(noun phrase); see also Ta; The response of living systems to environmental stress, that is, their ability to adapt, varies widely from system to system and stress to stress. Typically, living systems follow some sort of catastrophe surface in response to environmental stress. The response will be continuous and typically not highly non-linear up to a point. However, beyond this point (called a threshold point), the system will undergo a radical change called a catastrophe. Such catastrophes are not necessarily negative events. Many systems take advantage of severe environmental conditions (for example pest outbreaks, fires, and windstorms) to test the survivability of the components of the system or eliminate the weak ones. Such systems have adapted to these potentially destructive perturbations to such a degree that they use them to enhance their overall health.

Reference: Kay, J, 1984, Self-Organization In Living Systems, Chapter 2, Ph.D. Thesis, Deparment of Systems Design Engineering, University of Waterloo