the tendency of the variables or components of a system to remain within defined and recognizable limits despite the impact of disturbances. (Young, p. l09) (expanded or global stability) The ability of a system to persist and to remain qualitatively unchanged in response either to a disturbance or to
fluctuation s of the system caused by a disturbance. This idea of stability combines the concepts of traditional stability and Holling's new concept of
resilience. (Holling) The capacity of an object or system to return to equilibrium after having been displaced. Note with two possible kinds of equilibrium one may have a static (linear) stability of rest or a dynamic (nonlinear) stability of an endlessly repeated motion. (Iberall) a system is stable if, when perturbed, it returns to its original state. The more quickly it returns, the more stable it is.
A property of a
system 's
behavior when its
equilibrium is disturbed. Equilibria may be unstable, neutral or stable. An illustration of the three types is provided by a ball respectively balanced on a ridge, placed on a flat and level surface and in a concave hole. The three types differ in response to displacements. An unstable equilibrium requires hardly any disturbance to be lost, typically forever, e.g., the state of a volatile fluid, the beginning of a competitive game, equality among human interactors. A neutral equilibrium is arbitrary or non-preferential, whereas a stable equilibrium is such that a system returns to it after the displacing disturbance is removed. E.g., in wartime, civil liberties,
production of consumer goods and
communications may be restricted only to be restored after hostilities cease. This marks a stable equilibrium. However, if these restrictions persist despite the absence of war this would indicate that the equilibrium was neutral. Equilibria are stable only relative to the magnitude of the disturbance. If a disturbance exceeds the threshold of a stable equilibrium, it may bring the system to another (unstable, neutral or stable) equilibrium (
see polystability, ultrastability ).
adaptation is a higher form of stability in which a stable equilibrium is maintained or regained in the face of disturbances that attempt or temporarily displace the equilibrium. (
Krippendorff )
