ABSTRACT
Chapter 23 asks the question, what regulates flow of energy and cycles of matter in ecosystems. To begin, a distinction is made between open and closed systems, with closed receiving no input from the outside. The world is green hypothesis by Hairston, Smith, and Slobotkin is then reviewed, presenting a top-down explanation for why plants proliferate on Earth despite the prevalence of herbivores. Building on this in the 1960s was a debate on whether eutrophication in lakes could best be controlled by adding predators at the top or by controlling nutrients at the bottom of a food chain. Ultimately, top predators can influence the ecosystem in pelagic conditions, but within the confines of the stoichiometry of a lake. For terrestrial situations forests are more of a shifting mosaic of patches in different successional stages than a climax forest. Ecosystems are open, they are not homogeneous, and some are vulnerable to regime changes.
