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Lesson OverviewLesson Overview4.3 Succession4.3 Succession

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Primary and Secondary SuccessionEcological succession a series of predictable changes that occur in a community over time. Ecosystems change over time, after disturbances, as some species die out and new species move in.

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Succession that begins in an area with no remnants of an older community is called primary succession.

Some disturbances that are followed by primary succession:Volcanic explosions create new land or sterilize existing areas. Retreating glaciers leaving only exposed bare rock behind them.

Retreating glaciersVolcanic explosions

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Primary Succession

Ex., in Glacier Bay, Alaska, a retreating glacier exposed barren rock. Over the course of more than 100 years, a series of changes has led to the hemlock and spruce forest currently found in the area. Changes in this community will continue for centuries.

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Primary Succession

The first species to colonize barren areas are called pioneer species. One ecological pioneer that grows on bare rock is lichen—a mutualistic symbiosis between a fungus and an alga.

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Secondary Succession

Secondary succession where existing communities are not completely destroyed by disturbances. Secondary succession proceeds faster than primary succession, because the soil survives the disturbance.

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Secondary Succession

Secondary succession often follows a wildfire (fires can stimulate seeds to grow)hurricane, or other natural disturbance. human activities like logging and farming.

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Why Succession Occurs Every organism changes the environment it lives in. When one species alters its environment, other species find it easier to compete for resources and survive. Ex. as lichens add organic matter and form soil, mosses and other plants can colonize and grow, other species move in and change the environment further.