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

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: starting over Primary 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 Secondary 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