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ICE Inquiry-based Curriculum Enhancement Lesson Plan: Species Interactions General Description This activity is designed to reinforce an understanding of basic concepts in ecology as well as the use of basic equations of population growth. It also serves to illustrate scientific study of biodiversity and conservation. Objectives Students will be able to describe the basic features of a network of species interactions using ecological concepts (predator, prey, interaction, stability). Students will be able to calculate population growth from exponential and logistic equations. Students will be able to comprehend how predictions are made and evaluated in the process of science Students will be able to apply their knowledge to a novel case in a homework assignment, inferring ecological dynamics from this prior knowledge. Students will be able to recognize and identify how understanding ecological networks and species interactions contributes to conservation efforts regarding biodiversity. Concepts Ecology, Prey, Predator, Keystone Predator, Exponential Population Growth, Logistic Population Growth, Conservation, Biodiversity, Hypothesis, Prediction Time 50 minutes Prerequisite Skills Nominal familiarity with most of the key concepts listed above. One or two lectures on ecology introducing growth equations. Materials Koosh ball sea urchins, paper kelp communities, sea otter puppet Overheads: Calculations, Questions Student Handout Optional Homework Assignment ICE Inquiry-based Curriculum Enhancement UTI Instructions: Species Interactions Introduction: This activity is designed to reinforce an understanding of basic concepts in ecology as well as the use of basic equations of population growth. It also serves to illustrate scientific study of biodiversity and conservation. Procedure: 1. Explain that you will be exploring two key concepts in ecology: the study of populations in their natural environment and the interactions they have with other species. We will utilize formulas frequently used in ecological studies and practice making predictions about how ecological communities respond to changes in the community. [1 minute] 2. Describe that there are two basic hypotheses about the interactions among species in ecological communities. (1) Species are interdependently interacting—if you remove one you dramatically affect the others (‘house of cards effect’); and, (2) Species are independently interacting—if you remove a species there is little or no effect on others (‘removal has little effect’). We will be focusing on species interactions among predators and prey in ecological communities. Distribute the student handout. Have students write one prediction on their worksheet that could be tested to distinguish between these two different hypotheses. Solicit two volunteers to share their predictions. [3 minutes] 3. Simulation 1—Ecology of offshore marine communities [5 minutes] a. In your sea floor community there are a number of different species. We will be focusing on three of them: sea otters, sea urchins, and kelp. b. Ask for four volunteers to be ‘sea otters’, three volunteers to be responsible for laying out paper sea urchins, and two individuals to lay out 20 paper kelp colonies. Ask other volunteers to be responsible for calculations during the activity (to keep track of relevant numbers on the Calculations Overhead). c. Some ecological details of our sea floor community: (1) Sea otters are predators of sea urchins (prey). (2) Each kelp colony supports 5-6 other species such as small fish, sea slugs, algae, or sea horses. Kelp colonies can only persist if there is enough space on the sea floor for them to be anchored. (3) The reproductive rate is at ‘replacement’ for the sea otters and kelp colonies, i.e. they reproduce such that the total number of organisms will be the same in each generation unless another factor (such as predation) intrudes. (4) If the sea urchin population rises above certain levels, kelp colonies die due to space unavailability. [sea urchins ≥ 60, two kelp colonies die; sea urchins ≥ 120, four colonies die; sea urchins ≥ 160, six colonies die; sea urchins ≥ 250, all remaining colonies die.] d. Place 20 paper sea urchins around the kelp colonies on the ‘sea floor’. If we use this as the starting population number (Nt) and take the reproductive rate of the sea urchins (r = 1.1), we can use our equation for exponential population growth to give us the population number in the next generation. Thus we would add 22 more sea urchins to our sea floor area. Simulate 4 more generations, filling in numbers on the transparency. 4. Simulation 2—Introducing predation. Each sea otter eats 5 sea urchins per generation. Thus, four sea otters eat 20 urchins and bring the population from 42 back down to 22. Simulate 4 more generations. [5 minutes] 5. Simulation 3—Introducing predation in higher trophic levels. A hungry killer whale strays into our marine community and eats one of our sea otters. With one sea otter gone, simulate five generations of sea urchin population growth. [5 minutes] 6. Analyzing the Simulations [8 minutes]. Divide the class into 4 groups and assign each group one question from the Questions Overhead. Each group has 3-4 minutes to work on their question. Then have students report their answers back to the class. Record the groups’ contributions on the board. 7. Simulation 4—Introducing logistic population growth [12 minutes] a. One problem with using the exponential population growth equation is that it doesn’t account for limited resources—there is only so much sea floor area for sea urchins to live on. The sea floow in this simulation can support a maximum of 250 sea urchins. This is the carrying capacity (K) of our sea urchin population. Knowing the carrying capacity of a population allows us to incorporate limited resources into our calculations of population growth. This is called the logistic population growth equation. b. Have students take 2 minutes to modify their original prediction to make a specific prediction for this new simulation. c. Simulate five generations using four sea otters for predation but with the new equation for calculating population growth. d. Have students take 2 minutes and evaluate their prediction. 8. Analyzing the Simulation [8 minutes]. Return to original groups and have students reconsider their first group question using the logistic population growth equation. [Begin a list on the chalkboard entitled “Differences with Limited Resources” off to one side of your previous summary notes.] Have students report back after 5 minutes on how these differences altered their earlier answers. [Remind students to write their answers down on the handout] 9. Put up the Big Questions Overhead and open up the discussion to the entire class for the remaining class time. [~ 5 minutes] Simulation Calculations KEY (1) Simulation: Exponential growth, No predation DN=Nt x r Nt+1=DN+Nt Generation 1 2 3 4 5 Nt 20 42 88 185 389 r 1.1 1.1 1.1 1.1 1.1 DN 22 46.2 96.8 203.5 427.9 Nt+1 42 88 185 389 817 # kelp deaths 0 2 6 all dead all dead Nt+1 22 26 35 54 93 # kelp deaths 0 0 0 0 2 Nt+1 27 42 73 138 275 # kelp deaths 0 0 2 4 all dead Nt+1 20 20 20 20 20 # kelp deaths 0 0 0 0 0 (2) Simulation: Exponential growth, Predation DN=Nt x r 1 otter eats 5 urchins each generation, 4 otters present Nt+1=DN+Nt-20 Generation 1 2 3 4 5 Nt 20 22 26 35 54 r 1.1 1.1 1.1 1.1 1.1 DN 42 24.2 28.6 38.5 59.4 (3) Simulation: Exponential growth, Predation DN=Nt x r 1 otter eats 5 urchins each generation, 3 otters present Nt+1=DN+Nt-15 Generation 1 2 3 4 5 Nt 20 27 42 73 138 r 1.1 1.1 1.1 1.1 1.1 DN 42 29.7 46.2 80.3 151.8 (4) Simulation: Logistic growth, Predation DN=Nt x r[1-(Nt/K)] 1 otter eats 5 urchins each generation, 4 otters present Nt+1=DN+Nt-20 Generation 1 2 3 4 5 Nt 20 20 20 20 20 r 1.1 1.1 1.1 1.1 1.1 1-(Nt/K) .92 .92 .92 .92 .92 DN 40 40 40 40 40 Group #1: What would happen if the reproductive rate of sea otters increased from r = 1 to r = 1.3? Do the calculations for five generations or until all kelp colonies are dead. Note: do a separate population growth calculation for the sea otters before calculating their sea urchin predation. Group #2: What would happen if the killer whale ate two sea otters instead of one? Do the calculations for five generations or until all kelp colonies are dead. Group #3: What would happen if the reproductive rate of sea urchins decreased from r = 1.1 to r = 1.04? Do the calculations for five generations or until all kelp colonies are dead. Group #4: What would happen if the reproductive rate of kelp colonies increased from r = 1 to r = 1.5? Do the calculations for five generations or until all kelp colonies are dead. Note: do a separate population growth calculation for the kelp colonies before calculating their removal due to sea urchins. (1) Simulation: exponential growth, no predation Generation Nt r DN Nt+1 kelp deaths 1 ___ ___ ___ ___ ___ 2 ___ ___ ___ ___ ___ 3 ___ ___ ___ ___ ___ 4 ___ ___ ___ ___ ___ 5 ___ ___ ___ ___ ___ (2) Simulation: exponential growth, predation Generation Nt r DN Nt+1 kelp deaths 1 ___ ___ ___ ___ ___ 2 ___ ___ ___ ___ ___ 3 ___ ___ ___ ___ ___ 4 ___ ___ ___ ___ ___ 5 ___ ___ ___ ___ ___ (3) Simulation: exponential growth, predation Generation Nt r DN Nt+1 kelp deaths 1 ___ ___ ___ ___ ___ 2 ___ ___ ___ ___ ___ 3 ___ ___ ___ ___ ___ 4 ___ ___ ___ ___ ___ 5 ___ ___ ___ ___ ___ Gen Nt r 1-( Nt/K) DN Nt+1 kelp deaths 1 ___ ___ ___ ___ ___ ___ 2 ___ ___ ___ ___ ___ ___ 3 ___ ___ ___ ___ ___ ___ 4 ___ ___ ___ ___ ___ ___ 5 ___ ___ ___ ___ ___ ___ Big Questions Each sea otter feeds on sea urchins from many different areas of the sea floor, which means the outcomes of species interactions in one area apply to many other areas. Sea otters are therefore ‘keystone predators’ in these ecological communities. Consider: ÿ What does our example imply about the stability of ecological habitats? Do all species contribute equally to stability? How does stability relate to our initial hypotheses about species interactions? ÿ If we discovered that a fish species living among kelp colonies in these marine communities was disappearing, what would a strategy to prevent it from going extinct? Given what we know, what should be done to preserve this fish species? Practically, will we be able to do what needs to be done? ICE Inquiry-based Curriculum Enhancement Pre-Activity Worksheet: Species Interactions General Description In the activity you will do this week during your learning/discussion group, you will be examining species interactions. In order to be prepared for this activity, complete this worksheet. Reading Browse the “Community Ecology” chapter in your text. Pay particular attention to figures 54.6, 54.8, and 54.10. Read the section on the Interspecific Interactions beginning on pages 1164-1167. Definitions Write a definition of the following words. Use your text, textbook glossary, and your previous knowledge to create the best definition possible. Remember to connect your definitions to species interactions. 1) community 2) predation 3) interspecific interactions 4) keystone species 5) hypothesis Questions Answer the following questions. You will explore your answers to these questions in-depth during learning/discussion group. 1) Which type of species interaction do you think has the most influence on communities and community structure? Defend your answer. 2) Predation and parasitism are both +/— interactions. Why do ecologists examine these interactions separately? Which type of interaction is more common in nature? What evidence do you have for your decision? 3) Name three keystone species of different communities that are not named in your textbook. What leads you to believe that these species are keystone species? ICE Inquiry-based Curriculum Enhancement Species Interactions In this activity you will create some predictions regarding species interactions and use a simulation to investigate these predictions. Different species interact in multiple ways: species can compete for the same resource, one species can prey on another, species can benefit each other, and in other ways. Focus specifically on predation. We can create two hypotheses to describe predation: A. Species are interdependent — any change in the predator or prey species will affect the other species. B. Species are independent — changes in the predator or prey species do not affect the other species. From these hypotheses, many predictions can be created; these predictions can either seek to support or refute one or the other. For example, consider this prediction: If there are too many predators in an ecological community, then some prey species will go extinct. If this situation occurs in nature, then hypothesis A is more likely to describe species interactions. Create two predictions about predator/prey interactions that each support or refute either of the above hypotheses. Identify which hypothesis each of your predictions addresses. Prediction 1 Prediction 2 (1) Simulation: Exponential growth, No predation DN=Nt x r Nt+1=DN+Nt Generation 1 2 3 4 5 Nt ___ ___ ___ ___ ___ r ___ ___ ___ ___ ___ DN ___ ___ ___ ___ ___ Nt+1 ___ ___ ___ ___ ___ # kelp deaths ___ ___ ___ ___ ___ Nt+1 ___ ___ ___ ___ ___ # kelp deaths ___ ___ ___ ___ ___ (2) Simulation: Exponential growth, Predation DN=Nt x r 1 otter eats 5 urchins each generation, 4 otters present Nt+1=DN+Nt-20 Generation 1 2 3 4 5 Nt ___ ___ ___ ___ ___ r ___ ___ ___ ___ ___ DN ___ ___ ___ ___ ___ (3) Simulation: Exponential growth, Predation DN=Nt x r 1 otter eats 5 urchins each generation, 3 otters present Nt+1=DN+Nt-15 Generation 1 2 3 4 5 Nt ___ ___ ___ ___ ___ r ___ ___ ___ ___ ___ DN ___ ___ ___ ___ ___ Nt+1 ___ ___ ___ ___ ___ # kelp deaths ___ ___ ___ ___ ___ Nt+1 ___ ___ ___ ___ ___ # kelp deaths ___ ___ ___ ___ ___ Answers to our question New prediction with logistic growth (4) Simulation: Logistic growth, Predation DN=Nt x r[1-(Nt/K)] 1 otter eats 5 urchins each generation, 4 otters present Nt+1=DN+Nt-20 Generation 1 2 3 4 5 Nt ___ ___ ___ ___ ___ r ___ ___ ___ ___ ___ 1-(Nt/K) ___ ___ ___ ___ ___ DN ___ ___ ___ ___ ___ Evaluate your prediction Did your prediction come true in the final simulation? Why or why not? Which hypothesis is more likely given the outcomes of the simulations? What evidence supports the hypothesis you chose? What changes could you make to either your predictions or the simulation details in order to better distinguish between the two hypotheses? Re-answer your question using logistic growth ICE Inquiry-based Curriculum Enhancement Individual Accountability: Species Interactions Demonstrate your new understanding of species interactions by answering the following question: Which of the following factors do you think has the greatest influence on a community — growth rate of the prey, growth rate of the predator, the number of predators, or the availability of food for the prey species? Defend your answer in four or five sentences. Use examples from today’s activity to support your answer. ICE Inquiry-based Curriculum Enhancement Take Home Worksheet: Species Interactions To practice with the concepts you learned in class today, answer the following questions. One good strategy for working with these questions is to answer them on your own to the best of your ability, then compare your answers with a fellow student. Together you will be able to create good answers to the questions. In all cases, be prepared to explain your reasoning clearly and succinctly. You were just hired as a wildlife biologist for the United States government to work in the upper Midwest. It has recently been brought to your attention that central Wisconsin deer populations are growing at an incredibly rapid rate in contrast to what has been the usual case over the past 50 years. You are not an expert on the local ecology but you have experience elucidating species interactions for marine sea floor communities. The only thing you know for sure is that it is not because of decreased hunting by humans. (1) What would be your first guess as to why the deer population has recently experienced explosive growth? (2) Calculate five generations of exponential growth for the deer population where Nt = 45 and r = 1.3. (3) Calculate five generations of logistic population growth with the same Nt and r, and with K = 450. (4) If the deer population continues to grow unchecked, what consequences would you expect for other species? Why? (5) What policy would you recommend to keep the deer population in check, if any? Assume you were asked to justify your policy. Respond with an ‘if-then’ predictive statement that you believe is true of this situation and could be evaluated once your policy is enacted.
