Download 3.3 Succession: How Ecosystems Change over Time

3.3 Succession: How
Ecosystems Change over Time
Unit A
Science 7
Key Terms
Pioneer species
Succession
Primary succession
Climax community
Secondary succession
Pioneer Species
• Pioneer Species are those
organisms, usually plants,
that colonize barren rock or
lava during primary
succession.
• Pioneer species physically
break up the rocks, extract
minerals, and provide
organic matter that will
decompose and become the
soil for later successional
species.
Lichens, mosses, ferns,
and weeds are often
pioneer species.
Lichens can secrete
acids that help
breakdown rock and
provide opportunities for
other types of plants to
move in.
Growing seedlings can
help split boulders
weighing more than
your family car! Without
pioneer species
paving the way,
ecosystems of a climax
community would never
develop.
Moss 
Give It A Try –p. 62
• Look at Figures 3.8 a) – c). Try to decide
which one(s) are pioneer species.
Explain.
Succession
• Succession is the process of community
change and development that happens
most obviously when a natural community
is disturbed or when new land become
available to life. But biological
communities are always changing. Many
lakes and wetlands gradually become
filled in and over thousands of years
become dry land.
•The lake at first (after glaciers formed it) is surrounded by
essentially scoured bare land. After a time, pioneer plants establish
themselves there. After more time, a forest grows there. Near the
shores of the lake grow reeds and cattails and floating mats of
sedges, which are cousin to grasses.
• Slowly, slowly, generations of
sedge-mats die and sink to the
bottom of the lake and
decompose. After centuries of
plant matter building up on the
lake bottom, the lake becomes
shallower. Given enough time,
the lake becomes a cattail
marsh or sphagnum peat bog.
• Eventually there is no open
water left. The lake has
transformed from an aquatic
community to a wetland
community and will eventually
This muskeg or peat bog was once a
become a wet meadow or,
lake
further north, a black spruce
forest growing on peat.
Primary Succession
• Some succession (primary succession), on the
other hand, is the process of life colonizing dead or
sterile areas such as volcanic lava flows and new
sand dunes, or rock left behind by retreating
glaciers, and transforms them into living
communities.
Secondary Succession
• Some succession
(secondary
succession) is an
ecosystem's response
to an injury, the way we
heal a cut.
– Such succession
transforms a disturbed
or damaged part of a
community. Example: a
tree falls and creates an
opening in the canopy
of leaves. Succession
fills in the opening.
Climax Community
• A climax
community is a
stable group of
plants and
animals that is
the end result of
the successional
process.
Redwood Forest
The redwood forest of
California is a climax
community. Those trees
are huge and can outcompete any invading tree
species. The redwoods also
provide a stable habitat for
other organisms that live in
the forest. The redwoods
serve as the foundation that
supports the rest of the
ecosystem. Huge trees are
the anchor for literally
thousands of other species
of organisms.
C and R - p. 64
• Do all questions.
C and R Answers –p.64
1. Students should recognize that plants (or plantlike living things such
as lichens) are always the pioneer species. Plants, as producers,
must colonize an area before animals can become established
because animals, being consumers, need producers to feed on.
2. Answers will vary, but students may identify stages like those below
(for primary succession). Encourage students to provide as much
detail as possible for each stage. Look in particular for evidence of
their understanding that pioneer species must be producers, and are
usually small and low-growing.
a) bare rock
b) rock covered with lichens
c) mosses and other small plants growing in the developing soil
d) grasses and small shrubs/bushes growing in more developed soil
e) trees growing in fully developed soil.
Note: for grasslands, the climax community will be d.
C and R Answers –p.64
3. In primary succession, a new community develops in an
area where no community existed before. In secondary
succession, a new community develops in an area
where a previously existing community has been
disturbed or destroyed by natural or human activity.
4. Students may suggest lichens, ferns, or mosses for
pioneer species. For climax species, they may suggest
any large trees such as pine, spruce, or poplar. However,
if they are describing grasslands, they should suggest
grasses or shrubs, not large trees.
C and R Answers –p.64
5. The most logical sequence is fireweed, grass, mouse,
birch tree, bear. Ask students to identify this sequence as
an example of primary or secondary succession, with
reasons.
6. These photos would be an example of secondary
succession. Because the land is no longer being used
for farming, native plants, shrubs, and trees have moved
back to re-establish themselves. Students should be
able to find many examples in their communities. They
just need to look at the edge of the schoolyard or open
lot to see examples of plants that are re-establishing
themselves.
AYL – p. 65
• Do All Questions
AYL Answers –p.65
1. a) Students may suggest floods, drought,
tornadoes, hurricanes, or other violent weatherrelated events.
b) The details students provide will vary, but most
answers will likely focus on loss (or reduced
numbers) of producer and/or consumer
populations, and the effects of those losses or
reductions (e.g., an increase in other
populations, which might eventually lead to
further reductions if food becomes scarce).
Students should provide sufficient detail to
explain the causes and effects they identify.
AYL Answers –p.65
2. Answers will vary but illustrations or
written work should be accurate and
clearly show how primary succession
takes place. Primary succession begins
with the arrival of a plant to an area that
has not had any life before. Over time, this
pioneer plant helps to break down rocks
into soil. As the soil becomes more fertile,
other plants move in.
AYL Answers –p.65
3. Population fluctuations can cause many changes in an
ecosystem. For example, with the lynx/hare cycle, an
increase in the food supply for the hares means that
more hares survive. When more hares survive, more
lynx can survive. However, when the hares decimate
their food supply, their numbers will decrease and then
so will the lynx numbers. The populations of organisms
are closely connected through the food chains.
4. Some of the following interactions can cause changes in
an ecosystem: predation, human impact, bioinvasion,
and resource competition.
AYL Answers –p.65
5. Secondary succession can occur in any ecosystem
where a community has been destroyed by natural
occurrences or human activities.
6. The removal of the bears would cause significant
changes in the ecosystem, because they are an
important part of the food chain. Students’ plans could
list measuring the biotic factors before the bears were
removed and then after the bears were removed.
Students’ plans may also provide a specific example of
how the removal of the bears will affect all the organisms
in the park.
Review Key Terms
Pioneer species
Succession
Primary succession
Climax community
Secondary succession