Designing Food Chains and Food Webs

Designing Food Chains and Food Webs

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Designing Food Chains and Food Webs

NGSSS:

SC.912.L.17.9 Use a food web to identify and distinguish producers, consumers, and decomposers. Explain the pathway of energy transfer through trophic levels and the reduction of available energy at successive trophic levels. AA

(Also addresses SC.912.E.7.1, SC.912.L.17.10)

Background: (Source: www.epa.gov)

All organisms in an ecosystem need energy to survive. This energy is obtained through food. Producers obtain energy by making their own food whereas consumers must feed on other organisms for energy. This dependence on other organisms for food leads to feeding relationships that interconnect all living things in an ecosystem. A food chain illustrates the simplest kind of feeding relationship. For example, in a forest ecosystem, a grasshopper feeds on plants. The grasshopper is consumed by a spider and the spider is eaten by a bird. Finally, that bird is hunted by a hawk. A food chain clearly shows this pathway of food consumption.

You could probably think of another food chain for a forest ecosystem. In fact, many different food chains exist in ecosystems. Although there are many different kinds of food chains, each food chain follows the same general pattern. A link in a food chain is called a trophic, or feeding level. The trophic levels are numbered as the first, second, third, and fourth levels, starting with the producers.

Each of the trophic levels is occupied by a certain kind of organism. Producers are always in the first trophic level since they do not feed on another organism. Consumers occupy the rest of the trophic levels. The second trophic level is the first consumer in the food chain and is called a primary consumer. Primary consumers eat plants and are therefore herbivores or omnivores. The next consumer in the food chain is the secondary consumer. The secondary consumer is in the third trophic level. Since the secondary consumer feeds on another animal, it is a carnivore or an omnivore. Similarly, the tertiary consumer occupies the fourth trophic level, and is a carnivore. The last link in a food chain is also referred to as the top carnivore since it is at the top of the food chain and is not hunted by other animals.

Problem Statement: Are food chains and food webs the same? How do organisms transfer energy?

Vocabulary: food chain, food web, producer, consumer, decomposer, energy transfer, trophic level

Materials (per group):

  • butcher paper or poster paper
  • markers

Procedures:

Group Assignment

Work in small groups of 3 – 4 to draw each of the connections in a food web of an ecosystem.

  1. On a piece of poster board, write the names of each organism starting with producers on the bottom and top predators at the top. (See accompanying list.)
  2. Identify the role of each organism in the ecosystem by coloring Green for producers, Red for Consumers and Orange for decomposers.
  3. Draw an arrow between each food source and the organism that eats that food. Remember that the arrow represents the flow of energy.

Observation/Data Analysis:

Individual Assignment: (On the back of your poster)

  1. Find and write as many food chains as you can from your team’s food web (minimum of 3). Two of the food chains must include a producer and three levels of consumers (primary, secondary, tertiary). Label them.

Results/Conclusion:

  1. Explain what would happen if all of the primary consumers became extinct.
  2. Predict what would happen if a non-native species is introduced into the food web.
  3. Explain why food webs with many species (biodiverse) are more resilient than those with few species.
  4. Large predatory fish usually are found at the 3rd or 4th trophic level of an energy pyramid. What does this mean in terms of energy loss?
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