Download Chapter 5.3

How Ecosystems Change
Grade 10
Biology
Spring 2011
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Do ecosystems change or do they remain
constant?
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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
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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
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Primary Succession: occurs on a surface
where no ecosystem existed before
◦ Such as rocks or sand dunes
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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
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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
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Climax Community: final and stable
community
◦ Continues to change in small ways
◦ May remain the same through time if it is not
disturbed
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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
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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
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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
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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