Succession in Ecosystems

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Transcript Succession in Ecosystems

Successiona series of changes in a
community in which new
populations of organisms
gradually replace existing ones
Succession Vocabulary
Pioneer species—first species to appear in
primary succession. Usually lichens and mosses.
Climax community—the final stage in a
succession. The plants tend to be larger and the
community has the most biodiversity. It is a stable,
mature community that undergoes little or no
succession
Biodiversity – different kinds (varieties) of life
forms found in an area. High biodiversity means
there is a large number of different species found
in one area.
Primary succession
Occurs where the surface is rock only. No soil present!
1. Pioneer organisms are the first species present.
Pioneer species tend to be mosses and lichens who release
weak acids that begin breaking the rock into smaller
pieces.
2. Simple plants such as grasses then appear. Roots are
shallow and continue breaking the rock into even smaller
pieces.
3. Insects and birds begin to appear. As plants and animals
die, their bodies mix with crumbling rocks to eventually
form soil.
Primary Succession continued…
4. Gradual appearance of more complicated
and larger plants and animals as the
habitat changes.
5. Ends with a “climax community” –
ecosystem stays constant, provided there
are no changes in abiotic influences.
Biodiversity is at its highest.
Primary successionNew bare rock comes from 2
sources:
1. volcanic lava flow cools
and forms rock
Primary successionNew bare rock comes from 2
sources:
2. Glaciers retreat and expose
rock
Bare Rock Lichens,Mosses  Small Herbs, ShrubsEvergreens,
Aspen
Climax Community
Primary succession-
Secondary successionsequence of community changes
that takes place when a
community is disrupted by
natural disaster or human
actions – takes place on
existing soil
Secondary succession
1. Begins in an area where soil is already present.
Much faster than primary succession (making soil is a
VERY slow process!)
2. First species in an area tend to be grasses + weeds.
3. Next community may include taller grasses + golden
rod
4. Then small trees (cherries, dogwood, sumac) begin
to appear.
5. Final step is a mature climax forest (oak, beechmaple, hickory)
Secondary successionEx:
A fire levels
portions of a
forest
Secondary successionEx:
A farmer
stops
plowing
his field
Secondary succession-
Secondary succession-
Pond Succession
Stages of Pond Succession
Stage 1: Plankton growth is rich enough to support animals
that entered when the pond was connected to the lake. Fish
make nests on the sandy bottom. Mussels crawl over the
bottom.
Stage 2: Cattails, bulrushes, and water lilies grow in the
pond. These plants have their roots in the bottom of the
pond, but they can reach above the surface of the water.
This pond is an ideal habitat for the animals that must
climb to the surface for oxygen. Aquatic insect larvae are
abundant. They serve as food for larger insects, which in
turn are food for crayfish, frogs, salamanders, and turtles.
Pond Succession continued…
Stage 3: Decayed bodies of plants and animals
form a layer of humus over the bottom of the
pond. Chara, a branching green algae, covers the
humus. Fish that build nests on the bare bottom
have been replaced by those that lay their eggs on
the Chara.
Stage 4: The pond is so filled with vegetation that
there are no longer any large areas of open water.
Instead, the pond is filled with grasses. The water
dries up during the summer months.
Pond Succession
Primary vs. Secondary
No soil
Pioneer species
Weathering of rock &
decomposition of pioneer
plants and insects build
soil base.
End = climax community
where biodiversity is at its
greatest
Soil already exists
Seeds have suitable soil
conditions from the
beginning.
Occurs much faster
End = climax community
where biodiversity is at its
greatest
May occur on dry land or
with ponds
Table 53.2 The Pattern of Succession on Moraines in Glacier Bay
Figure 53.20 Alders and cottonwoods covering the hillsides
Figure 53.20 Spruce coming into the alder and cottonwood forest
Figure 53.20 Spruce and hemlock forest