Dungeoneering 101 : dungeon ecology

[Lyr_Levaine]

This is a post for PnP Dms. If this does not describe you, you need read no further, I don't want to waste anyone's time.
Ok, for those still reading, I want to talk about dungeon ecology.
It is easy to overlook the ecosystem involved in a surface wilderness environment ... most of the time, a few rolls on an encounter table is all that is required, and no one needs to devote much time to thinking about how the spiders managed to keep alive and grow in number for the encounter that the players are going to have to negotiate. In the subterranean dungeon environment, however, more attention needs to be paid to ecology. Those Gnolls need to eat ... what are they eating? Surely there aren't enough wandering adventurers coming in to the gnoll territory to satisfy the appetites of the critters, so ... what do they eat?
When designing a dungeon adventure, start with the base of the ecological system; that means molds, slimes, and fungi; these do not need to be a hostile encounter in and of themselves, although some of them certainly can be, but they must be there in order for the higher forms of life to exist. Follow this with insects, lizards, rats, and perhaps some other fungus grazing creature like Rothe. All of these creatures need to be represented in the environment, along with their incidental predators and the detritus that they leave behind. Your higher end species are going to be farming or hunting these creatures, or they must be getting their sustenance from some other source .. what is it?
Characters journeying through this area with Kn nature or Kn the Underdark should be able to glean some clues about what kind of creatures might inhabit this area based upon the clues that the minor inconsequential flora and fauna of an area. I like to make notes about what non hostile, non important things are in a location, since these things, although they do not directly impact gameplay, shape the world that the PCs are traveling through..
Periodically having players roll spot and listen checks to pick up on the mundane inhabitants and architecture of the environment adds to the sense of realism in the adventure, and also makes those times when they are making checks for a serious encounter unpredictable for them, and hence more exciting.

[Enderoc]

Actually that played a huge role in D&D at its beginning. There in explaining the game in using examples in narratives it engineered a detailed world. Some of the creatures interacted whether in aiding one another or a type of master servant or predator prey, or even simply pests, or pets.

Without any realism, and where creatures are simply experience points, you lose the entire feel you are reaching for.