What is a trophic level?

A trophic level is the position in an ecosystem an organism occupies in relation to primary sources of energy and the food chain.

The first trophic level is always composed of primary producers that convert either solar or chemical energy into biomass.

The second level will be made up of primary consumers or herbivores, those organisms that consume the primary producers and get their energy from those organisms.

The third level is carnivores that consumer herbivores.

A fourth level would be composed of carnivores that consume other carnivores. An example would be orcas because they consume seals.

An example of trophic levels in a marine ecosystem is shown below:
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There are far more primary producers than there are herbivores, and there are more herbivores than there are carnivores. This is because each time we go up a trophic level, we lose some energy. This is because green plants take their energy from the sun, but if you were to eat that green plant, you wouldn't consume the same amount of energy the plant did because the plant used some of that energy for growth and other processes.

The image below illustrates this process:
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