, when to perform them and which direction to travel in; however, little is known about how they do so. Here, we model the fitness consequences of two possible decision-making mechanisms: 'despotism' and 'democracy'. We show that under most conditions, the costs to subordinate group members, and to the group as a whole, are considerably higher for despotic than for democratic decisions. Even when the despot is the most experienced group member, it only pays other members to accept its decision when group size is small and the difference in information is large. Democratic decisions are more beneficial primarily because they tend to produce less extreme decisions, rather than because each individual has an influence on the decision per se. Our model suggests that democracy should be widespread and makes quantitative, testable predictions about group decision-making in non-humans.
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Tang, A. C., Reeb, B. C., Romeo, R. D., & McEwen, B. S. (2003). Modification of Social Memory, Hypothalamic-Pituitary-Adrenal Axis, and Brain Asymmetry by Neonatal Novelty Exposure. The Journal of Neuroscience, 23(23), 8254–8260.
Abstract: Although corticosterone (a stress hormone) is known to influence social behavior and memory processes, little has been explored concerning its modulatory role in social recognition. In rats, social recognition memory for conspecifics typically lasts <2 hr when evaluated using a habituation paradigm. Using neonatal novelty exposure, a brief and transient early life stimulation method known to produce long-lasting changes in the hypothalamic-pituitary-adrenal axis, we found that social recognition memory was prolonged to at least 24 hr during adulthood. This prolonged social memory was paralleled by a reduction in the basal blood concentration of corticosterone. The same neonatal stimulation also resulted in a functional asymmetry expressed as a greater right-turn preference in a novel environment. Rats that preferred to turn right showed better social recognition memory. These inter-related changes in basal blood corticosterone concentration, turning asymmetry, and social recognition memory suggest that stress hormones and brain asymmetry are likely candidates for modulating social memory. Furthermore, given that neonatal stimulation has been shown to improve learning and memory performance primarily under aversive learning situations, the neonatal novelty exposure-induced enhancement in social recognition broadens the impact of early life stimulation to include the social domain.
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Sighieri, C., Tedeschi, D., De Andreis, C., Petri, L., & Baragli, P. (2003). Behaviour patterns of horses can be used to establish a dominantsubordinate relationship between man and horse. Animal Welfare, 12, 705–708.
Abstract: This paper describes how man can enter the social hierarchy of the horse by mimicking the behaviour and stance it uses to establish dominance. A herd is organised according to a dominance hierarchy established by means of ritualised conflict. Dominance relationships are formed through these confrontations: one horse gains the dominant role and others identify themselves as subordinates. This study was conducted using five females of the Haflinger breed, totally unaccustomed to human contact, from a free-range breeding farm. The study methods were based on the three elements fundamental to the equilibrium of the herd: flight, herd instinct and hierarchy. The trainer-horse relationship was established in three phases: retreat, approach and association. At the end of the training sessions, all of the horses were able to respond correctly to the trainer. These observations suggest that it is possible to manage unhandled horses without coercion by mimicking their behaviour patterns.
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Sluyter F., Arseneault L., Moffitt T.E., Veenema A.H., de Boer S., & Koolhaas J.M. (2003). Toward an Animal Model for Antisocial Behavior: Parallels Between Mice and Humans: Aggression. Behavior Genetics, 33, 563–574.
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Fleck C., & Eifler D. (2003). Deformation behaviour and damage accumulation of cortical bone specimens from the equine tibia under cyclic loading. Journal of Biomechanics, 36, 179–189.
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Waeber P.O., & Hemelrijk C.K. (2003). Female Dominance and Social Structure in Alaotran Gentle Lemurs. Behaviour, 140(10), 1235–1246.
Abstract: Abstract:
Lemur social systems have the striking social feature, that adult females consistently evoke submissive behaviour of adult males. In the Alaotran gentle lemur, Hapalemur griseus alaotrensis, however, female dominance has not been studied yet. Here we confirm female dominance over males on the basis of a 5-month field study of the social behaviour of four groups, in the Lake Alaotra marshland of eastern Madagascar. Further, we found that dominant individuals initiated aggressive interactions significantly more often than lowerranking ones, they initiated group movements more often and higher-ranking individuals were groomed more often. The spatial configuration was remarkable, since individuals were closer in space to those more distant in rank.
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Scheibe, K. M., & Streich, W. J. (2003). Annual Rhythm of Body Weight in Przewalski Horses (Equus ferus przewalskii). Biological Rhythm Research, 34(4), 383–395.
Abstract: The live-weight of female Przewalski horses in a semi-natural reserve has been recorded continuously over 6 years by means of an automatic weighing machine and automatic identification. Data were tested for cyclic as well as for linear trend effects and a mathematical model was developed. A clear annual rhythm of live-weight with the maximum in October was demonstrated. During the first 2 years of recording, the level of the annual rhythm was constant but, thereafter, different individual trends were found. Those individuals showing a steeply rising trend suffered from laminitis after three annual cycles. The periods of rising body weight corresponded to unusual mild winters. Animals newly introduced into the reserve from zoos showed a rise in their body weight in an adaptation phase. Furthermore, there was evidence for a phase adjustment of the annual rhythm. The results are discussed against a background of the theory of annual rhythms, and can be used as a basis for seasonal variations of feeding in zoos and for a re-evaluation of recommendations for population density in similar reserves. For reintroductions as well as for a transfer from zoos to semi-natural reserves, a longer adaptation phase is recommended.
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