The environment may be changed greatly through the activities of organisms, including humans, or when climate changes.

Although sometimes these changes occur quickly, in most cases species gradually replace others, resulting in long term changes in ecosystems.

These changes in an ecosystem over time are called ecological succession.

Ecosystems may reach a point of stability that can last for hundreds or thousands of years.

If a disaster occurs, the damaged ecosystem is likely to recover in stages that eventually result in a stable system similar to the original one

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