种间合作行为的演化维持机制是社会行为学和进化生物学研究的核心问题之一。鸟类混合群作为典型的社会合作组织，是开展群落构建与适应进化研究的理想模型系统，但基于竞争排斥的相似性限制假说无法解释混合群中众多近缘种的互利共栖现象。本项目拟在资源竞争理论上引入正相互作用研究，从种间合作策略、局域生态选择和区域谱系进化三个层次检验混合群构建成因及合作均衡假说：1）鸟类集群采取“竞争+合作”非对称混合策略，其均衡状态受“遗传相似性”、“互惠系数”与“资源胁迫”的影响；2）正相互作用提高多物种群落的丰富度与共存时间，种间关联强度与表型相似性显著相关，且在胁迫条件下具种群密度调节功能；3）历史进化过程中的种间共存，由生境过滤和竞争排斥对功能性状的共同约束所导致，正相互作用能驱动群落谱系结构从聚集转变为发散。研究结果可丰富动物社会组织的合作共存理论，对胁迫环境下生物多样性保护、生态修复提供科学指引。

Explaining the evolution of cooperation remains one of the central topics in both biology and social science. As a characteristic feature of social organization of forest avifauna, mixed-species bird flocks represent an adaptive advantage of community assembly process, which result from an interaction between ecological and evolutionary effects. However, the mutualism pattern of phenotypic similar species can not be explained by the limiting similarity hypothesis and niche differentiation, especially for mixed flocks. The present study will incorporate positive interactions into main stream competition theories, and testify community assembly rules and equilibrium stable strategies based on interspecific cooperation, ecological selection and evolutionary processes. Specifically, (I) interspecific facilitation and competition collectively attribute to the interacting species, and the equilibrium of cooperation system are affected by genetic similarity, mutualism index and environmental stress; (II) positive interactions can increase the diversity and coexistent lifetime of flocking community, while the association strengths to be strongly related to phenotypic similarity for congeneric species pairs, and determine population dynamics under stress conditions; (III) the evolution of interspecific social cooperation are jointly constrained by habitat filtering and competition exclusion at regional scales, while processes structuring local flocking assemblages were better explained by positive interaction and traits dispersion. The study will enhance understanding of the cooperation strategies and community assembly rules for animal social organization, and contribute to biodiversity conservation and ecological restoration under environmental stress in practice.