LESSON 5: ഩTROUT: PREDATOR OR PREY?പ49

ACTIVITY 5.2 ͵ CHANGES IN A FOOD WEBACTIVITY 5.2 ͵ CHANGES IN A FOOD WEB

What Will We Do?We will describe relationships between different organisms in the Great Lakes, and predict the effects of population changes.

ProcedureUsing the Great Lakes food web at the end of this activity, answer the questions about the model food web you made in class with yarn.

1. What organism in the Great Lakes did you represent?

2. If your organism were removed from the food web . . .

How many organisms would you directly affect?

How many organisms would you indirectly affect?

Draw three different food chains that would be affected by removing your organism. (Use + or – to show the increase and decrease of the populations.)

Example:

പ

Changes in a Food WebThe answers to these quesƟ ons will vary depending on the organism the students represented in AcƟ vity 5.1. All chains should show an increase in the populaƟ on to the leŌ of their organism in the chain, and show a decrease in the populaƟ ons to the right of their organism.

Lake Trout

1.

2.

3.

Algae Snails Chub

Answers will vary.

Answers will vary.

Answers will vary.

 50പWHERE HAVE ALL THE CREATURES GONE?

3. Imagine that the lake herring and the lake whitefish have been eliminated from the Great Lakes food web. Use your Great Lakes food web diagram to fill in the following chart to show what organisms would be affected by the removal of the herring and the whitefish.

DirectDirect IndirectIndirectLake Herring whitefish, walleye, yellow perch, aquatic

plants, clamsany organism that feeds on the organisms directly affected or organisms that they feed on

Lake Whitefish trout, insect larvae, great blue heron, clams, humans, walleye, herrings, yellow perch, lake trout

any organism that feeds on the organisms directly affected or the organisms that they feed on

4. Why would the removal of the herring and the whitefish affect other organisms indirectly?

Because the herring or whitefish population decreased, organisms that feed on them will have less food to eat, and they will either die off or not have enough food to reproduce suc-cessfully. Also, if the herring or whitefish populations decrease, then organisms that are usually preyed upon will grow in number since one of their predators or consumers will be gone. These changes will affect other organisms that are eaten by or eat these organisms.

5. Do you think any land organisms would be affected by these changes in the Great Lakes? Explain your ideas.

Yes, some land organisms are connected to the herring and the whitefish. For example, the great blue heron eats whitefish. Also, humans use both whitefish and herring for food.

Making SenseUsing the food web diagram of the Great Lakes, highlight (or circle in red) organisms that would have an indirect effect on the trout if something happened to it. Explain your ideas.

Assess answers on the basis of correct application of the concepts of direct and indirect rela-tionships in student explanations and correct linkages in the web. Follow up with this in class at the beginning of Lesson 6. This is a good activity for assessing students’ understanding of direct/indirect interactions.

 LESSON 5: ഩTROUT: PREDATOR OR PREY?പ51

Great Lakes Food Web