Problem Set Answers: Trophic Level Calculations
1) Calculate the number of grasshoppers a hen needs per year.
25 grasshoppers/day
1 hen
X
365 days = 9,125 grasshoppers/year
In other words, one hen requires 9,125 grasshoppers per year.
2) How many grasshoppers are needed for year’s supply of hens for the farmer
each year?
365 days x 9125 grasshoppers = 3,330,625 grasshoppers
In other words, a year supply of hens requires 3,330,625 grasshoppers.
3) What is the total mass, in kilograms, of the grasshoppers needed to feed all
the hens for one year?
1000 grasshoppers have a mass of 1 kg. Therefore…
3330625 = 3330.625 kg/year
1000
4) How many kilograms of soybeans are needed to feed all the grasshoppers for
one year?
1 grasshopper requires about 30 g of soy/year
30 g of soy/year x 3330625 grasshoppers = 99918750 g of soy beans
99918750 g/1000g = 99918.75 kg of soy bean
5) How many people could the grasshoppers feed, compared to the one person
that the hen fed?
1 human requires about 600 grasshoppers/day. Therefore…
600 grasshoppers x
day
365 days = 219,000 grasshoppers/year
year
3,330,625 grasshoppers/year by hen = 15.2 people
219,000 grasshoppers/year by person
6) The farmer needs to consume 3,000 cal/day. If he ate only soybeans instead of
the hens or the grasshoppers, how many people would his soybean crop feed (see
response to question 4)
99,918,750 grams of soy beans
3,000 cal x 365 day = 1,095,000 cal/year/person requirement
day
year
99,918,750 grams x 3.3 cal = 329,731,875 cal/yr/person via hens
gram
329,731,875 cal/yr by hen = 301.125 people
1,095,000
~ 300 people can be supported by direct consumption of soy beans.