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Author  |
Cameron, E.Z.; du Toit, J.T. |
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Title |
Winning by a neck: tall giraffes avoid competing with shorter browsers |
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Year |
2007 |
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The American naturalist |
Abbreviated Journal |
Am Nat |
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169 |
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1 |
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130-135 |
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Keywords |
Acacia/growth & development; Animals; Feeding Behavior/*physiology; Neck/*anatomy & histology; Plant Leaves/growth & development; Ruminants/*anatomy & histology/*physiology; South Africa |
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Abstract |
With their vertically elongated body form, giraffes generally feed above the level of other browsers within the savanna browsing guild, despite having access to foliage at lower levels. They ingest more leaf mass per bite when foraging high in the tree, perhaps because smaller, more selective browsers deplete shoots at lower levels or because trees differentially allocate resources to promote shoot growth in the upper canopy. We erected exclosures around individual Acacia nigrescens trees in the greater Kruger ecosystem, South Africa. After a complete growing season, we found no differences in leaf biomass per shoot across height zones in excluded trees but significant differences in control trees. We conclude that giraffes preferentially browse at high levels in the canopy to avoid competition with smaller browsers. Our findings are analogous with those from studies of grazing guilds and demonstrate that resource partitioning can be driven by competition when smaller foragers displace larger foragers from shared resources. This provides the first experimental support for the classic evolutionary hypothesis that vertical elongation of the giraffe body is an outcome of competition within the browsing ungulate guild. |
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Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa. ezcameron@zoology.up.ac.za |
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1537-5323 |
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PMID:17206591 |
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refbase @ user @ |
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410 |
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Author |
Conradt, L.; Krause, J.; Couzin, I. D.; Roper, T. J. |
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Title |
“Leading According to Need” in Self-Organizing Groups |
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Journal Article |
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Year |
2009 |
Publication |
The American Naturalist |
Abbreviated Journal |
Am Nat |
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173 |
Issue |
3 |
Pages |
304-312 |
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Keywords |
behavioral synchrony, collective group decisions, democracy and egalitarianism in animals, public goods experiments, sexual segregation, social choice theory |
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Abstract |
Self‐organizing‐system approaches have shed significant light on the mechanisms underlying synchronized movements by large groups of animals, such as shoals of fish, flocks of birds, or herds of ungulates. However, these approaches rarely consider conflicts of interest between group members, although there is reason to suppose that such conflicts are commonplace. Here, we demonstrate that, where conflicts exist, individual members of self‐organizing groups can, in principle, increase their influence on group movement destination by strategically changing simple behavioral parameters (namely, movement speed, assertiveness, and social attraction range). However, they do so at the expense of an increased risk of group fragmentation and a decrease in movement efficiency. We argue that the resulting trade‐offs faced by each group member render it likely that group movements are led by those members for which reaching a particular destination is most crucial or group cohesion is least important. We term this phenomenon leading according to “need” or “social indifference,” respectively. Both kinds of leading can occur in the absence of knowledge of or communication about the needs of other group members and without the assumption of altruistic cooperation. We discuss our findings in the light of observations on fish and other vertebrates. |
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Equine Behaviour @ team @ |
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5121 |
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Author |
Detto, T.; Jennions, M. D.; Backwell, P. R. Y. |
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Title |
When and Why Do Territorial Coalitions Occur? Experimental Evidence from a Fiddler Crab |
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Journal Article |
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Year |
2010 |
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The American Naturalist |
Abbreviated Journal |
Am Nat |
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175 |
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5 |
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E119-E125 |
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coalitions, cooperation, dear enemy, fiddler crabs, fighting, territoriality. |
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Neighboring territory owners are often less aggressive toward each other than to strangers (“dear enemy” effect). There is, however, little evidence for territorial defense coalitions whereby a neighbor will temporarily leave his/her own territory, enter that of a neighbor, and cooperate in repelling a conspecific intruder. This is surprising, as theoreticians have long posited the existence of such coalitions and the circumstances under which they should evolve. Here we document territorial defense coalitions in the African fiddler crab Uca annulipes, which lives in large colonies wherein each male defends a burrow and its surrounding area against neighbors and “floaters” (burrowless males). Fights between a resident and a floater sometimes involve another male who has left his territory to fight the floater challenging his neighbor. Using simple experiments, we provide the first evidence of the rules determining when territorial coalitions form. Our results support recent models that suggest that these coalitions arise from by‐product mutualism. |
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doi: 10.1086/651588 |
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Equine Behaviour @ team @ |
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5112 |
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Author |
Dubois, F.; Giraldeau, L.-A. |
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Title |
The forager's dilemma: food sharing and food defense as risk-sensitive foraging options |
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Journal Article |
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Year |
2003 |
Publication |
The American Naturalist |
Abbreviated Journal |
Am Nat |
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162 |
Issue |
6 |
Pages |
768-779 |
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Keywords |
Animals; Competitive Behavior/*physiology; *Environment; Feeding Behavior/*physiology; *Game Theory; *Models, Biological; Population Density; Population Dynamics |
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Abstract |
Although many variants of the hawk-dove game predict the frequency at which group foraging animals should compete aggressively, none of them can explain why a large number of group foraging animals share food clumps without any overt aggression. One reason for this shortcoming is that hawk-dove games typically consider only a single contest, while most group foraging situations involve opponents that interact repeatedly over discovered food clumps. The present iterated hawk-dove game predicts that in situations that are analogous to a prisoner's dilemma, animals should share the resources without aggression, provided that the number of simultaneously available food clumps is sufficiently large and the number of competitors is relatively small. However, given that the expected gain of an aggressive animal is more variable than the gain expected by nonaggressive individuals, the predicted effect of the number of food items in a clump-clump richness-depends on whether only the mean or both the mean and variability associated with payoffs are considered. More precisely, the deterministic game predicts that aggression should increase with clump richness, whereas the stochastic risk-sensitive game predicts that the frequency of encounters resulting in aggression should peak at intermediate clump richnesses or decrease with increasing clump richness if animals show sensitivity to the variance or coefficient of variation, respectively. |
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Departement des Sciences Biologiques, Universite du Quebec a Montreal, Case postale 8888, Succursale Centre-Ville, Montreal, Quebec H3C 3P8, Canada. fdubois@u-bourgogne.fr |
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0003-0147 |
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Notes |
PMID:14737714 |
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no |
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Call Number |
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2132 |
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Author |
Dubois, F.; Giraldeau, L.-A.; Hamilton, I.M.; Grant, J.W.A.; Lefebvre, L. |
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Title |
Distraction sneakers decrease the expected level of aggression within groups: a game-theoretic model |
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Journal Article |
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Year |
2004 |
Publication |
The American Naturalist |
Abbreviated Journal |
Am Nat |
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Volume |
164 |
Issue |
2 |
Pages |
E32-45 |
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*Aggression; Animals; Behavior, Animal/*physiology; Columbidae/*physiology; Competitive Behavior; Cooperative Behavior; *Game Theory; Hawks/*physiology; Models, Biological |
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Hawk-dove games have been extensively used to predict the conditions under which group-living animals should defend their resources against potential usurpers. Typically, game-theoretic models on aggression consider that resource defense may entail energetic and injury costs. However, intruders may also take advantage of owners who are busy fighting to sneak access to unguarded resources, imposing thereby an additional cost on the use of the escalated hawk strategy. In this article we modify the two-strategy hawk-dove game into a three-strategy hawk-dove-sneaker game that incorporates a distraction-sneaking tactic, allowing us to explore its consequences on the expected level of aggression within groups. Our model predicts a lower proportion of hawks and hence lower frequencies of aggressive interactions within groups than do previous two-strategy hawk-dove games. The extent to which distraction sneakers decrease the frequency of aggression within groups, however, depends on whether they search only for opportunities to join resources uncovered by other group members or for both unchallenged resources and opportunities to usurp. |
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Departement des Sciences Biologiques, Universite du Quebec a Montreal, Case postale 8888 Succursale Centre-Ville, Montreal, Quebec H3C 3P8, Canada. frede_dubois@yahoo.fr |
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1537-5323 |
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PMID:15278850 |
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2130 |
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Author |
Flack, J.C.; de Waal, F.B.M.; Krakauer, D.C. |
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Title |
Social structure, robustness, and policing cost in a cognitively sophisticated species |
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Journal Article |
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Year |
2005 |
Publication |
The American Naturalist |
Abbreviated Journal |
Am Nat |
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Volume |
165 |
Issue |
5 |
Pages |
E126-139 |
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Keywords |
Animals; *Behavior, Animal; Cognition; Conflict (Psychology); Female; Macaca nemestrina/*physiology; Male; Models, Biological; *Social Behavior |
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Abstract |
Conflict management is one of the primary requirements for social complexity. Of the many forms of conflict management, one of the rarest and most interesting is third-party policing, or intervening impartially to control conflict. Third-party policing should be hard to evolve because policers personally pay a cost for intervening, while the benefits are diffused over the whole group. In this study we investigate the incidence and costs of policing in a primate society. We report quantitative evidence of non-kin policing in the nonhuman primate, the pigtailed macaque. We find that policing is effective at reducing the intensity of or terminating conflict when performed by the most powerful individuals. We define a measure, social power consensus, that predicts effective low-cost interventions by powerful individuals and ineffective, relatively costly interventions by low-power individuals. Finally, we develop a simple probabilistic model to explore whether the degree to which policing can effectively reduce the societal cost of conflict is dependent on variance in the distribution of power. Our data and simple model suggest that third-party policing effectiveness and cost are dependent on power structure and might emerge only in societies with high variance in power. |
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Santa Fe Institute, Santa Fe, New Mexico 87501, USA. jflack@santafe.edu |
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1537-5323 |
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PMID:15795848 |
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refbase @ user @ |
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168 |
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Author |
Gardner, A., West, S. A. |
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Title |
Cooperation and Punishment, Especially in Humans |
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Journal Article |
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Year |
2004 |
Publication |
The American Naturalist |
Abbreviated Journal |
Americ. Natur. |
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164 |
Issue |
6 |
Pages |
753-764 |
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Keywords |
kin selection, neighbor-modulated fitness, repression of |
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Abstract |
Explaining altruistic cooperation is one of the greatest
challenges faced by sociologists, economists, and evolutionary biologists.
The problem is determining why an individual would carry
out a costly behavior that benefits another. Possible solutions to this
problem include kinship, repeated interactions, and policing. Another
solution that has recently received much attention is the threat
of punishment. However, punishing behavior is often costly for the
punisher, and so it is not immediately clear how costly punishment
could evolve. We use a direct (neighbor-modulated) fitness approach
to analyze when punishment is favored. This methodology reveals
that, contrary to previous suggestions, relatedness between interacting
individuals is not crucial to explaining cooperation through punishment.
In fact, increasing relatedness directly disfavors punishing
behavior. Instead, the crucial factor is a positive correlation between
the punishment strategy of an individual and the cooperation it
receives. This could arise in several ways, such as when facultative
adjustment of behavior leads individuals to cooperate more when
interacting with individuals who are more likely to punish. More
generally, our results provide a clear example of how the fundamental
factor driving the evolution of social traits is a correlation between
social partners and how this can arise for reasons other than genealogical
kinship. |
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University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, |
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refbase @ user @ |
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341 |
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Author |
Gittleman, J.L. |
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Title |
Carnivore Life History Patterns: Allometric, Phylogenetic, and Ecological Associations |
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Journal Article |
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Year |
1986 |
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The American Naturalist |
Abbreviated Journal |
Am Nat |
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127 |
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6 |
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744-771 |
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The University of Chicago Press for The American Society of Naturalists |
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0003-0147 |
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Equine Behaviour @ team @ |
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5453 |
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Author |
Gosden, T. P.; Svensson, E. I. |
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Title |
Density-Dependent Male Mating Harassment, Female Resistance, and Male Mimicry |
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Journal Article |
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2009 |
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The American Naturalist |
Abbreviated Journal |
Am Nat |
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173 |
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6 |
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709-721 |
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tolerance, sexual conflict, path analysis, mating behavior, polymorphism, fecundity. |
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Abstract:
Genetic variation in female resistance and tolerance to male mating harassment can affect the outcome of sexually antagonistic mating interactions. We investigated female mating rates and male mating harassment in natural populations of a damselfly (Ischnura elegans). This damselfly species has a heritable sex‐limited polymorphism in females, where one of the morphs is a male mimic (androchrome females). The three female morphs differ in mating rates, and these differences are stable across populations and years. However, the degree of premating resistance toward male mating attempts varied across generations and populations. Male mating harassment of the female morphs changed in a density‐dependent fashion, suggesting that male mate preferences are plastic and vary with the different morph densities. We quantified morph differences in male mating harassment and female fecundity, using path analysis and structural equation modeling. We found variation between the morphs in the fitness consequences of mating, with the fecundity of one of the nonmimetic morphs declining with increasing male mating harassment. However, androchrome females had lower overall fecundity, presumably reflecting a cost of male mimicry. Density‐dependent male mating harassment on the morphs and fecundity costs of male mimicry are thus likely to contribute to the maintenance of this female polymorphism. |
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Equine Behaviour @ team @ |
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4999 |
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Horrocks, J.A.; Hunte, W. |
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Rank Relations in Vervet Sisters: A Critique of the Role of Reproductive Value |
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1983 |
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The American Naturalist |
Abbreviated Journal |
Am. Nat. |
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122 |
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417-421 |
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10.1086/284144 |
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Equine Behaviour @ team @ |
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4903 |
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