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 Neolamprologus multifasciatus 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.

中文翻译：

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社会和空间冲突导致群体生活的鱼类对外来者产生攻击性


群居动物经常会经历群体内对庇护所、空间等资源以及社会地位的竞争。由于这种冲突，居民可能会强烈抵制新成员的加入尝试。在这里，我们询问不同形式的竞争是否会调节这种反应，特别是对 1) 庇护所、2) 群体内空间位置以及 3) 社会或性角色的竞争。我们对坦噶尼喀湖的野生新鳗鱼群体进行了实验，增加或减少其领地内的庇护所（空蜗牛壳）的数量。我们预测，资源丰富度的增加将减少冲突并降低居民对当前同种人的攻击性，而资源的减少将增加攻击性。我们通过引入同性或异性同种生物，与居住地的距离或远或近，探讨了社会冲突和空间安排的影响。我们发现，改变贝壳的丰度对居民对呈现的同种动物的反应没有明显影响。相反，攻击行为很大程度上取决于性别，男性居民几乎只攻击出现的男性，而女性居民几乎只攻击出现的女性。对于雌性来说，这种攻击性受到当前同种动物和居住的雌性亚领地之间空间距离的影响，攻击性随着距离的接近而增加。相比之下，呈现距离并不影响常驻雄性，无论位置如何，它们都会对所有呈现的雄性具有攻击性。总体而言，我们的结果表明，群体居民对所呈现的同种人的反应有所不同，具体取决于这些潜在加入者构成的竞争威胁的类型。