Of the various aspects of stability, an initial distinction can be made between the resilience of a community (or any other system) and its resistance. Resilience describes the speed with which a community returns to its former state after it has been perturbed and displaced from that state. Resistance describes the ability of the community to avoid displacement in the first place. (Figure 20.7 provides a figurative illustration of these and other aspects of stability.)
The second distinction is between local stability and global stability. Local stability describes the tendency of a community to return to its original state (or something close to it) when subjected to a small perturbation. Global stability describes this tendency when the community is subjected to a large perturbation.
A third aspect is related to the local/global distinction but concentrates more on the environment of the community. The stability of any com munity depends on the environment in which it exists, as well as on the densities and characteristics of the component species. A community that is stable only within a narrow range of environmental conditions, or for only a very limited range of species' characteristics, is said to be dynamically fragile. Conversely, one that is stable within a wide range of conditions and characteristics is said to be dynamically robust.
Lastly, it remains for us to specify the aspect of the community on which we will focus. Ecologists have often taken a demographic approach. They have concentrated on the structure of a community. However, it is also possible to focus on the stability of ecosystem processes, especially productivity.
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