Communities in Transition

Ecological Succession – The replacement of
one community by another until a climax
community is reached

May take hundreds or thousands of years

Each new community makes it harder for the
old communities to survive.

New environmental conditions allow one group
of species in a community to replace other
groups.

All communities change their structure and
composition in response to changing
environmental conditions.

During succession:
 Pioneer species arrive first.

(Examples only – Write what will help you)

A forest hundreds of years old may have been
a shallow lake thousands of years ago.

A dead tree falls and allow sunlight to reach
the forest floor. Sunlight allows seeds to
germinate. Wildflowers and shrubs grow.

Moss, shrubs, and small trees cover the
concrete of an old city building.

Pioneer Species – The first organisms to
colonize any newly available area and begin
the process of ecological succession.
 The pioneer organism will alter the environment
so that a bigger and better organism can move in.

Climax Community – A final and stable
community.


A climax community can only be disrupted by
a catastrophe.
After the catastrophe it will then rebuild itself
back up again.

Primary Succession – Succession that occurs
on a surface where an ecosystem did not
previously exist

Secondary Succession – Succession that
occurs on a surface where an ecosystem had
previously existed.
Starting from Scratch
Exposed
rocks
Lichens
and mosses
Fig. 7-11, p. 156

DEFINITION: Succession that occurs on a surface
where an ecosystem did not previously exist
 Examples: Bare rock, newly cooled lava, abandoned
highway or parking lot

Takes a long time because there is no fertile soil
to provide the nutrients needed to establish a
plant community.

Begins when pioneer species arrive and attach
themselves to bare rock.
 Examples of pioneer species: Lichens and mosses
Exposed
rocks
Lichens
and mosses
Fig. 7-11, p. 156
Starting Over With Some Help

Succession that occurs on a surface where an
ecosystem had previously existed.
 Examples: Abandoned farmland, burned/cut
forests, heavily polluted streams, and land that
has been flooded

New vegetation can usually germinate within
a few weeks from seeds in the soil and those
brought in from nearby plants by wind or by
birds and other animals.

Secondary succession occurs in ecosystems
that have been disturbed or disrupted by
humans, animals, or natural processes.
Fig. 7-12, p. 157
Secondary Succession: Post-fire
Secondary Succession: Old Field
Secondary Succession: Post-Volcano