Data from: Concede or clash? Solitary sharks competing for food assess rivals to decide.

To adapt to their environment, organisms can either directly interact with their surroundings or use social information, namely information provided by neighbouring individuals. Social information relates to the external features of surrounding peers, and little is known about its use by solitary species. Here, we investigated the use of social cues in a solitary marine predator by creating artificial aggregations of free-ranging sicklefin lemon sharks (Negaprion acutidens). Using a novel monitoring protocol, we analysed both dominance interactions and tolerance associations between sharks competing for food in relation with the number, the morphology and the behaviour of rivals. Sharks produced more agonistic displays and spent more time around the bait as competitors were more abundant. Moreover, the morphological attributes of competitors had very limited influence on the structure of shark social interactions. Instead, sharks appeared to establish tolerance relationships with competitors according to their individual behaviour. Furthermore, the more two sharks were observed together at a given study site, the fewer agonistic interactions they exchanged. We discuss these findings as evidence of the use of social cues in a non-gregarious predatory species and suggest directions for future research.

为适应生存环境，生物可通过两种途径实现适应性调整：一是直接与周遭环境进行互动，二是借助社会信息（social information）——即由邻近个体所提供的各类信息。目前学界对独居物种利用这类社会信息的具体模式仍知之甚少。本研究以独居海洋捕食者为对象，通过构建自由活动的弯鳍柠檬鲨（Negaprion acutidens）人工聚集群，探究其对社会线索的利用情况。我们采用新型监测方案，分析了鲨鱼在争抢食物时的支配互动与容忍关联，并探讨了竞争者的数量、形态特征与行为模式对上述互动的影响。结果显示，随着竞争者数量增多，鲨鱼展现出的敌对展示行为更多，且在诱饵周边停留的时间更长。此外，竞争者的形态特征对鲨鱼社会互动结构的影响极为有限；与之相反，鲨鱼似乎会根据竞争者的个体行为建立容忍关联。进一步分析发现，在同一研究站点被共同观测到的频次越高的两条鲨鱼，彼此间发生的敌对互动越少。最后，我们将上述研究结果作为非群居性捕食物种利用社会线索的佐证展开讨论，并提出了未来的研究方向。