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An overview of ecological succession, a process of predictable changes in a community over time after disturbances. It discusses primary and secondary succession, the role of pioneer species, and the impact of natural and human-caused disturbances on ecosystems. The document also explores the concept of climax communities and the importance of studying succession patterns.
Typology: Summaries
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How do communities change over time?
Ecosystems change over time, especially after disturbances, as some species die out and new species move in.
Volcanic explosions can create new land or sterilize existing areas.
Retreating glaciers can have the same effect, leaving only exposed bare rock behind them.
Succession that begins in an area with no remnants of an older community is called primary succession.
For example, in Mount Saint Helens, Washington, an erupting volcano decimated all nearby living organisms.
Changes in this community will continue for centuries.
Mt. St. Helens immediately after eruption
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.
Over time, lichens convert, or fix, atmospheric nitrogen into useful forms for other organisms, break down rock, and add organic material to form soil.
Certain grasses are also pioneer species.
Mt. St. Helens 15-35 years post eruption
Mt. St. Helens 15-35 years post eruption
Mt. St. Helens 35-80 years post eruption
Sometimes, existing communities are not completely destroyed by disturbances. In these situations, secondary succession occurs.
Secondary succession proceeds faster than primary succession, in part because soil survives the disturbance. As a result, new and surviving vegetation can regrow rapidly.
This series shows secondary succession taking place in abandoned fields of the Carolinas’ Piedmont.
Over the last century, these fields have passed through several stages and matured into oak forests. Changes will continue for years to come.
Every organism changes the environment it lives in.
One model of succession suggests that as one species alters its environment, other species find it easier to compete for resources and survive.
For example, as lichens add organic matter and form soil, mosses and other plants can colonize and grow.
As organic matter continues to accumulate, other species move in and change the environment further.
Over time, more and more species can find suitable niches and survive.