Animals that live in groups may experience positive interactions such as cooperative behavior or negative interactions such as competition from group members depending on group size and similarity between individuals. The effect of group size and phenotypic and ecological similarity on group assembly has not been well-studied. Mixed-species flocks are important subsets of bird communities worldwide. We examined associations within these in relation to flock size, to understand rules of flock assembly, in the Western Ghats of India. We examined the relationship between phenotypic clumping and flock richness using four variables—body size, foraging behavior, foraging height and taxonomic relatedness. Using a null model approach, we found that small flocks were more phenotypically clumped for body size than expected by chance; however, phenotypic clumping decreased as flocks increased in size and approached expected phenotypic variation in large flocks. This pattern was not as clear for foraging height and foraging behavior. We then examined a dataset of 55 flock matrices from 24 sites across the world. We found that sites with smaller flocks had higher values of phenotypic clumping for body size and sites with larger flocks were less phenotypically clumped. This relationship was weakly negative for foraging behavior and not statistically significant for taxonomic relatedness. Unlike most single-species groups, participants in mixed-species flocks appear to be able to separate on different axes of trait similarity. They can gain benefits from similarity on one axis while mitigating competition by dissimilarity on others. Consistent with our results, we speculate that flock assembly was deterministic up to a certain point with participants being similar in body size, but larger flocks tended to approach random phenotypic assemblages of species.

中文翻译：

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混种鸟群中的表型聚集随着鸡群丰富度的增加而减少

生活在群体中的动物可能会经历积极的互动，例如合作行为或消极的互动，例如来自群体成员的竞争，这取决于群体规模和个体之间的相似性。群体规模、表型和生态相似性对群体组装的影响尚未得到充分研究。混种群是全球鸟类群落的重要子集。我们研究了这些与羊群大小相关的关联，以了解印度西高止山脉的羊群组装规则。我们使用四个变量——体型、觅食行为、觅食高度和分类学相关性检查了表型结块和鸡群丰富度之间的关系。使用空模型方法，我们发现小鸡群在表型上比预期的体型更聚集；然而，随着鸡群规模的增加并接近大鸡群的预期表型变异，表型结块减少。这种模式对于觅食高度和觅食行为来说并不那么清楚。然后，我们检查了来自世界各地 24 个地点的 55 个鸡群矩阵的数据集。我们发现，鸡群较小的站点的体型表型聚集值较高，而鸡群较大的站点的表型聚集较少。这种关系对觅食行为呈弱负面影响，对分类学相关性没有统计学意义。与大多数单一物种群体不同，混合物种群体中的参与者似乎能够在不同的特征相似轴上分开。他们可以从一个轴上的相似性中获益，同时通过在其他轴上的不同来减轻竞争。与我们的结果一致，