Trophic Levels

Trophic levels are the different biological hierarchy stages in food chains and food webs that demonstrate the transfer of energy and biomass between organisms. Food webs are often very complex and thus trophic levels are used to represent these energy transfers in a simplified manner.

There are usually 3 – 4 trophic levels per food chain, with energy transfer beginning with primary producers (plants), moving to primary consumers (herbivores), then to secondary consumers (carnivores) and finally tertiary consumers (top carnivores). This energy transfer is very inefficient at about 10% of biomass energy being transferred. Consequently, visual representations of the energy stored as biomass in each trophic level are bottom heavy, and known as trophic pyramids (as seen in the diagram below).  Decomposers are often included in the trophic levels alongside bacteria and fungi species – breaking down organic matter into nutrients, in order to allow the producers to supply the necessary biomass and energy for the rest of the food chain.

However, although great at simplifying food webs, trophic diagrams are often limited when dealing with certain food interactions such as omnivory, were organisms feed on both producers and primary consumers.Trophic levels 2“Ecological Pyramid”, 2018, Graphic, CK-12 modified by Khan Academy “Ecological Pyramid”. Source:https://www.khanacademy.org/science/high-school-biology/hs-ecology/trophic-levels/a/hs-trophic-levels-review

Figure 1 – Trophic levels of a food chain in Lake Ontario, Canada

trophic levels 1

“Untitled, 2016, Graphic, Principles of Biology. Source: https://cnx.org/contents/24nI-KJ8@24.18:ySSSOHNm@5/Studio-Biology-What-is-it

 

Key Terms

Food webs – The food interactions between all the species of a certain ecosystem.

Food chains – A series of organisms each dependent on the next as a food source.

Primary producer – An organisms which creates energy from inorganic compounds.

Primary consumer – An organisms which feed upon primary producers.

Secondary consumer – An organisms which feed upon primary consumers.

Tertiary consumer – An organism which feeds upon secondary consumers.

Herbivores – An animal that feeds solely on plants.

Carnivore – An animal that feeds solely on other animals.

Omnivore – An animal that feeds on both plants and other animals.

Biomass – The total weight of an organism as a volume.

Trophic pyramids – A visual representation of trophic levels and the energy stored in each.

 

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