Feeding on Different Trophic Levels
A farmer grows soybeans and keeps chickens.
Grasshoppers feed on the soyabeans and the chickens eat the grasshoppers.
Soybeans 
Grasshoppers 
Chickens 
Farmer 
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/da
1. Calculate the number of grasshoppers eaten by one chicken per year.
1chicken = 50 gh = 1day
1 chicken = ? = 365days
=365x50
=18,250 grasshoppers
2. Calculate the number of grasshoppers eaten by all the chickens that the farmer eats in one year.
365 x18250
=6,661,250 grasshoppers
3. What is the mass of all the grasshoppers calculated in #2
6661250x1g
=6,661,250g
4. What is the mass of all the soybeans needed for all the grasshoppers calculated in #2
1 gh = 500g
6661250ghs=?
=3,330,625kg
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.
1
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.
5kj = 1sb
8700 kj = ?
=1740sb
=1740g
=1.74kg
7. Calculate how much mass of soybeans the farmer would need for one year.
1.74kgx365
=635.1kg
8. Compare the mass of soybeans in #7 and #4. How many people could the soybeans calculated in #4
feed.
=3330625kg/635.1
=5244people.
9. What are three pros and three cons for people to eat at a lower trophic level?
Pros
1. Planet could sustain far more people. If the farmer eats hens the ecosystem supports less people. When the
farmer eats soybeans, it can sustain far more people.
2. Feeding directly on the producers rather than feeding on the 3rd trophic level can support more people in this
situation.
3. An additional advantage is that eating vegetables Is healthier, especially if eating a well-balanced diet. Too
much meat can be bad for one’s health.
Cons
1. Feeding on lower tropic levels could result in broader areas used for monoculture, therefore reducing
biodiversity.
2. Also, without the hens, the grasshopper population could explode, causing a decrease in the soybeans
population.
3. Until the grasshopper population stabilized, there would need to be higher soy production to support both the
farmers and the grasshoppers.
10. Explain, using your knowledge of the laws of thermodynamics, why it is more efficient to eat at a
lower trophic level.

Nations with scarcity of food, it makes more sense for people to eat the producers rather than the consumers.
Much energy is lost between the producers and chickens, then between the chickens and the people.
Developing nations (as well as developed nations) could support more people or have a lower environmental
impact if people eats at lower trophic levels.
© Dr. Zoe Badcock, InThinking
www.thinkib.net/ess