How many trophic levels are there typically in a community?

Typically there are three or four trophic levels in a community because after this point, it becomes very hard to sustain organisms. The amount of energy lost at each trophic level makes it harder and harder to sustain life.

As we can see in the image below, less and less energy is available as one moves up the energy pyramid.

In this image, the producer is the first trophic level, thus the owl would be the fourth, or the level of carnivores that consume other carnivores. At this point, only 1kcal out of the original 1,000 from the producer remains available to the owl.

Thus, we typically see far more producers than consumers, far more herbivores than carnivores, and far more carnivores that consume herbivores than carnivores that consume other carnivores.

Each organism uses some of the energy it consumed (or produced) for growth and cellular respiration and so forth. Thus, less energy is available to the next level, as seen below.