"A certain area within a channel may function as a “gate”; the constellation of the forces before and after the gate region is decisively different in such a way that the passing or not passing of the unit through the whole channel depends to a high degree upon what happens in the gate region. This holds not only for food channels but also for the travelling of a news item through certain communication channels in a group, for movement of goods, and the social locomotion of individuals in many organizations."