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3.3
How Ecosystems Change
Succession

Regular pattern of changes over time
in the type of species in a community
– hundreds/thousands of yrs
– each new comm. makes it hard for previous
one to survive

Climax Community: eventually forms if
the land is left undisturbed
Secondary Succession

Occurs on a surface where an
ecosystem has previously existed
– burned areas around Mount St. Helens
– FIG 3-14

Pioneers: 1st organisms to colonize any
newly available area and start the process
of succession
Secondary Succession

Pioneers:
– FIG 3-16
– farmer stops cultivating a field
Secondary Succession

Natural fires caused by lightning are a
necessary part of secondary succession in
some communities
– remove accumulation of brush/deadwood
– species feed on vegetation after fire
Primary Succession

Occurs on surfaces where no
ecosystem existed before
– new islands created by volcanoes
– areas where glacier retreats
Primary Succession

Begins where there is no soil

Takes several hundred-thousand yrs

Lichens form first; FIG 3-17
– Fungus/Algae that have a mutualistic
relationship
– Breaks up rock
Primary Succession

Soil forms when:
– mosses decay
– dust particles in air are trapped
– dead organisms accumulate

Primary Succession also occurs on city
streets
– mosses, lichens in cracks of sidewalks