If the grass contains 100,000 kcal of energy, how much energy will a fox obtain from eating a bird?

1,000 kcal

Explanation:

As a general rule, every trophic level only gains 10% of the energy from the trophic level.

So, the grass has 100,000 kcal of energy.  Assuming the bird eats grass, it only gets 10,000 kcal of energy.  Assuming the fox eats the bird, it only gains 1,000 kcal of energy.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.