Download Ecological Succession

Changes in Ecosystems:
Ecological Succession
Succession Definition:
• Natural, gradual changes in the types
of species that live in an area; can be
primary or secondary
• The gradual replacement of one plant
community by another through natural
processes over time
What is Succession?
• Succession is the series of predictable
changes that occur in a community
over time.
• A community is all the different
organisms that live together.
– A community in an ecosystem is in
equilibrium, or a state of balance, when the
numbers and species of organisms in it do
not change suddenly.
What causes succession?
• Fires
• Volcanoes
• Floods
• Hurricanes
Types of Succession!!
• After a disaster, succession helps an
ecosystem recover. There are two Main
types of ecological succession:
– Primary succession
– Secondary succession
Primary Succession
• Begins in a place without any soil
– Sides of volcanoes
– glaciers melting away
• Starts with the arrival of living things such
as lichens and moss that do not need soil
to survive Called PIONEER SPECIES
Primary Succession
• Primary Succession - series of changes that occur
in an area where no ecosystem previously existed.
– Example: An area might be a new island formed by the
eruption of an undersea volcano
– Example 2: An area of rock uncovered by a melting
sheet of ice.
• The first species to populate the area are called
Pioneer Species.
– Lichens and mosses – carried by the wind or water
Primary succession - occurs on an area of newly exposed
rock, sand, or lava or any area that has not been occupied
previously by a living (biotic) community
Glaciers scrape the Earth as it moves.
Some land may have been buried
under ice for thousands of years.
Rocks are carried along by the ice.
As the glacier melts, the rocks are
left behind. After about a year,
lichens begin to grow on the rock
surface. Lichens slowly break the
rock down.
Primary succession areas have no
soil.
Changes by Fire
Volcanoes create new land on which primary
succession occurs.
Primary Succession
• Soil starts to form as lichens and the
forces of weather and erosion help
break down rocks into smaller pieces
• When lichens die, they decompose,
adding small amounts of organic
matter to the rock to make soil
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Primary Succession
• Simple plants like grasses, mosses and
ferns can grow in the new soil
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Primary Succession
• The simple plants die, adding more
organic material
• The soil layer thickens, and grasses,
wildflowers, and other plants begin to
take over
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Primary Succession
• These plants die, and they add more
nutrients to the soil
• Shrubs and trees can survive now
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Primary Succession
• Insects, small birds, and mammals
have begun to move in
• What was once bare rock now supports
a variety of life
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Primary Succession
Climax Community - is a community of organisms in
equilibrium, which does not change drastically unless
the ecosystem is disturbed.(The final step in the process)
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, flooding etc.
Secondary Succession
• Secondary Succession- the series of changes
that occur after a disturbance in an EXISTING
ecosystem.
– Unlike primary succession, secondary
succession occurs in a place where an
ecosystem has previously existed.
– Secondary succession restores the
ecosystem to a state in which equilibrium can
be maintained.
• occurs somewhat more rapidly than
primary succession.
Changes by Fire
Forest fires create the opportunity
for secondary succession.
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Secondary succession - takes place where a
community has been removed, e.g., in a plowed field or
a clear-cut forest or fire.
Pioneer Community
The pioneer community is made up of grasses.
Insects, small mammals and reptiles make their home
here. If the soil has been disturbed, weeds are the
first plants to grow. They secure the soil.
Shrubs and bushes begin to grow. Other mammals,
such as rabbits and birds, join the developing
community.
A climax community of trees can support a wide
variety of larger mammals such as foxes and badgers.
Climax Community
Weeds appear first, followed by grasses. The next to appear are shrubs, then a pine
forest. The mature hardwood oak and hickory trees form the climax community. This is
the last stage of succession. These are plants that can reproduce successfully beneath
their own shade and can maintain the community indefinitely if conditions don’t change.
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
Wrap Up!
• Succession occurs when
a disaster occurs and
disturbs the equilibrium of
a community.
• There are two types of
succession:
– Primary Succession occurs
where no previous
ecosystem exists and
establishes equilibrium.
– Secondary Succession
occurs after a disturbance
and restores equilibrium in
an already existing
ecosystem.
• Vocabulary:
– Community
– Equilibrium
– Succession
– Primary Succession
– Pioneer Species
– Secondary
Succession