Transcript Chapter 5.3
How Ecosystems Change Grade 10 Biology Spring 2011 Do ecosystems change or do they remain constant? List two types of ecological succession Explain how a pioneer species contributes to ecological succession Explain what happens during old-field succession Describe how lichens contribute to primary succession Ecological Succession: gradual process of change and replacement of some or all of the species in a community ◦ May take hundreds or thousands of years Primary Succession: occurs on a surface where no ecosystem existed before ◦ Such as rocks or sand dunes Secondary Succession: occurs on a surface where an ecosystem has previously existed ◦ More common ◦ Can occur in ecosystems that have been disturbed or disrupted by humans, animals, or natural disasters Mount St. Helens example Pioneer species: first organisms to colonize any newly available area and begin the process of ecological succession ◦ Will make new area habitable for others Climax Community: final and stable community ◦ Continues to change in small ways ◦ May remain the same through time if it is not disturbed Natural fires caused by lightening are a natural cause of secondary succession Jack pine can only release seeds after they have been exposed to intense heat of fire Minor forest fires remove accumulation of brush and deadwood Some animals depend on fires for vegetation that sprouts after An example of secondary succession Old field succession: occurs when farmland is abandoned Grasses and weeds grow quickly Taller plants, such as grasses Pioneer plants soon die from lack of sunlight and water Taller plants get deprived of light and water by growing trees Slower growing trees take over and block sunlight to smaller trees Primary Succession: occurs in an area not previously supported by life Much slower than secondary succession because begins where there is no soil First pioneer species: bacteria or lichen Lichen: producer that is actually composed of two different species, a fungus and alga ◦ Alga photosynthesize, fungi absorbs nutrients from rocks and holds water ◦ They begin to break down rock, helping trap soil