Gübel Jakob, Bose Aneesh P H, Jordan Alex
Department of Collective Behaviour, Max Planck Institute of Animal Behavior, Universitätsstraße 10, 78464, Konstanz, Germany.
Centre for the Advanced Study of Collective Behaviour, University of Konstanz, Universitätsstraße 10, 78464, Konstanz, Germany.
Behav Ecol. 2021 May 25;32(5):826-834. doi: 10.1093/beheco/arab045. eCollection 2021 Sep-Oct.
Group-living animals often experience within-group competition for resources like shelter and space, as well as for social status. Because of this conflict, residents may aggressively resist joining attempts by new members. Here, we asked whether different forms of competition mediate this response, specifically competition over 1) shelter, 2) spatial position within groups, and 3) social or sexual roles. We performed experiments on wild groups of cichlids in Lake Tanganyika, either increasing or decreasing the number of shelters (empty snail shells) within their territories. We predicted that increases in resource abundance would reduce conflict and lower the aggression of residents toward presented conspecifics, while decreases in resources would increase aggression. We explored the effects of social conflict and spatial arrangement by introducing same or opposite sex conspecifics, at greater or lesser distances from resident subterritories. We found that changing the abundance of shells had no detectable effect on the responses of residents to presented conspecifics. Rather, aggression was strongly sex-dependent, with male residents almost exclusively aggressing presented males, and female residents almost exclusively aggressing presented females. For females, this aggression was influenced by the spatial distances between the presented conspecific and the resident female subterritory, with aggression scaling with proximity. In contrast, presentation distance did not influence resident males, which were aggressive to all presented males regardless of location. Overall, our results show that group residents respond to presented conspecifics differently depending on the type of competitive threat these potential joiners pose.
群居动物常常会在群体内部为获取诸如庇护所和空间等资源以及社会地位而展开竞争。由于这种冲突，群体中的原有成员可能会积极抵制新成员的加入尝试。在此，我们探讨了不同形式的竞争是否会介导这种反应，具体而言，即围绕以下三个方面的竞争：1）庇护所；2）群体内部的空间位置；3）社会或性别角色。我们对坦噶尼喀湖中的野生丽鱼科鱼群体进行了实验，要么增加要么减少其领地内庇护所（空蜗牛壳）的数量。我们预测资源丰富度的增加会减少冲突，并降低原有成员对引入的同种个体的攻击性，而资源减少则会增加攻击性。我们通过在距离原有成员领地不同远近的位置引入同性或异性的同种个体，来探究社会冲突和空间布局的影响。我们发现，改变贝壳的数量对原有成员对引入的同种个体的反应没有可检测到的影响。相反，攻击性强烈地依赖于性别，雄性原有成员几乎只攻击引入的雄性，而雌性原有成员几乎只攻击引入的雌性。对于雌性来说，这种攻击性受到引入的同种个体与雌性原有成员领地之间空间距离的影响，攻击性随着距离的接近而增强。相比之下，引入个体的距离对雄性原有成员没有影响，无论引入个体位于何处，雄性原有成员都会对所有引入的雄性表现出攻击性。总体而言，我们的结果表明，群体中的原有成员会根据这些潜在加入者所构成的竞争威胁类型，对引入的同种个体做出不同的反应。
