Ecological stability is a concept which is mainly based on theoretical considerations and approaches. More recently, it is used in the context of human impacts on ecosystems. A number of different terms, for example constancy, inertia, resistance, elasticity, resilience, and metastability, are used to describe the static and dynamic behaviour of diverse ecological systems. These are derived from mechanical analogies.
The properties of stable ecosystems are based on theories and field observations. Stable systems are described as being (a) relatively simple in community structure, (b) undergo random disturbances to avoid fixed interactions, and (c) are differentiated in space and time in their abiotic and biotic components. These criteria are discussed in relation to different properties of aquatic ecosystems for example complexity of community structure, predictability of the environment, composition of the habitat and special features of species. Examples of natural aquatic ecosystems are used to discuss predictions based on theoretical considerations and on models.
There are difficulties to reconcile theories and practical needs. They can be partially solved if the concept of stability is applied to components of an ecosystem and not to the whole system. For whole ecosystems, long-term field investigations and careful systems analyses are necessary.