Trophic Mysteries: Solving the Cascade Effect

Work with a partner ecologist to solve this mystery case study. This is based on a real-world problem that actually happened. Use your knowledge of trophic cascades, biomass pyramids, food webs, and bioaccumulation to problem solve like a real scientist!

Source 1

You are an environmental scientist, and a case was dropped on your desk this morning. Within the National Park, all of the songbird species are having issues with laying eggs. The eggs that are laid in 25/32 nests within the park had eggs that were too thin for the birds to incubate them, and they have broken, all within a 3 week time period. You must figure out what is causing this issue with bird fertility as soon as possible, before the bird populations within the National Park decrease any further.

Source 2

Image Osprey 3 eggs - thin egg shells crushed the baby birds within when the birds went to nest on them

Source 3

Egg color is also altered for only the birds within the National Park.

Group 1

Evidence: You and your partner collected remnants of broken eggs from 3 park nests, as well as the remnants of eggs from hatched chicks (of the same species) of 3 healthy nests not found in the park. Here is what you find: 

Eggshells Data Report:

Look for patterns in data tables:
An easy way to outline patterns is to 1) practice looking at data tables and 2) using colors to highlight the words and numbers that are similar vs. different. On MISA, you will have the opportunity to highlight in 2 different colors on the test screen.

Source 1.1

Notice the nests inside the park don't just look different, and they're not just hatching too soon - they also have fewer numbers of eggs in each nest than a non-affected nest. This implies that there is an issue with the bird laying the eggs.

Source 1.2

You notice that not only are the National Park’s eggs thin and crack easily, but there are fewer eggs per nest as well!

You and your partner brainstorm and research - what can cause this to happen to birds? A suspicious toxin, DDT, comes up in your research.

What is DDT?

DDT is a chemical used as a pesticide (chemical to kill unwanted bugs) for crops. It is a known toxic substance, but it has never been used inside National Park before. This is important because we have to use our knowledge to figure out how the birds inside the park were exposed to this poison. Otherwise, we won’t be able to fix the problem.

Testing:

You test the eggshells from National Park and from the other healthy locations. Your partner does the same test separately. Both of you determine the same results:

Again, look at the data table and use colors to highlight the patterns.

Source 1.3

Source 1.4

But How?!

Now, your job is to determine how the birds of National Park became poisoned by pesticide that was never present in the park. Use your knowledge of the trophic cascade, the rule of 10’s, bioaccumulation, and energy cycling within an ecosystem to determine how the birds were exposed to toxic levels of DDT. 


This is your purpose/goal. All of the quiz questions are designed to build together to answer this one essential question: How were the birds exposed to toxic levels of DDT?

Group 2

What did the birds eat?
Complete the following trophic pyramid to determine where the birds are within this ecosystem’s food chain. Be sure to include the following organisms and identify whether they are producers or (levels of) consumers.

Source 2.1

Question 2a

Multiple choice

What organism represents Trophic Level 1:

Mosquitoes
“Mr. Whiskers” the feral orange cat that roams around National Park
Pond algae affected by DDT (Dichlorodiphenyltrichloroethane) at the nearby farm
Songbirds of National Park

Question 2b

Multiple choice

What organism represents Trophic Level 2:

Mosquitoes
“Mr. Whiskers” the feral orange cat that roams around National Park
Pond algae affected by DDT (Dichlorodiphenyltrichloroethane) at the nearby farm
Songbirds of National Park

Question 2c

Multiple choice

What organism represents Trophic Level 3:

Mosquitoes
“Mr. Whiskers” the feral orange cat that roams around National Park
Pond algae affected by DDT (Dichlorodiphenyltrichloroethane) at the nearby farm
Songbirds of National Park

Question 2d

Multiple choice

What organism represents Trophic Level 4:

Mosquitoes
“Mr. Whiskers” the feral orange cat that roams around National Park
Pond algae affected by DDT (Dichlorodiphenyltrichloroethane) at the nearby farm
Songbirds of National Park

Question 2e

Multiple choice

Which trophic level represents producers?

Trophic Level 1
Trophic Level 2
Trophic Level 3
Trophic Level 4

Question 2f

Multiple choice

Which trophic level represents primary consumers?

Trophic Level 1
Trophic Level 2
Trophic Level 3
Trophic Level 4

Question 2g

Multiple choice

Which trophic level represents secondary consumers?

Trophic Level 1
Trophic Level 2
Trophic Level 3
Trophic Level 4

Question 2h

Multiple choice

Which trophic level represents tertiary consumers?

Trophic Level 1
Trophic Level 2
Trophic Level 3
Trophic Level 4

Group 3

You and your partner sample some pond algae from a nearby farm just outside of National Park.  The farmer admitted that he applied DDT last month to the stagnant pond as a pesticide to decrease the number of mosquitos that were propagating there.  You run tests to determine that one sample of algae contains 58,900 ppm of DDT.

Use your knowledge of trophic cascades and the Rule of 10's to determine how much DDT had accumulated in the songbirds' bodies prior to laying their eggs. 

(You may use a whiteboard to solve the data table and submit your answers here):

Question 3a

Multiple choice

How much DDT in ppm is calculated to be carried by the mosquitoes that were born in the DDT-contaminated pond?

58,900
58.9
0.589
5,890

Question 3b

Multiple choice

How much DDT in ppm is calculated to be consumed by the songbirds when they eat an affected mosquito?

58,900
589
0.589
5,890

Question 3c

Multiple choice

What percentage of matter is transferred to the next trophic level during consumption of one organism?

100%
50%
10%
5%

Question 4

Multiple choice

As Mr. Whiskers, the feral park cat, goes trotting by you and your partner during the investigation, he jumps up and swipes a small bird out of the air and takes off running with his hunted prize. 

How much DDT is Mr. Whiskers ingesting when he consumes one songbird?

58,900 ppm
58.9 ppm
0.589 ppm
5,890 ppm

Question 5

Short answer

Based on what you know about the trophic cascade, and the amount of energy and matter that is used after being consumed, do you think Mr. Whiskers could get sick if he eats 15 birds within a 1-2 week time period? Why or why not?

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