A food chain is a linear network of links in a food web, often beginning with an autotroph, also called a producer, and typically ending at an apex predator, detritivore, or decomposer. A food web is distinct from a food chain. A food chain illustrates the associations between organisms according to the energy sources they consume in trophic levels, and the most common way to quantify them is in length: the number of links between a trophic consumer and the base of the chain.