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Transcript
UNIT 3 Changes in Ecosystems: Ecological Succession • Ecological Succession - The Natural, gradual change in the types of species that live in an area; can be primary or secondary • Primary succession is a type of succession that occurs on a surface where no ecosystem existed before. It begins in an area that previously did not support life. – can occur on rocks, cliffs, or sand dunes. • Primary Succession begins in a place without any soil such as: – Sides of volcanoes – Landslides – Flooding • It starts with the arrival of living things such as lichens that do not need soil to survive • This is called a PIONEER SPECIES Primary Succession • Soil starts to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces. • Lichens consiss of a fungus and a photosynthetic partner growing together in a symbiotic relationship. • When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil. Primary Succession • Simple plants like mosses and ferns can grow in the new soil Primary Succession • The simple plants die, adding more organic material • The soil layer thickens, and grasses, wildflowers, and other plants begin to take over Primary Succession • These plants die, and they add more nutrients to the soil • Shrubs and tress can survive now Primary Succession • Insects, small birds, and mammals have begun to move in • What was once bare rock now supports a variety of life • Secondary succession occurs on a surface where an ecosystem has previously existed. It is the process by which one community replaces another community that has been partially or totally destroyed. • Secondary succession can occur in ecosystems that have been disturbed or disrupted by humans, animals, or by natural process such as storms, floods, earthquakes, or volcanic eruptions. Secondary Succession • Begins in a place that already has soil and was once the home of living organisms • Occurs faster and has different pioneer species than primary succession • Example: after forest fires http://www.geo.arizona.edu http://www.ux1.eiu.edu http://www.agen.ufl.edu • A pioneer species is a species that colonizes an uninhabited area and that starts an ecological cycle in which many other species become established. • Over time, a pioneer species will make the new area habitable for other species. • A climax community is the final, stable community in equilibrium with the environment. • Even though a climax community may change in small ways, this type of community may remain the same through time if it is not disturbed. Climax Community • A stable group of plants and animals that is the end result of the succession process • Does not always mean big trees – Grasses in prairies – Cacti in deserts