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Transcript
Changes in Ecosystems: Ecological Succession Ecological Succession • Ecosystems are constantly changing in response to natural and human disturbances. • As an ecosystem changes, older inhabitants gradually die out and new organisms move in, causing further changes in the community. – Ecological Succession – Series of predictable changes that occurs in a community over time Some Causes of Ecological Succession • Can result from slow changes in the physical environment or from sudden disturbances (either natural or man made). – Some causes include: 1. Clearing land 2. Climate change 3. Introduction of nonnative species 4. Natural disasters such as volcanic eruptions, forest fires, hurricanes, & floods Succession: • Natural, gradual changes in the types of species that live in an area; can be primary or secondary • The gradual replacement of one plant community by another through natural processes over time Primary Succession • Begins in a place without any soil – Sides of volcanoes – Landslides – Flooding • Starts with the arrival of living things such as lichens that do not need soil to survive • Called PIONEER SPECIES http://botit.botany.wisc.edu http://www.saguaro-juniper.com/ Primary Succession • Soil starts to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces • When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil http://www.life.uiuc.edu Primary Succession • Simple plants like mosses and ferns can grow in the new soil http://www.uncw.edu http://uisstc.georgetow n.edu Primary Succession • The simple plants die, adding more organic material • The soil layer thickens, and grasses, wildflowers, and other plants begin to take over http://www.cwrl.utexas.edu Primary Succession • These plants die, and they add more nutrients to the soil • Shrubs and tress can survive now http://www.rowan.edu Primary Succession • Insects, small birds, and mammals have begun to move in • What was once bare rock now supports a variety of life http://p2-raw.greenpeace.org Mount St. Helen Before Eruption in 1980 Mount St. Helen 6 Years After Eruption Mount St. Helen After Eruption Mount St. Helen 10 Years After Eruption Mount St. Helen 19 Years After Eruption Secondary Succession • Begins in a place that already has soil and was once the home of living organisms • A disturbance of some kind changes an existing community • Occurs faster and has different pioneer species than primary succession • Example: after forest fires http://www.geo.arizona.edu http://www.ux1.eiu.edu 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