Ecosystems are comprised of a community of organisms and their physical environment. Ecologists study the interactions among these organisms and the factors that affect organisms’ distribution. The structure of an ecosystem can be represented by a pyramid made up of trophic levels such that producers are on the bottom, followed by primary consumers, secondary consumers, and so on.

This Click & Learn illustrates examples of what can happen when the top of the pyramid changes.

PART 1:   Click on the Kelp Example (top menu bar)

1.  Explain what the negative  symbol ⊝   on  the diagram means.     _____

2.  What do sea otters eat?  _____    What do urchins eat?  _____

3. What happened to the sea otters during the 1800s?  _____

4.  As a result, what happened to the urchin populations?  _____

5.  What happened to the kelp population?  _____

6.  What does a dashed arrow mean on the diagram?  _____

7.  What does a positive symbol ⊕ mean?  _____

EXPLORING TROPHIC CASCADES   -  HHMI Click and Learn                   ~home edition

Go to http://www.hhmi.org/biointeractive/exploring-trophic-cascades

8.  Glaucous-winged Gull

     What do the gulls primarily consume?  _____
      What happened to the diet of the Glaucous-winged gull when the otters disappeared?  _____

9.  Bald Eagle

      What do bald eagles specialize in eating?  _____                  What else can they eat?   _____

      What happened to their diet when the otters disappeared?    _____

10.  How does the story of the sea otter illustrate an example of a TROPHIC CASCADE?   

Part 2 - Case Studies    Click on “case studies” in the top menu.  You will do each one of these and answer questions.   

Arctic Tundra 

11.   Complete the table below on the tundra:

Positive + or Negative -

Direct or  Indirect

Foxes →  seabirds          

Seabirds → soil nutrients

Soil nutrients → grass

Foxes → grass

12.  Summarize what happened to the arctic landscape when foxes were introduced.  What changed?

Midwestern Lake

13.  Complete the table

Positive + or Negative -

Direct or  Indirect

Bass fish → minnows  

Minnows → zooplankton

Zooplankton → phytoplankton

Phytoplankton → carbon influx

Bass → carbon influx

14. Summarize what happened to the lake ecosystem when bass were removed.  Describe the appearance of the lakes in this example.

African Savanna

15.  What is rinderpest?     _____   
      Why would the government institute a vaccination program? _____

16.  Complete the table: 

Positive + or Negative -

Direct or  Indirect

Rinderpest → wildebeest

Wildebeest → vegetation

Vegetation → fire

Rinderpest → fire

17.  Which graph illustrates the eradication of rinderpest?   

            A       B

18. Summarize the effect of the vaccination program on the ecosystem.  

Venezuelan Jungle

19. Complete the table: 

Positive + or Negative -

Direct or  Indirect

Predators → Herbivores

Herbivores → Vegetation

Carnivores  → Vegetation

20.  Summarize the effect predators have on jungle ecosystems. 

EXPLORING TROPHIC CASCADES   -  HHMI Click and Learn                   ~home edition

Go to http://www.hhmi.org/biointeractive/exploring-trophic-cascades

Ecosystems are comprised of a community of organisms and their physical environment. Ecologists study the interactions among these organisms and the factors that affect organisms’ distribution. The structure of an ecosystem can be represented by a pyramid made up of trophic levels such that producers are on the bottom, followed by primary consumers, secondary consumers, and so on.

This Click & Learn illustrates examples of what can happen when the top of the pyramid changes.

PART 1:   Click on the Kelp Example (top menu bar)

1.  Explain what the negative  symbol ⊝   on  the diagram means.     _____

2.  What do sea otters eat?  _____    What do urchins eat?  _____

3. What happened to the sea otters during the 1800s?  _____

4.  As a result, what happened to the urchin populations?  _____

5.  What happened to the kelp population?  _____

6.  What does a dashed arrow mean on the diagram?  _____

7.  What does a positive symbol ⊕ mean?  _____

8.  Glaucous-winged Gull

     What do the gulls primarily consume?  _____
      What happened to the diet of the Glaucous-winged gull when the otters disappeared?  _____

9.  Bald Eagle

      What do bald eagles specialize in eating?  _____                  What else can they eat?   _____

      What happened to their diet when the otters disappeared?    _____

10.  How does the story of the sea otter illustrate an example of a TROPHIC CASCADE?   

Part 2 - Case Studies    Click on “case studies” in the top menu.  You will do each one of these and answer questions.   

Arctic Tundra 

11.   Complete the table below on the tundra:

Positive + or Negative -

Direct or  Indirect

Foxes →  seabirds          

Seabirds → soil nutrients

Soil nutrients → grass

Foxes → grass

12.  Summarize what happened to the arctic landscape when foxes were introduced.  What changed?

Midwestern Lake

13.  Complete the table

Positive + or Negative -

Direct or  Indirect

Bass fish → minnows  

Minnows → zooplankton

Zooplankton → phytoplankton

Phytoplankton → carbon influx

Bass → carbon influx

14. Summarize what happened to the lake ecosystem when bass were removed.  Describe the appearance of the lakes in this example.

African Savanna

15.  What is rinderpest?     _____   
      Why would the government institute a vaccination program? _____

16.  Complete the table: 

Positive + or Negative -

Direct or  Indirect

Rinderpest → wildebeest

Wildebeest → vegetation

Vegetation → fire

Rinderpest → fire

17.  Which graph illustrates the eradication of rinderpest?   

            A       B

18. Summarize the effect of the vaccination program on the ecosystem.  

Venezuelan Jungle

19. Complete the table: 

Positive + or Negative -

Direct or  Indirect

Predators → Herbivores

Herbivores → Vegetation

Carnivores  → Vegetation

20.  Summarize the effect predators have on jungle ecosystems.