Problem Set Answers: Trophic Level Calculations



Problem Set Answers: Trophic Level Calculations

1) Calculate the number of grasshoppers a hen needs per year.

25 grasshoppers/day X 365 days = 9,125 grasshoppers/year

1 hen

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 365 days = 219,000 grasshoppers/year

day 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.

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