Data from: Positive relationships between association strength and phenotypic similarity characterize the assembly of mixed-species bird flocks worldwide

Competition theory predicts that communities at small spatial scales should consist of species more dissimilar than expected by chance. We find a strikingly different pattern in a multi-continent dataset (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, important subunits of local bird communities the world over. Using null models and randomization tests followed by meta-analysis, we find the association strength of species in flocks to be strongly related to similarity in body size and foraging behavior, and higher for congeneric compared with non-congeneric species pairs. Given the small spatial scale of our individual analyses, differences in habitat preferences of species are unlikely to have caused these association patterns; therefore, the patterns are most likely the outcome of species interactions. Extending group-living and social information use theory to a heterospecific context, we discuss potential behavioral mechanisms leading to positive interactions among similar species in flocks as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.

竞争理论预测：小空间尺度下的群落，其组成物种的相异性应显著高于随机预期水平。我们在一项跨大洲数据集（涵盖全球24个采样点的55张物种出现-缺失矩阵）中，针对全球各地本地鸟类群落的重要组成单元——混合物种类鸟群（mixed-species bird flocks）的组成模式，发现了截然不同的结果。我们借助零模型（null model）、随机化检验（randomization test）结合元分析（meta-analysis）方法，发现鸟群内物种的关联强度与体型大小和觅食行为的相似性显著相关；同物种种对的关联强度显著高于非同属（non-congeneric）物种种对。由于我们的单次分析均基于小空间尺度，物种的生境偏好差异不太可能解释上述关联模式，因此该模式极大概率源于物种间的相互作用。我们将集群生活与社会信息利用理论拓展至异种（heterospecific）情境，探讨了驱动鸟群内相似物种种间正向互作的潜在行为机制，以及物种降低竞争成本的具体途径。我们的研究结果表明，在解释群落构建（community assembly）机制时，需同时关注物种间的正向互作与竞争关系。