Guangxi Key Laboratory for Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning, Guangxi, 530004, China.
Centre for Ecological Sciences, Indian Institute of Science, Bengaluru, Karnataka, 560012, India.
Biol Rev Camb Philos Soc. 2020 Aug;95(4):889-910. doi: 10.1111/brv.12591. Epub 2020 Feb 25.
Mixed-species animal groups (MSGs) are widely acknowledged to increase predator avoidance and foraging efficiency, among other benefits, and thereby increase participants' fitness. Diversity in MSG composition ranges from two to 70 species of very similar or completely different phenotypes. Yet consistency in organization is also observable in that one or a few species usually have disproportionate importance for MSG formation and/or maintenance. We propose a two-dimensional framework for understanding this diversity and consistency, concentrating on the types of interactions possible between two individuals, usually of different species. One axis represents the similarity of benefit types traded between the individuals, while the second axis expresses asymmetry in the relative amount of benefits/costs accrued. Considering benefit types, one extreme represents the case of single-species groups wherein all individuals obtain the same supplementary, group-size-related benefits, and the other extreme comprises associations of very different, but complementary species (e.g. one partner creates access to food while the other provides vigilance). The relevance of social information and the matching of activities (e.g. speed of movement) are highest for relationships on the supplementary side of this axis, but so is competition; relationships between species will occur at points along this gradient where the benefits outweigh the costs. Considering benefit amounts given or received, extreme asymmetry occurs when one species is exclusively a benefit provider and the other a benefit user. Within this parameter space, some MSG systems are constrained to one kind of interaction, such as shoals of fish of similar species or leader-follower interactions in fish and other taxa. Other MSGs, such as terrestrial bird flocks, can simultaneously include a variety of supplementary and complementary interactions. We review the benefits that species obtain across the diversity of MSG types, and argue that the degree and nature of asymmetry between benefit providers and users should be measured and not just assumed. We then discuss evolutionary shifts in MSG types, focusing on drivers towards similarity in group composition, and selection on benefit providers to enhance the benefits they can receive from other species. Finally, we conclude by considering how individual and collective behaviour in MSGs may influence both the structure and processes of communities.
混合物种动物群体（MSGs）被广泛认为可以提高捕食者回避和觅食效率等，从而提高参与者的适应性。MSG 组成的多样性范围从两种到 70 种非常相似或完全不同表型的物种。然而，组织的一致性也可以观察到，一种或几种物种通常对 MSG 的形成和/或维持具有不成比例的重要性。我们提出了一个二维框架来理解这种多样性和一致性，重点关注两种个体之间可能存在的相互作用类型，通常是不同的物种。一个轴代表个体之间交易的利益类型的相似性，而第二个轴则表示收益/成本的相对量的不对称性。考虑到利益类型，一个极端代表了单物种群体的情况，其中所有个体都获得相同的补充、与群体大小相关的利益，另一个极端则由非常不同但互补的物种组成（例如，一个伙伴创造获取食物的机会，而另一个提供警戒）。在这个轴的补充侧，社交信息的相关性和活动的匹配（例如运动速度）最高，但竞争也最高；在这个梯度上，当收益超过成本时，物种之间的关系就会发生。考虑给予或接收的利益数量，当一个物种是唯一的利益提供者，而另一个是利益使用者时，就会出现极端的不对称性。在这个参数空间内，一些 MSG 系统被限制在一种相互作用中，例如相似物种的鱼群或鱼类和其他分类群中的领头-跟随者相互作用。其他 MSG，如陆地鸟类群，同时可以包括各种补充和互补的相互作用。我们回顾了物种在各种 MSG 类型中获得的利益，并认为应该测量而不仅仅是假设利益提供者和使用者之间的不对称程度和性质。然后，我们讨论了 MSG 类型的进化转变，重点讨论了群体组成相似性的驱动因素，以及对利益提供者的选择，以增强他们从其他物种获得的利益。最后，我们通过考虑 MSG 中的个体和集体行为如何影响群落的结构和过程来结束讨论。
