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Science 20: Unit D – Living Systems Changing Populations
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Ecological Succession Ecological succession is a community change in which new populations of organisms gradually replace existing ones. Succession occurs from natural causes (competition, fire, earthquakes, etc) or due to man (logging, mining, farming etc).
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Primary Succession Primary succession-succession that begins in an area where there is no existing community. Causes of primary succession: volcanic eruption, glacier retreat. Primary Succession Animation
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The first group of organisms to occupy an area in primary succession is called a pioneer community. Pioneer organisms must be hardy and able to live on minimal resources. Lichens are pioneer organisms; humus is the organic component of soil created from decomposing organisms.
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Steps in Primary Succession: Glacier Retreats exposing Parent rock Pioneer community (lichens, mosses) Soil formation (lichens die/ break up rock) Enough soil = grasses out compete lichens Grasses die = more soil = shrubs and weeds take over Increased soil = shallow rooted trees (pine) Increased pine = more shade = favorable for deeply rooted plant (maple/ birch) Climax Community *Climax community is the stable community that results.
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Primary Succession:
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Occurs when water collects in a basin; algae starts to grow; eggs are planted in water; fish hatch and attract birds to the water. Nutrients from runoff create soil for plants to grow; plants grow on edge (cattails). When lots of plants overtake water = terrestrial ecosystem. Aquatic Succession
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Secondary Succession Secondary succession: occurs in an area where an existing community has been partially destroyed. Examples: Fires, logging, farming Occurs more rapidly then primary succession A community that achieves relative stability is called a climax community. Climax communities tend to have greater species diversity than the communities that precede them.
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http://www.geowords.org/ensci/imagesbook/ 04_03_succession.swf
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Question: Why are there prescribed burns? Is this a good thing?
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Prescribed burns:
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Assignment Please complete the following: – Environmental changes and succession worksheet.
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