Ecological stability

Ecological Stability can take on any connotation in a continuum ranging from resilience (returning quickly to a previous state) to constancy (lack of change) to persistence (simply not going extinct). The precise definition depends on the ecosystem in question, the variable or variables of interest, and the overall context. In the context of conservation ecology, stable populations are often defined as ones that do not go extinct. Researchers using mathematical models of system dynamics will usually mean Lyapunov stability.


Types of ecological stability

Due to the inconsistent usage of the term stability in ecological literature, many have proposed using more specific terms.

Constancy and persistence

Observational studies of ecosystems use constancy to describe living systems that can remain unchanged.

Resistance and inertia (or persistence)

These terms deal with a system's response to some perturbation. A perturbation is any externally imposed change in conditions, usually happening in a short time period. Resistance is a measure of how little the variable of interest changes in response to external pressures. Inertia (or persistence) implies that the living system is is able to resist external fluctuations. In the context of changing ecosystems in post-glacial North America, E.C. Pielou remarked at the outset of her overview,

"It obviously takes considerable time for mature vegetation to become established on newly exposed ice scoured rocks or glacial till.... It also takes considerable time for whole ecosystems to change, with their numerous interdependent plant species, the habitats these create, and the animals that live in the habitats. Therefore, climatically caused fluctuations in ecological communities are a damped, smoothed-out version of the climatic fluctuations that cause them."

Resilience, elasticity and amplitude

Resilience is the tendency of a system to return to a previous state after a perturbation. Elasticity and Amplitude are measures of resilience. Elasticity is the speed with which a system returns. Amplitude is a measure of how far a system can be moved from the previous state and still return. Ecology borrows the idea of neighbourhood stability and a domain of attraction from dynamical systems theory.