Human impacts are dramatically altering our natural ecosystems but the exact repercussions on ecological sustainability and function remain unclear. As a result, food web theory has experienced a proliferation of research seeking to address these critical areas. Arguing that the various recent and classical food web theories can be looked at collectively and in a highly consistent and testable way, this book synthesizes and reconciles modern and classical perspectives into a general unified theory. The book brings together outcomes from population-, community-, and ecosystem-level approaches under the common currency of energy or material fluxes. It shows that these approaches—often studied in isolation—all have the same general implications in terms of stability of the population dynamics. Specifically, increased fluxes of energy or material tend to destabilize populations, communities, and whole ecosystems. With this understanding, stabilizing structures at different levels of the ecological hierarchy can be identified and any population-, community-, or ecosystem-level structures that mute energy or material flow also stabilize systems dynamics. The book uses this powerful general framework to discuss the effects of human impact on ecological stability and sustainability, and it demonstrates that there is clear empirical evidence that the structures supporting ecological systems have been dangerously eroded. Uniting the latest research on food webs with classical theories, this book will be a standard source in the understanding of natural food web functions.