Download Ecological succession - Northwest ISD Moodle

TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
What is ecological succession?
•
•
•
Ecological succession is the series of more or less
predictable changes in ecological communities following a
disturbance.
Ecologists once thought that succession in a given area
would always proceed through the same stages, in the
same order. When the process was completed, there
would be a stable climax community.
Today, however, most ecologists agree that there is no
one path through the events and processes of
succession.
1. Define What is ecological succession?
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
What events set primary
succession in motion?
•
•
Primary succession occurs in an area with no remains of an older
community.
Primary succession can begin when a catastrophic event, such as a
volcanic eruption, completely destroys an ecosystem, when new land
surfaces emerge, or when a depression becomes filled in with water
for the first time.
2. Sequence What kinds of
event starts primary
succession?
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
What events set secondary
succession in motion?
•
•
Secondary succession occurs when a disturbance seriously disrupts
an existing community, but does not destroy it. Unlike primary
succession, soil is present at the start of secondary succession.
Secondary succession may follow a natural disturbance such as a
hurricane, or it may follow human activities such as logging.
3. Compare and
Contrast How
does secondary
succession differ
from primary
succession?
(contd.)
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
•
Secondary succession in aquatic ecosystems may eventually lead to
the formation of a terrestrial ecosystem.
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
What processes cause
succession to continue?
•
•
•
Both primary and secondary succession occur
because every living organism changes its
environment.
Lichens, for example, release acids that break
down rocks and helps form soil.
Lichens are a pioneer species. A pioneer species
is the first species to colonize a barren area.
4. Relate Cause and Effect How do lichens enable soil to form?
Lichens
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
How do the events of primary
succession affect populations?
•
•
•
Events that start primary succession typically cause drastic reductions
in the populations of many organisms. Some populations may be
eliminated entirely.
After the event, conditions may be favorable for pioneer species.
For example, the eruption of Mount Saint Helens killed off entire
populations of plants and animals. Lichens, however, could grow on the
newly barren ground. The lichen population increased dramatically.
5. Infer After the eruption of Mount Saint Helens, why did the lichen population increase?
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
How do the events of secondary
succession affect populations?
•
•
•
Like the events that cause primary succession, the events that cause
secondary succession typically reduce populations dramatically.
However, these events rarely kill off entire populations.
Limiting factors may be eliminated, allowing some populations to
increase. After a forest fire, for example, populations of sun-loving
plants may increase.
6. Relate Cause and Effect Why can sun-loving plants thrive after forest fires?
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
How do the processes of
succession affect populations?
•
•
•
Colonization and environmental change are two processes that
continue throughout succession.
As each species colonizes an area, it changes environmental
conditions.
The new conditions may cause some populations to increase and
others to decrease.
7. Identify What are two processes that play a role in ecological succession?
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
How does competition
affect populations?
•
•
As ecological succession proceeds, population density increases,
making the process of competition among organisms more intense.
Eventually, competition can reduce the populations of early colonizers.
As grassland gradually becomes forest, for example, tall trees may
prevent sunlight from reaching the grasses.
8. Infer Why does increased population density intensify competition?
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
How do the events of succession
affect species diversity?
•
•
•
The events that set off ecological succession, such as volcanic
eruptions and hurricanes, usually reduce species diversity in the
immediate area of the disturbance.
Events that start primary succession may eliminate species diversity
entirely.
Ash and lava from Mount Saint Helens buried and destroyed plant life
throughout a large area.
9. Define What is species diversity?
TEKS 11D: Describe how events and process that occur during ecological succession
can change populations and species diversity.
How do succession processes
affect species diversity?
•
•
•
•
The processes of succession can have complex effects on species
diversity.
As succession takes place, processes such as soil formation may
gradually increase species diversity.
At some points in succession, the process of competition may decrease
species diversity.
In general, mature communities have higher species diversity than areas
in earlier stages of succession.
10. Relate Cause and Effect Why can soil formation increase species diversity?