  Complex systems are often characterized by large-scale hierarchical
organizations. Whether the prominent elements, at the top of the hierarchy,
share and control resources or avoid one another lies at the heart of a
system's global organization and functioning. Inspired by network perspectives,
we propose a new general framework for studying the tendency of prominent
elements to form clubs with exclusive control over the majority of a system's
resources. We explore associations between prominence and control in the fields
of transportation, scientific collaboration, and online communication.
