A nutrient cycle is the repeated movement of a nutrient between living organisms and the non-living environment. Carbon, nitrogen, water and mineral ions all cycle through ecosystems.

Producers take materials from the abiotic environment, and consumers obtain materials by feeding on producers or other consumers. Consumers return carbon dioxide, water and excretory products to the abiotic environment through respiration and excretion. Death, faeces and excretion transfer material from consumers to dead material and waste. Decomposers break down this material and return nutrients to the abiotic environment.