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Changes in Ecosystems: Ecological Succession EQ: How do communities change over time? Succession is… • a series of predictable changes in types of species that occurs in a community over time • Two types: primary and secondary Primary Succession • Occurs on surfaces where no soil exists • Events which expose bare rock: – volcanoes – flooding – glaciers • Begins with arrival of organisms such as lichens that do not need soil • Lichen are the pioneer species (first organisms to arrive in an area) Primary Succession • Soil starts to form as lichens, weathering, and erosion break down rocks into smaller pieces • When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil • Over time, the soil layer thickens, and grasses, wildflowers, and other plants begin to take over Primary Succession • In time insects, birds, and mammals move in • What was once bare rock now supports a variety of life, including trees Secondary Succession • Occurs in an area with soil that contains seeds, spores, roots, or other plant parts • Events that destroys most of an ecosystem • forest fire • harvesting • Hurricane • Happens faster and weeds are a typical pioneer species in secondary succession Secondary Succession http://www.ux1.eiu.edu/~cfruf/bio3002/secondary_succession.htm Climax Community • Climax Community = mature community made up of plants and animals • Does not always mean big trees – tall grasses in prairies – cacti in deserts • Species can continue to change in response to climate and other factors Succession: summary Primary Secondary • No soil is available and must be created by pioneer species • Lichens are usually the pioneer species • Usually the result of a volcano or glacier • Soil is still available and pioneer species can take root • Weeds/plants are usually the pioneer species • Usually the result of a forest fire or hurricane