Transcript Succession - Science

What is ecological
succession?
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The gradual change of the type of species
that line in an area.
Explain the difference
between primary and
secondary succession.
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Primary succession begins on rock.
Secondary succession begin on soil.
What is the difference between
pioneer species and climax
communities?
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Pioneer species are the first species that
settle or colonize an area.
Climax communities are made of species
that are stable and don’t change very
much.
Rosie heard about an ecosystem that was a
climax forest community before a devastating fire
occurred 50 years ago. She wants to know if the
forest is again a climax community, so she
makes some observations about the ecosystem.
– Explain what is meant by a climax community.
– Describe three observations that would
indicate that the forest Rosie is observing has
been restored to equilibrium.
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A climax community is the last stage in
succession, a stage where an ecosystem
reaches a stable state. It is a mature
ecosystem.
One clue is that a wide variety of plants have
had time to move into the area. There could be
grasses, shrubs, mosses, and other plants.
Another clue to look for is mature trees. These
are the last type of plants to move into an
area.
The rate of change in species is also a clue.
Climax communities are stable. So, there
should be little if any change in the mix of
species.
A large area of bare rock becomes exposed by a
glacier that has retreated.
– Describe the changes that occur in the
organisms living in the area as the bare rock area
is transformed into a forest over time in four
distinct steps. Each step you describe should
include the organisms that live in the area and
how those organisms change over time.
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The process begins when a pioneer species, such as lichens, colonize the
rock. Lichens can grow in areas that lack nutrients and are exposed to
harsh conditions. The growth of lichens attracts microscopic plants and
animals. The lichens produce materials that dissolve the surface of the
rock, thereby beginning the process in which soil forms. Eventually, the
lichens die. As they decompose, they add nutrients to the soil.
As the soil builds up, organisms such as bacteria, mosses, worms, and
insects can inhabit the region. Eventually the soil is able to support small
plants, such as weeds and plants that die after one growing season
(annuals). These small plants crowd out and replace the moss and
pioneer communities.
In time, the small plants die. As they decay, the soil layer becomes
thicker and richer in nutrients. This makes it able to support grasses,
woody shrubs, and plants that live many years (perennials). In time, the
shrubs crowd out the grasses.
Eventually, trees take root and crowd out the shrubs. Over the course of
many years, the bare rock has been transformed into a forest. Many
different types of animals live in the forest. The organisms of the forest
make up a stable climax community, which can exist for many years.
Diagram the stages of primary
succession.
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