  A general theory of top-down cascades in complex networks is described which
explains two similar types of perturbation amplifications in the complex
networks of business supply chains (the `bullwhip effect') and ecological food
webs (trophic cascades). The dependence of the strength of the effects on the
interaction strength and covariance in the dynamics as well as the graph
structure allows both explanation and prediction of widely recognized effects
in each type of system.
