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Food webs and trophic levels

A food chain is one pathway through a feeding network; a food web joins many such pathways. Trophic levels summarize distance from primary production, but omnivores, detritus, changing diets, and cross-habitat subsidies make real organisms harder to place than a simple pyramid suggests.

Scope: A conceptual guide to feeding relationships and energy flow; actual food webs change across habitats, seasons, life stages, and levels of taxonomic detail · Last updated 2026-07-16

Image: Purple Sea Stars - Flickr - brewbooks by brewbooks · CC BY-SA 2.0 · Resized and converted to WebP; displayed with a crop.

01 / THE LIVING WORLD

Trace pathways, then reconnect them

A linear chain such as plant to caterpillar to bird isolates one route. A web adds alternative prey, competitors, scavengers, decomposers, and links across land and water. By convention, many ecological diagrams point arrows from food to eater, but always check the legend because other fields sometimes use arrows differently. [1][2][3]

A Canada lynx crouching low as it stalks across snowy ground in a boreal forest. — Field frame · Editorial contextA contextual view from How predator–prey cycles work.Image: Lynx stalking prey by Erwin and Peggy Bauer / U.S. Fish and Wildlife Service · Public domain

02 / THE LIVING WORLD

Treat trophic level as a position, not a rank

Primary producers occupy the first level, herbivores the next, and predators that eat those herbivores a higher one. An omnivore can feed at several positions, and a species can shift diet with age or season. Trophic position can therefore be fractional or context-dependent rather than a permanent label attached to a species. [2][3][5]

Bracket fungi growing in rows along the damp wood of a fallen forest log. — Field frame · Editorial contextA contextual view from Decomposition and nutrient cycling.Image: Fungi on fallen log by Steve Jurvetson · CC BY 2.0 · Resized and converted to WebP; displayed with a crop.

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Energy flows while nutrients cycle

Photosynthesis supplies much of the energy entering familiar webs. Organisms use energy for metabolism, movement, and maintenance, so less remains available to the next feeding step. Decomposers and detritivores return nutrients from waste and dead material to forms that can re-enter production; they act across levels rather than forming a single final rung. [1][3][4][5]

A lacewing insect caught between the toothed lobes of a closed Venus flytrap leaf. — Field frame · Editorial contextA contextual view from How carnivorous plants trap prey.Image: CSIRO ScienceImage 1766 Venus Fly Trap by Malcolm Paterson / CSIRO · CC BY 3.0 · Resized and converted to WebP; displayed with a crop.

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Ask what evidence built the web

Researchers infer feeding links through gut contents, stable isotopes, and genetic analysis. Each method has limits: stomach evidence is detailed but time-limited, isotopes describe trophic position and carbon sources rather than prey quantities, and genetic methods can reveal soft-bodied prey. Note the habitat, season, life stages, and resolution represented before treating a missing arrow as a missing interaction. [2][6]

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Source-checked editorial guide. Last updated 2026-07-16. This guide teaches identification and field skills; it is not a substitute for expert verification when it matters.