1
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Arseneau-Robar TJ, Teichroeb JA, Macintosh AJJ, Saj TL, Glotfelty E, Lucci S, Sicotte P, Wikberg EC. When population growth intensifies intergroup competition, female colobus monkeys free-ride less. Sci Rep 2024; 14:14363. [PMID: 38906888 DOI: 10.1038/s41598-024-64188-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Accepted: 06/06/2024] [Indexed: 06/23/2024] Open
Abstract
Intergroup aggression often results in the production of public goods, such as a safe and stable social environment and a home range containing the resources required to survive and reproduce. We investigate temporal variation in intergroup aggression in a growing population of colobus monkeys (Colobus vellerosus) to ask a novel question: "Who stepped-up to produce these public goods when doing so became more difficult?". Both whole-group encounters and male incursions occurred more frequently as the population grew. Males and females were both more likely to participate in whole-group encounters when monopolizable food resources were available, indicating both sexes engaged in food defence. However, only females increasingly did so as the population grew, suggesting that it was females who increasingly produced the public good of home range defence as intergroup competition intensified. Females were also more active in male incursions at high population densities, suggesting they increasingly produced the public good of a safe and stable social environment. This is not to say that males were chronic free-riders when it came to maintaining public goods. Males consistently participated in the majority of intergroup interactions throughout the study period, indicating they may have lacked the capacity to invest more time and effort.
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Affiliation(s)
| | - Julie A Teichroeb
- Department of Anthropology, University of Toronto Scarborough, Toronto, Canada
| | | | - Tania L Saj
- Department of Anthropology, University of Calgary, Calgary, Canada
| | - Emily Glotfelty
- Department of Anthropology, University of Texas San Antonio, San Antonio, USA
| | - Sara Lucci
- Department of Anthropology, University of Texas San Antonio, San Antonio, USA
| | - Pascale Sicotte
- Department of Biology, Concordia University, Montreal, QC, Canada
| | - Eva C Wikberg
- Department of Anthropology, University of Texas San Antonio, San Antonio, USA.
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2
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Potel H, Niatou Singa FS, Cipolletta C, Neba Fuh T, Bardino G, Konyal E, Strampelli P, Henschel P, Masi S. Lethal combats in the forest among wild western gorillas. iScience 2024; 27:109437. [PMID: 38523787 PMCID: PMC10960106 DOI: 10.1016/j.isci.2024.109437] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Revised: 01/13/2024] [Accepted: 03/04/2024] [Indexed: 03/26/2024] Open
Abstract
Lethal intergroup encounters occur in many species because of sexual selection. While documented in mountain gorillas, they are absent in western gorillas as, instead, it is predicted by their higher feeding (frugivory) and mate competition (single-vs. multi-male groups). We investigate whether the injuries on three dead silverbacks and one adult female from four groups of western gorillas in the Central African Republic, resulted from interactions with gorillas or leopards. We identified two distinct injury patterns caused by gorillas (isolated lacerations, round wounds) and leopards (punctures clustered on head/neck) by analyzing injuries caused by mountain gorillas and leopards to gorillas and non-gorilla species, respectively. The western gorilla injury pattern is similar to that of mountain gorillas suggesting that lethal encounters occur, albeit infrequently, as predicted by sexual selection in a one-male society. While sexual dimorphism and polygynous sociality favored the evolution of violent encounters, multiple males in groups may influence their frequency.
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Affiliation(s)
- Hugo Potel
- Ecoanthropologie, Centre National de la Recherche Scientifique/Muséum National d’Histoire Naturelle, University Paris Diderot, Sorbonne Paris Cité, Musée de l’Homme, Paris, France
| | | | - Chloé Cipolletta
- Dzanga-Sangha Protected Areas, World Wide Fund for Nature, Bangui, Central African Republic
| | - Terence Neba Fuh
- Dzanga-Sangha Protected Areas, World Wide Fund for Nature, Bangui, Central African Republic
| | - Giulia Bardino
- Ecoanthropologie, Centre National de la Recherche Scientifique/Muséum National d’Histoire Naturelle, University Paris Diderot, Sorbonne Paris Cité, Musée de l’Homme, Paris, France
- “La Sapienza” University, Department of Environmental and Evolutionary Biology, Rome, Italy
| | - Emmanuel Konyal
- Dzanga-Sangha Protected Areas, World Wide Fund for Nature, Bangui, Central African Republic
| | | | | | - Shelly Masi
- Ecoanthropologie, Centre National de la Recherche Scientifique/Muséum National d’Histoire Naturelle, University Paris Diderot, Sorbonne Paris Cité, Musée de l’Homme, Paris, France
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3
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Lousa TC, Mendes FDC. Disputes over provisioned resources are no more intense between groups than within groups in free-ranging Sapajus libidinosus. Primates 2024; 65:61-68. [PMID: 37938471 DOI: 10.1007/s10329-023-01105-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2022] [Accepted: 10/27/2023] [Indexed: 11/09/2023]
Abstract
Socioecological models predict that disputes between primate groups will be more intense than those within groups, given that the systematic loss of contests over a given resource will restrict the access of all of the members of that group to that resource. Higher levels of aggression are also expected for provisioned resources that have a more lucrative cost:benefit ratio. The levels of aggression in and between two free-ranging tufted capuchin monkey (Sapajus libidinosus) groups in the context of daily provisioning with bananas were evaluated. The aim of a complementary analysis was to identify possible predictors of the frequency of disputes at the site of the provisioned resource. The disputes were recorded using all-events sampling, while the social behaviour of the study groups was recorded by instantaneous scan sampling. The data were analysed using t-test, Mann-Whitney's U, and generalised linear modelling. Between-group disputes were no more intense than within-group events, and did not involve more individuals, or more adult females. The frequency of disputes increased as the number of individuals eating bananas increased. No evidence was found that disputes between groups were any more intense than those within groups. Dominance patterns may have affected these findings, by mediating intergroup disputes. An increase in the number of competitors affected the frequency of disputes at the site of the provisioned resource.
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Affiliation(s)
- Túlio Costa Lousa
- Department of Basic Psychological Processes, Institute of Psychology, University of Brasília, Brasília, DF, 70910-900, Brazil.
| | - Francisco D C Mendes
- Department of Basic Psychological Processes, Institute of Psychology, University of Brasília, Brasília, DF, 70910-900, Brazil
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4
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Morrison RE, Eckardt W, Stoinski TS, Rosenbaum S. Cumulative early-life adversity does not predict reduced adult longevity in wild gorillas. Curr Biol 2023; 33:2307-2314.e4. [PMID: 37192615 PMCID: PMC10264970 DOI: 10.1016/j.cub.2023.04.051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 02/24/2023] [Accepted: 04/21/2023] [Indexed: 05/18/2023]
Abstract
Extensive research across fields has repeatedly confirmed that early-life adversity (ELA) is a major selective force for many taxa, in part via its ties to adult health and longevity.1,2,3 Negative effects of ELA on adult outcomes have been documented in a wide range of species, from fish to birds to humans.4 We used 55 years of long-term data collected on 253 wild mountain gorillas to examine the effects of six putative sources of ELA on survival, both individually and cumulatively. Although cumulative ELA was associated with high mortality in early life, we found no evidence that it had detrimental consequences for survival later in life. Experiencing three or more forms of ELA was associated with greater longevity, with a 70% reduction in the risk of death across adulthood, driven specifically by greater longevity in males. Although this higher survival in later life is likely a consequence of sex-specific viability selection5 during early life due to the immediate mortality consequences of adverse experiences, patterns in our data also suggest that gorillas have significant resilience to ELA. Our findings demonstrate that the detrimental consequences of ELA on later life survival are not universal, and indeed largely absent in one of humans' closest living relatives. This raises important questions about the biological roots of sensitivity to early experiences and the protective mechanisms that contribute to resiliency in gorillas, which could be critical for understanding how best to encourage similar resiliency to early-life shocks in humans.
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Affiliation(s)
- Robin E Morrison
- Dian Fossey Gorilla Fund, PO Box 105, Musanze, Rwanda; Centre for Research in Animal Behaviour, Department of Psychology, University of Exeter, Exeter EX4 4QG, UK.
| | | | | | - Stacy Rosenbaum
- Department of Anthropology, University of Michigan-Ann Arbor, Ann Arbor, MI 48109, USA.
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5
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Iyer N, Kahlenberg SM, Williamson EA, Kyungu J, Syaluha EK, Mbeke JK, de Merode E, Caillaud D. Viability analysis for population reinforcement of Grauer's gorillas at Mount Tshiaberimu, Democratic Republic of the Congo. J Wildl Manage 2023. [DOI: 10.1002/jwmg.22384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/08/2023]
Affiliation(s)
- Neetha Iyer
- Department of Anthropology, 328 Young Hall, One Shields Avenue University of California Davis CA 95616 USA
| | - Sonya M. Kahlenberg
- Kasiisi Project 1 Carley Road Lexington MA 02421 USA
- Gorilla Rehabilitation and Conservation Education (GRACE) Center, Kasugho, North Kivu, Democratic Republic of the Congo
| | | | - Jean‐Claude Kyungu
- Institut Congolais pour la Conservation de la Nature, Kinshasa, Democratic Republic of the Congo
| | - Eddy K. Syaluha
- Gorilla Doctors (MGVP, Inc.), Karen C. Drayer Wildlife Health Center University of California Davis CA 95616 USA
| | - Jackson K. Mbeke
- Gorilla Rehabilitation and Conservation Education (GRACE) Center, Kasugho, North Kivu, Democratic Republic of the Congo
| | - Emmanuel de Merode
- Institut Congolais pour la Conservation de la Nature, Goma, Democratic Republic of the Congo
| | - Damien Caillaud
- Department of Anthropology, 328 Young Hall, One Shields Avenue University of California Davis CA 95616 USA
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6
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McGuire KM, Sauther ML. Characterizing group and individual engagement in intergroup encounters between small groups of ring-tailed lemurs (Lemur catta) on St. Catherines Island, USA. Primates 2023; 64:161-176. [PMID: 36418748 DOI: 10.1007/s10329-022-01036-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 11/02/2022] [Indexed: 11/25/2022]
Abstract
Primate species exhibit considerable variation in behavior and outcomes during intergroup encounters (IGEs). Social group characteristics, like group size, and individual traits, such as sex, rank, and reproductive status, within those groups can influence both IGE engagement and outcomes. To better understand the impact of group heterogeneity on IGEs, we must examine individual strategies to elucidate individual costs and benefits of engaging in these interactions. Here, we present a descriptive study of the IGEs between two small social groups of ring-tailed lemurs (Lemur catta) on St. Catherines Island, GA, USA. We distinguish between dyadic and multiple-individual interactions between groups to compare collective and individual agonistic engagement. All encounters occurred when the East Road group (N = 7 individuals) traveled from the center of their home range to the boundary with Windmill group's (N = 5 individuals) home range, indicating that East Road might have been actively testing this boundary for access to food resources, sleeping trees, and mating opportunities. We also found notable individual variation in participation during IGEs. The daughters of the highest-ranking females were the most-engaged in dyadic intergroup and intragroup aggression, had high "win" rates during intergroup dyadic encounters, and engaged in intergroup multiple-individual interactions at high levels. These findings indicate that they might value their home range more as "potential alphas" compared to other group members. Dominant females were the most engaged in multiple-individual interactions, suggesting that they contribute heavily to collective action that might result in a gain or loss of access to resources. Finally, these two small groups might be equally matched despite the two-individual group size disparity due to individual free-riding strategies. Future research should focus on individual strategies during IGEs to characterize the complex decisions and trade-offs that influence participation.
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Affiliation(s)
- Kathleen M McGuire
- Department of Anthropology, University of Colorado Boulder, Boulder, CO, 80302, USA.
| | - Michelle L Sauther
- Department of Anthropology, University of Colorado Boulder, Boulder, CO, 80302, USA
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7
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Morrison RE, Hirwa JP, Ndagijimana F, Vecellio V, Eckardt W, Stoinski TS. Cascading effects of social dynamics on the reproduction, survival, and population growth of mountain gorillas. Anim Conserv 2022. [DOI: 10.1111/acv.12830] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- R. E. Morrison
- Dian Fossey Gorilla Fund, Ellen DeGeneres Campus of the Dian Fossey Gorilla Fund Kinigi Rwanda
- Centre for Research in Animal Behaviour, Department of Psychology University of Exeter Exeter UK
| | - J. P. Hirwa
- Dian Fossey Gorilla Fund, Ellen DeGeneres Campus of the Dian Fossey Gorilla Fund Kinigi Rwanda
| | - F. Ndagijimana
- Dian Fossey Gorilla Fund, Ellen DeGeneres Campus of the Dian Fossey Gorilla Fund Kinigi Rwanda
| | - V. Vecellio
- Dian Fossey Gorilla Fund, Ellen DeGeneres Campus of the Dian Fossey Gorilla Fund Kinigi Rwanda
| | - W. Eckardt
- Dian Fossey Gorilla Fund, Ellen DeGeneres Campus of the Dian Fossey Gorilla Fund Kinigi Rwanda
| | - T. S. Stoinski
- Dian Fossey Gorilla Fund, Ellen DeGeneres Campus of the Dian Fossey Gorilla Fund Kinigi Rwanda
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8
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Ridley AR, Nelson-Flower MJ, Wiley EM, Humphries DJ, Kokko H. Kidnapping intergroup young: an alternative strategy to maintain group size in the group-living pied babbler ( Turdoides bicolor). Philos Trans R Soc Lond B Biol Sci 2022; 377:20210153. [PMID: 35369755 PMCID: PMC8977656 DOI: 10.1098/rstb.2021.0153] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Both inter- and intragroup interactions can be important influences on behaviour, yet to date most research focuses on intragroup interactions. Here, we describe a hitherto relatively unknown behaviour that results from intergroup interaction in the cooperative breeding pied babbler: kidnapping. Kidnapping can result in the permanent removal of young from their natal group. Since raising young requires energetic investment and abductees are usually unrelated to their kidnappers, there appears no apparent evolutionary advantage to kidnapping. However, kidnapping may be beneficial in species where group size is a critically limiting factor (e.g. for reproductive success or territory defence). We found kidnapping was a highly predictable event in pied babblers: primarily groups that fail to raise their own young kidnap the young of others, and we show this to be the theoretical expectation in a model that predicts kidnapping to be facultative, only occurring in those cases where an additional group member has sufficient positive impact on group survival to compensate for the increase in reproductive competition. In babblers, groups that failed to raise young were also more likely to accept extragroup adults (hereafter rovers). Groups that fail to breed may either (i) kidnap intergroup young or (ii) accept rovers as an alternative strategy to maintain or increase group size. This article is part of the theme issue 'Intergroup conflict across taxa'.
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Affiliation(s)
- Amanda R Ridley
- Centre for Evolutionary Biology, School of Biological Sciences, University of Western Australia, Perth, Australia.,Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Cape Town, Western Cape, South Africa
| | - Martha J Nelson-Flower
- Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Cape Town, Western Cape, South Africa.,Department of Biology, Langara College, Vancouver, BC, Canada
| | - Elizabeth M Wiley
- Centre for Evolutionary Biology, School of Biological Sciences, University of Western Australia, Perth, Australia
| | - David J Humphries
- Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Cape Town, Western Cape, South Africa
| | - Hanna Kokko
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
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9
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Smith JE, Fichtel C, Holmes RK, Kappeler PM, van Vugt M, Jaeggi AV. Sex bias in intergroup conflict and collective movements among social mammals: male warriors and female guides. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210142. [PMID: 35369756 DOI: 10.1098/rstb.2021.0142] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Intergroup conflict is a major evolutionary force shaping animal and human societies. Males and females should, on average, experience different costs and benefits for participating in collective action. Specifically, among mammals, male fitness is generally limited by access to mates whereas females are limited by access to food and safety. Here we analyse sex biases among 72 species of group-living mammals in two contexts: intergroup conflict and collective movements. Our comparative phylogenetic analyses show that the modal mammalian pattern is male-biased participation in intergroup conflict and female-biased leadership in collective movements. However, the probability of male-biased participation in intergroup conflicts decreased and female-biased participation increased with female-biased leadership in movements. Thus, female-biased participation in intergroup conflict only emerged in species with female-biased leadership in collective movements, such as in spotted hyenas and some lemurs. Sex differences are probably attributable to costs and benefits of participating in collective movements (e.g. towards food, water, safety) and intergroup conflict (e.g. access to mates or resources, risk of injury). Our comparative review offers new insights into the factors shaping sex bias in leadership across social mammals and is consistent with the 'male warrior hypothesis' which posits evolved sex differences in human intergroup psychology. This article is part of the theme issue 'Intergroup conflict across taxa'.
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Affiliation(s)
- Jennifer E Smith
- Biology Department, Mills College, 5000 MacArthur Boulevard, Oakland, CA 94631, USA
| | - Claudia Fichtel
- Behavioral Ecology and Sociobiology Unit, German Primate Center, Leibniz Institute for Primate Research, Göttingen, Germany
| | - Rose K Holmes
- Biology Department, Mills College, 5000 MacArthur Boulevard, Oakland, CA 94631, USA
| | - Peter M Kappeler
- Behavioral Ecology and Sociobiology Unit, German Primate Center, Leibniz Institute for Primate Research, Göttingen, Germany.,Department Anthropology/Sociobiology, University of Göttingen, Göttingen, Germany
| | - Mark van Vugt
- Department of Experimental and Applied Psychology, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Adrian V Jaeggi
- Institute of Evolutionary Medicine, University of Zurich, Zurich, Switzerland
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10
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Morris-Drake A, Kennedy P, Braga Goncalves I, Radford AN. Variation between species, populations, groups and individuals in the fitness consequences of out-group conflict. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210148. [PMID: 35369741 PMCID: PMC8977661 DOI: 10.1098/rstb.2021.0148] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Out-group conflict is rife in the natural world, occurring from primates to ants. Traditionally, research on this aspect of sociality has focused on the interactions between groups and their conspecific rivals, investigating contest function and characteristics, which group members participate and what determines who wins. In recent years, however, there has been increasing interest in the consequences of out-group conflict. In this review, we first set the scene by outlining the fitness consequences that can arise immediately to contest participants, as well as a broader range of delayed, cumulative and third-party effects of out-group conflict on survival and reproductive success. For the majority of the review, we then focus on variation in these fitness consequences of out-group conflict, describing known examples both between species and between populations, groups and individuals of the same species. Throughout, we suggest possible reasons for the variation, provide examples from a diverse array of taxa, and suggest what is needed to advance this burgeoning area of social evolution. This article is part of the theme issue 'Intergroup conflict across taxa'.
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Affiliation(s)
- Amy Morris-Drake
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Patrick Kennedy
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Ines Braga Goncalves
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Andrew N Radford
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
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11
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Time budget and foraging strategies of two provisioned groups of tufted capuchin monkeys, Sapajus libidinosus, in a small, seasonal urban forest fragment. Primates 2022; 63:387-395. [DOI: 10.1007/s10329-022-00993-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2021] [Accepted: 05/10/2022] [Indexed: 10/18/2022]
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12
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Love thy neighbour: behavioural and endocrine correlates of male strategies during intergroup encounters in bonobos. Anim Behav 2022. [DOI: 10.1016/j.anbehav.2022.02.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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13
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Lousa TC, Mendes FDC. Inter-group conflicts involving adult female and male bearded capuchins, Sapajus libidinosus (Primates: Cebidae), in the context of provisioned resources: resource defense or sexual selection? ZOOLOGIA 2022. [DOI: 10.1590/s1984-4689.v39.e21020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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14
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Morris-Drake A, Linden JF, Kern JM, Radford AN. Extended and cumulative effects of experimentally induced intergroup conflict in a cooperatively breeding mammal. Proc Biol Sci 2021; 288:20211743. [PMID: 34875195 PMCID: PMC8651417 DOI: 10.1098/rspb.2021.1743] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 11/17/2021] [Indexed: 12/05/2022] Open
Abstract
Conflict between rival groups is rife in nature. While recent work has begun exploring the behavioural consequences of this intergroup conflict, studies have primarily considered just the 1-2 h immediately after single interactions with rivals or their cues. Using a habituated population of wild dwarf mongooses (Helogale parvula), we conducted week-long manipulations to investigate longer-term impacts of intergroup conflict. Compared to a single presentation of control herbivore faeces, one rival-group faecal presentation (simulating a territorial intrusion) resulted in more within-group grooming the following day, beyond the likely period of conflict-induced stress. Repeated presentations of outsider cues led to further changes in baseline behaviour by the end of the week: compared to control weeks, mongooses spent less time foraging and foraged closer to their groupmates, even when there had been no recent simulated intrusion. Moreover, there was more baseline territorial scent-marking and a higher likelihood of group fissioning in intrusion weeks. Consequently, individuals gained less body mass at the end of weeks with repeated simulated intrusions. Our experimental findings provide evidence for longer-term, extended and cumulative, effects of an elevated intergroup threat, which may lead to fitness consequences and underpin this powerful selective pressure.
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Affiliation(s)
- Amy Morris-Drake
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Jennifer F. Linden
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Julie M. Kern
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
- School of Environmental and Rural Science, University of New England, Armidale, New South Wales 2351, Australia
| | - Andrew N. Radford
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
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15
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Humphries DJ, Nelson‐Flower MJ, Bell MBV, Finch FM, Ridley AR. Kinship, dear enemies, and costly combat: The effects of relatedness on territorial overlap and aggression in a cooperative breeder. Ecol Evol 2021; 11:17031-17042. [PMID: 34938490 PMCID: PMC8668771 DOI: 10.1002/ece3.8342] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 08/29/2021] [Accepted: 10/13/2021] [Indexed: 11/30/2022] Open
Abstract
Many species maintain territories, but the degree of overlap between territories and the level of aggression displayed in territorial conflicts can vary widely, even within species. Greater territorial overlap may occur when neighboring territory holders are close relatives. Animals may also differentiate neighbors from strangers, with more familiar neighbors eliciting less-aggressive responses during territorial conflicts (the "dear enemy" effect). However, research is lacking in how both kinship and overlap affect territorial conflicts, especially in group-living species. Here, we investigate kinship, territorial overlap, and territorial conflict in a habituated wild population of group-living cooperatively breeding birds, the southern pied babbler Turdoides bicolor. We find that close kin neighbors are beneficial. Territories overlap more when neighboring groups are close kin, and these larger overlaps with kin confer larger territories (an effect not seen for overlaps with unrelated groups). Overall, territorial conflict is costly, causing significant decreases in body mass, but conflicts with kin are shorter than those conducted with nonkin. Conflicts with more familiar unrelated neighbors are also shorter, indicating these neighbors are "dear enemies." However, kinship modulates the "dear enemy" effect; even when kin are encountered less frequently, kin elicit less-aggressive responses, similar to the "dear enemy" effect. Kin selection appears to be a main influence on territorial behavior in this species. Groups derive kin-selected benefits from decreased conflicts and maintain larger territories when overlapping with kin, though not when overlapping with nonkin. More generally, it is possible that kinship extends the "dear enemy" effect in animal societies.
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Affiliation(s)
- David J. Humphries
- Department of Biological SciencesMacquarie UniversitySydneyNew South WalesAustralia
- Pied Babbler Research ProjectUniversity of Cape TownRondeboschWestern CapeSouth Africa
| | - Martha J. Nelson‐Flower
- Pied Babbler Research ProjectUniversity of Cape TownRondeboschWestern CapeSouth Africa
- Department of BiologyLangara CollegeVancouverBritish ColumbiaCanada
| | - Matthew B. V. Bell
- Pied Babbler Research ProjectUniversity of Cape TownRondeboschWestern CapeSouth Africa
- Institute of Evolutionary BiologySchool of Biological SciencesUniversity of EdinburghEdinburghUK
| | - Fiona M. Finch
- Pied Babbler Research ProjectUniversity of Cape TownRondeboschWestern CapeSouth Africa
| | - Amanda R. Ridley
- Pied Babbler Research ProjectUniversity of Cape TownRondeboschWestern CapeSouth Africa
- DST/NRF Centre of ExcellencePercy FitzPatrick Institute for African OrnithologyUniversity of Cape TownRondeboschSouth Africa
- School of Biological SciencesUniversity of Western AustraliaPerthWestern AustraliaAustralia
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16
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Braga Goncalves I, Richmond E, Harding HR, Radford AN. Impacts of additional noise on the social interactions of a cooperatively breeding fish. ROYAL SOCIETY OPEN SCIENCE 2021; 8:210982. [PMID: 34350024 PMCID: PMC8316797 DOI: 10.1098/rsos.210982] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 07/06/2021] [Indexed: 05/10/2023]
Abstract
Anthropogenic noise is a global pollutant known to affect the behaviour of individual animals in all taxa studied. However, there has been relatively little experimental testing of the effects of additional noise on social interactions between conspecifics, despite these forming a crucial aspect of daily life for most species. Here, we use established paradigms to investigate how white-noise playback affects both group defensive actions against an intruder and associated within-group behaviours in a model fish species, the cooperatively breeding cichlid Neolamprologus pulcher. Additional noise did not alter defensive behaviour, but did result in changes to within-group behaviour. Both dominant and subordinate females, but not the dominant male, exhibited less affiliation and showed a tendency to produce more submissive displays to groupmates when there was additional noise compared with control conditions. Thus, our experimental results indicate the potential for anthropogenic noise to affect social interactions between conspecifics and emphasize the possibility of intraspecific variation in the impacts of this global pollutant.
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Affiliation(s)
- Ines Braga Goncalves
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Emily Richmond
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Harry R. Harding
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
| | - Andrew N. Radford
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK
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Chest beats as an honest signal of body size in male mountain gorillas (Gorilla beringei beringei). Sci Rep 2021; 11:6879. [PMID: 33833252 PMCID: PMC8032651 DOI: 10.1038/s41598-021-86261-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 03/04/2021] [Indexed: 11/29/2022] Open
Abstract
Acoustic signals that reliably indicate body size, which usually determines competitive ability, are of particular interest for understanding how animals assess rivals and choose mates. Whereas body size tends to be negatively associated with formant dispersion in animal vocalizations, non-vocal signals have received little attention. Among the most emblematic sounds in the animal kingdom is the chest beat of gorillas, a non-vocal signal that is thought to be important in intra and inter-sexual competition, yet it is unclear whether it reliably indicates body size. We examined the relationship among body size (back breadth), peak frequency, and three temporal characteristics of the chest beat: duration, number of beats and beat rate from sound recordings of wild adult male mountain gorillas. Using linear mixed models, we found that larger males had significantly lower peak frequencies than smaller ones, but we found no consistent relationship between body size and the temporal characteristics measured. Taken together with earlier findings of positive correlations among male body size, dominance rank and reproductive success, we conclude that the gorilla chest beat is an honest signal of competitive ability. These results emphasize the potential of non-vocal signals to convey important information in mammal communication.
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18
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Cheng L, Lucchesi S, Mundry R, Samuni L, Deschner T, Surbeck M. Variation in aggression rates and urinary cortisol levels indicates intergroup competition in wild bonobos. Horm Behav 2021; 128:104914. [PMID: 33373622 DOI: 10.1016/j.yhbeh.2020.104914] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Revised: 12/09/2020] [Accepted: 12/10/2020] [Indexed: 01/08/2023]
Abstract
Intergroup competition is a widespread phenomenon across taxa and groups typically compete over access to limited resources, such as food and mates. Such competition may be quantified by changes in individuals' behavioral and physiological status in response to intergroup encounters (IGEs). Bonobos, one of our closest living relatives, are often regarded as xenophilic and exhibit high tolerance towards out-group individuals. This tolerance between groups may still be accompanied by intergroup competition over resources. We hereby compared variation in aggression rates and urinary cortisol levels of bonobos during and outside contexts of IGEs in the Kokolopori Bonobo Reserve and investigated whether food and mate availability influenced males' and females' aggression and cortisol levels, when controlling for dominance rank and the number of individuals present. We found that although females had higher aggression rates and urinary cortisol levels during than outside contexts of IGEs, these increases were not related to food availability or changes in between-group dynamics when maximally tumescent females were present, rather than absent. Furthermore, males showed higher aggression rates and urinary cortisol levels during than outside contexts of IGEs. However, males' responses during IGEs were not related to the presence of maximally tumescent females and food availability. Taken together, while competition intensified during seemingly tolerant IGEs in bonobos, such competition was unrelated to short-term changes in food and mate availability. Despite physical and physiological costs of aggression, bonobos associate with out-group individuals frequently and for extended periods. This suggests potential benefits of bonobo intergroup associations.
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Affiliation(s)
- Leveda Cheng
- Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA; Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
| | - Stefano Lucchesi
- Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA; Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Roger Mundry
- Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Liran Samuni
- Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA; Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Tobias Deschner
- Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Martin Surbeck
- Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA; Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
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19
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Group-level cooperation in chimpanzees is shaped by strong social ties. Nat Commun 2021; 12:539. [PMID: 33483482 PMCID: PMC7822919 DOI: 10.1038/s41467-020-20709-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 12/07/2020] [Indexed: 01/30/2023] Open
Abstract
Humans maintain extensive social ties of varying preferences, providing a range of opportunities for beneficial cooperative exchange that may promote collective action and our unique capacity for large-scale cooperation. Similarly, non-human animals maintain differentiated social relationships that promote dyadic cooperative exchange, but their link to cooperative collective action is little known. Here, we investigate the influence of social relationship properties on male and female chimpanzee participations in a costly form of group action, intergroup encounters. We find that intergroup encounter participation increases with a greater number of other participants as well as when participants are maternal kin or social bond partners, and that these effects are independent from one another and from the likelihood to associate with certain partners. Together, strong social relationships between kin and non-kin facilitate group-level cooperation in one of our closest living relatives, suggesting that social bonds may be integral to the evolution of cooperation in our own species.
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Morrison RE, Hirwa JP, Mucyo JPS, Stoinski TS, Vecellio V, Eckardt W. Inter‐group relationships influence territorial defence in mountain gorillas. J Anim Ecol 2020; 89:2852-2862. [DOI: 10.1111/1365-2656.13355] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Accepted: 08/06/2020] [Indexed: 11/27/2022]
Affiliation(s)
- Robin E. Morrison
- The Dian Fossey Gorilla Fund Musanze Rwanda
- Centre for Research in Animal Behaviour University of Exeter Exeter UK
| | | | | | - Tara S. Stoinski
- The Dian Fossey Gorilla Fund Musanze Rwanda
- The Dian Fossey Gorilla Fund Atlanta GA USA
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21
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Interactions with conspecific outsiders as drivers of cognitive evolution. Nat Commun 2020; 11:4937. [PMID: 33024110 PMCID: PMC7538913 DOI: 10.1038/s41467-020-18780-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 09/14/2020] [Indexed: 11/23/2022] Open
Abstract
The social intelligence hypothesis (SIH) posits that within-group interactions drive cognitive evolution, but it has received equivocal support. We argue the SIH overlooks a major component of social life: interactions with conspecific outsiders. Competition for vital resources means conspecific outsiders present myriad threats and opportunities in all animal taxa across the social spectrum (from individuals to groups). We detail cognitive challenges generated by conspecific outsiders, arguing these select for ‘Napoleonic’ intelligence; explain potential influences on the SIH; and highlight important considerations when empirically testing these ideas. Including interactions with conspecific outsiders may substantially improve our understanding of cognitive evolution. The social intelligence hypothesis predicts that social organisms tend to be more intelligent because within-group interactions drive cognitive evolution. Here, authors propose that conspecific outsiders can be just as important in selecting for sophisticated cognitive adaptations.
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22
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Seiler N, Robbins MM. Using long-term ranging patterns to assess within-group and between-group competition in wild mountain gorillas. BMC Ecol 2020; 20:40. [PMID: 32677937 PMCID: PMC7367404 DOI: 10.1186/s12898-020-00306-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 06/30/2020] [Indexed: 11/28/2022] Open
Abstract
Background Competition within and between social groups determines access to resources and can be inferred from space use parameters that reflect depletion of food resources and competitive abilities of groups. Using location data from 1998 to 2017, we investigated within- and between-group competition in 12 groups of wild mountain gorillas (Gorilla beringei beringei). As within-group feeding competition is expected to increase with group size, an increase in group size is predicted to lead to an increase in the size of annual home ranges and core areas, but to a decrease in fidelity (reuse of an area). Due to asymmetries in competitive abilities, larger groups are expected to have higher exclusivity (degree of non-shared space) of annual home ranges and core areas than smaller groups. Results We found evidence of within-group feeding competition based on a positive relationship between group size and both annual home range and core area size as well as a negative relationship between group size and core area fidelity. Additionally, fidelity of core areas was lower than of home ranges. Between-group competition was inferred from a trend for groups with more members and more males to have more exclusive home ranges and core areas. Lastly, annual core areas were largely mutually exclusive. Conclusions Our study suggests that non-territorial, group-living animals can have highly dynamic, long-term avoidance-based spacing patterns, both temporally and spatially, to maintain annual core area exclusivity among groups while concurrently shifting these areas annually within overlapping home ranges to avoid resource depletion. Despite ranging in larger home ranges and core areas, larger groups were able to maintain more exclusive ranges than smaller groups, suggesting a competitive advantage for larger groups in between-group competition in a non-territorial species. Together, these findings contribute to understanding how social animals make behavioral adjustments to mitigate the effects of intraspecific competition.
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Affiliation(s)
- Nicole Seiler
- Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103, Leipzig, Germany.
| | - Martha M Robbins
- Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103, Leipzig, Germany
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23
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Fighting for what it’s worth: participation and outcome of inter-group encounters in a pair-living primate, the Javan gibbon (Hylobates moloch). Behav Ecol Sociobiol 2020. [DOI: 10.1007/s00265-020-02879-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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24
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Cooksey K, Sanz C, Ebombi TF, Massamba JM, Teberd P, Magema E, Abea G, Peralejo JSO, Kienast I, Stephens C, Morgan D. Socioecological Factors Influencing Intergroup Encounters in Western Lowland Gorillas (Gorilla gorilla gorilla). INT J PRIMATOL 2020. [DOI: 10.1007/s10764-020-00147-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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25
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Abstract
The evolutionary origins of how modern humans share and use space are often modelled on the territorial-based violence of chimpanzees, with limited comparison to other apes. Gorillas are widely assumed to be non-territorial due to their large home ranges, extensive range overlap, and limited inter-group aggression. Using large-scale camera trapping, we monitored western gorillas in Republic of Congo across 60 km2. Avoidance patterns between groups were consistent with an understanding of the “ownership” of specific regions, with greater avoidance of their neighbours the closer they were to their neighbours’ home range centres. Groups also avoided larger groups’ home ranges to a greater extent, consistent with stronger defensive responses from more dominant groups. Our results suggest that groups may show territoriality, defending core regions of their home ranges against neighbours, and mirror patterns common across human evolution, with core areas of resident dominance and larger zones of mutual tolerance. This implies western gorillas may be a key system for understanding how humans have evolved the capacity for extreme territorial-based violence and warfare, whilst also engaging in the strong affiliative inter-group relationships necessary for large-scale cooperation.
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26
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Furuichi T. Variation in Intergroup Relationships Among Species and Among and Within Local Populations of African Apes. INT J PRIMATOL 2020. [DOI: 10.1007/s10764-020-00134-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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27
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Mirville MO, Ridley AR, Samedi JPM, Vecellio V, Ndagijimana F, Stoinski TS, Grueter CC. Intragroup Behavioral Changes Following Intergroup Conflict in Mountain Gorillas (Gorilla beringei beringei). INT J PRIMATOL 2020. [DOI: 10.1007/s10764-020-00130-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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28
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Morris-Drake A, Christensen C, Kern JM, Radford AN. Experimental field evidence that out-group threats influence within-group behavior. Behav Ecol 2019; 30:1425-1435. [PMID: 31579132 PMCID: PMC6765380 DOI: 10.1093/beheco/arz095] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 05/20/2019] [Accepted: 05/29/2019] [Indexed: 11/13/2022] Open
Abstract
In social species, conspecific outsiders present various threats to groups and their members. These out-group threats are predicted to affect subsequent within-group interactions (e.g., affiliation and aggression) and individual behavior (e.g., foraging and vigilance decisions). However, experimental investigations of such consequences are rare, especially in natural conditions. We used field-based call playbacks and fecal presentations on habituated wild dwarf mongooses (Helogale parvula)-a cooperatively breeding, territorial species-to examine postinteraction responses to the simulated threat of a rival group. Dwarf mongooses invested more in grooming of groupmates, foraged closer together, and more regularly acted as sentinels (a raised guard) after encountering indicators of rival-group presence compared to control conditions. These behavioral changes likely arise from greater anxiety and, in the case of increased vigilance, the need to seek additional information about the threat. The influence of an out-group threat lasted at least 1 h but individuals of different dominance status and sex responded similarly, potentially because all group members suffer costs if a contest with rivals is lost. Our results provide field-based experimental evidence from wild animals that out-group threats can influence within-group behavior and decision making, and suggest the need for greater consideration of the lasting impacts of social conflict.
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Affiliation(s)
- Amy Morris-Drake
- School of Biological Sciences, University of Bristol, Bristol, UK
| | | | - Julie M Kern
- School of Biological Sciences, University of Bristol, Bristol, UK
| | - Andrew N Radford
- School of Biological Sciences, University of Bristol, Bristol, UK
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29
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Using the research on intergroup conflict in nonhuman animals to help inform patterns of human intergroup conflict. Behav Brain Sci 2019; 42:e138. [PMID: 31407992 DOI: 10.1017/s0140525x19000827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
There is a large body of research on conflict in nonhuman animal groups that measures the costs and benefits of intergroup conflict, and we suggest that much of this evidence is missing from De Dreu and Gross's interesting article. It is a shame this work has been missed, because it provides evidence for interesting ideas put forward in the article.
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30
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Pisor AC, Surbeck M. The evolution of intergroup tolerance in nonhuman primates and humans. Evol Anthropol 2019; 28:210-223. [DOI: 10.1002/evan.21793] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2018] [Revised: 04/05/2019] [Accepted: 07/05/2019] [Indexed: 12/31/2022]
Affiliation(s)
- Anne C. Pisor
- Department of AnthropologyWashington State University Pullman Washington
- Department of Human Behavior, Ecology, and CultureMax Planck Institute for Evolutionary Anthropology Leipzig Germany
| | - Martin Surbeck
- Department of Human Evolutionary BiologyHarvard University Cambridge Massachusetts
- Department of PrimatologyMax Planck Institute for Evolutionary Anthropology Leipzig Germany
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31
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Eckardt W, Stoinski TS, Rosenbaum S, Santymire R. Social and ecological factors alter stress physiology of Virunga mountain gorillas ( Gorilla beringei beringei). Ecol Evol 2019; 9:5248-5259. [PMID: 31110676 PMCID: PMC6509442 DOI: 10.1002/ece3.5115] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2018] [Revised: 02/05/2019] [Accepted: 03/01/2019] [Indexed: 11/12/2022] Open
Abstract
Living in a rapidly changing environment can alter stress physiology at the population level, with negative impacts on health, reproductive rates, and mortality that may ultimately result in species decline. Small, isolated animal populations where genetic diversity is low are at particular risks, such as endangered Virunga mountain gorillas (Gorilla beringei beringei). Along with climate change-associated environmental shifts that are affecting the entire population, subpopulations of the Virunga gorillas have recently experienced extreme changes in their social environment. As the growing population moves closer to the forest's carrying capacity, the gorillas are coping with rising population density, increased frequencies of interactions between social units, and changing habitat use (e.g., more overlapping home ranges and routine ranging at higher elevations). Using noninvasive monitoring of fecal glucocorticoid metabolites (FGM) on 115 habituated Virunga gorillas, we investigated how social and ecological variation are related to baseline FGM levels, to better understand the adaptive capacity of mountain gorillas and monitor potential physiological indicators of population decline risks. Generalized linear mixed models revealed elevated mean monthly baseline FGM levels in months with higher rainfall and higher mean maximum and minimum temperature, suggesting that Virunga gorillas might be sensitive to predicted warming and rainfall trends involving longer, warmer dry seasons and more concentrated and extreme rainfall occurrences. Exclusive use of smaller home range areas was linked to elevated baseline FGM levels, which may reflect reduced feeding efficiency and increased travel efforts to actively avoid neighboring groups. The potential for additive effects of stress-inducing factors could have short- and long-term impacts on the reproduction, health, and ultimately survival of the Virunga gorilla population. The ongoing effects of environmental changes and population dynamics must be closely monitored and used to develop effective long-term conservation strategies that can help address these risk factors.
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Affiliation(s)
| | | | - Stacy Rosenbaum
- Departmet of AnthropologyNorthwestern UniversityEvanstonIllinois
- Davee Center for Epidemiology and EndocrinologyLincoln Park ZooChicagoIllinois
| | - Rachel Santymire
- Davee Center for Epidemiology and EndocrinologyLincoln Park ZooChicagoIllinois
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