Ecological Succesion
Succession
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Do ecosystems ever change?
Were there ALWAYS forests?
SUCCESSION is the name given to a
predictable series of changes in an
ecosystem over time
– Organisms themselves can
change the environment (ex.
Nutria burrows)
– The new environment becomes
no longer suitable for the original
group of organisms
– One set of organisms gradually
replaces another…
Forces of Change
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What factors can cause
ecosystems to change?
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Volcanoes
Floods
Hurricanes
Human activity
Disease
Drought
Fire
Stages of succession
– PIONEER stage (ex.
Moss, Water Plants)
– CLIMAX community (ex.
Mature rainforest)
Primary & Secondary
Succession
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PRIMARY Succession
– When the starting point is
an abiotic environment
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Volcano
Flood
SECONDARY
Succession
– When an existing
ecosystem is disturbed
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Fire/lightning
Disease
Hurricanes
Human activities
Ecosystem recovers after a major volcanic
eruption in Mount St. Helens
• 1973: The Mountain
Peak 10 years before
eruption
• 1983: 3 years after
eruption
• 2000: Vegetation regrowth around the
volcano
Gradual Changes
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Wetland Succession
– p36-37
– As water plants colonize, sediments are
trapped by the roots, and the ecosystem
becomes drier
– As the environment dries out, water plants
can no longer compete for resources, and
larger “land” plants colonize, which shade-out
the other plants
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Forest Succession
– Fires & tree-falls create opportunities for
different species to colonize (ex. Yellowstone
National Park)
– Tree falls create canopy gaps (sunlight comes
in, allowing other plants to colonize)
Wetland Succession
6
4
3
5
1
2
Fig 10.7 Diagram of bog
succession.
Wetland Succession
1
Wetland
Succession
Sedges and
floating plants
close over the
open water,
trapping
sediments in their
roots, and
gradually drying
out the pond.
2
3
© 2003 John Wiley and Sons Publishers
Forest Succession
Primary Succession
Transects
Because of the change in availability of sunlight and water,
there is a predictable pattern of change in the vegetation as
you walk from a field into a forest. This transitional zone
between ecosystems is called an ecotone.