The Ecology of Environmental Association: Density, Spillover, Competition, and Membership in Sierra Club, 1984-2016

ABSTRACT What factors affect the size of advocacy organizations? Some theories suggest that the existence of political opportunities, resources, and grievances in a locality influences advocacy organization size. In this article, we advance an ecological approach to the study of advocacy organizations, arguing that the presence of other collective actors in a locality may also impact the size of advocacy organizations. Analyzing cross-sectional, time-series data on membership in the Sierra Club from 1984 to 2016, we find evidence for the positive role of environmental organization density, but the deleterious effects of competition from labor unions and a state’s Republican Party, on the number of Sierra Club members in a state. Furthermore, we report mixed evidence that a state’s economic resources and environmental grievances affect membership in the Sierra Club. The findings hold significant implications for the study of advocacy organizations, social movements, and contentious politics more generally.