6. Food Webs - Lesson Plan
For organism research
- Tell students that they are going to spend the next day(s) researching an organism in preparation for a field trip. Their job is to become the resident expert on their organism and to be able to spot it and identify it when we are in the field. To gather information, they will be using field guides (and the Internet). Tell them how their organisms will be chosen.
- Show them the overhead of the Field Guide page. Using an organism of your choice, lead them through the field guide page, clarifying any questions and vocabulary words. This is a good opportunity to demonstrate using a published field guide to find information. For example, a "habitat" means the place or environment in which an organism is typically found. The habitat includes where that organism finds food, water, shelter and space. Particularly confusing for some students is concept of diagramming a life cycle. Use your example organism to diagram the life cycle since many students may not have used a life cycle diagram before.
- Answer any final questions then allow students to pick their organisms and get started. I had my students pick their organism out of a hat and allowed them one extra pick if they did not like their first pick.
- Circulate among the students as they research their animals, answering questions and helping students who are stuck.
For food web activity:
- Have students sit in a large circle at the edge of the classroom. Ask for a volunteer to share their animal. Have that student go sit in the middle of the circle. Throughout this whole process, allow each student no more than 1 minute to share since time will run short very quickly otherwise. In the interest of time, I had each student share the animal's food chain, one interesting piece of information from the life cycle, and to describe whether there is anything currently threatening your organism's survival.
- Ask if anyone has an organism that is part of the same food chain. Encourage that student to share in the middle of the circle. Give the 2 students a ball of yarn and stretch a length of yarn between them.
- Continue getting students to join the length of yarn until the longest possible food chain is created. Have volunteers help add the sun, a producer, and a decomposer to the food chain using the appropriate index cards. Stretch the line the entire length of the circle and spread the students out evenly along the line.
- Cut the yarn and set the yarn down on the floor, leaving the student's field guide pages and index cards arrayed along the yarn. The students can rejoin the circle. You should now have a 4-5 organism long food chain that stretches the length of the classroom.
- Ask if anyone else could have been part of the food chain but was not. Discuss why a food chain is only the simplest representation of who eats who in an ecosystem. Introduce the idea of a food web - tangled food chains that represent the interdependence of organisms in an ecosystem.
- Begin adding additional organisms to the food web. Give each student an opportunity to share briefly then use yarn to add his or her organism to the food web. Students will discover that some organisms share the same role in the food web, eating the same sources of food and being eaten by the same predators (such as all small mammals: rodents, squirrels, and rabbits). These organisms can all be placed beside one another in the food web and do not need to be connected to other organisms with separate pieces of yarn since they share the same connections as the others next to them.
- When everyone has shared, ask students to make observations about what they see. Some questions you may want to consider:
- Why is a food web a better representation of who eats who in an ecosystem than a food chain? Is a food chain useful at all?
- Where are the producers in the food web? The herbivores? The carnivores? The omnivores? The dentritivores?
- How many different herbivores are there compared to carnivores?
- If we had created pages for producers, would you expect there to be more producers or herbivores? Why?
- How can several organisms share the same food sources and not have 1 organism outcompete the others?
- Which organisms are endangered/threatened? What does that mean? Why are they endangered?
- What would happen to the rest of the food web if an organism became extinct? Does it matter if the extinct species is a herbivore or a carnivore? Why?
- What would happen to the rest of the food web if the habitat was damaged by pollution or construction?
- Allow some time to gather up the field guide pages, the index cards, and the yarn before the next class enters.