Biology 103
Ecology Activity Worksheet for
Some Animals Are More Equal than Others:
Trophic Cascades and Keystone Species
Video Link for Activity
PROCEDURE: After watching the video, use the information to answer the following questions in the space provided.
*Then upload the completed work to the appropriate assignment box by the assignment due date.
1. Are all members of a food web equal in abundance and in their relative effects on one another? Why or why not?
2. Explain the reasoning or evidence you used to answer Question 1.
3. Is every member of a food web the prey of another member of the food web?
4. Explain the reasoning and include evidence you used to answer Question 3.
5. When Robert Paine removed the starfish from an outcrop in Mukkaw Bay, what did he find happened to the number of different species that were also present on the rocky outcrop over time? (Did they increase or decrease?)
a. What species population increased significantly in number on the rocky outcrop, and why?
6. Before the 1960s, most ecologists thought that the number of producers in an ecosystem was the only variable that limits the number of herbivores. The idea was that every level was regulated by the amount of food from the trophic level below it.
a. How did the green world hypothesis differ from this “bottom-up” view?
b. Imagine a simple food chain: Grass -> Grasshoppers -> Mice. If snakes that eat mice are added to the ecosystem, how would you redraw the food chain to represent this change? Using names and arrows is acceptable.
c. After the snakes are added, would you expect the amount of grass to increase or decrease? Explain your reasoning.
7. Since 1972, Dr. Jim Estes had been studying a food chain of kelp -> urchins -> sea otters. In the early 1990s, sea otter numbers started decreasing due to a new apex predator eating the sea otters. What was the new apex predator and what circumstances caused it to depend on sea otters as a food source?
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Ecology Activity Worksheet for Biology 103
Some Animals Have Greater Equality Than Others:
Keystone Species and Trophic Cascades
Activity Video Link
PROCEDURE: After watching the video, fill in the blanks with the answers to the following questions.
*Then, by the assignment due date, upload the finished work to the relevant assignment box.
1. Are all members of a food web equally abundant and have the same relative impact on one another? If so, why or why not?
2. Explain your reasons or evidence for answering Question 1.
3. Is every member of a food web prey to another food web member?
4. Explain the reasoning and include evidence you used to answer Question 3.
5. When Robert Paine removed the
