An ecosystem is a source of energy that animals live on, then it starts the food chain, because all animals need energy to live, so all animals rely on plants or other animals for energy. All food chains end in decomposers. Decomposers are things that decompose other things, For example, worms decompose animals and molds decompose food, or leaves. Decomposers are helpful to the environment because, if they weren’t there there would be junk all over the place, and that wouldn’t be good. The sun is the main force of energy, so all ecosystems start with the sun because it is a ball of gas so it doesn’t need to get energy anywhere else. If one animal runs out/ is extinct, the whole ecosystem can go wrong and no animal can get its energy, so then it can’t live.