Trophic level

A trophic level is an organism’s position in a food chain or food web, determined by how it obtains energy and matter.

Food chain: A sequence showing how energy and matter pass from one organism to another through feeding. Trophic levels mark positions along this linear feeding pathway.
Primary production: The rate at which autotrophs create organic matter from inorganic sources in an ecosystem. It sets the energy and biomass available to organisms at higher trophic levels.
Stable isotope analysis: A method that uses isotope ratios in materials to infer sources, processes, or diets. Nitrogen isotope patterns can estimate an organism’s trophic position.
Functional group (ecology): A set of organisms grouped by similar effects or functions in an ecosystem. Functional groups classify ecological roles, which need not correspond to a single feeding level.
Food web: A network of interconnected food chains showing feeding relationships in an ecosystem. Organisms can occupy different trophic positions across its interconnected pathways.
Trophic transfer efficiency: The fraction of energy or production transferred from one trophic level to the next. Low transfer efficiency helps explain why food chains usually have few levels.
Biomagnification: The increasing concentration of a persistent substance in organisms at successively higher trophic levels. Feeding position predicts exposure to contaminants that accumulate through food webs.
Ecological niche: The conditions, resources, and interactions that define a species’ role and persistence in an ecosystem. A niche includes far more than an organism’s position in energy transfer.
Producer: An organism that builds organic matter from inorganic sources, usually using sunlight or chemical energy. Producers form the first trophic level by introducing energy into most food webs.
Ecological pyramid: A diagram comparing energy, biomass, or organism abundance across trophic levels. Its stacked levels visualize how ecosystem quantities change with feeding position.

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