In ecology Secondary Consumers are the guys that consume the primary consumers which consume the Primary Producers which tap the soil for their nutritional needs. Lizardmen devour Omnoms which are primary comsumer to Slimemosses. Typically secondary consumers are carnivores or in some cases omnivores like Dragons are. Secondary consumers will usually only consume the guys immediately under them, but like with Dragons there are exceptions.
I would think that Demons count as Secondary consumers but then again their diets are so wonky that it's hard to say. I mean look, their seals ingest spirits and that's more of a primary consumer thing. Then again that isn't the scope of a simple article based around a flipping ecosystem simulation, which is really cool by the way.