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This Takes Guts!
Investigating food webs and trophic levels through gut content analysis
7-4.2 Illustrate energy flow in food chains, food webs, and energy pyramids.
To understand feeding behavior and ecology, scientists will often analyze the food items found
inside an organism's stomach. These findings help scientists understand where a particular
animal falls in food chains and food webs.
In front of you are three stomachs that have been removed from three different species of
sharks found in South Carolina waters (labeled A, B, and C). It is your job to figure out where
these sharks and their prey items fall in a food web. Possible prey items may include large fish,
small fish, shrimp, squid, or possibly other sharks.
Step 1: Using the information above, fill in the headings of the table below (the
highlighted cells):
Step 2: Start with shark stomach A. Carefully cut open the stomach and search inside
for prey items. Remove the prey items from the stomach and record the numbers of
each type of prey in your data table.
Step 3: Now let’s try stomach B. Again, cut open and record the number of prey items.
Make sure you do not mix up the prey from stomach A with those from stomach B.
Step 4: Do the same thing for stomach C- cut open the stomach and record the number
of prey items.
Question 1: Did you see a difference in the size of the prey items in the three
stomachs? Which stomach had the largest prey, and which stomach had the smallest?
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A
B
C
Step 5: Fill in the Venn diagram above with the prey items found in each of the
stomachs.
Step 6: Using your Venn diagram, fill in the shaded cells with the prey items going from
the lowest trophic level to the highest (bottom of the food chain to the top). Then, in
the next three rows, color in the cells of the prey items found in each stomach.
Low trophic level
High trophic level
A
B
C
Question 2: Using the information from your Venn diagram and the chart above, are
these sharks on the same trophic level or different trophic levels? How do you know? If
they are on different trophic levels, rank them from lowest to highest.
Question 3: Now put everything you have discovered together and draw a food web of
this system, including all of the prey items and all of the sharks:
Question 4: Finally, we are going to take everything we know about this system and
create an energy pyramid. An energy pyramid shows the amount of energy that moves
from one trophic level to another in a food chain. Energy availability decreases as it
moves up the energy pyramid, so the producers (with the most energy) will be the base
of the pyramid and the top predators (with the least energy) will be at the very top.
In the spaces of the pyramid below, fill in the names of the organisms that occupy the
corresponding tropic level:
Level 7- Top Carnivores
Level 6- Carnivores
Level 5- Carnivores
Level 4- Carnivores
Level 3- Predators
Level 2- Herbivores
Phytoplankton etc.
Level 1- Primary producers