An ecosystem is all of the living and non-living things in a habitat. Every organism in a food web is a producer, consumer or a decomposer.
As you all know, to decompose means to rot. A producer can be called a plant or a autotroph, and a consumer can be called an animal or heterotroph. All decomposers feed on dead organisms and waste.
Decomposers recycle the nutrients into the ecosystem. Fungi and bacteria are decomposers. All food chains start with a decomposer then a producer then a 1st level consumer then a 2nd level consumer, and so on...
Nutrients are recycled by decomposers. The food consumed will have to separate into 3 groups; 30% lost as heat, 10% used for growth, 60% lost in waste.