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5.2 Impact of Feeding on Different Trophic Levels

In this activity you will explore the energy transfer impacts of feeding on different trophic levels. This will help to explain why meat consumption has a big impact on climate change.

 Teacher only box

This has amazing effects when students complete the exercise and they realise the energy impacts of eating meat. It always stimulates a lot of debate. Sometimes I have used it early in the course when I discover misconceptions about "being more efficient" to eat meat, otherwise it can be used in topic 5 or 6.

The answer key can be found here Feeding on Different Trophic Levels - Answers . Teachers can choose when to turn this page on for students.

Here is a link to the handout.

Student Task

A farmer grows soybeans and keeps chickens.

Grasshoppers feed on the soyabeans and the chickens eat the grasshoppers.

For this exercise:

  • The farmer eats one chicken per day
  • The farmer weighs 100 kg
  • An average chicken weighs 3 kg
  • The chicken eats 50 grasshoppers per day
  • A farmer needs to eat 800 grasshoppers per day to survive
  • A grasshopper eats 500 g of soya per year
  • 1000 grasshoppers have a mass of about 1kg
  • dry soyabeans contain about 5 kJ/g
  • A farmer needs about 8700 kJ/day

Soybeans

Edamame by mdid

Grasshoppers

American Bird Grasshopper

Chickens

Farmer

  1. Calculate the number of grasshoppers eaten by one chicken per year.
  2. Calculate the number of grasshoppers eaten by all the chickens that the farmer eats in one year.
  3. What is the mass of all the grasshoppers calculated in #2
  4. What is the mass of all the soybeans needed for all the grasshoppers calculated in #2
  5. Draw an ecological pyramid of biomass showing the biomass of hens / grasshoppers / soybeans eaten by one farmer if he only consumes one hen per day. Use the numbers for one year in your pyramid. Make sure you use a scale and show this scale.
  6. Now calculate the mass of soybeans a farmer would need to eat in one day to provide him with his daily needs of energy.
  7. Calculate how much mass of soybeans the farmer would need for one year.
  8. Compare the mass of soybeans in #7 and #4. How many people could the soybeans calculated in #4 feed.
  9. What are three pros and three cons for people to eat at a lower trophic level?
  10. Explain, using your knowledge of the laws of thermodynamics, why it is more efficient to eat at a lower trophic level.

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