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How Stable is Your Food Web?


The following lesson, Our Hungry Planet, is brought to you by the California Academy of Sciences.


Life Science, Systems & System Models




Prep Time: 15 minutes

Activity Time: 105 minutes

In this lesson, your students will design and use a simple model to test cause and effect relationships or interactions concerning the functioning of a marine food web, ranking their hypothetical ecosystems according to their stability when faced with a natural or man-made disturbance.

Essential Question: What makes a stable ecosystem?

This lesson follows the 5-E pattern. Day 1 (50 minutes) features Engage, Explore, and Explain. Day 2 (50 minutes) covers Elaborate and Evaluate.

Feel free to take your time with this sequence of activities, turning the lesson into a sub-unit. Note: The suggested time frames are on the tight side.


After this activity focusing on the kelp forest ecosystem, students will be able to

  1. Recognize a food web as a system, and describe a food web in terms of its components and its interactions.
  2. Provide examples of how a healthy ecosystem is one in which multiple species of different types are each able to meet their needs in a relatively stable web of life.
  3. Design and use a simple model to test cause and effect relationships or interactions concerning the functioning of a marine food web.


Related Files

Scientific Terms for Students

  • biodiversity: the variety of life on Earth or some other specified geographic region of the planet
  • carnivore: an animal that eats meat (i.e., other animals)
  • consumer: an organism, such as a cow or a shark, that must eat other organisms to obtain energy-rich food molecules because they cannot make the molecules themselves; consumers are also called heterotrophs
  • decomposer: an organism that breaks down organic material over time
  • detritus: dead and decaying matter, including animal waste
  • ecosystem: the community of different species in a particular geographic area and all of their interactions with each other and the physical environment; ecosystems are also called ecological networks
  • energy: the ability to do work or cause change
  • food chain: a series of events in which one organism eats another and obtains energy
  • food web: the pattern of overlapping food chains in an ecosystem
  • herbivore: an animal that eats plants; also called a primary consumer
  • kelp forest: marine ecosystem where large, brown algae called giant kelp grow omnivore: an animal that eats both plants and animals
  • organism: a living or formerly living thing
  • plankton: microscopic organisms that live in the ocean and other bodies of water; phytoplankton are plant-like and can photosynthesize; zooplankton are animal-like and cannot photosynthesize
  • producer: an organism, such as a plant, that can make its own energy-rich food molecules from inorganic materials and an energy source such as sunlight; producers are also called autotrophs
  • stable: resistant to change, or able to return to a steady condition when disturbed

Day 1: Educator Prep

  1. Print out one animal sheet per student. Because your class size may vary, here’s a ranking of organisms to produce functional food chains for this demonstration (for example, if you only have 12 students, print up to the barnacle, and the activity will still work): zooplankton, crab, small fish (anchovy), phytoplankton, big fish (salmon), squid, seal, shark, kelp, shrimp, sea bird, barnacle, sea star, mussel, rock snail, baleen whale, octopus, toothed whale, sea urchin, sea otter, limpet, clam, abalone. This isn’t a true ranking; it merely sets you up for success if you have a small class size.
  2. Test the video quality on your school’s internet connection. Note that you can click the Settings cog in the footer to adjust the Quality to up to 1080HD, and you can also toggle on Full Screen.

Select a location in the classroom to serve as the sun, from which all food chains will start (e.g., drawing on the board, your desk).

Engage (15 minutes)

  1. Pass out organism cards randomly.
  2. Have kids play games to explore the animals in the ecosystem to notice similarities and differences, and connect to prior knowledge.
    • Find a partner who … (makes food from the sun, is smaller than a cell phone, swims with fins or flippers). Talk and share.
    • Line up in size order from the smallest creature to the biggest one. Use your best guess!
    • Organize in five clumps according to your role: producer vs herbivore vs carnivore vs decomposer vs omnivore.

Explore (20 minutes)

  1. Task for the class: Self-organize into many food chains by standing in a line from the start of energy production at the sun to the end of the energy flow, placing your hand on the shoulders of the student who is giving you energy. Each food chain should include at least three organisms (teacher tip: a producer + consumer + decomposer OR a producer + herbivore consumer + carnivore consumer). See examples below, starting at the sun:
    • – kelp – sea urchin – sea otter – shark
    • – kelp – abalone – octopus
    • – phytoplankton – krill – baleen whale
    • – phytoplankton – limpet – anchovy – squid
    • – zooplankton– anchovy – salmon – seal
    • – phytoplankton – clam – sea otter
  2. Freeze and verbally review. In turn, have producers, consumers, etc., raise their hand, and have students notice the pattern. Discuss the size of the creatures, and the size of the population of said creatures. Review the transfer of matter and energy, and highlight how it starts at the suns. (Teacher tip: this is where the content in the Disciplinary Core Idea LS2.A is made explicit!)
  3. Pass out two pieces of yarn per student. They can remain the same organism for the next task. Explain that the yarn represents the interaction between the organisms, in the same way that our arms connected us before.
  4. Task for the class: Self-organize to make a full web, connecting yourself to two other organisms. (Teacher tip: this is the part of the activity where Systems are made explicit.)
  5. Through discussion, walk through the following:
    • What are the component parts? (living organisms with different roles in the food web)
    • How are they related? (they interact by eating each other, which translates into sharing matter and energy)
    • What does the yarn symbolize as an interaction? What is flowing through the system? (sharing matter and energy)
    • The yarn doesn’t show the direction of energy flow. How can we model this? (students receiving the energy could wiggle or raise their fingers) Teacher tip: If you’d like to focus on LS2.B Matter and Energy, this would be one food place to do so, while the web is intact. This Causal Patterns in Science Rubric may help you gauge student understanding. Depending on your class level, you can discuss the cycling of matter and how energy is lost.
    • Can we find an organism that could be removed from the web, without leaving another species high-and-dry with nothing at all to eat?

Explain (20 minutes)

  1. Sit back down with student notebooks out. Show students the Take a Virtual Dive in a Kelp Forest clip. As they watch, students should pay attention to:
    • Which animals from our class food web did you notice? How were they described?
    • What were the main points from the video?
  2. Show students selected sections from the Ecosystems and Ecological Networks tutorial, as appropriate for their level.
    • What are the main points from the video?
    • What makes an ecosystem extra resilient to change/keeps it stable?
    • Considering the kelp forest as an example of an ecosystem network, which of the organisms might play a more crucial role than others?

Day 2: Educator Prep

  1. Post up butcher paper on three walls or the ground.

Elaborate (25 minutes)

  1. Split class into three large groups.
  2. Group task: ask your students to design the most healthy, most stable kelp forest ecosystem on your piece of butcher paper. Yesterday they stood up to make the model with their bodies – now they will make a flat one on this piece of butcher paper. This is a model that shows how energy and matter is traveling through the food web, and how each organism interacts with others. After 25 minutes, the class will test these three ecosystems against each other by altering the circumstances according to a real-life scenario for the coast of California, so students should try to make your food web as realistic and stable as possible (teacher tip: this involves including as many different kinds of species as possible, but don’t spill the beans). Have the students refer to their notes from yesterday. They will have only 25 minutes and can use all these pictures, yarn, colored dots, markers, etc. Keep it messy, but be sure to include:
    • The sun
    • Something that shows the number and variety of organisms (the components of the system)
    • Something that shows how energy and matter is being transferred through the food web (the interactions of the system)
    • Check for understanding: As students are working, remind them to indicate how many of each creature exists. While the numbers don’t matter, the relative numbers do – producers should outnumber consumers. Also, check their understanding of the energy flow up the chain.

As students finish, write the "Which Ecosystem is Most Stable?" table on the board, along with a rough numeric rubric.

Evaluate (25 minutes)

  1. Teacher tip: this is where the Crosscutting Concepts of Stability and Change & Cause and Effect come into play. Explain that when you read through the scenarios, the class will discuss what domino effects will occur in each sample ecosystem, and rate each one on their stability.
  2. Using the students’ ideas, walk through the cause and effects. We’ve listed some sample effects, but it’s more important that the students themselves do the thinking. Don’t adjust the physical webs; simply discuss and use as a springboard to tackle key content. The teacher can assign a 1-5 rating for each ecosystem for stability, and add it to the chart on the board.
  3. Total up the columns. Which of the three ecosystems was highest functioning when changes came along? Why?
  4. Ecosystems need to be balanced, but involve regular change. What are some examples of changes that might be beneficial for the ecosystem as a whole?


In their science notebooks, have students explain how they would revise the most stable ecosystem model based on what they learned through the scenarios.

Also, have them answer the following review questions:

  • What are the components of the food web system, and how do they interact with each other?
  • Why does a healthy ecosystem need multiple species of different types to remain stable?
  • List one example of a natural ecosystem disturbance, and another that is caused by humans.


For elementary and middle school

Explore how people can engage in activities that help monitor changes to ecosystems so that we can keep them stable. Examples include:

For middle school

Expand the lesson to categorize and discuss types of interactions such as competitive, predatory, and mutually beneficial. See Ecosystems and Ecological Networks for more background information, discussion questions, and vocabulary.

Focus on LS2.B: Cycle of Matter and Energy Transfer in Ecosystems in a deeper way. Causal Pattern in Ecosystems by Project Zero at Harvard’s Graduate School of Education is a useful curriculum guide.

Background for Educators

California Coast Ecosystem

The California Coast is home to some of the richest temperate marine ecosystems. This environment is prosperous due to an abundance of algae and phytoplankton that support large populations of organisms. Algae and phytoplankton combine organic compounds with the energy from the sun to form sugar in the process called photosynthesis. This production of their own food is why these photosynthetic organisms are referred to as producers. Phytoplankton are microscopic, plant-like organisms that live in the ocean. They are the most common food source for marine herbivores.

Primary consumers such as zooplankton and limpets feed on algae and phytoplankton to obtain their energy. Zooplankton are tiny animals and animal-like organisms, usually with a calcium carbonate shell, that eat phytoplankton. A few examples are krill and fish larvae. They are a major food source for small fish, baleen whales, gastropods, and birds. In turn, the zooplankton (and other primary consumers) nourish even larger organisms, from anchovies to seabirds to whales. Other organisms such as sea otters and white sharks eat these consumers. Another important group of organisms in the ocean food web are decomposers. Decomposers such as bacteria and crabs break down dead organic matter and keep the marine ecosystems healthy.

There are many scenarios that demonstrate the complex level of interdependence of organisms along the California Coast. To illustrate this, students can make a food web. A food web is used to show the relationships between organisms in an ecosystem, overlapping food chains to demonstrate how these organisms are all connected and rely on each other for food. While this activity focuses on biotic components of an ecosystem, The Concept of the Ecosystem includes abiotic factors, too.

Next Generation Science Standards

Disciplinary Core Ideas (5-9)

  • LS2.A: Interdependent Relationships in Ecosystems
  • LS2.B: Cycle of Matter and Energy Transfer in Ecosystems
  • LS2.C: Ecosystem Dynamics, Functioning, and Resilience

Science and Engineering Practices (5-9)

  • Developing and Using Models: Develop a model to predict and/or describe phenomena. Use a model to test cause and effect relationships or interactions concerning the functioning of a natural or designed system.

Cross-Cutting Concepts (5-9)

  • Systems and System Models: A system can be described in terms of its components and their interactions.
  • Stability and Change: Small changes in one part of a system might cause large changes in another part. Some systems appear stable, but over long periods of time they will eventually change.
  • Cause and Effect: Cause and effect relationships may be used to predict phenomena in natural or designed systems.


For more standard alignments, resources, and references, visit How Stable is Your Food Web on the California Academy of Sciences educator website.