There are 4000 units of energy available to grass at the first trophic level of an ecosystem. if the grass is eaten by a mouse and the mouse is eaten by an owl, how many units of energy will be left for the bobcat that eventually eats the owl?

10% of the energy in a trophic level is passed to the next.

Amount to mouse = 10% x 4000 = 400 units
Amount to owl = 10% x 400 = 40 units
Amount available to bobcat = 10% x 40 = 4 units

4 units of energy will be available to the bobcat that eats the owl.