• John J. O'Hara

Why You Should Consider the Ecology of Your D&D Dungeon

There aren't many D&D stereotypes more widely known than the dungeon filled with nasty monsters. However, not many Dungeon Masters (we call them Quest Masters) stop to ask themselves how these monsters survive and interact with each other. In a previous article, I argued the importance of working out who built the dungeon and why. This article offers guidance on creating a dungeon ecosystem that makes sense and supports itself.

The Challenge Rating Food Pyramid

Most monsters are carnivores or at least omnivores—that’s what makes them a threat to PCs—so it stands to reason that more powerful monsters prey on weaker monsters. This should be true not only for individual monsters, but for groups as well. For example, a small group of seasoned kobold hunters could take down an owlbear, whose meat will feed their tribe, but an owlbear will make short work of a lone kobold.

In a dynamic dungeon ecosystem, the PCs aren’t the only ones in danger. What happens when the party encounters that group of kobolds engaged in battle with an owlbear? Do they allow the owlbear to overtake the hunting party, or step in and help take down the owlbear, winning the favor of the grateful kobold clan?

The point of all this is that while a kobold or a goblin isn’t much of a threat on its own, groups of weak-but-intelligent monsters can find themselves higher up the food chain. A simplified dungeon food chain might look like this:

Predators and Intelligent Monsters

Omnivores and Mundane Animals

Decomposers and Scavengers

What this means for your game is that you might find dragons and aboleths leaving their lairs deep in the dungeon and stalking the upper regions for prey, or that the party should stumble upon carrion crawlers and oozes even in the deeper levels of the dungeon, where they fill an ecological niche as decomposers and scavengers.

All ecosystems need producers (plants that produce nutrients), consumers (creatures that require nutrients), and decomposers (things that break down matter to feed the producers) to survive, and the dungeon ecosystem is no different.

As long as you think about all three roles when stocking a dungeon with monsters, animals, plants, and water sources, your dungeon will seem like a plausibly self-sustaining environment.

However, creatures—and adventuring parties—invading the dungeon ecosystem can have profound effects on this delicate balance through over-hunting and over-harvesting (i.e., killing and taking everything in sight). Such an ecological disaster can be reflected in your campaign world through events such as monsters attacking cattle and livestock on the outskirts of civilization as they search for new food sources.

Overall, think less about making each level “balanced” and more about making it feel like a dynamic, unpredictable environment, even if it means making your level 4 party hide from an adult red dragon (that dragon is probably after something more interesting than a low-level adventuring party anyway).

Flora, Fauna, and Water

A dungeon doesn’t just contain monsters. If it is to resemble a living ecosystem, those monsters are not going to feed only on other monsters, but on more mundane flora and fauna, as well. There are all sorts of cave-dwelling creatures in the real world that can be easily incorporated into the dungeon such as bats (and their nutritious guano), fish, crustaceans, and insects.

Consider the relationship between these animals and the monsters in the dungeon. They may be competing for the same resources, or the animal life of the dungeon may be prey for monsters. These relationships will add believability to your world and enhance immersion.

For example, you can establish in your campaign that goblins love the taste of bat meat, while cave scorpions are a delicacy of grimlocks. The next time your party runs into a pile of cave scorpion exoskeletons, they’ll be preparing for an encounter with grimlocks.

I Just Work Here

The monsters that PCs encounter might not even live in the dungeon. If they are intelligent, they might be there for the same reason the PCs are: they’re looking for treasure. They might also be scouting new settlement locations or hunting and foraging. Non-intelligent monsters could be looking for food and water or a place to lay eggs or hibernate.

Intelligent monsters who have goals similar to those of the PCs are inherently more interesting because they aren’t just there to be killed. If they’re also looking for treasure, these monsters would be just as likely to try to recruit the party as allies or take them prisoner to extract information as they would be to fight.

Non-intelligent monsters who are only visiting the dungeon might simply run when encountered by the party, or they might be hungry, injured, or protecting their young, making them more aggressive.

Beyond the Dungeon

Clues the Quest Master leaves in the wilderness can help the party prepare for certain kinds of monsters when they venture into the dungeon.

Just as monsters may visit the dungeon to hunt, dungeon denizens may also range into the wilderness beyond to find food. In this case, an adventuring party might stumble upon evidence on their way to the dungeon: the remnants of a campfire, littered with bones that have been cooked, the tracks or spoor of a creature known to live underground, or the remains of an animal bearing the bite or claw marks of a subterranean monster.

Imagining these relationships help the Quest Master (QM) to develop a more logical, and as a result more immersive, sense of the game world as a living, dynamic environment. But not all QMs subscribe to a high level of naturalism in their games.

Are realistic—or at least plausible, internally-consistent—dungeon ecosystems important to you? Let us know how you go about building a believable ecosystem in your dungeons.


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