Call of the Wild. Investigating Predator/Prey Relationships

Transcription

1 Biology Call of the Wild Investigating Predator/Prey Relationships MATERIALS AND RESOURCES EACH GROUP calculator computer spoon, plastic 100 beans, individual pinto plate, paper ABOUT THIS LESSON This lesson is designed to introduce the concept of predator/prey population cycles. One of the main points of this activity is to help students see that population sizes of predators and their prey fluctuate according to the same pattern, but one is offset in relation to the other. The data collected in this activity can be used as a reference point for terms used during presentations on community and ecosystem ecology. T E A C H E R P A G E S OBJECTIVES Students will: Investigate how a wolf and an elk population change over time in response to the other s presence and how each population relates to the other Participate in a guided inquiry activity using a computer simulation that is used to test studentcreated questions about the population cycles of sheep and wolves under several populationlimiting factors LEVEL Biology i

2 NEXT GENERATION SCIENCE STANDARDS COMMON CORE STATE STANDARDS DEVELOPING AND USING MODELS ANALYZING AND INTERPRETING DATA (LITERACY) RST Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text. CAUSE AND EFFECT PATTERNS (LITERACY) RST Translate quantitative or technical information expressed in words in a text into visual form (e.g., a table or chart) and translate information expressed visually or mathematically (e.g.in an equation) into words. LS2: ECOSYSTEMS (LITERACY) W.3 Write narratives to develop real or imagined experiences or events using effective technique, wellchosen details, and well-structured event sequences. (LITERACY) W.4 Produce clear and coherent writing in which the development, organization, and style are appropriate to task, purpose, and audience. (MATH) A-CED.2 Create equations in two or more variables to represent relationships between quantities; graph equations on coordinate axes with labels and scales. T E A C H E R P A G E S ii

3 ASSESSMENTS The following types of formative assessments are embedded in this lesson: Assessment of prior knowledge Discussions with students regarding proper graphing technique Discussions with students regarding proper interpretation of the graphs ACKNOWLEDGMENTS CONNECTIONS TO AP* AP BIOLOGY 2 D.1 All biological systems from cells and organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy. Wilensky, U., and Reisman, K. (1999). Connected Science: Learning Biology through Constructing and Testing Computational Theories An Embodied Modeling Approach. International Journal of Complex Systems, M. 234, pp This model is a slightly extended version of the model described in the paper. Wilensky, U., and Reisman, K. (2006). Thinking like a Wolf, a Sheep or a Firefly: Learning Biology through Constructing and Testing Computational Theories An Embodied Modeling Approach. Cognition & Instruction, 24(2), pp AP BIOLOGY 4 A.5 Communities are composed of populations of organisms that interact in complex ways. A.6 Interactions among living systems and with their environment result in the movement of matter and energy. B.3 Interactions between and within populations influence patterns of species distribution and abundance. B.4 Distribution of local and global ecosystems changes over time. T E A C H E R P A G E S *Advanced Placement and AP are registered trademarks of the College Entrance Examination Board. The College Board was not involved in the production of this product. iii

4 TEACHING SUGGESTIONS The students pretend to be the wolves with their spoon. The students can decorate their spoons to look like wolves. Prior to the activity, you will need to set out each group s materials. This activity should be conducted in a classroom setting rather than a laboratory setting since the students will be simulating predation by eating the prey (beans). Be sure to check for food allergies before conducting this activity. As an alternative, you may choose to use a non-food item for this simulation. For example, you could use colored beads as the prey. Discuss how to properly use a two-cycle semi-log graph. This simulation utilizes the Java application. Make sure that this application is updated to the latest version. You will need to have the following specifications to run the simulation. Windows users: Microsoft Windows XP/ Vista/2000/7 and Java 6 or later Mac users: OS 10.4 or later and Sun Java 6 or later If you have any technical issues, please refer to troubleshooting page on the website If you have computers and internet readily available, encourage your students to do the Challenge at the end of the activity. If you do not have access to the Internet in your classroom, the simulation can be downloaded to your computer or multiple computers in order to facilitate the lesson. If you only have one computer, you could project the image on a screen and facilitate Part II as a classroom discussion. This would also be a good idea for students who are struggling to get started with Part II. You could go through one or two of the prompts with them until they understand the methodology and then let them start asking their own questions. If you need to raise the rigor for students who can be pushed further than the parameters of this lesson, you might try the following suggestions: Participate in the Challenge at the end of the lesson. Have the students investigate other ecological disturbances due to density-independent and density-dependent factors. T E A C H E R P A G E S iv

5 HYPOTHESIS The elk population and wolf population will rise and fall at the same rate. DATA AND OBSERVATIONS PART I: PREDATOR/PREY CYCLES Generation Initial Elk Population Table 1. Elk and Wolf Data Elk Eaten Elk Survivors Initial Wolf Population Wolf Survivors Wolves Born A N S W E R K E Y v

6 ANALYSIS GRAPH 1: WOLF VS. ELK POPULATION SIZES OVER 25 GENERATIONS Figure A. Wolf vs. elk population sizes over time A N S W E R K E Y vi

7 ANALYSIS (CONTINUED) PART II: WOLF/SHEEP PREDATION Question #1 What would the affect be on the three different populations if the field consisted of four times as many wolves as sheep? Answers may vary depending on the data that the students collect. For example, the students should include all of the following criteria: A. Question: What would the affect be on the three different populations if the field consisted of four times as many wolves as sheep? B. Hypothesis: The wolves would kill all of the sheep and then, without any food, the wolves will either leave or die off. C. Methodology: I started the simulation by pressing Setup. Then I turned on grass? so that the simulation would keep track of its population. I then set the initial wolf population to 100 and the initial sheep population to 25, and then pressed the go button. I let the simulation run for 20 seconds and then observed what happened. D. Results: In a relatively short amount of time, all the wolves died off and the sheep and grass populations exhibited the same predator/prey cycles exhibited as the wolf and elk in Part I. E. Conclusion: As seen in Figure B, at the very beginning the wolf population had very little food and thus many of them died off. Eventually, there were not enough sheep to keep any of the wolves alive, and they all perished or left the area. Figure B. Wolf, sheep, and grass populations However, there were a few sheep left at this time, which began to repopulate. The sheep population rose whereas the grass population fell. There was a point where there was not enough grass to feed all of the sheep, and the sheep population began to decline. The rest of the graph shows the rise and fall cycles of the sheep and grass populations slightly offset from each other, which is indicative of predator/prey relationships. A N S W E R K E Y vii

8 ANALYSIS (CONTINUED) CONCLUSION QUESTIONS CHALLENGE Find three ways in which your group can manipulate the simulation so that both populations die off. When you figure this out, describe the limiting factors involved in creating this situation, and then explain why both populations were not able to survive. There are many ways in which students could create a situation where both the sheep and wolf populations would die off. One example is setting the grassregrowth-time very low (Figure C). This type of situation would be caused by a drought. The sheep population rises drastically, which consequently causes the grass population to drop. The grass has a tough time repopulating, which causes the sheep population to decrease to zero. With no food left, the wolf population also drops to zero. Figure C. Wolf and sheep populations dying off This challenge could be a competition between individuals or teams. 1. Write a statement describing the relationship between a predator population and a population of its primary prey. The population of the prey rises due to the low number of predators. Increased prey population causes the predator population to rise drastically. However, when there is not enough prey for the rising predator population, the number of predators begins to decline. This cycle continues if all other variables are held constant (adequate food for the prey, for example). 2. Look at the peaks and troughs seen in both populations. Explain how they relate to each other. The two populations have peaks and troughs that correlated to each other but are slightly offset of each other. 3. Describe a density-independent factor that might affect the elk population size. What effect would this have on the wolf population? A hurricane hits the area and kills off all but a few elk. This drastic decrease in the number of elk might cause the population to die off due to predation. This would consequently cause the wolf population to die off or emigrate to a new area due to a lack of food. 4. Describe a density-dependent factor that might affect the elk population size. What effect would this have on the wolf population? Increased temperature due to a drought might cause the elk population s food source to become less plentiful. This would drastically decrease the number of elk, which might cause the population to either die off or emigrate to another place. This would consequently cause the wolf population to either die off or emigrate form that area as well. A N S W E R K E Y viii

9 CONCLUSION QUESTIONS (CONTINUED) 5. Describe the relationship between the wolf and sheep populations over the time period indicated by the simulation. Justify your answers with evidence from the graph. As seen by the graph in the simulation, the wolf and sheep populations follow the same patterns as the wolf and elk populations in Part I of the activity. The population of the sheep rises due to the low number of wolves. Increased sheep population causes the wolf population to rise drastically. However, when there are not enough sheep for the rising wolf population, the number of wolves begins to decline. This cycle continues if all other variables are held constant (adequate food for the prey, for example). 6. Describe the relationship between the grass and sheep populations over the time period indicated by the simulation. Justify your answers with evidence from the graph. As seen by the graph in the simulation, the sheep and the grass populations follow the same pattern as the wolf and sheep populations. However, in this case the sheep are the predators and grass is the prey. 7. What indirect effect does grass have on the wolf population? Justify your answer with evidence from the graph. When the grass population is rising, this will inevitably initiate in a rise in the sheep population. This would inevitably cause a rise in the wolf population. On the other hand, a decline in the grass population would initiate a decline in the sheep population, which would initiate a decline in the wolf population. 8. Describe another predator/prey relationship that might follow a similar pattern as the ones seen in this lesson. Answers will vary. One example is the lynx and snowshoe hare populations of the boreal forest in Canada. 9. Contrast the different effects that occur between when all of the sheep die off and when all of the wolves die off. If all of the sheep die off, there will not be any food left for the wolves, and therefore they will either die off as well or emigrate to a new place. If all of the wolves die off, the sheep population with adequate amounts of food will continue to grow. 10. The brown tree snake still thrives on the island of Guam. Why is it still able to thrive while so much of its food has been eliminated? The brown tree snake also feeds on other organisms like small mammals and lizards. Therefore, even though the bird population has been drastically depleted, there are still other types of food of which the brown tree snake can feed. 11. Hypothesize what other community and ecosystem consequences have most likely occurred due to the introduction of the brown tree snake. Explain how each might affect the community and ecosystem. Answers may vary. One example is an increased population size of the bird s prey, such as spiders. The spider population on Guam has significantly increased since the bird population decreased. A N S W E R K E Y ix

10 Call of the Wild Biology Call of the Biology Wild Investigating Predator/Prey Relationships MATERIALS calculator computer spoon, plastic 100 beans, individual pinto plate, paper In the 1940 s, the island of Guam experienced one of the worst ecological disasters ever recorded. The brown tree snake (Boiga irregularis) was accidentally introduced to the island sometime between the end of the World War II and It was originally native to Australia and the South Pacific. The brown tree snake feeds mainly on birds, lizards, and small mammals. When it was introduced to the island of Guam, it started feeding primarily on the native bird population. To date, ten of the twelve native bird species have been completely decimated by the brown tree snake. The other two species are heavily protected to conserve their numbers. The effects of this invasive species are still being felt today on both community relationships and the ecosystem as a whole. PURPOSE In this activity, you will investigate predator/prey relationships. In the first part of this lesson, you will investigate how a wolf and an elk population change over time in response to the other s presence, and how each population relates to the other. In the second part, you will get to ask your own questions regarding a similar scenario, and use a computer simulation to experimentally test your hypotheses. 1

11 FOR THE SIMULATION This activity shows the predator/prey relationship between wolves and the elk that they feed on in a field habitat. The following rules must be followed in this simulation: The field will only sustain up to 100 elk. After predation has occurred, the remaining elk population will double. Due to immigration, the habitat will always contain at least 10 elk. Due to immigration, the habitat will always contain at least 1 wolf. Each wolf must eat up to 5 elk or it will die or emigrate (leaves the habitat in search of food somewhere else). For every 5 elk that a wolf eats, it has enough energy to produce 1 wolf cub. FOR THE GRAPH When displaying your data on a two-cycle semi-log graph, make sure that you follow the following rules: Label the y-axis starting with 1, not 0, at the bottom. Number each line increasing by 1 individual (2, 3, 4 ) until you reach 10 individuals. After 10 individuals, each line represents 10 more individuals than before (20, 30, 40 ). Label the rest of the y-axis until you get to 100 individuals. Give the y-axis a title. The x-axis represents the 25 generations. Give this axis a title as well. 2

12 PROCEDURE PART 1: PREDATOR/PREY CYCLES 1. How do you think that, over many generations, the wolf the elk population size relate to each other? Write your hypothesis on your student answer page. 2. Set up the habitat by placing 10 elk (beans) in a petri dish. One swipe of your spoon represents 1 wolf. Enter your initial populations of elk and wolf into Table With your eyes closed and one continuous swipe through the dish, pick up as many beans as you can with your spoon. Set the beans on the table beside the plate and count them. The number of beans represents the amount of elk that the wolf was able to consume. Record this number in Table Determine the number of surviving elk, surviving wolves, and if the wolves were able to reproduce or not, and record these numbers in Table 1. Remember that each wolf must consume at least 5 elk for 1 cub to be born. 5. Record the initial populations for the next generation. Remember that the surviving elk population will double. Count the number of surviving wolves and do not forget to add the number of new wolves to the starting population, as they will need to consume 5 elk as well. 6. Repeat Step 2 through Step 5 until you have 25 generations of data. When you have multiple wolves, then you will swipe that many times through the dish to generate your prey count. Do not forget to abide by the six rules as stated previously. 7. Graph the initial populations for both the elk and the wolves in Graph 1 (two lines). Graph 1 is a two-cycle semi-log graph that allows us to see both populations despite the large discrepancy in both values for wolves and elk. Now it s your turn! PART II: WOLF/SHEEP PREDATION For this activity, you will use a computer simulation as a tool to perform predator/prey experiments on a population of wolves and sheep. 1. Navigate to Click on the link, Run Wolf Sheep Predation in your browser. 2. Click on the red tab in the box that says grass? to turn on the grass. 3. Click on setup, then click go and let it run for 20 seconds. 4. After 20 seconds, click on go again to stop the simulation. 3

13 HYPOTHESIS DATA AND OBSERVATIONS PART I: PREDATOR/PREY CYCLES Table 1. Elk and Wolf Data Generation Initial Elk Population Elk Eaten Elk Survivors Initial Wolf Population Wolf Survivors Wolves Born

14 ANALYSIS GRAPH 1: WOLF VS. ELK POPULATION SIZES OVER 25 GENERATIONS 5

15 ANALYSIS (CONTINUED) PART II: WOLF/SHEEP PREDATION 1. Besides the presence of grass, what other variables are you able to manipulate in this simulation? RESEARCH QUESTIONS Following the steps of the scientific method, use the simulation to perform the following investigations to answer the questions or problems. After you have completed each investigation and have gathered the data, communicate your results in a brief paragraph using the following format: A. State the question. B. State your hypothesis. C. Briefly describe how you manipulated the simulation to run your investigation. Include in your description the following factors: Limiting factors Control groups Experimental groups Independent variables Dependent variables. Make sure that you write precise enough descriptions of your methodology so that other students could follow your exact procedure and get the same results. D. Make a screenshot of the generated graph to show your results. You might have to increase the size of the picture. E. Using data from the graph, describe what changes occurred to the wolf, sheep, and grass populations in the simulation. Explain why these changes occurred. 6

16 ANALYSIS (CONTINUED) Question #1 What would the affect be on the three different populations if the field consisted of four times as many wolves as sheep? Now it s your turn! Create your own questions and then use the simulation to investigate each one. Write your question in the space provided and then write your conclusion paragraph as outlined in Steps A E previously. Question #2 Question #3 CHALLENGE Find three ways in which your group can manipulate the simulation so that both populations die off. When you figure this out, describe the limiting factors involved in creating this situation, and then explain why both populations were not able to survive. 7

17 CONCLUSION QUESTIONS 1. Write a statement describing the relationship between a predator population and a population of its primary prey. 2. Look at the peaks and troughs seen in both populations. Explain how they relate to each other. 3. Describe a density-independent factor that might affect the elk population size. What effect would this have on the wolf population? 4. Describe a density-dependent factor that might affect the elk population size. What effect would this have on the wolf population? 8

18 CONCLUSION QUESTIONS (CONTINUED) 5. Describe the relationship between the wolf and sheep populations over the time period indicated by the simulation. Justify your answers with evidence from the graph. 6. Describe the relationship between the grass and sheep populations over the time period indicated by the simulation. Justify your answers with evidence from the graph. 7. What indirect effect does grass have on the wolf population? Justify your answer with evidence from the graph. 8. Describe another predator/prey relationship that might follow a similar pattern as the ones seen in this lesson. 9

19 CONCLUSION QUESTIONS (CONTINUED) 9. Contrast the different effects that occur between when all of the sheep die off and when all of the wolves die off. 10. The brown tree snake still thrives on the island of Guam. Why is it still able to thrive while so much of its food has been eliminated? 11. Hypothesize what other community and ecosystem consequences have most likely occurred due to the introduction of the brown tree snake. Explain how each might affect the community and ecosystem. 10