Using a 22 -year study of an elite university's faculty networks and their work activities, we extend network ecology to concern top -down processes of environmental selection and bottom -up processes of individual adaptation. We argue that faculty enact distinct types of collaborative work activity that are central to their role: research training (co -advising), publishing (co-authoring), and financing (co -granting). STEM (hard science) and HSS (humanities and social science) cultures train and expect their members to perform these activities in different ways reflective of distinct networking styles. STEM faculty anchor their work relations in grants and extend those relations liberally to advising and publishing collaborations, forming an egalitarian interdisciplinary network reflective of a guild system. HSS faculty anchor their work relations in advising and layer and extend their ties locally around star faculty to form a restrictive patronage system. However, individual faculty vary in their adherence to these styles, and those adopting the STEM style of networking are more likely to survive in the university and achieve tenure. New faculty increasingly learn and adapt to this, and the STEM model increasingly diffuses and transforms the university social structure, illustrating the salience of top -down and bottom -up processes of network ecology in explaining social structural change.