If the coyote needs 1,500 calories a day to survive...?

Question

If the coyote needs 1,500 calories a day to survive, how much energy must be available in the grass level of the food chain grass → rabbit → coyote to supply this

a. 15 calories

b. 150 calories

c. 1500 calories

d. 15,000 calories

e. 150,000 calories

Im really not sure how to find this answer, could somebody please explain how to solve this problem?

Answer 1

This is a question of energy conversions as you go up the food chain (producers get energy from the sun and convert it to use themselves, consumers get their energy by eating the producers or other consumers.)  Because all organisms use the energy for their own lives and not all parts are properly digested, not all of energy is transferred up the line.

What level of class are you taking?  For an introductory college class or lower (high school and down), you would be safe using the 10% rule - where only 10% of the energy is transferred as you go up a trophic level.  So, for this problem - coyotes need 1,500 calories a day (but he only gets 10% of "rabbit energy" - so multiply by 10 to get the "conversion" for the rabbit level.  1,500 X 10 = 15,000.  The rabbits also only get 10%, so you would have to multiply by 10 again to get the conversion for "grass energy".  So 15,000 X 10 = 150,000.

the 10% rule is just an average - herbivore conversions are actually more efficient and carnivore conversions are less efficient - so if you are in a higher level course (like grad school), you will need to look up those conversions.  Otherwise, stick to the 10% average.  I think you'll be safe with that since all the answers are multiples of 10.