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Eating at A Lower Trophic Level – What’s the Point?

Background
A trophic level, or feeding level, is made up of all the organisms whose energy source is the same number of consumption steps fromthe sun in a given ecosystem. The trophic level of plants (autotrophs, primary producers) is 1, herbivores (heterotrophs, primary consumers) is 2, those that eat herbivores (carnivores, heterotrophs,secondary consumers) is 3, and so on. Higher trophic levels can exist for animals even higher on the food chain. In this exercise you will compute numerical values for human energy needs based ondiets at different trophic levels.

Situation
The owner of a soybean farm raises chickens for food & for insect control. Chickens will eat grasshoppers and other insect pests & ticks. They alsoact as a ‘watchdog’ by making a lot of noise when intruders approach their territory. The farmer allows the chickens to eat in his fields during the day & provides a shelter for them at night.

Forthe purposes of the following excercises, you may make these assumptions:
• The farmer can survive eating 1 chicken/day for a year
• 1 chicken eats 25 grasshoppers/day
• 1,000grasshoppers have a mass of 1 kg
• 1 grasshopper eats about 30g of soy/year
• 1 human requires 600 grasshoppers/day to survive
• dry soybeans provide about 3.3 calories of energy/gram

Answerthe following questions on a separate sheet of paper. Write the question in pen, but do all work and answer all questions in pencil. For questions that require calculations, show all of your work andcircle your answer.

1. Calculate the number of grasshoppers a chicken needs in a year.




2. How many grasshoppers are needed to supply the farmer with all the chickens he needs in a year?3. What is the total mass (in kg) of grasshoppers needed to feed all of the chickens for a year?




4. How many kg of soybeans are needed to feed all the grasshoppers (answer #2) for...