Predator Prey Interactions Lab

Name : ANSWER KEY Ecology Lab - Predator Prey Interactions *home edition In any ecosystem, there are interactions between predators and prey, and herbivores, carnivores, and omnivores. The population numbers of each group depends on those interactions. Too many predators might cause the loss of a prey species. Not enough prey, could eliminate the predators because they won’t have enough to eat. This simulation will explore interactions of organisms that live in a forest ecosystem. Process 1. Open the simulator *You may want to split your screen so you can look at this document while running the simulation. 2. The simulation will start with two plants highlighted. What do you think will happen to these plants in this ecosystem? Can they both survive together? Why or Why not. Most students will say yes, because there are a lot of plants in the world that do survive fine together. 3. Run the simulation until it stops at Day 100. Observe the population in the graph. . 4. Describe what happened to Plant A and to Plant B: Plant A did well, plant B died. 5. The competitive exclusion principle states that two species in the same environment will compete for resources. In those cases, one species will be the winner and one will be the loser. Consider the two plants. What resources are they competing for, and why would one of them be the winner? Your answer requires you to make some assumptions about how these plants live. Answers vary. Plants can compete for light and for space and for soil nutrients. Plant A was the “winner” in this case. What happens when a herbivore is added? 6. RESET the simulation. Choose the rabbit and then determine what happens when it eats plant A and then plant B. Enter the final totals in the data table by estimating from the graph. Run the simulation until it reaches 100 days. Reset between each test. Note: You can roll your mouse over the line on the graph to get the population number. Plant A final population Plant B final population Rabbit final population Rabbit (eats only plant A) 3335 4998 2055 Rabbit (eats only plant B) 10,000 0 0 0 3333 6667 Rabbit (eats both Plant A & B) 7. In which scenario is the ecosystem the most stable? Suggest a reason for this and use the word COMPETITION in this explanation. When the rabbit only eats plant A, that allows the opportunity for B to grow. The rabbit keeps plant A numbers low, which reduces competition. 8. Most herbivores are GENERALISTS , and will eat almost any plant available to them as food. It is unrealistic to have a herbivore that only eats plant A. Though some animals are SPECIALISTS and do only eat one type of food. -Reset the simulation and activate all 3 herbivores and set them to eat both plant A and plant B. What happened to plants A and B when all three herbivores were present and ate them both? Plant A became extinct, plant B died. 9. This scenario is different from when there was just a rabbit present. Some generalists also have a preference for certain food types. Suggest a reason for the outcome when all three herbivores were present. The animals may have had a preference for plant A and it became overgrazed. When plant A was gone, the animals switched to plant B. 10. Add a squirrel to the ecosystem that also eats both plant A and Plant B. Describe what happens to the squirrel in this setting. The squirrels died 11. Why do you think this outcome occurs in this setting? What is wrong with the squirrel? Squirrels could not compete with the other herbivores. 12. Squirrels are omnivores. Rest the simulation and change the squirrels’ food source to include snails and a tree (plant C). What happens to the squirrels now? What happens to the herbivores? they did very well they died 13. Suggest a reason that added a food source that only the squirrels ate impacted the ecosystem so much: When the squirrels were able to populate the area, they ate all the other plants and snails, and those populations declined 14. CHALLENGE: How can you get the herbivores and plants and the squirrel to coexist in this ecosystem? You will need to adjust what each one eats until you can create a graph where they all survive. What each eats: Rabbit Snail Deer Squirrel plant A plant B plant A plant A, herbivore B *there may be other combinations that work. The trick is to have the herbivores mainly eat plant A which is the dominant species. 15. Describe the populations of each of the organisms in this food web. *Answers may vary Which plant has the greatest population size? Which type of animal has the lowest population size (herbivores or omnivores)? B omnivores 16. Another aspect of the competitive exclusion principle is that animals that compete within the same environment may eventually come to occupy their own NICHE . A niche is a way of life, and includes how the animal lives, what it eats, reproduction strategies and more. For example, a hawk and owl both eat the same kinds of food, but the owl hunts at night and the hawk during the day. How did your final ecosystem (The Challenge from #14) illustrate this aspect of the competitive exclusion principle? Each animal feeds from a different type of plant. This reduces competition among them. Graph of completed challenge: Part 2: Explore Predator and Prey Interactions Predators and prey populations often cycle. For example, if there are more rabbits in an ecosystem, there can be more wolves. As the wolves increase in number, the number of rabbits will begin to decline. This is called a PREDATOR PREY CYCLE. Process: Click the green button that says “presets” to clear your other data and start fresh. In this simulation, we are going to simplify things. You will have a rabbit, plant A, and a wolf. - Set the simulation to run with these plant A, a rabbit, and a wolf. - This time, use the “STEP” button to run the simulation to year 30. 17. Complete the table below. ( - Scroll over the lines to determine the population size at each time period.) Day 0 Day 5 Day 10 Day 15 Day 20 Day 25 Day 30 Plant A 5000 3824 2821 4010 3850 3534 4148 Rabbit 1000 3114 2047 1705 2306 1977 1847 Wolf 10 13 30 31 41 60 70 18. What happened to the plant population between day2 and day 10? Explain why this occurred. it decreased because it was being eaten by rabbits 19. What happened to the rabbit population between day 5 and day 10? Explain why this occurred. the rabbit population declined because the wolves were eating them 20. What happened to the plant population between day 10 and day 20? Explain why this occurred. plants increased because there were fewer rabbits eating them 21. At 30 days, compare the wolf population to the rabbit population: the wolf population increased, but it was never greater than the rabbit population 22 Click the run button to take the simulation to day 200. What ultimately happens to all three populations? The populations seem to stabilize, the numbers didn’t change as much 23. Predict what would happen if we added another herbivore to the system. *You can run this sim if you want* Assessment Would the number of wolves increase? Why or why not It would increase the number of wolves because they would have more to eat, or the herbivore would deplete the resources and wolves would have nothing to eat Would the number of rabbits increase? Why or why not? it may increase the number of rabbits because the wolves would have more to eat, it may also decrease the number of rabbits if resources get depleted *These answers are not in the simulation, APPLY what you have learned. 24. Pandas are animals that are SPECIALISTS and only eat one type of food (bamboo) in the forest where they live. If another animal moves into the forest and also eats that type of food. What will likely happen to the panda? The panda might become extinct, because the other animal would eat all of its food. 25. Two species of barnacles live in shallow areas of the ocean. One species tends to live at the top of rocks and the other lives in the lower areas. Explain how this illustrates the COMPETITIVE EXCLUSION PRINCIPLE ? The two animals don’t COMPETE with each other because they are in different spots and can share resources. 24. A wolf is a KEYSTON E species. Explain how the wolf indirectly affects the population numbers of plants. The wolf keeps herbivore species down so that there is less grazing on plants.