An ecosystem is a community of living organisms and their physical environment interacting together. It includes all the living things such as plants, animals, and microorganisms in a given area, interacting with each other and with their non-living environments such as weather, earth, sun, soil, climate, and atmosphere. The term "eco" refers to a part of the world, and "system" refers to the coordinating units. Ecosystems can be natural or artificial, land-based or water-based, and can vary in size from small tide pools to large rainforests. Each organism in an ecosystem has its own niche or role to play, and the biotic and abiotic components are linked together through nutrient cycles and energy flows. Ecosystems are dynamic systems, and a static ecosystem would be a dead ecosystem. Ecosystems provide a variety of goods and services upon which people depend, including water, food, fuel, construction material, and medicinal plants. A healthy ecosystem has an energy source and decomposers that break down dead plants and animal matter, returning essential nutrients to the ecosystem.