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Berger, J. (1977). Organizational systems and dominance in feral horses in the Grand Canyon. Behav. Ecol. Sociobiol., 2(2), 131–146.
Abstract: 1. Several aspects of the behavioral ecology of feral horses (Equus caballus) were studied in Grand Canyon, Arizona, USA. Most bands contained three to five horses that included one stallion and his harem. Males that did not obtain a harem remained solitary. Throughout the study bands remained stable in composition.
2. Home ranges for all bands decreased in size in successive warm months, probably due to increased ambient temperature and drought. This resulted in greater utilization of spring areas that led to increased interband confrontation and agonistic display. 3. Territoriality was not observed in individual horses or bands, but bands hierarchial in both inter- and intraband structures. Interband stallion dominance was reinforced through posturing and fighting. Intraband hierarchies, as determined by dominance coefficients, were independent of individual size in three of four bands. 4. Indexes of nervousness (NER), calculated while horses were drinking, showed that stallions were less nervous than mares. A low NER was correlated with individuals leading toward drinking areas, whereas a high NER existed in individuals initiating flight although no single horse acted consistently as a leader. 5. Diurnal activity patterns were correlated with ambient temperatures. |
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Dugatkin, L. A. (1997). Winner and loser effects and the structure of dominance hierarchies. Behav. Ecol., 8(6), 583–587.
Abstract: In the literature on dominance hierarchies, “winner” and “loser” effects usually are denned as an increased probability of winning at time T, bated on victories at time T-l, T-2, etc, and an increased probability of losing at time T, based on losing at T-1, T-2, etc., respectively. Despite some early theoretical work on winner and loser effects, these factors and how they affect the structure of dominance hierarchies have not been examined in detail. I developed a computer simulation to examine winner and loser effects when such effects are independent of one another (as well as when they interact) and when combatants assess each other's resource-holding power. When winner effects alone were important, a hierarchy in which all individuals held an unambiguous rank was found. When only loser effects were important, a dear alpha individual always emerged, but the rank of others in the group was often unclear because of the scarcity of aggressive interactions. Increasing winner effects for a given value of the loser effect increase the number of individuals with unambiguous positions in a hierarchy and the converse is true for increasing the value of the loser effect for a given winner effect Although winner and loser effects have been documented in a number of species, no study has documented both winner and loser effects (using some controlled, pairwise testing system) and the detailed nature of behavioral interactions when individuals are in groups. I hope the results of this model will spur such studies in the future.
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Cant, M. A., & Field, J. (2005). Helping effort in a dominance hierarchy. Behav. Ecol., 16(4), 708–715.
Abstract: In many cooperatively breeding species, group members form a dominance hierarchy or queue to inherit the position of breeder. Models aimed at understanding individual variation in helping behavior, however, rarely take into account the effect of dominance rank on expected future reproductive success and thus the potential direct fitness costs of helping. Here we develop a kin-selection model of helping behavior in multimember groups in which only the highest ranking individual breeds. Each group member can invest in the dominant's offspring at a cost to its own survivorship. The model predicts that lower ranked subordinates, who have a smaller probability of inheriting the group, should work harder than higher ranked subordinates. This prediction holds regardless of whether the intrinsic mortality rate of subordinates increases or decreases with rank. The prediction does not necessarily hold, however, where the costs of helping are higher for lower ranked individuals: a situation that may be common in vertebrates. The model makes two further testable predictions: that the helping effort of an individual of given rank should be lower in larger groups, and the reproductive success of dominants should be greater where group members are more closely related. Empirical evidence for these predictions is discussed. We argue that the effects of rank on stable helping effort may explain why attempts to correlate individual helping effort with relatedness in cooperatively breeding species have met with limited success.
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Vahl, W. K., Lok, T., van der Meer, J., Piersma, T., & Weissing, F. J. (2005). Spatial clumping of food and social dominance affect interference competition among ruddy turnstones. Behav. Ecol., 16(5), 834–844.
Abstract: In studying the success of foraging animals, studies of interference competition have put emphasis on effects of competitor density, whereas studies of resource defense have focused on the effects of the spatial distribution of food within patches. Very few studies have looked at both factors simultaneously, that is, determined whether the effects of competitor density on foraging success depend on the spatial distribution of food. We studied the behavior and the foraging success of ruddy turnstones (Arenaria interpres) using an experiment in which we varied both the presence of a competitor and the food distribution. Because turnstones may differ strongly in their relative dominance status, we also experimentally varied the foragers' relative dominance status. We found that the presence of a competitor only reduced the foraging success of subordinate birds foraging at the clumped food distribution. At this condition, dominant and subordinate birds differed markedly in their foraging success. Contrary to our expectations, we did not observe more agonistic behavior at the clumped food distribution. This indicates that the amount of agonistic behavior observed may be a bad indicator of interference effects. These findings have specific implications for models of interference competition. Most notably they show that the effects of competitor density on agonistic behavior and foraging success may well depend on the spatial distribution of food and the foragers' relative dominance status. Additionally, our results suggest that social dominance will not be fully understood without considering long-term processes such as the formation and maintenance of social dominance hierarchies.
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Barton, R. A., Byrne, R. W., & Whiten, A. (1996). Ecology, feeding competition and social structure in baboons. Behav. Ecol. Sociobiol., 38(5), 321–329.
Abstract: Predictions of the model of van Schaik (1989) of female-bonding in primates are tested by systematically comparing the ecology, level of within-group contest competition for food (WGC), and patterns of social behaviour found in two contrasting baboon populations. Significant differences were found in food distribution (percentage of the diet from clumped sources), feeding supplant rates and grooming patterns. In accord with the model, the tendencies of females to affiliate and form coalitions with one another, and to be philopatric, were strongest where ecological conditions promoted WGC. Group fission in the population with strong WGC was “horizontal” with respect to female dominance rank, and associated with female-female aggression during a period of elevated feeding competition. In contrast, where WGC was low, females' grooming was focused on adult males rather than other females. Recent evidence suggests that group fission here is initiated by males, tends to result in the formation of one-male groups, and is not related to feeding competition but to male-male competition for mates. An ecological model of baboon social structure is presented which incorporates the effects of female-female competition, male-male competition, and predation pressure. The model potentially accounts for wide variability in group size, group structure and social relationships within the genus Papio. Socio-ecological convergence between common baboons and hamadryas baboons, however, may be limited in some respects by phylogenetic inertia.
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Shrader, A. M., Kerley, G. I. H., Kotler, B. P., & Brown, J. S. (2007). Social information, social feding, and competition in group-living goats (Capra hircus). Behav. Ecol., 18(1), 103–107.
Abstract: There are both benefits (e.g., social information) and costs (e.g., intraspecific competition) for individuals foraging in groups. To ascertain how group-foraging goats (Capra hircus) deal with these trade-offs, we asked 1) do goats use social information to make foraging decisions and 2) how do they adjust their intake rate in light of having attracted by other group members? To establish whether goats use social information, we recorded their initial choice of different quality food patches when they were ignorant of patch quality and when they could observe others foraging. After determining that goats use social information, we recorded intake rates while they fed alone and in the presence of potential competitors. Intake rate increased as the number of competitors increased. Interestingly, lone goats achieved an intake rate that was higher than when one competitor was present but similar to when two or more competitors were present. Faster intake rates may allow herbivores to ingest a larger portion of the available food before competing group members arrive at the patch. This however, does not explain the high intake rates achieved when the goats were alone. We provide 2 potential explanations: 1) faster intake rates are a response to greater risk incurred by lone individuals, the loss of social information, and the fear of being left behind by the group and 2) when foraging alone, intake rate is no longer a trade-off between reducing competition and acquiring social information. Thus, individuals are able to feed close to their maximum rate.
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Ginsberg, J. R., & Rubenstein, D. I. (1990). Sperm competiton and variation in zebra mating behaviour. Behav. Ecol. Sociobiol., 26(6), 427–434.
Abstract: Data are presented on the breeding behavior of two zebra species to test whether intra- and interspecific variation in male reproductive behavior and physiology are correlated with differences in female promiscuity. In one species, plains zebra (Equus burchelli) females live in closed membership single male groups and mate monandrously. In the other species, the Grevy's zebra (E. grevyi) females live in groups whose membership is much more temporary. Typically, associations with individual males are brief and mating is polyandrous. However, some females – those having just given birth – reside with one male for long periods, mating monandrously. These differences in female mating behavior generate variability in the potential for sperm competition. We show that behavioral differences in male investment in reproductive activities correlate with the potential for sperm competition. When mating with promiscuous mares, Grevy's zebra stallions made a greater investment in reproductive behavior (calling, mounting, ejaculations) than did stallions of either species when mating with monandrous females. The evolution of large testes size in the Grevy's zebra, when compared to the congeneric plains zebra, horse, and mountain zebra, allows for this increased investment.
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Cameron, E. Z., Linklater, W. L., Stafford, K. J., & Minot, E. O. (2000). Aging and improving reproductive success in horses: declining residual reproductive value or just older and wiser? Behav. Ecol. Sociobiol., 47(4), 243–249.
Abstract: In many mammalian species, female success in raising offspring improves as they age. The residual reproductive value hypothesis predicts that each individual offspring will be more valuable to the mother as she ages because there is less conflict between the current and potential future offspring. Therefore, as mothers age, their investment into individual offspring should increase. Empirical evidence for an influence of declining residual reproductive value on maternal investment is unconvincing. Older mothers may not invest more, but may be more successful due to greater experience, allowing them to target their investment more appropriately (targeted reproductive effort hypothesis). Most studies do not preclude either hypothesis. Mare age significantly influenced maternal investment in feral horses living on the North Island of New Zealand. Older mares, that were more successful at raising foals, were more protective for the first 20 days of life, but less diligent thereafter. Total maternal input by older mothers did not seem to be any greater, but was better targeted at the most critical period for foal survival and a similar pattern was observed in mares that had lost a foal in the previous year. In addition, older mothers were more likely to foal in consecutive years, supporting the hypothesis that they are investing less than younger mares in individual offspring. Therefore, older mothers seem to become more successful by targeting their investment better due to experience, not by investing more in their offspring.
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Anderson, C., & Franks, N. R. (2001). Teams in animal societies. Behav. Ecol., 12(5), 534–540.
Abstract: We review the existence of teams in animal societies. Teams have previously been dismissed in all but a tiny minority of insect societies. “Team” is a term not generally used in studies of vertebrates. We propose a new rigorous definition of a team that may be applied to both vertebrate and invertebrate societies. We reconsider what it means to work as a team or group and suggest that there are many more teams in insect societies than previously thought. A team task requires different subtasks to be performed concurrently for successful completion. There is a division of labor within a team. Contrary to previous reviews of teams in social insects, we do not constrain teams to consist of members of different castes and argue that team members may be interchangeable. Consequently, we suggest that a team is simply the set of individuals that performs a team task. We contrast teams with groups and suggest that a group task requires the simultaneous performance and cooperation of two or more individuals for successful completion. In a group, there is no division of labor--each individual performs the same task. We also contrast vertebrate and invertebrate teams and find that vertebrate teams tend to be associated with hunting and are based on individual recognition. Invertebrate teams occur in societies characterized by a great deal of redundancy, and we predict that teams in insect societies are more likely to be found in large polymorphic (“complex”) societies than in small monomorphic (“simple”) societies.
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Dugatkin, L. A. (1991). Dynamics of the TIT FOR TAT strategy during predator inspection in the guppy (Poecilia reticulata). Behav. Ecol. Sociobiol., 29(2), 127–132.
Abstract: One well-known solution to the iterated Prisoner's Dilemma is the TIT FOR TAT strategy. This strategy has three “characteristics” associated with it. TIT FOR TAT is nice (cooperates on the first move of a game), retaliatory (plays defect against an individual that defected on the prior move), and forgiving (cooperates with an individual which has defected in the past but cooperates in the present). Predator inspection behavior in guppies (Poecilia reticulata) was examined in order to determine whether guppies displayed these three characteristics. Results indicate that while it can be quite difficult to translate the abstract concepts of niceness, retaliation, and forgiveness into measurable behaviors, the data support the hypothesis that guppies display the three characteristics associated with the TIT FOR TAT strategy.
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