Why Are There So Few Ecosystems with More Than Four

Multiple Choice

Why are there so few ecosystems with more than four levels of consumers?

A) because biomass decreases by about 90% at each trophic level moving up
B) because top consumers compete with and kill each other with increasing population size
C) because consumers at these highest trophic levels typically form social groups that stop reproducing at high densities
D) because predators at the highest trophic levels simply are not intelligent enough to hunt other top predators