Which statement best describes one of the stages represented in the diagram below?

• The mature forest will most likely be stable over a long period of time.

• If all the weeds and grasses are destroyed, the number of carnivores will increase.

• As the population of the shrubs increases, it will be held in check by the mature forest community.

• The young forest community will invade and take over the mature forest community.

Answer explanation

This diagram represents succession: the replacement of one type of community by another until the stable climax community. The mature forest community is the climax community in this case. This community will remain until it is destroyed by some catastrophe.

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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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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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NGSS.MS-LS2-4

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.

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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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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Which statement best describes the diagram?

• Community A is the most stable community.

• Community B replaced community C after a period of 100 years.

• Community C developed into community A after a period of 75 years.

• Community D modified the environment, making it more suitable for community E.

Answer explanation

This diagram shows ecological succession, the replacement of one type of community by another until the stable climax community. This community remains until it is destroyed by some catastrophe. Each community modifies the environment, making it more suitable for the next community.

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The diagram represents an ecological process. Which statement is most closely related to the process shown in the diagram?

• Climax communities do not develop in aquatic habitats.

• Ecosystems tend to change with time until a stable system is formed.

• Humans have modified the environment through the use of technology and pollution.

• Succession involves changes in plant species only.

Answer explanation

The pond environment is changing to a land environment. This is succession which will continue until a stable system is formed.

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Which is a characteristic of pioneer organisms?

• They cannot survive under conditions of direct sunlight.

• They are always the last organisms to inhabit an environment.

• They modify their environment, making it favorable for the next community.

• They have no effect on other organisms in their environment.

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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