How Ecosystems Can Recover Over Time

Events that occur in four different ecosystems are shown in the chart below. Which ecosystem would most likely require the most time for ecological succession to restore it to its original state? (a)  

• A
• B
• C
• D

Answer explanation

Generally speaking, primary succession takes a longer period of time than does secondary succession.

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A new island formed by volcanic action may eventually become populated with biotic communities as a result of

• a decrease in the amount of organic material present

• decreased levels of carbon dioxide in the area

• the lack of abiotic factors in the area

• the process of ecological succession

Answer explanation

A new volcanic island would be considered barren. This means it would have plenty of abiotic factors at first but over time may develop biotic factors.

What would most likely be the predominant lifeform found in stage I?

• ferns

• tracheophytes

• mushrooms

• pioneer species

Answer explanation

An area that is just rock would need some hardy organisms that can survive with little to no resources. Mosses and Lichens would be two good examples of these organisms.

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Years after the lava from an erupting volcano destroyed an area, lichens started to grow in that area. These were gradually replaced by grasses, shrubs, conifers, and finally, by a deciduous forest. In this sequence of events, the lichens functioned as

• primary consumers

• climax organisms

• abiotic factors

• pioneer organisms

Answer explanation

An area that is just rock would need some hardy organisms that can survive with little to no resources. Mosses and Lichens would be two good examples of these organisms.

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Changes in an ecosystem over a long period of time are shown in the diagram below. These changes will most likely lead to a

• stable ecosystem that can last for many years

• loss of heterotrophs that cannot be recovered

• long-term rise in environmental temperatures

• forest consisting of only producers and decomposers

Answer explanation

This diagram is showing succession, the replacement of one type of community by another until the stable climax community, which remains until it is destroyed by some catastrophe.

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If the ecosystem is not altered, which stage would be the most stable?

• grass

• shrub

• pine forest

• hardwood forest

Answer explanation

The stage that remains is the stable climax community.

Scientists have studied the return of plant life on Mount St. Helens ever since the volcano erupted in 1980. Wildflowers began colonizing the area, followed by shrubs and small trees. Scientists predict that it will likely take hundreds of years before the area returns to a forest dominated by fir and hemlock trees. These changes are an example of

• humans degrading an ecosystem by removing wildflowers

• the loss of genetic variation in a plant species

• the growth of a forest through ecological succession

• the biological evolution of wildflowers, shrubs, and trees

Answer explanation

Small plants are being replaced by larger species over time. Ecological succession is the replacement of one community by another until the final climax community.

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The graph shows the masses of different types of plants found in an area of the Adirondack Mountains after a forest fire occurred. The mass of plants shown in the graph refers to the mass of a number of

• populations

• decomposers

• ecosystems

• communities

Answer explanation

There are different types of trees in the ecosystem. Plant populations make up the mass.

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Which statement describes an event in this process?

• Community B modifies the environment, making it suitable for community C.

• Community D modifies the environment, making it suitable for community C.

• Community E will develop into community A, if the environment remains stable.

• Community A organisms will develop directly into community D organisms.

Answer explanation

This diagram shows ecological succession. Each community modifies the environment, making it suitable for the next community.

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Over a long period of time, the stages represented in the diagram below were each present in a particular ecosystem. After a forest fire, what is the most likely order in which these stages appeared?

• D --> C --> A --> B

• B --> D --> C --> A

• A --> B --> C --> D

• B --> C --> D --> A

Answer explanation

The diagram shows ecological succession: the replacement of one type of community by another until the stable climax community, which remains until it is destroyed by some catastrophe.

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