Trophic Level Lab
Lesson 19 of 23
Objective: Students will be able to construct an energy pyramid using trophic levels and explain the flow of energy and its components. Students will be able to describe the effect competition, density-dependent factors and density independent factors have on an ecosystem.
Warm-up: Spend five minutes soliciting input from students to complete the graphic organizer. Conduct the activity whole group, with you selecting students to contribute responses. Use a LCD projector to project the organizer. If you have an interactive board, allow students write in the responses on the board.
Look for students to be able to identify how food webs and foods are alike and different.
Introduce New Material
Start the lesson with a review of concepts from the previous lesson, Food Chain, Food Webs. Ask students 5-7 questions that will help to you assess whether or not you will need to review previous content more or less before beginning the lab. For example,
- What is used to indicate the flow of energy in a food chain or web?
- What happens to energy as we move from step to step in a food chain or web?
- Define food web.
- What is meant by trophic levels?
- Define autotroph.
- The 1st trophic level consists of what group?
- What are detritivores? What do they eat?
- What organism feeds on dead plants and animals and helps recycle them?
Make sure that you are selecting several students throughout the review. Make it a point to call on the “silent” students who do not raise their hands; not as punishment but in an effort to find it if they are “lost” in the concept comprehension.
Based on students’ understanding of the content, decide whether to delay introducing the lab until after previous concepts are remediated. Do not move forward with new material the there is a sense that all or most students understand the concepts that have already been taught.
Once the review is complete, introduce the Trophic Level Lab. Introduce new vocabulary terms: density-dependent factors and density-independent factors. Provide information and examples of both types of limiting factors. Display the definitions as you talk. Read the Australian rabbit problem aloud to students. Use this problem to tie the new terms to a real world situation. Ask student to identify what factors in this situation are density dependent or density-independent? Require students to explain their answer.
Distribute the Trophic level lab Instructions to students. Project the instructions on a LCD project and provide a verbal summary of the lab materials and procedures. Display the instructions for the lab while summarizing the lab procedure to meet the needs of different learners. Distribute the lab report form so that students are able to refer to it as you explain the lab process.
Display and Explain the five ecological roles for this lab. Assign students to one of five roles: Producers, Rabbits, Snakes, Hawks and recorder:
- Grass: hold bags of popcorn; consumable source of energy for entire system, producers
- Rabbits: consume grass and try to avoid being eaten by higher level consumers
- Snakes: consumers who try to consume as many rabbits as possible (collect their bags) and aviod being eaten by hawk
- Hawk: consume both rabbits and snakes (collect both rabbit and snake bags)
- Data Collector: assists with the count after each round of the game and records values on data table
Be sure to reinforce the safety rules. Students tend to get a little carried away with the game so make frequent reminders that this is not a tackle activity. Model how a touch on the sleeve is sufficient. Also remind students that grass doesn’t run. Share the rubric that will be used to grade the assignment.
Take the class outside to conduct the lab. Conduct three trials of the lab following the changes noted in the ecosystem for each of the three trials. After completing all three trials, return inside. The recorder will write the data from the lab on the board for students’ use to complete the data tables and graph. Instruct students to complete the analysis questions and graph.
I included these three examples of student work because each evidences mastery in different ways for different reasons. This student accurately depicts the energy pyramid, even including the sun as the source of energy. This student also evidences understanding of concepts but shows lesser detail with the energy pyramid and more with the graphic display of the lab findings. Finally, this student shows great detail in constructing complete and accurate responses to the analysis questions. All three are correct, with each showing a distinct strength.
Ask, “What effect will there be on a population in an ecosystem that has no competition or natural predators?” Use the experience from the lab to help students consider what would occur. Ask questions like, what if there were no snakes in the lab today, how would the rabbit population be affected? Or, ask How would the grass be affected if the rabbit population had no predators.
Look for students to identify that life will grow until a point that the available resources will be diminish due to overpopulation of organisms.
If students struggle with this question, plan to revisit food chains and food webs in the next class session using a game or questioning session as a means to review concepts.