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Changes in Ecosystems: Ecological Succession Definition: • Natural, gradual changes in the types of species that live in an area • The gradual replacement of one plant community by another through natural processes over time Examples: • A glacier recedes, leaving bare earth. First lichens colonize the area. They are eventually replaced by tundra plants and animals. • A building is demolished. Mosses, the grasses, then shrubs, and eventually trees cover the area. Types of Succession • Primary Succession – The sequence of communities that inhabit a lifeless environment. – Sides of volcanoes Types of Succession • Primary Succession – The sequence of communities that inhabit a lifeless environment. – Sides of volcanoes – Receding glacier Types of Succession • Primary Succession – The sequence of communities that inhabit a lifeless environment. – Sides of volcanoes – Receding glacier – Newly formed island Types of Succession • Primary Succession – The sequence of communities that inhabit a lifeless environment. – Sides of volcanoes – Receding glacier – Newly formed island – Abandoned parking lot Types of Succession • Primary Succession – The sequence of communities that inhabit a lifeless environment. – Sides of volcanoes – What happens after the lava cools down?? Primary Succession • PIONEER SPECIES arrive and colonize the area. • Pioneer species are able to survive in harsh environments. They can survive without soil. • Pioneers tend to thrive in areas of intense sunlight and scarce water. Primary Succession • Lichens are a common pioneer. • Lichens are a mutualistic relationship between a fungus and an algae. • The algae is photosynthetic (autotroph) and the fungus holds water and absorbs nutrients from the rocks. • Over time the lichens break down the rocks. Primary Succession • As the water freezes and thaws, it breaks the rocks up further. • Lichens die and accumulate in the cracks. • These lichens decompose and create soil. • Mosses will begin to grow on the rocks. Primary Succession • Mosses grow and die, adding to the soil. The mosses will shade the lichens, which will die out. • Eventually, enough soil will be there to support grasses and weeds. The grasses will shade out the mosses. • The grasses and weeds grow and die, increasing the depth of the soil. http://www.life.uiuc.edu Primary Succession • Shrubs and bushes will eventually replace the grasses. The grasses will be shaded out and die. • Eventually, the soil will become deep enough to support larger trees. The tall trees will shade out the shrubs and bushes. Primary Succession • The point where the ecosystem stops changing is called a climax community. • What was once bare rock now supports a wide variety of species. 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 – Sawgrass in the Everglades – Wildflowers and short trees in the tundra Primary succession can be seen happening in any lifeless area. If left alone, New York City would turn into a cement filled woodland. Primary Succession • This is a SLOW process. It may take hundreds of years for the ecosystem to go through all of the stages of primary succession. • Each community alters its environment. Those alterations make it possible for the new community to take over. 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 Secondary Succession • The pioneer would be grasses and weeds. • The changes in the ecosystem would follow the same sequence we saw in primary succession. • However, the progression from pioneer to climax community would occur much faster. http://www.ux1.eiu.edu Fires • Fires are a natural part of many ecosystems. – They clear out underbrush, leaving rich ash behind. – Some species of trees need fire for their seeds to germinate. Slash Pines Subclimax community Secondary Succession • Example: – after a forest fire – after a flood Secondary Succession • Example: – after a forest fire – after a flood – after a hurricane Secondary Succession • Example: – after a forest fire – after a flood – after a hurricane – An abandoned field or building