Changes in Ecosystems

Changes in Ecosystems

7th Grade Science!

What is succession?

• Succession is the gradual development of an ecological community or its replacement by another.

• Ecosystems may change gradually, as months and years

  pass, or quite suddenly if a storm hits or a volcano erupts.

Multiple Choice

What is succession?

• It is a community that is overrun by another community.

• It is a gradual development of an ecological community.

Multiple Choice

How may ecosystems change?

• suddenly

• gradually

• neither

• both

Example of a Gradual Succession

• Natural eutrophication is one example of a gradual change that transforms a body of water, such as a lake or a pond, into a meadow.

• It occurs when a body of water receives enough nutrients to support large amounts of plant or algal growth.

• Human actions sometimes result in artificial eutrophication, such as when fertilizer washes into a lake from farms or lawns.

Eutrophication is an example of gradual succession.

Multiple Choice

What is an example of gradual succession?

• natural eutrophication

• artificial eutrophication

• neither

• both

Example of a Sudden Succession

• Sudden changes to ecosystems can occur due to natural events, such as severe storms, fires, and volcanic eruptions.

• The eruption of Mount St. Helens buried the surrounding area in ash and debris, yet the ecosystem recovered quickly.

• Fires also clear out understory vegetation that blocks light and adds nitrogen rich ash to the soil.

Multiple Choice

What is an example of sudden succession?

• volcanos

• fires

• hurricanes

• tornados

• all of them

Primary Succession

In primary succession,

a community develops where no life exists and there is no soil.

The photos on the following slide show 100 years of succession on the William S. Cooper plots in Glacier Bay, Alaska.

Pioneer Species

• Pioneer species, which are the first organisms to arrive, help break down rock and form soil. 

• Producers, such as lichens, are the first pioneer species to arrive.

• After the pioneer species come

  a succession of plants, including

  mosses, ferns, grasses and herbs.

100 years of primary succession

Multiple Choice

Which producer is a primary species?

• ferns

• lichens

• shrubs

• trees

Multiple Choice

What are pioneer species?

• They are the first producers to arrive, such as lichens.

• Opportunistic species, such as dandelions, are often considered weeds.

Secondary Succession

• Secondary succession occurs where soil still exists.

• Examples include the succession that occurs after a natural disturbance or disaster, or even on an abandoned farm.

• Secondary succession occurs much faster than primary succession.

Multiple Choice

Where does secondary succession occur?

• It occurs where no life exists.

• It occurs where the soil still exists.

Climax Community

• Over time, succession creates a climax community.

• A climax community does not last forever. It will be replaced by a community of different species following another natural disturbance.

Thank you for your participation. Please try again for practice. Quiz will be on Thursday.