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

Background information: (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.

Materials * poster paper * markers * Pictures

Procedures:
Assignment
Create an Everglades food web. 1. On a piece of construction paper, or poster board, paste at least 20 pictures of organisms that live in the Everglades. Make sure to include producers, consumers and decomposers. Paste the pictures randomly over the entire piece of paper. Write the name of each organism under the picture. 2. Identify the role of each organism in the ecosystem by writing one of the following letters beneath the name of the organism: (P) Producer, (C) Consumer, (D) Decomposer 3. Color code their role and include a key. 4. Draw an arrow between each food source and the organism that eats that food. Remember that the arrow represents the flow of energy. 5. On the back of the paper, name and paste the pictures of 3 invasive (nonnative) species.

Observation/Data Analysis:

1. Find and write 3 food chains. The food chains must include a producer and three levels of consumers (primary, secondary, tertiary). Label them. 2. Sketch a trophic pyramid using one the food chains you created and place the names of your organism at the proper level.

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. Review your trophic pyramid, do you think there are more organisms at the base and less organisms as you travel up the pyramid. 5. In theory, the earth could support many more people if we ate at a lower trophic level. a. List 2 benefits of doing this. b. List 2 drawbacks of eating lower on the food chain. 6. 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? 7. Large predatory animals can also be problematic to eat because of bioaccumulation and biomagnifications of toxins such as lead or mercury in their habitats. What do those two big words mean and why should this be considered when discussing food chains and trophic levels. 8. How do nonnative species affect an ecosystem? Give and explain a specific example from your project.

Summary-Use the seven questions to write a summary for this activity. Must be at least 15 lines typed.