Download Ecological Disturbances and Succession

Ecological Disturbances and
Succession
SC.912.L.17.4 Describe changes in ecosystems resulting from
seasonal variations, climate change and succession.
By Dr. Suris Soto
What Is Disturbance?

A disturbance

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
Is an event that changes a community
Removes organisms from a community
Alters resource availability
Disturbances
Natural

They are common in
ecosystems
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Fire
Hurricanes
Floods
Volcanic Eruptions
Human-Caused

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Are the most widespread
agents of disturbance
Usually reduces species
diversity
Humans also prevent some
naturally occurring
disturbances
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Deforestation and land cleared
Farming
Urbanization (Developments)
Ecological Succession
 Ecological
succession

Is the gradual sequence of community and
ecosystem changes after a disturbance

One community of organisms replaces another
Types of Ecological Succession:
 Primary succession
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Occurs where no soil, (barren terrain) exists when
succession begins
No pre-existing plant or animal life
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Examples: After volcanic eruption, retreating glacier (natural),
abandon parking lot (human-caused)
Secondary succession


Begins in an area where soil remains after a disturbance
Some organisms may still be there
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Examples: After a flood, hurricane, tornado (natural) or after
land cleared for farming, deforestation (human-caused)
Primary Succession ---- No Soil, barren rock

Glacier Retreating
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Volcanic Eruption

Abandon parking lot
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Secondary Succession after a fire
A Fire
 Is a significant disturbance in most terrestrial ecosystems
 Is often a necessity in some communities
Figure a–c
(a) Before a controlled burn.
A prairie that has not burned for
several years has a high proportion of detritus (dead grass).
(b) During the burn. The detritus
serves as fuel for fires.
(c) After the burn. Approximately one
month after the controlled burn,
virtually all of the biomass in this prairie
is living.

The large-scale fire in Yellowstone National Park in 1988

Demonstrated that communities can often respond very rapidly
to a massive disturbance
(a) Soon after fire. As this photo taken soon after the fire shows, the
burn left a patchy landscape. Note the unburned trees in the
distance.
Figure 53.22a, b
(b) One year after fire. This photo of the same general area taken the
following year indicates how rapidly the community began to recover. A
variety of herbaceous plants, different from those in the former forest,
cover the ground.
Secondary Succession
Pioneer species

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Always the first species to move into a devastated area
Must be able to live on limited resources
Must be able to live in barren rock
They include
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Bacteria
Lichens
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Lichens are a symbiosis (close relationship) of a fungus and a green
algae
Each organisms depends on each other for survival (mutualism)
Fungus anchors lichen to a surface, absorbs water and nutrients, and
protects the algae from direct sunlight.
The algae performs photosynthesis to make its own food and also
feed the fungus
As lichens grow, they make break down rock , help form soil. When it
dies it decomposes enriching the soil.
Pioneer species
Lichens
Bacteria
Mosses
Primary Succession
Climax community
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Fairly stable community
Marks the end of succession in an area
Organisms present depend on the climate and physical
features of the area
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Ex. In areas with little rain the climax is a grassland
Nothing lasts forever: A new disturbance can happen at
any time
Disturbances in climax communities can lead to
secondary succession or primary in the event of volcanic
eruption covering the soil with lava, hardened to rock
Draw it yourself:
Which of the following is not a possible
cause of secondary succession?
Fire
B. Flood
C. Earthquake
D. Change of seasons
A.
Which of the following is an example of
primary succession?
A.
B.
C.
D.
Lichens growing on rocks after a volcanic eruption
Grasses growing after a forest fire
Oak trees replacing pine trees in a forest
Nonnative species introduced into a climax community
Which term refers to final forest’s
development?
A.
B.
C.
D.
Pioneer forest
Secondary forest
Climax forest
Conifer forest