Social relations are embedded in material, cultural, and institutional settings that affect network dynamics and the resulting topologies. For example, romantic entanglements are subject to social and cultural norms, interfirm alliances are constrained by country-specific legislation, and adolescent friendships are conditioned by classroom settings and neighborhood effects. In short, social contexts shape social relations and the networks they give rise to. However, how and when they do so remain to be established. This paper presents network ecology as a general framework for identifying how the proximal environment shapes social networks by focusing interactions and social relations, and how these interactions and relations in turn shape the environment in which social networks form. Tie fitness is introduced as a metric that quantifies how well particular dyadic social relations would align with the setting. Using longitudinal networks collected on two cohorts each in 18 North American schools, i.e., 36 settings, we develop five generalizable observations about the time-varying fitness of adolescent friendship. Across all 252 analyzed networks, tie fitness predicted new tie formation, tie longevity, and tie survival. Dormant fit ties cluster in relational niches, thereby establishing a resource base for social identities competing for increased representation in the relational system.

Keywords: Coevolution; Dynamics; Interactions; Network ecology; Network theory; Relational; Relational niches; Tie fitness; Timescale separation.

社交关系嵌入于物质、文化和制度环境中，这些环境影响着网络动态及其产生的拓扑结构。例如，浪漫纠葛受社会和文化规范的影响；企业间的联盟受到特定国家法律的限制；青少年友谊则由教室设置和邻里效应所决定。简而言之，社会背景塑造了社交关系以及由此产生的网络。然而，它们如何及何时产生这种影响仍需进一步明确。本文提出了一个一般框架——网络生态学，用于识别近端环境是如何通过聚焦互动与社交关系来形成社交网络的，以及这些互动和关系又如何反过来影响社交网络形成的环境。文中引入了“关系适应度”作为衡量特定二元社会关系在多大程度上符合设置情况的标准。通过对北美18所学校中两个年级的学生进行纵向研究收集的数据，即36个环境下的数据，我们得出了关于青少年友谊随时间变化的适应性的五项可推广观察结果。在所有252个分析网络中，“关系适应度”预测了新关系的形成、关系持久性和关系生存能力。“休眠适配关系”聚集于关系生态位，从而为争夺在关系系统中更大表示的社会身份建立了资源基础。

关键词：协同进化；动态性；互动；网络生态学；网络理论；关系；关系生态位；关系适应度；时间尺度分离。