Producers are the bottom of the food chain, their role is to take nutrition or magic and distribute it around the dungeon. The only producers are spirits and slimemoss. As the bottom of the food chain they are also the most numerous and also the weakest of the bunch.
Since these guys are the start of the upward rise of nutrients and magic if something were to happen to them the whole system would come crashing down. So take care of the little guys or those awesome secondary consumers will be nothing but a pile of nutrients lodged in the walls of your dungeon.