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Hemelrijk, C. K., & Wantia, J. (2005). Individual variation by self-organisation. Neurosci Biobehav Rev, 29(1), 125–136.
Abstract: In this paper, we show that differences in dominance and spatial centrality of individuals in a group may arise through self-organisation. Our instrument is a model, called DomWorld, that represents two traits that are often found in animals, namely grouping and competing. In this model individual differences grow under the following conditions: (1) when the intensity of aggression increases and grouping becomes denser, (2) when the degree of sexual dimorphism in fighting power increases. In this case the differences among females compared to males grow too, (3) when, upon encountering another individual, the tendency to attack is 'obligate' and not conditional, namely 'sensitive to risks'. Results resemble phenomena described for societies of primates, mice, birds and pigs.
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Hemelrijk, C. K., Wantia, J., & Gygax, L. (2005). The construction of dominance order: comparing performance of five methods using an individual-based model. Behaviour, 142(8), 1043–1064.
Abstract: In studies of animal behaviour investigators correlate dominance with all kinds of behavioural
variables, such as reproductive success and foraging success. Many methods are used to
produce a dominance hierarchy from a matrix reflecting the frequency of winning dominance
interactions. These different methods produce different hierarchies. However, it is difficult to
decide which ranking method is best. In this paper, we offer a new procedure for this decision:
we use an individual-based model, called DomWorld, as a test-environment. We choose this
model, because it provides access to both the internal dominance values of artificial agents
(which reflects their fighting power) and the matrix of winning and losing among them and,
in addition, because its behavioural rules are biologically inspired and its group-level patterns
resemble those of real primates. We compare statistically the dominance hierarchy based on
the internal dominance values of the artificial agents with the dominance hierarchy produced
by ranking individuals by (a) their total frequency of winning, (b) their average dominance
index, (c) a refined dominance index, the David`s score, (d) the number of subordinates each
individual has and (e) a ranking method based on maximizing the linear order of the hierarchy.
Because dominance hierarchies may differ depending on group size, type of society, and the
interval of study, we compare these ranking methods for these conditions.We study complete
samples as well as samples randomly chosen to resemble the limitations of observing real
animals. It appears that two methods of medium complexity (the average dominance index
and David`s score) lead to hierarchical orders that come closest to the hierarchy based on
internal dominance values of the agents. We advocate usage of the average dominance index,
because of its computational simplicity.
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Broom, M., & Cannings, C. (2002). Modelling Dominance Hierarchy formation as a Multi-player game. J. Theor. Biol., 219(3), 397–413.
Abstract: Animals who live in groups need to divide available resources amongst themselves. This is often achieved by means of a dominance hierarchy, where dominant individuals obtain a larger share of the resources than subordinate individuals. This paper introduces a model of dominance hierarchy formation using a multi-player extension of the classical Hawk-Dove game. Animals play non-independent pairwise games in a Swiss tournament which pairs opponents against those which have performed equally well in the conflict so far, for a fixed number of rounds. Resources are divided according to the number of contests won. The model, and its emergent properties, are discussed in the context of experimental observations.
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Jameson, K. A., Appleby, M. C., & Freeman, L. C. (1999). Finding an appropriate order for a hierarchy based on probabilistic dominance. Anim. Behav., 57(5), 991–998.
Abstract: Methods of ranking individuals in a dominance hierarchy that use transitivity of relationships may obscure irregularities. Furthermore, these methods use only a small proportion of the information available from dominance encounters. This paper presents an intuitively appealing and easily implemented alternative to existing methods for ordering dominance data, developed from the work of Batchelder et al. (1992Journal of Mathematical Psychology36, 185-212). The procedure presented here is based on a mathematical model of paired comparisons and it involves only simple estimation procedures. We illustrate its use with data on dominance among red deerCervus elaphus, stags. The results indicate that dominance relationships are well characterized by the scale values that the model provides, and, because the method provides predictions for all pairings of animals, dominance predictions also exist for pairs of animals that have yet to be observed. Moreover, the dominance outcomes predicted by the model using the order scale are highly correlated with actual dominance observations at all levels. Overall, the procedure described provides a solution to the problem of identifying an appropriate order for a near-linear dominance hierarchy.
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Gammell, M. P., de Vries, H., Jennings, D. J., Carlin, C. M., & Hayden, T. J. (2003). David's score: a more appropriate dominance ranking method than Clutton-Brock et al.'s index. Anim. Behav., 66(3), 601–605.
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RHO, J. R., SRYGLEY, R. B., & CHOE, J. C. (2004). Behavioral ecology of the Jeju pony (Equus caballus): Effects of maternal age, maternal dominance hierarchy and foal age on mare aggression. Ecol. Res., 19(1), 55–63.
Abstract: On Jeju Island, Korea, dominance hierarchy and maternal care according to maternal age were studied in a herd of Jeju ponies (Equus caballus), consisting of 73 mares, their foals and one stallion. Dominance ranks were nearly linear and increased significantly with the age of mares. Most aggressive encounters involved mares under 5 years old. Mares under the age of 5 years have apparently not established their rank. The mean frequency of aggressive actions of mares per hour increased significantly as the day of parturition approached. Aggressive actions of mares with foals decreased significantly as their foals aged. The overall frequency of aggression of mares with foals also decreased significantly with the age of the mares. Our results suggest that the cost of maternal care is lower for older, more dominant mares than for subordinate ones.
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Feh, C. (1999). Alliances and reproductive success in Camargue stallions. Anim. Behav., 57(3), 705–713.
Abstract: A study of a herd of Camargue horsesEquus caballus, showed that while the majority of high-ranking stallions held single-male harems, some sons of low-ranking mares, being low ranking themselves, formed alliances that could last a lifetime. The two stallions were each other's closest associate and preferential grooming partner. Alliances were based on coalitions in which either both partners confronted an intruder synchronously or the dominant of the pair tended the female(s) while the subordinate simultaneously displayed towards the rival. Alliance partners were of similar age but were not more closely related to each other than to other stallions in the herd. Long-term paternity data revealed that subordinates sired close to a quarter of the foals born into the alliance group, and significantly more foals than low-ranking stallions in the herd adopting a `sneak'-mating strategy. The dominant appeared to benefit from the presence of his subordinate partner. Fights occurred all year round, and the subordinate stallion of each alliance pair fought outside competitors more than twice as often as the dominant. Forming short-term alliances before defending mares on their own may enhance long-term reproductive success for both partners. Other benefits to both partners include higher survivorship of their foals and increased access to proven reproductive mares. These results suggest that the relationship between alliance partners is based on mutualism, but several conditions for reciprocity seem to be fulfilled: the benefit to the dominant (assistance in fights), and the benefit to the subordinate (access to reproduction), are both costly to the other partner and delayed in time.
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Moons, C., Heleski, C. R., Leece, C. M., & Zanella, A. J. (2002). Conflicting Results in the Association Between Plasma and Salivary Cortisol Levels in Foals. Retrieved June 4, 2024, from http://www3.vet.upenn.edu/labs/equinebehavior/hvnwkshp/hv02/zanella.htm
Abstract: Introduction
Glucocorticoids are present in many biological fluids as a free fraction or bound to Corticoid
Binding Globulins (CBG) (Matteri et al, 2000). There are conflicting claims regarding the validity of
saliva as a biological fluid to measure cortisol in horses (Lebelt et al, 1996; McGreevy and Pell, 1998;
van der Kolk et al, 2001). Measuring changes in salivary cortisol levels in normal horses and horses
with Cushing`s disease van der Kolk and collaborators (2001) demonstrated the validity of saliva to
assess adrenal function. Puzzling results were reported by McGreevy and Pell (1998) who suggested
that plasma and salivary cortisol concentrations in horses showing oral stereotypies were correlated
but this association was non-existent in control animals. Investigating the responses of foals to
branding and foot-trimming Zanella et al (unpublished results) were unable to identify a relationship
between plasma and salivary cortisol levels in foals. In several species, levels of cortisol in plasma and
saliva are tightly correlated (Fenske, 1996). Cortisol found in blood consists of a fraction bound to
corticoid binding globulin (CBG) and a free, unbound fraction. Free cortisol represents the
biologically active fraction of this steroid hormone. Salivary cortisol reflects the unbound fraction
found in plasma or serum and it passes readily through the parotid membrane (Riad-Fahmy, 1983;
Horning Walker et al,1977). Unbound steroids transfer rapidly between plasma and saliva
(Walker,1989; Scott et al 1990). Saliva flow-rate does not appear to influence saliva cortisol levels in
different species (Hubert and de Jong-Meyer, 1989; Walker 1989, Scott et a, 1990). In horses, Lebelt
et al (1996) reported that salivary and plasma total cortisol in stallions were correlated. We
hypothesized that changes in salivary cortisol in foals would show a pattern that is correlated to that of
plasma free and plasma total cortisol concentrations in foals. In addition, we anticipated that the lack
of good sampling techniques provides an explanation for the failure in determining the association
between salivary and plasma cortisol in foals.
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Feh, C. (2005). Relationships and Communication in Socially Natural Horse Herds. In D. S. Mills, & S. M. McDonnell (Eds.), The domestic horse : the origins, development, and management of its behaviour. Cambridge: Cambridge University Press 2005.
Abstract: Horses are quite unique. In most mammals, sexes segregate and maintain bonds only during the breeding season (Clutton-Brock, 1989). Some canids, a few rodents and primate species such as gorillas, hamadryas baboons and red howler monkeys are the exception, where the same males stay with the same females all year round and over many breeding seasons. Typically, both sexes disperse at puberty in these species. In horses, it was clearly shown that the causes for female dispersal were incest avoidance and not intra-specific competition (Monard, 1996). As a rule, this is confirmed for mammal species where tenure length by males exceeds the age at first reproduction in females (Clutton-Brock, 1989). When horses are allowed to choose their mating partner freely, the inbreeding coefficient of the offspring is lower than expected should they mate randomly (Duncan et al, 1984).
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Nicol, C. J. (2000). Equine Stereotypies. In: Houpt K.A. (Ed.),. In Recent Advances in Companion Animal Behavior Problems. International Veterinary Information Service.
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