What usually happenstance an ecosystem after a sudden catastrophic change?

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Succession occurs after sudden catastrophic change.

Explanation:

In communities, organisms occupy specific niches. These gradually evolve over time as these organisms interact with their geosphere. In ecological succession, a community may undergo several dynamic changes. These include primary succession and secondary succession- these communities eventually try to achieve equilibrium over time.

After catastrophic events, the microorganisms, primary succession occurs. Here, a colonizing species exploits a non-habitable region. These eventually make the region more habitable through nutrient cycling, weathering, etc. which ushers in secondary succession. Here, the communities become more complex with time, becoming more varied and an increasingly large food web.

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