WLHS/Ecology Field Studies/Oppelt
Name__________________________
Food Web Activity
Introduction
A food web describes the flowing cycle of energy within an ecosystem. In turn, each food web is made
up of many food chains. While food webs consist of multiple interwoven feeding relationships, involving
many animals eating more than one kind of food, a food chain is a simple line of feeding relationships
between organisms, with each organism generally eating only one other in the chain. Each step in a food
chain is known as a trophic (or “feeding”) level. The first trophic level consists of producers, such as
seaweed and algae that capture the sun’s energy through photosynthesis converting it into nutrients that
can be used by themselves and other organisms. The second trophic level consists of primary
consumers, like damselfish and queen conch (refer to Figure 1) that gain energy (nutrients) by feeding
on producers. Primary consumers are also known as herbivores, because they eat only plants. At the
next trophic level are secondary consumers, like sea stars and grouper, which feed on primary
consumers. Tertiary consumers can be found even further up the food chain and consist of larger
consumers, like sharks or barracuda that eat secondary consumers. Many secondary and tertiary
consumers are carnivores, meaning that they eat only meat. However, some, like hawksbill turtles or
hairy clinging crabs, are omnivores, meaning that they eat both plants and animals. Depending on the
number of organisms in an ecosystem, and their food preferences, there can be varying numbers of
further trophic levels, including both carnivores and omnivores in their ranks.
Scavengers and decomposers are two other important kinds of organisms, located at the base of every
food web. Scavengers, including such organisms as spiny lobsters and shrimp, are essentially garbage
collectors, feeding on others’ leftovers and bits of dead organisms. Decomposers, including certain
bacteria and fungi, break down nonliving organic matter into nutrients that can then reenter the food web,
beginning the cycle of energy all over again.
Figure 1: Aquatic food web
Questions from Introduction
1. What is a food web?
2. What is each level in a food chain called?
3. What do primary consumers primarily feed on? _________________ Give an example____________
4. True/False (circle one). Scavengers and decomposers are found at every trophic level.
5. a. Give an example of a scavenger.______________________________
b. Give an example of a decomposer_____________________________
