Question

if an apex predator enters the fifth trophic level in an ecosystem, what trophic level is usually the only one affected directly instead of indirectly?
a. fourth
b. third
c. second
d. first

Explanation:

Apex predators at the fifth trophic level directly prey on the fourth - level organisms. The third, second, and first levels are affected indirectly as changes in the fourth level (due to predation by the fifth - level apex predator) can then impact the lower levels through trophic cascades. For example, if the fourth - level organisms (which are prey for the fifth - level apex predator) decrease in number, the third - level organisms (prey for the fourth - level) may increase, and this change can ripple down to the second and first levels. But the direct interaction is between the fifth and fourth levels.

Answer:

A. fourth