How Ecosystems Change - Ecological Succession

How Ecosystems Change - Ecological Succession
What do you think?

Before you read, decide if you agree or disagree with each of these statements. As you read this lesson, see if you change your mind about any of the statements.

     1. An ecosystem never changes.

Disagree. Ecosystems are constantly changing in response to climate changes and other abiotic factors. Humans also can change ecosystems.

     2. Nothing grows in the area where a volcano has erupted.

How did this happen?

Paul Bradforth/Alamy

This object was once part of a mining system used to move copper and iron ore. Today, so many forest plants have grown around it that it is barely recognizable. How do you think this happened? What do you think this object will look like after 500 more years?

 

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1 NOTE

How do communities change?

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Prep: 5 min Class: 15 min

Purpose
To illustrate the concept of succession.

Materials
Student: two pictures of the same ecosystem community at different stages of succession (on-screen)

Before You Begin
Discuss how places can gradually change. Ask students to describe gradual changes that they’ve noticed in their school or neighborhoods.

Guide the Investigation
• Urge students to keep their drawings as simple as possible to clearly illustrate their ideas.

• Encourage students to use labels in their drawings if that seems helpful to them.

• Have volunteers present their drawings with explanations.

Launch Lab: How do communities change?

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An ecosystem can change over time. Change usually happens so gradually that you might not notice differences from day to day.

1. Above are two pictures of ecosystem communities. One is labeled A and the other is labeled B.

2. Imagine community A changed and became like community B. On a blank piece of paper, draw 
    what you think community A might look like midway in its change to becoming like community 
    B.

 

Think About This

1.What changes did you imagine? How long do you think it would take for community A to become  
    like community B?

Student answers may vary but should include discussion on sequencing of events from start to finish.

2. Key Concept Summarize the changes you think would happen as the community changed from A
     to B.

Student answers will vary but should be well-reasoned.

 

12 NOTES

How Land Ecosystems Change

Primary Succession

Visual Literacy : Figure 1

Secondary Succession

Visual Literacy : Figure 2

Teacher Demo

Differentiated Instruction

Differentiated Instruction

Differentiated Instruction

Teacher Demo

Real - World Science

Fun Fact

How Land Ecosystems Change

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Have students read about how land ecosystems change. Then use the questions below to assess students’ understanding.

Guiding Questions

What happens during ecological succession?

Students’ answers should reflect an understanding that succession is a process of one community gradually changing to another and that the process involves a series of steps that can usually be predicted.

Key Concept Check What is a climax community?

A climax community is a stable community that no longer goes through major ecological changes. It is the final stage of ecological succession.

What signs could you look for to determine if a community is a climax community?

Answers may vary. Sample answer: I could look at all new plants growing in the area and determine if they are the same species as the much older plants, or I could compare the community to other communities in the same biome.

Primary Succession

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Tell students there are two types of ecological succession—primary succession and secondary succession. Then have students read the paragraph and the captions about primary succession. Use the questions below to gauge students’ understanding of the reading.

Guiding Questions

Where does primary succession occur?

Primary succession occurs in new areas of land with little or no soil, such as on a lava flow, a sand dune, or exposed rock.

What are the first organisms to grow in an area with little or no soil?

Pioneer species, such as lichens and mosses, are the first organisms to grow in an area with little or no soil.

How do different pioneer species create soil?

Sample answer: Lichens release an acid, which helps break down the rock and create soil. All pioneer species help create soil when they die and decompose.

Visual Literacy: Figure 1

Students may need help understanding how organisms get to and grow on the rock in Figure 1. Use the questions below to help students understand the diagram and check for understanding.

Ask: How do lichen spores get to an area that is bare rock?

They are carried by the wind.

Ask: What has to happen before grasses and other plants can grow in the area?

Enough soil has to be created to support the plants before they can grow in the area.

Secondary Succession

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Have students read the paragraph about secondary succession. Then use the following questions to check understanding.

Guiding Questions

What happens to the land if a farmer clears part of a forest but doesn’t grow crops on the land?

Answers should reflect an understanding that succession takes place, and trees eventually grow back.

Reading Check Where does secondary succession occur?

Secondary succession occurs in areas where existing ecosystems have been disturbed or destroyed.

How are primary succession and secondary succession similar?

Answers should reflect an understanding that they both are a process of one ecological community gradually changing into another, and they both eventually end in a climax community.

Visual Literacy: Figure 2

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Use the questions below to help students understand Figure 2 and check for understanding.

Ask: Where did the seeds growing in the illustration on the right come from?

Sample answer: The seeds could have been in the soil, carried by the wind, or carried by animals to the area.

Ask: If a beech and maple climax community was cleared to make the field in the illustration on the left, what will eventually grow if the area is left alone?

A beech and maple climax community will eventually grow.

Teacher Demo

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Local Succession Display photos that show ecological succession in your area. Examples could include small plants growing in cracks of a sidewalk or in a vacant lot, weeds growing in a garden, small trees sprouting in a grassy area, or small plants growing in a rain gutter. Ask students to explain what is happening and what they think will happen if people don’t interfere with the processes. If possible, display a photo of a climax community in your area.

Differentiated Instruction

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A Series of Changes Have pairs of students choose one of the types of succession and create a flip book showing the changes that might occur. Have students share their flip books with other pairs.

Differentiated Instruction

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Changes Over Time Have students write diary entries for a 90-year-old person who has lived his or her life in an area where a deciduous forest was destroyed by a wildfire when the person was 15 years old. Write an entry for when the person was 10, 15, 25, 50, 75, and 90. Each entry should focus on the ecosystem and describe what species are living in it.

Differentiated Instruction

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Using Succession Words Have pairs of students review the section How Land Ecosystems Change and create two lists of words and phrases. One list should apply to primary succession, and the other list should apply to secondary succession. Then have students take turns using the words and phrases to explain the two types of succession.

Teacher Demo

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Rocks and Soil Display a large rock and a container of soil. Ask students what they could grow on the rock or in the soil. Then ask what could grow in an ecosystem made of just rock or just soil.

Real-World Science

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Prescribed Prairie Burns Some ecosystems, such as prairies, need fire to maintain a climax community. Fire removes dead vegetation, returns nutrients to the soil, stimulates the growth of prairie plants, and helps prevent non-prairie plants from growing. In the past, prairie fires occurred naturally when prairies were struck by lightning. Native Americans also started fires in controlled areas. On the prairies that remain today, prescribed burns help maintain them and keep them from becoming forests.

Fun Fact

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Rock v. Ash Some volcanoes spew out ash and rocks instead of lava. The hot ash kills and covers plants growing in the area, but succession occurs much faster than in areas covered with lava. Some seeds and animals can even survive underground.

How Land Ecosystems Change

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Have you ever seen weeds growing up through cracks in a concrete sidewalk? If they were not removed, the weeds would keep growing. The crack would widen, making room for more weeds. Over time, the sidewalk would break apart. Shrubs and vines would move in. Their leaves and branches would grow large enough to cover the concrete. Eventually, trees could start growing there.

This process is an example of ecological succession—the process of one ecological community gradually changing into another. Ecological succession occurs in a series of steps. These steps can usually be predicted. For example, small plants usually grow first. Larger plants, such as trees, usually grow last.

The final stage of ecological succession in a land ecosystem is a climax community—a stable community that no longer goes through major ecological changes. Climax communities differ depending on the type of biome they are in. In a tropical forest biome, a climax community would be a mature tropical forest. In a grassland biome, a climax community would be a mature grassland.

Climax communities are usually stable over hundreds of years. As plants in a climax community die, new plants of the same species grow and take their places. The community will continue to contain the same kinds of plants as long as the climate remains the same.

1. Key Concept Check What is a climax community?

A climax community is a stable community that no longer goes through major ecological changes. It is the final stage of ecological succession.

Primary Succession

What do you think happens to a lava-filled landscape when a volcanic eruption is over? As shown in Figure 1, volcanic lava eventually becomes new soil that supports plant growth.
Ecological succession in new areas of land with little or no soil, such as on a lava flow, a sand dune, or exposed rock, is primary succession.
The first species that colonize new or undisturbed land are pioneer species. The lichens and mosses in Figure 1 are pioneer species.

Figure 1 Following a volcanic eruption, a landscape undergoes primary succession.

 

Secondary Succession

In areas where existing ecosystems have been disturbed or destroyed, secondary succession can occur. One example is forestland in New England that early colonists cleared hundreds of years ago. Some of the cleared land was not planted with crops. This land gradually grew back to a climax forest community of beech and maple trees, as illustrated in Figure 2.

2. Reading Check Where does secondary succession occur?

Secondary succession occurs in areas where existing ecosystems have been disturbed or destroyed.

Figure 2 When disturbed land grows back, secondary succession occurs.

 

1 NOTE

REVIEW VOCABULARY

Ask: Do the animals in a community change during ecological succession or only the plants? Explain.

Yes; as different plants begin to grow in an area, animals that use these plants for food and shelter move into the area.

REVIEW VOCABULARY

community - all the organisms that live in one area at the same time

 

1 NOTE

SCIENCE USE V. COMMON USE

Remind students that human pioneers are the first human settlers of their origin and culture who move into an area. Other humans, such as Native Americans, may already live in the area.

Ask: How is the land colonized by pioneer species different from the land the first human settlers found?

Pioneer species colonize land that has little or no soil. Human settlers found land that was new to them and unsettled by other pioneers. The land would have included some climax communities.

SCIENCE USE V. COMMON USE

pioneer
Science Use the first species that colonize new or undisturbed land

Common Use the first human settlers in an area

 

4 NOTES

How Freshwater Ecosystems Change

Visual Literacy : Figure 3

Eutrophication

Reading Strategy

How Freshwater Ecosystems Change

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Have students read the paragraph under Aquatic Succession and the caption and labels in Figure 3. Use the questions below to informally assess students’ understanding.

Guiding Questions

What is aquatic succession?

Aquatic succession is the natural, predictable process of change over time in freshwater ecosystems.

Key Concept Check What happens to a pond, a lake, or a wetland over time?

The water fills in with soil from decayed matter and from sediment that is washed in from rainwater and streams. Eventually it becomes a land ecosystem.

Visual Literacy: Figure 3

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Use the questions below to help students analyze the process of aquatic succession in Figure 3 and to assess their understanding.

Ask: How has the pond changed over time?

Some of the pond has filled in with soil, so the pond is not as deep and the fish have disappeared. Plants have started to grow where the pond is shallow and where the pond is now land.

Ask: What will happen if this process continues?

The pond will be completely filled in and will be a land ecosystem.

Eutrophication

Explain that eutrophication is a natural part of aquatic succession. Make certain students recognize that humans contribute to eutrophication. Use the questions below to informally assess students’ understanding.

Guiding Questions

What is eutrophication?

Eutrophication is the process of a body of water becoming nutrient-rich.

How is eutrophication a natural process?

As plants, animals, and other organisms living in the water die, they decay and nutrients in their bodies are added to the water.

How do human activities speed up aquatic succession?

Answers should reflect an understanding of what happens when fertilizers and other pollutants produced by human activities are carried by runoff into bodies of water.

Reading Strategy

Outline Have pairs of students make an outline of the text and visuals in this lesson. Encourage students to share their outlines and make revisions if necessary. The outlines can be used to help students understand and remember the Key Concepts and the details that support them.

How Freshwater Ecosystems Change

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Like land ecosystems, freshwater ecosystems change over time in a natural, predictable process. This process is called aquatic succession.

 

Aquatic Succession

Aquatic succession is illustrated in Figure 3. Sediments carried by rainwater and streams accumulate on the bottoms of ponds, lakes, and wetlands. The decomposed remains of dead organisms add to the buildup of soil. As time passes, more and more soil accumulates. Eventually, so much soil has collected that the water disappears and the area becomes land.

 

1. Key Concept Check What happens to a pond, a lake, or a wetland over time?

The water fills in with soil from decayed matter and from sediment that is washed in from rainwater and streams. Eventually it becomes a land ecosystem.

Figure 3 The water in a pond is slowly replaced by soil. Eventually, land plants take over and the pond disappears.

 

Eutrophication

As decaying organisms fall to the bottom of a pond, a lake, or a wetland, they add nutrients to the water. Eutrophication (yoo troh fuh KAY shun) is the process of a body of water becoming nutrient-rich.

 

Eutrophication is a natural part of aquatic succession. However, humans also contribute to eutrophication. The fertilizers that farmers use on crops and the waste from farm animals can be very high in nutrients. So can other forms of pollution. When fertilizers and pollution run off into a pond or lake, nutrient concentrations increase. High nutrient levels support large populations of algae and other microscopic organisms. These organisms use most of the dissolved oxygen in the water and less oxygen is available for fish and other pond or lake organisms. As a result, many of these organisms die. Their bodies decay and add to the buildup of soil, speeding up succession.

 

1 NOTE

WORD ORIGIN

Write the words eutrophos and eutrophication on the board.

Ask: Why do you think the origin of the word eutrophication makes sense?

The origin means “nourishing,” and eutrophication is the process of a body of water becoming nutrient-rich.

WORD ORIGIN

eutrophication
from Greek eutrophos, means “nourishing”

Lesson Review

Visual Summary

Ecosystems change in predictable ways through ecological succession.

The final stage of ecological succession in a land ecosystem is a climax community.

The final stage of aquatic succession is a land ecosystem.

 

What do you think NOW?

You first read the statements below at the beginning of the lesson.

1. An ecosystem never changes.

2. Nothing grows in the area where a volcano has erupted.

Did you change your mind about whether you agree or disagree with the statements? Rewrite any false statements to make them true.

Lesson Assessment

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Use Vocabulary

1. Define pioneer species in your own words.

Pioneer species are the first species that colonize new or undisturbed land.

2. The process of one ecological community changing into another is __________.

ecological succession

3. Compare and contrast succession and eutrophication in freshwater ecosystems.

Possible answer: Both are part of the natural processes that gradually turn a water body into a land ecosystem. In succession, soil is built up from decay and washed-in sediments. In eutrophication, nutrient levels increase.

Understand Key Concepts4. Draw a picture of what your school might look like in 500 years if it were abandoned.

Drawings will vary, but should show vegetation taking over the yard and the buildings.

5. Which process occurs after a forest fire?

         A.eutrophication

         B.photosynthesis

         C.primary succession

         D.secondary succession

6. Which organism below would be the first to settle an area that has been buried in lava?

         A.A

         B. B

         C.C

         D.D

7. What is a forest called that has had the same species of trees for 200 years?

         A.climax community

         B.pioneer species

         C.primary succession

         D.secondary succession

8. What is eutrophication?

         A.decreasing nutrients

         B.decreasing salinity

         C.increasing nutrients

         D.increasing salinity

Interpret Graphics

9. Determine What kind of succession— primary or secondary—might occur in the environment
    pictured? Explain.

Primary succession might occur in the environment pictured, because the lava from the volcano will harden and become rock with no soil.

10. Summarize Information Copy the graphic organizer below and fill it with the types of
      succession an ecosystem can go through.

In any order: primary succession, secondary succession, aquatic succession

Critical Thinking

11. Reflect What kinds of abiotic factors might cause a grassland climax community to slowly
      become a forest?

Possible answers: increase in rainfall high enough to support tree growth, reduction in length of dry season, disappearance of grazing animals that trample or eat tree seedlings

12. Hypothesize Why are the first plants that appear in primary succession small?

Soil is thin or absent. The roots of larger plants cannot yet take hold.

Writing in Science

13. Write a paragraph explaining the succession process that might occur in a microhabitat, such as a
       garden with weeds. Include a main idea, supporting details, and concluding sentence.

 

Science is Awesome!

Answers will vary but should cover the natural process of succession where native weeds can crowd out non-native vegetable plants, decaying matter builds soil, and where the decay of plants, as well as fertilizer or garden compost, increases nutrient levels.

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