How a Food Web Is Formed
What are food chains and food webs? Are they related? Answer these questions by playing this engaging and informative card game.
- Food web
- Tropic relationships
There are many types of organisms in an ecosystem. Organisms such as plants and algae are autotrophic. Autotrophs, or “self-feeders,” are able to produce their own food using the Sun’s energy. Other animals known as heterotrophs, or “other feeders,” cannot produce their own food. For example, deer which are heterotrophs, eat grasses which are autotrophs. Some heterotrophic animals, known as predators, eat other animals. Examples of predators are largemouth bass, sharks and coyotes. The animals that are fed upon by predators are known as prey.
One way to study the relationships between organisms in an ecosystem is to look at their feeding habits. Trophic relationships deal with the types of food organisms eat and how organisms are dependent on one another. The word trophic is defined as “to eat” and is a root word found in both the terms autotrophic and heterotrophic. Autotrophs and heterotrophs are also respectively known as producers and consumers (see Figure 1).
Producers are autotrophic and at the bottom of the food chain. Consumers are heterotrophic and are generally classified into three other subgroups—herbivores, carnivores and omnivores. Herbivores obtain energy by only eating plants. Examples of herbivores are cows, deer and rabbits. Carnivores, such as snakes and owls, only eat other animals. Omnivores, such as humans and bears, eat both plants and animals. All consumers are dependent upon producers in one way or another. Consumers may be further broken down into groups based on how far removed their food of choice is from the producers. Primary consumers feed directly upon producers, secondary consumers feed upon a primary consumers, tertiary consumers feed upon a secondary consumer and so on.
Within specific ecosystems food chains are formed. A food chain is a direct relationship between a producer, primary consumer, secondary consumer and a tertiary consumer. In some instances, a quaternary consumer may be involved. Other organisms known as scavengers and decomposers are involved in food chains as well. Scavengers eat dead animal and/or plant material. They do not directly hunt or prey upon animals. Turkey vultures are classic scavengers. Decomposers are organisms that break down tissues of living or non-living organisms. Decomposers absorb nutrients from organisms they feed upon. Fungi and bacteria are good examples of this group.
In nature, not all feeding relationships between organisms are formed directly in a food chain. There are many individuals that may prey or be preyed upon by different types of organisms. A food web more accurately defines these types of relationships. Food webs are networks of complex interactions formed by the feeding relationships among the various organisms in an ecosystem.
The number and types of producers and consumers in an ecosystem depend on the region where the ecosystem exists. Earth is divided into several different areas known as biomes. Biomes are defined by the types of animals, flowers and climate they contain. In general, there are five main biomes—aquatic, desert, forest, grassland and tundra. Biomes are further divided into different habitats or areas where an organism naturally lives.
In this activity, organisms from five different habitats—marine, desert, tropical rainforest, hardwood forest and swamp—will be studied. Food chains and webs will be formed for each of these habitats.
Desert Food Web Sheet
Desert habitat card set, yellow
Hardwood Forest Food Web Sheet
Hardwood forest habitat card set, red
Marine Food Web Sheet
Marine habitat card set, blue
Modeling clay, 1 stick
Rainforest Food Web Sheet
Rainforest habitat card set, green
String, approximately 25 feet
Swamp Food Web Sheet
Swamp habitat card set, purple
Wash hands thoroughly with soap and water before leaving the laboratory. Follow all normal classroom guidelines.
- Obtain one of the habitat card sets from the instructor. Each person should also obtain the appropriate Food Web Sheet from the instructor.
- Pick one member of the group to be the dealer.
- The dealer should shuffle the deck of habitat cards.
- Deal five cards to each person in the group.
- Place the remaining cards face down on the table top.
- The person to the left of the dealer should draw a card from the top of the pile.
- The card should be placed in the first person’s hand.
- The object of the game is to complete a food chain containing five organisms.
- Use the appropriate Food Web Sheet to confirm whether or not a food chain of five organisms has been formed.
- If a complete food chain of five organisms is not in the first person’s hand, one of the first person’s cards must be discarded face-down next to the original draw pile.
- The next player to the left may either pick up a card from the draw pile or the discard pile.
- Play continues clockwise until a food chain is formed.
- If cards run out in the draw pile, reshuffle the discard pile and use that as the new draw pile.
- When a player completes a food chain, it should be checked to make sure that it is complete and realistic.
- Resume play until all members of the group create complete food chains.
- When everyone in the group has a complete food chain, the first group member to complete their food chain should place their cards on the table top.
- The first member should cut four 5" pieces of string.
- Using clay, attach the pieces of string to the cards to form a food chain.
- Steps 17 and 18 should then be repeated by the other members of the group.
- Once the four food chains have been formed, determine what organisms from the different food chains may be linked together based on their trophic levels.
- Use additional clay and pieces of string to attach these organisms and form a food web.
- Answer the Post-Lab Questions.
- If time allows, obtain a different habitat card set from another group and repeat steps 1–21.
- All materials may be saved and reused.
- What is a trophic level?
- Are most habitats better described as a food chain or a food web? Why?
- What roles do decomposers and scavengers play in a habitat? What would happen if these organisms were not present?
- What would happen if a predator organism was removed from a certain habitat? Use specific examples from your group’s constructed food web.
- Can an organism be a secondary and tertiary consumer in the same ecosystem? Explain using examples from the game.
- In general, are there more tertiary consumers or producers in a healthy habitat? Why?
- Draw a food chain and a food web for organisms living in your area.