1. If the decomposers are not present in an ecosystem the remains of the other organisms accumulate.
2. Eventually the world would run out of carbon dioxide or nitrate or phosphate or other inorganisms material essential for life.
3. The decomposers breakdown the organic waste products and dead remains of organisms into the inorganic substances needed by the producers.
4. Most decomposition is carried out by saprophytic fungi, by bacteria and by invertebrates.