Question: Predators are animals that hunt other animals, called prey. How do predator and prey populations affect one another?

Student Exploration: Food Chain

Vocabulary: consumer, ecosystem, equilibrium, food chain, population, predator, prey, producer

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

The Food Chain Gizmo™ shows a food chain with hawks, snakes, rabbits, and grass. In this simulation, the hawks eat snakes, the snakes eat rabbits, and the rabbits eat grass.

Producers are organisms that do not need to eat other organisms to obtain energy

Which organism is a producer in this food chain?.

Where does the producer get its energy?

Consumers must eat other organisms for energy. Which organisms are consumers in this food chain? 

Gizmo Warm-up

The SIMULATION pane of the Gizmo shows the current population, or number, of each organism in the food chain.

What are the current populations of each organism?

Hawks:    Snakes: Rabbits: Grass:

Select the BAR CHART tab, and click Play (). What do you notice about each population as time goes by?

If populations don’t change very much over time, the ecosystem is in equilibrium.

Compare the equilibrium populations of the four organisms. Why do you think populations decrease at higher levels of the food chain?.

Activity A: Predator-prey relationships

Get the Gizmo ready: Click Reset (). Check that the BAR CHART tab is selected.

Question: Predators are animals that hunt other animals, called prey. How do predator and prey populations affect one another?

Observe: Run the Gizmo with several different starting conditions. You can use the +or – buttons to add or remove organisms, or you can choose Diseased from the dropdown lists.

Form hypothesis: How do you think predator and prey populations affect one another?

Predict: Based on your hypothesis, predict how changing the rabbit population will affect the other organisms at first. Write “Increase” or “Decrease” next to each “Prediction” in the table.

Test: Add rabbits until the population is about twice as large as it was (200% of balance). Click Play, and then Pause () after approximately ONE month. Next to each “Result” line in the table, write “Increase” or “Decrease.” Click Reset and then halve the rabbit population (50% of balance). Record the results for this experiment in the table as well.

How did doubling the rabbit population affect the grass, snakes, and hawks at first?

How did halving the rabbit population affect the grass, snakes, and hawks at first?

(Activity A continued on next page)

Activity A (continued from previous page)

Predict: Predict how changing the snake and hawk populations will affect the other organisms within the first month. In the tables below, write your predictions.

Test: Click Reset. Try each experiment with the Gizmo. Record each result after one month.

How did increasing the snakes affect the grass?

Explain why:

How did increasing the hawks affect the rabbits?

Explain why:

Draw conclusions: In general, what effect did removing prey have on predators?

What effect did removing predators have on prey?

Activity B: Long-term changes

Get the Gizmo ready: Click Reset. Select the GRAPH tab.

Question: An ecosystem is a group of living things and their physical environment. How do ecosystems react to major disturbances?

Observe: Kill off most of the hawks using the – button, and then click Play. Observe the GRAPH for about 12 months, and then click Pause. What happens?

Analyze: Explain why you think the population of each organism changed the way it did. (Use extra paper if necessary.)

Experiment: Click Reset. Try making other changes to the ecosystem. Use the + or –buttons, or choose Diseased from the dropdown lists. Click Play and observe for at least 12 months. Record what happens on another sheet of paper or in your notes.

Summarize: Give at least one example of each of the following:

A major disturbance that the ecosystem was able to recover completely from.

A major disturbance that caused the ecosystem to stabilize at a new equilibrium.

A major disturbance that caused the ecosystem to completely collapse.  

(Challenge) A major disturbance that almost caused a total collapse, but that the ecosystem was able to recover from eventually.