Syntrophy is the phenomenon that one species lives of the products of another species.

House dust mites, for instance, live of human skin flakes; a healthy human being produces about 1 gram of skin flakes per day.A less pleasant property of these mites is that they can produce compounds that stimulate the production of skin flakes, and people can become allergic for these compounds.

Another example is feaces or dung. A cow eats a lot of grass, because it needs the protein, which is not abundant in grass. The cellulose of grass is transformed into lipids by micro-organisms in the gut of the cow, and these micro-organisms can't use the lipids because of lack of dioxygen in the gut. The cow does not take up all lipid, and when it leaves the gut and comes into open air, many organisms feast on the dung.

Yet another example is the community of micro-organisms in the soil that lives of leave litter (leaves typically last one year and are then replaced by a new ones).These micro-organisms mineralize the leaves and release nutrients that are taken up by the plant. Such relationships are called reciprocal syntrophy, because the plant lives of the products of micro-organisms. Many symbiontic relationships are based on syntrophy.

Syntrophic interactions are very important in all communities, and a conerstone in the Dynamic Energy Budget theory.