Transcript Succession: Equilibrium in Ecosystems

Succession: Equilibrium in
Ecosystems
What Happened
Here?
The two
photographs
at the right
show the
same area in
Yellowstone
National
Park in
Wyoming.
Photograph
A was taken
soon after a
major fire.
Photograph
B was taken
a few years
later.
Observe the
photographs
carefully.
What are all the
differences
you notice
between the
two scenes?
• A community is all the different organisms
that live together in an area.
• 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.
• Events such as fires, floods, volcanoes,
and hurricanes disrupt the equilibrium of a
community by changing it drastically in a
very short time.
Succession- What is it?
• Succession is the series of predictable
changes that occur in a community over
time. After a fire, volcano, or other
disaster, succession enables an
ecosystem to recover. There are two main
types of succession: primary and
secondary.
Primary Succession
Primary succession is the series of changes that occur in an area
where no ecosystem previously existed.
For example: a new island formed by the eruption of an undersea
volcano, or an area of rock uncovered by a melting sheet of ice.
The first species to populate the area are called pioneer species.
Pioneer species are often lichens and mosses carried to the area by
wind or water. These species can grow on bare rocks with little or no
soil. As these organisms grow, they help break up the rocks. When
they die, they enrich the thin layer of soil that is forming.
As the soil gets richer and richer, new plant species will grow. Over
time primary succession may lead to a community of organisms
in equilibrium, which does not change drastically unless the
ecosystem is disturbed. Reaching this stable community can take
centuries.
Prentice Hall
Secondary Succession
Secondary succession is the series of changes
that occur after a disturbance in an existing
ecosystem.
Both natural and human activities can cause
secondary succession.
Examples:
• Natural disturbances: fires, hurricanes, and
tornadoes
• Human activities: farming, logging, or mining
• Prentice Hall
Succession in Action
http://www.sparknotes.com/testprep/books/sat2/biology/chapter10section4.rhtml
Succession in a Pond
Succession in a pond follows a similar pattern.
Originally, the pond will contain protozoa, some small
fish, and algae. As individual organisms die and water
runs into the pond, sediment builds up at the bottom
and the pond grows shallower. The shallower pond
becomes marsh-like and fills with reeds and cattails.
The standing water eventually disappears, and the
land is merely moist: grasses and shrubs dominate. As
the land grows even less moist, it becomes woodland
and as trees come to dominate, the climax community
will arise from a species that
can grow in the shade of its neighbors.
http://www.sparknotes.com/testprep/books/sat2/biology/chapter10section4.rhtml
Pond Secondary Succession
Compare Primary and Secondary
Succession
•
•
Primary Succession
Happens ONLY with brand new •
areas never before colonized by
life.
Takes centuries to become a
•
stable environment at
equilibrium.
Secondary Succession
Happens ONLY with an area that was
once colonized by life, but has been
destroyed.
Takes about one century to become a
stable environment at equilibrium.
Both
Lead to a community of organisms in equilibrium.
• Pioneer species move in first, followed by a series of
vegetation which eventually leads to the "climax
forest".
• Plant types depend on the biome.
•