Phase Transitions

(Chapters 9, 12, 13, 14 & 16) Ecosystems are complex and adaptive, displaying nontrivial forms of organization in both space and time. An important component of change in ecological systems involves the rapid response of some communities to slow changes in external variables. It has been shown in different contexts that constant changes in water availability, decline of some plant or fish species or increasing temperatures can trigger sudden changes in ecosystem organization. The outcome of such changes is often a shift from one stable state to another. This can affect a large geographic area, as happened with the transition from green to desert in the Sahara, and discussed in chapter 3. Such changes are the result of nonlinearities coupling external inputs and internal responses. In terms of dynamical systems, populations can shift suddenly from one state to another as a limiting input parameter changes beyond some given threshold. A perfect illustration of the type of sudden changes that can occur in complex ecosystems is provided by the dynamics of semiarid vegetation.

Read