Download Ecological Succession

 Biomes are dynamic – they change as the Earth
changes. This process is called succession.
 Ecosystem succession takes two forms, depending on
the starting point.
 Organisms that thrive during the early stages of
succession are called pioneer species. (e.g. Lichens)
 Lichens- composite organism that emerges from algae or
cyanobacteria (or both) living among filaments of a
fungus
 Algae/Cyanobacteria provide food through
photosynthesis
 Fungus provides minerals, nutrients, and anchor to soil
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 Primary succession occurs when a new ecosystem
develops where there was none before.
 A combination of wind, water, and pioneer species
such as lichens break down rock into soil
(facilitation).
 Once the soil has enough organic matter, small
plants and shrubs can be supported. Over time,
trees spout and become dominant.
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 Secondary succession occurs following the
disruption of an existing ecosystem.
 Fire, flood, clear-cutting, etc.
 This form of ecological succession does not take as
long. Soil is already in place, and pioneer species
appear within days or weeks.
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(a) Soon after fire
(b) One year after fire
Succession on the moraines in Glacier Bay, Alaska,
follows a predictable pattern of change in vegetation
and soil characteristics
1. The exposed moraine is colonized by pioneering
plants including lichens, liverworts, mosses,
fireweed, Dryas, willows, and cottonwood
© 2011 Pearson Education, Inc.
1941
1907
1 Pioneer stage, with
fireweed dominant
1860
Glacier
Bay
Alaska
1760
0 5 10 15
Kilometers
1 Pioneer stage, with
fireweed dominant
2. Dryas dominates the plant community
© 2011 Pearson Education, Inc.
1941
1907
2 Dryas stage
1 Pioneer stage, with
fireweed dominant
1860
Glacier
Bay
Alaska
1760
0 5 10 15
Kilometers
2 Dryas stage
3. Alder invades and forms dense thickets
© 2011 Pearson Education, Inc.
1941
1907
2 Dryas stage
1 Pioneer stage, with
fireweed dominant
1860
0 5 10 15
Kilometers
Glacier
Bay
Alaska
1760
3 Alder stage
3 Alder stage
4. Alder are overgrown by Sitka spruce, western
hemlock, and mountain hemlock
© 2011 Pearson Education, Inc.
1941
1907
2 Dryas stage
1 Pioneer stage, with
fireweed dominant
1860
0 5 10 15
Kilometers
Glacier
Bay
Alaska
1760
4 Spruce stage
3 Alder stage
4 Spruce stage
 Succession is the result of changes induced by the
vegetation itself
 On the glacial moraines, vegetation lowers the soil
pH and increases soil nitrogen content
© 2011 Pearson Education, Inc.
Soil nitrogen (g/m2)
60
50
40
30
20
10
0
Pioneer
Dryas
Alder
Successional stage
Spruce
 Today, only about 2% of Haiti’s original forest
cover remains.
 Even this remains at risk, because most of the
people depend on charcoal as a source of heat.
 The lack of forests has made the country much
more susceptible to flooding, mudslides, and
erosion.
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 Neighboring Dominican Republic, which gained
its independence with much less strife, is the
second largest economy in the Caribbean.
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 Haiti’s hopes for recovery hinge on its ability to
speed the process of ecological succession – to
encourage reforestation and find an alternative
fuel to charcoal.
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a)
b)
Discuss the expected changes in biodiversity as the stages of
succession progress as shown in the diagram above
Describe and explain THREE changes in abiotic conditions
over time that lead to succession, as shown in the diagram
above
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c. For each of the following disturbances, discuss the
immediate and long-term effects on ecosystem
succession
(i) A volcano erupts, covering a 10-squarekilometer portion of a mature forest with lava
(ii) A 10-square-kilometer portion of a mature
forest is clear-cut
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 Biodiversity increases (plants, animals, decomposers).
 Explanation of why biodiversity increases/changes are observed:
 • Some populations facilitate biodiversity/succession (by developing
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conditions more suitable for other species and/or developing
conditions less suitable for their progeny).
• Some populations inhibit biodiversity/succession (by developing
conditions less suitable for other species and/or developing conditions
more suitable for their progeny).
• Increase in plant stratification (increased layering of plants; e.g.,
canopy, understory).
• More niches/habitats formed (plants, animals, decomposers).
• Pioneer plant species → dominants (more shade-tolerant plants
emerge).
• Increase in producer diversity brings about increase in consumer
diversity.
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Description of change in
abiotic condition
Explanation (why abiotic condition changes)
Explanation (why it enhances succession)
Increase in soil
quality
More detritus increases humus;
decreased erosion because more
plants hold soil
Provides more anchoring for plants
Improvement in soil
quality
Soil gains organic matter (humus)
Provides more nutrients for plant growth
More N available to
ecosystem
Caused by decomposition and/or by
nitrogen fixation
Favors plants with higher nitrogen needs
More P available
Caused by decomposition
Favors plants with higher phosphorus needs
Increase in water
retained in soil
Increased organic matter retains
water; increased shading reduces
evaporation
More water is available for plants
Decrease in pH of soil
Acids released during decomposition
lower pH
Mobilizes cations facilitating mineral uptake (e.g. Fe++, Ca++);
favors acid-tolerant plants
Increase in pH of soil
Soil gets more basic with increase in
ammonia
Favors plants with higher N requirement; alkaline tolerant plants
Decrease in light
availability
Caused by shading
Increased shading favors shade-tolerant species; inhibits shadeintolerant species
Decrease in
temperature
Caused by shading
Favors species that are not heat tolerant; inhibits plants needing
higher temps
Higher humidity
Caused by more transpiration
Facilitates transition from xerophytic to mesophytic
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Volcano erupts
Immediate- primary succession/ no soil
Long term lava must be degraded by weathering, microbes, lichens,
fungi to form soil
 Lots of light is available (phototrophic organisms will
thrive when soil is present)
Mature forest is clear-cut
Immediate- secondary succession/ soil present
 All life is not destroyed
 Seed banks are present
 Different/ other habitats/ niches open/closed
Long-term- loss of trees may lead to erosion and soil loss
 Lots of light is available
 Many smaller plants actually benefit
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