Assignment II. 2 Food Chain Gizmo

lOMoARcPSD|23780900 Student Exploration: Food Chain Vocabulary: consumer, ecosystem, energy pyramid, equilibrium, food chain, population, predator, prey, producer 3 points for each response in a question. 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. 1. Producers are organisms that do not need to eat other organisms to obtain energy. A. Which organism is a producer in this food chain? grass B. Where does the producer get its energy the sun 2. Consumers must eat other organisms for energy. Which organisms are consumers in this food chain? Hawks, snakes, and rabbits Gizmo Warm-up The SIMULATION pane of the Gizmo shows the current population, or number, of each organism in the food chain. 1. What are the current populations of each organism? Hawks: 42 Snakes: 278 Rabbits: 2566 Grass: 27300 2. Select the BAR CHART tab, and click Play ( ). What do you notice about each population as time goes by? The population of rabbits and grass increases. If populations don’t change very much over time, the ecosystem is in equilibrium. 3. Notice the populations decrease as you go from the bottom of the food chain to the top. Why do you think this is so? It works out because there are more producers than consumers. lOMoARcPSD|23780900 Get the Gizmo ready: Activity A: Predator-prey relationships  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? 1. 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. 2. Form hypothesis: How do you think predator and prey populations affect one another? The prey will become overpopulated and be a problem if the predators do not kill them. 3. 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. Change Doubling rabbit population Halving rabbit population Grass Snakes Hawks Prediction: Prediction: Prediction: Result: Result: Result: Prediction: Prediction: Prediction: Result: Result: Result: 4. 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. A. How did doubling the rabbit population affect the grass, snakes, and hawks at first? Snakes and hawks increased while grass decreased. B. How did halving the rabbit population affect the grass, snakes, and hawks at first? It led to a rise in grass and a decrease in hawks and snakes. ___________________________________________________________________ (Activity A continued on next page) lOMoARcPSD|23780900 Activity A (continued from previous page) 5. 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. Change Doubling snake population Halving snake population Grass Hawks Prediction: Prediction: Prediction: Result: Result: Result: Prediction: Prediction: Prediction: Result: Result: Result: Change Doubling hawk population Halving hawk population Rabbits Grass Rabbits Snakes Prediction: Prediction: Prediction: Result: Result: Result: Prediction: Prediction: Prediction: Result: Result: Result: 6. Test: Click Reset. Try each experiment with the Gizmo. Record each result after one month. A. How did increasing the snakes affect the grass? The grass also grew when there were more snakes. B. Explain why: Expanding the snake populace caused a reduction in bunny populace which permitted the grass to increase. C. How did increasing the hawks affect the rabbits? The increase in hawks led to an increase in rabbits. D. Explain why: The population of snakes decreased as a result of an increase in hawks, allowing the rabbit population to rise. 7. Draw conclusions: In general, what effect did removing prey have on predators? Because they won't have anything to eat, there won't be as many predators. What effect did removing predators have on prey? Because there are no predators to eat them, it lets the number of preys grow. Extend your thinking: In North America, many top predators, such as wolves, have been driven nearly to extinction. What effect do you think this has on their main prey, deer? Write your answer on a separate sheet, and/or discuss with your classmates and teacher. Activity B: Long-term changes Get the Gizmo ready:  Click Reset.  Select the GRAPH tab. lOMoARcPSD|23780900 Question: An ecosystem is a group of living things and their physical environment. How do ecosystems react to major disturbances? 1. 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? While the rabbit population decreased, the snake and grass populations increased. This happened because there are more snakes because there are no hawks to eat them, which made the population of grass and rabbits shrink. 2. Analyze: Explain why you think the population of each organism changed the way it did. (Use extra paper if necessary.) Since snakes are eating more rabbits, the grass grew because rabbits aren't eating it. Additionally, there are more snakes because there are no animals to eat them. 3. 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. 4. Summarize: Give at least one example of each of the following: A. A major disturbance that the ecosystem was able to recover completely from. a reduction in predators and prey B. A major disturbance that caused the ecosystem to stabilize at a new equilibrium. reduction in hawks C. A major disturbance that caused the ecosystem to completely collapse. a reduction in grass D. (Challenge) A major disturbance that almost caused a total collapse, but that the ecosystem was able to recover from eventually. eradicating the entire rabbit population