Updated November 22, 2019 By Derek King
Trophic levels are the feeding positions of all organisms in a specific ecosystem. You can think of them as food chain levels or as a trophic level pyramid. The first trophic level, or base, of an ecosystem has the highest energy concentration. This energy is dispersed among animals in the subsequent three or four levels. Certain organisms, because of their size, function or eating behavior, belong in a particular trophic level, though sometimes it's difficult to place animals with more complex behaviors.
Trophic levels describe what organisms eat. There are five key trophic levels in an ecosystem, from simple plants that get energy from sunlight to apex predators at the top of the food chain.
Plants and algae comprise the lowest level of the trophic system. Called primary producers or autotrophs, plants and other organisms create their own food using photosynthesis. By using energy gleaned from the sun and nutrients gathered from the soil or water, plants and algae can manufacture food. Therefore, plants and algae are the primary producers of energy and don't need to consume food from other sources. They can be either terrestrial or aquatic.
Herbivores belong in the second level of the trophic system. Called primary consumers, herbivores eat only plants and algae as their sources of energy. Herbivores cannot manufacture their own food. Common herbivores include:
In an ocean ecosystem, animals such as zoo plankton or krill that consume algae belong to the second level. Primary consumers use the energy naturally created by plants to function.
A specialized type of carnivore belongs to the third level of the trophic system. Carnivores are organisms that prey on and eat other animals. Animals that consume only herbivores belong to Level 3 and are referred to as secondary consumers. This type of carnivore uses the energy the primary consumer gathered from the plants it ate. Animals such as foxes, which primarily eat rabbits, are as secondary consumers. Even animals such as fish, rats, spiders and ants can be secondary consumers.
The fourth trophic level includes carnivores and omnivores which eat the animals that belong to the third level. Omnivores are animals that eat both plants and animals. Omnivores consume both primary producers and secondary consumers. Animals on this level are called tertiary consumers. These animals tend to receive less energy from their food than animals in the third level. This is because the energy created by primary producers has been transferred and converted at least twice by animals in the previous groups. Each time you go up a trophic level, available energy is reduced by at least one magnitude.
The fifth trophic level is the final level in an ecosystem. It is composed of apex predators that prey on and eat the carnivores and herbivores in the fourth level. Apex predators are at the top of the food chain and have no predators of their own. They allow each different trophic level to sustain stable levels of animals. Lions, alligators, bears, anacondas, killer whales and hawks are common apex predators.
The classic example of a pyramid is shown here. But the pyramid structure can also represent the decrease in a measured substance from the lowest level on up. In ecology, pyramids model the use of energy from the producers through the ecosystem.
The feeding positions in a food chain or web are called trophic levels. The different trophic levels are defined in the Table below. Examples are also given in the table. All food chains and webs have at least two or three trophic levels. Generally, there are a maximum of four trophic levels.
Many consumers feed at more than one trophic level. Humans, for example, are primary consumers when they eat plants such as vegetables. They are secondary consumers when they eat cows. They are tertiary consumers when they eat salmon.
Energy is passed up a food chain or web from lower to higher trophic levels. However, generally only about 10 percent of the energy at one level is available to the next level. This is represented by the ecological pyramid in Figure below. What happens to the other 90 percent of energy? It is used for metabolic processes or given off to the environment as heat. This loss of energy explains why there are rarely more than four trophic levels in a food chain or web. Sometimes there may be a fifth trophic level, but usually there’s not enough energy left to support any additional levels. Ecological Pyramid. This pyramid shows how energy and biomass decrease from lower to higher trophic levels. Assume that producers in this pyramid have 1,000,000 kilocalories of energy. How much energy is available to primary consumers? Ecological pyramids can demonstrate the decrease in energy, biomass or numbers within an ecosystem.
With less energy at higher trophic levels, there are usually fewer organisms as well. Organisms tend to be larger in size at higher trophic levels, but their smaller numbers result in less biomass. Biomass is the total mass of organisms at a trophic level. The decrease in biomass from lower to higher levels is also represented by Figure above.
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