Ecological Succession
Part 1: Ecological Succession
Ecosystems constantly ……………………. A tree falling in a forest affects the forest ecosystem. A fire might alter
the forest habitat so much that some species cannot survive and others can thrive. The process of one
community replacing another as a result of changing abiotic and biotic factors is called
…………………………………………………………………..
How does soil form in primary succession?
There are two types of ecological succession – primary and secondary succession. Primary succession is the
establishment of a community in an area of bare rock that does not have topsoil. For example, suppose a lava
flow alters an ecosystem. The lava hardens to form bare rock. Usually, lichens begin to grow on the rock first.
Because lichens and some mosses are among the first organisms to appear, they are called ………………..
species.
Pioneer species secrete acids that help break down rocks. As pioneer species die, their decaying organic
materials mix with small pieces of rock. This is the first stage of ……………. development. Small weedy plants
begin to grow in the soil. These organisms die, adding to the soil. Seeds brought by animals, water, and wind
begin to grow. Eventually, enough soil forms to support trees and shrubs.
It might take hundreds of years for the ecosystem to become balanced and achieve equilibrium. When an
ecosystem is in equilibrium, there is no net change in the number of species. New species come into the
community at about the same rate that others leave the community. This is a ……………………………… – a stable,
mature community in which there is little change in the number of species.
How does secondary succession occur?
Disturbances such as fire or flood can disrupt a community. After a disturbance, new species of plants and
animals might occupy the habitat. Over time, the species belonging to the climax community are likely to
return. Secondary succession is the orderly and predictable change that takes place after a community of
organisms has been removed but the soil remains. Pioneer species begin the process of restoring a habitat
after a disruption. The figure below shows how the community changes after a forest fire, leading again to a
mature climax community.
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Ecological Succession Questions
Part 1: Comprehension Questions
1. What are two things mentioned in the reading that can happen that might affect an ecosystem?
2. Define ecological succession.
3. What is primary succession?
4. Describe an example of primary succession.
5. What is a pioneer species?
6. How long might it take for an ecosystem to become balanced?
7. What happens when an ecosystem is in equilibrium?
8. Define climax community.
9. Name two things that can disrupt a community.
10. What is secondary succession?
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Multiple Choice Questions
1. After a volcanic eruption has covered an area with lava, which of the following is the most likely order
of succession in the repopulation of the area?
A. lichens → grasses → shrubs → trees
B. mosses → grasses → lichens → trees
C. grasses → trees → mosses → lichens
D. shrubs → grasses → trees → lichens
2. The diagram below illustrates the relationship between organisms in an ecosystem.
In addition to sunlight, which factor would need to be added to make this a stable ecosystem?
A. Predators B. Prey C. Decomposers D. Herbivores E. Carnivores
3. The food web is shown above. If the rabbit population increases, which of the following is most likely
to happen soon afterward?
A The deer population will increase.
B The plant population will decrease.
C Different birds will move into the area.
D The insect population will be eliminated.
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