Succession
Succession
• Gradual change in species occupying
an area, due to changes in 1 or more
abiotic or biotic factors favoring some
species over another.
Primary Succession
• Gradual establishment of an ecosystem
where one did not exist before (Ex: on
bare rock).
• Examples:
• Primary Succession on a Sand Bar
• Primary Succession on a Rock
Secondary Succession
• Gradual reestablishment of an
ecosystem from an area where it
previously existed.
• Examples: old farm lands, after a fire or
natural disaster
Pioneer species
• Plant or animal species that are the first
to occupy a newly exposed or
disturbed area.
• Examples: lichens, moss
Climax species
• Last stage of succession. One in which
populations of all organisms are in
balance w/ each other & existing abiotic
factors.
• Examples: Old Growth Forest
Changes Which Occur During
Succession
• Soil Structure changes:
• Ecosystem Structure changes:
Soil Structure changes
Soil
Depth
Early Successional Stages
Late Successional Stages
(Pioneer Plants)
(Climax Community)
None or Shallow
Deeper
Organic
Few
Nutrients
Numerous
Moisture Poor
Retention
Good
Ecosystem Structure changes
Early Successional Stages
Late Successional Stages
(Pioneer Plants)
(Climax Community)
Plant Size
Species Diversity
Trophic Structure
Small
Low: few species
Large, or a mix from small to
large.
High: many species
Mostly producers,
Many producers, herbivores
a few decomposers
carnivores & decomposers
Ecological Niches
Few
Many
# of Food Web Links
Few
Many; Complex
connections between food
chains.
Factors Affecting the
Distribution of :
Animal Species
Plant Species
a) Temperature
a) Temperature
b) Water
b) Water
c) Food Supply
c) Quantity of Light
d) Breeding & Nesting
Sites
e) Territory
d) soil pH
e) Minerals (includes
salts)
Competitive Exclusion Principle
• When 2 species compete very directly
for resources, one eventually excludes
the other from the area.
Biodiversity
• In the natural world, all living species,
ecosystems, and genetic diversity
within the species.
– Known Species: 1.75 million plants,
animals & microbes.
– Estimated totals: 4-112 million
unidentified species.
Extinction
• Death of all members of a species. All
the genes of the species are lost
forever.
Does the picture below represent
primary or secondary succession?
• Explain how you would know before
clicking.
Primary succession occurs in areas where no
well developed soil exists (bare rock, desert
sands, or very fire sterilized soils as examples).
Secondary succession occurs in places where
well-developed soils already exist.
Explain why primary succession takes
longer to occur than secondary succession.
• Explain how you would know before clicking.
Primary succession takes longer to occur than
secondary succession because:
– soil which is ready for plants to grow in does not
exist yet.
– Plants are not able to grow well on bare rock,
desert sands, or on soil sterilized by extremely
hot fires.
– It thus takes years to centuries longer then for
primary succession to occur
– secondary succession occurs faster because the
soil already exists and is ready for new plant life.
In this example, what are 2
examples of pioneer plants?
The 2 examples of
pioneer plants are the
lichens & mosses.
How do the pioneer plants change the
landform so other plants can live there?
• Answer before clicking.
The pioneer plants change the
landform so other plants can live
there by adding soil to the rock (as
they die and decay) and also by
physically breaking down the rock
into smaller particles (the
beginning of soil).
Explain how the “heath mat” might change
the landform so that Jack pine and black
spruce can live there.
The heath change the landform by
adding to the depth of soil and the
nutrients found there. This occurs as
the leaves of the heath drop to the
ground and decay. In addition, the roots
help break rock and thicker soil up. The
result is that the soil soon becomes
deep enough for the young trees to live
there.
Why aren't the heath able to live
there forever?
The heath are unable to live there forever
because when the trees begin to get
big, they change the habitat further.
They do this by stealing water and
nutrients from the smaller heath, and
more importantly, by shading the heath
so it doesn't receive enough sunlight.
What is the last stage of
succession called?
• Note that this is the stable, unchanging stage
where only a large change (like disease or fire)
reverts succession back to an earlier stage.
The climax community. In Pacific
Northwest forests, the climax
community is known as old growth
forest. Note that climax is the most
correct term for all habitats when
speaking of the final successional
stage.
Why does the climax or last stage of succession not
change into a different successional stage unless a
major change occurs?
• Because the plants that live there are adapted to
living under those environmental conditions.
• In this case, the fir, spruce, and birch trees all
are tall as adults so they easily can get plenty of
sunlight. In addition, all have wide-ranging root
systems to find water and minerals.
• More importantly, their seedlings need shade
(not light) to survive. Since all these conditions
are met, the older climax species are constantly
replaced by their same species.
Does this diagram illustrate an example
of primary or secondary succession?
Explain how you would know.
Primary succession.
Primary succession occurs in where
no developed soil exists (at the area
with exposed rocks below).