Trophic Encounter Tables

We had a fabulous chat yesterday on the Wandering DMs Sunday talk show about our favorite Content Generators, starting with the monster tables in Original D&D provided as a way to populate dungeons and wilderness with a minimum of DM effort.

On that note, here's another guest article by our friend Angela Black: can we use real-world Trophic levels as a way to structure our random-table ecology simulators?

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I've recently become bothered by encounter tables that propose that a certain wilderness area might be infested with all manner of huge and lethal monsters. Perhaps I'm too literal, but when I see that this particular forest contains dragons and owlbears and displacer beasts and wargs and and and... I always ask myself, "what are the EATING?" I suppose the answer might be 'each other,' but that's oftentimes too glib for me. I frequently find myself wishing for a more 'realistic' model of what monsters live in a given area.

Fortunately, scientists are great at modeling all aspects of the real world, and this sort of thing is not exception. Ecologists use a concept called "trophic levels" to describe the flow of energy through a given environment, which incidentally gives us a nice model of the relationships between predators and prey. Without wading too deeply into the very complicated math of this fascinating concept, we can use it to gain some traction on a more realistic model of encounter tables for fantasy roleplaying.

To sum up the ideas at play very briefly, we can imagine a pyramid-shape divided into zones that are called Trophic Levels.

• At the base, the largest level is Trophic Level 1, where we find plants that form the base of the ecological system. Plants are rarely - but not never! - threats to PCs, so we don't normally list all the plants in a given region on the encounter tables.
• Just above this we have Trophic Level 2, where we find the herivores that feed on the lower level These tend to be small creatures and likewise not *usually* a threat to PCs, so we don't tend to put all the squirrels and rabbits and whatnot on the encounter tables, either.
• Trophic Level 3 is for smaller predators that feed on the herbivores in Trophic Level 2, like foxes and weasels and whatnot. These are usually only threats to humans in the real world if they feel directly threatened or they are protecting their young.
• The next level if Trophic Level 4, where we find predators who feed at least partially on other predators, like hawks that might eat foxes. The important observation here is that creatures that occupy Trophic Level 4 are accustomed to attacking other creatures that are in themselves dangerous, as long as those creatures seem vulnerable. That will be important for gaming!
• Finally, at the very top, we have so-called "apex predators," who can and will prey on anything in the area. Not every region will have an apex predator, but if it does, the apex predator will present a clear threat to PCs!

Now, we can already make some observations that will inform our encounter tables. We can (for now) ignore anything that would live at Trophic Level 1 or 2 in our region. On the other hand, we must account for the creatures that live at levels 3 and 4, as well as the apex predator(s), if any.

But the populations at these trophic levels live in very predictable relationships - for instance, there can't be more creatures at level 4 than at level 3, unless the creatures at level 4 are vastly smaller (for some reason) than the ones at level 3. If creatures at level 3 were rare and creatures at level 4 were abundant, the creatures at level 4 would quickly run out of food!

Generally speaking, the ratio of creatures from Trophic Level N to Trophic Level N + 1 is 10:1 or thereabouts. This is a very rough gloss of the actual math, but it works for our purposes. This also assumes similar body mass, but we'll ignore that for now. This figure of 10:1 gives us a great starting point for roughing out an encounter table.

Let's start with creatures at Trophic Level 3, since anything at levels 1 or 2 will only present a threat to PCs under very rare circumstances. Let's look at the Temperate Wilderness Forest tables in the MMII to get some ideas.

We should start by picking out a handful of animals for Trophic Level 3. These are animals that feed largely on herbivores (though they may themselves be omnivores that also eat plants). Some good candidates from the table we're look at might be badgers, boars, poisonous toads, snakes, weasels, and wolves. That's a great start.

2Then we move on to Trophic Level 4. What are some creatures that might prey on (at least some of) those creatures? We should choose fewer of them, maybe about three or four. We'll pick bears, hawks, and - just to add a fantasy element - owlbears.

Finally, we should choose an apex predator (and it is recommended there not be more than one, but this rule can be broken with careful consideration). For fun, I'll say there are fire lizards in this forest. Found under "Lizard, Giant," in the Monster Manual, the fire lizard is essentially a drake, a very dragon-like creature that is not intelligent but more of an animal. It has 10 HD and can breathe fire so it can certainly fill the role of apex predator!

Now to create the table. Let's start by observing the ratios. Collectively, the creatures at level 4 should be approximately ten times more likely to be encountered than the apex predator, and likewise the creatures at level 3 should be approximately ten times more likely to be encountered than the creatures at level 4. Now, we can't quite accommodate that on a standard percentile table, but we can approximate with the following standard layout:

• 1%: Apex Predator
• 2% to 11%: all the creatures at level 4
• 12% to 99%: all the creatures at level 3
• 100%: everything else

This layout preserves a realistic relative frequency of encounters - it wouldn't make sense for fire lizards to be massively more common than, say, bears, or even wolves! Likewise, the creatures at a higher level should be more dangerous overall than creatures at a lower level.

If the DM wants to adjust some, a 1:5 ratio could be used without stretching credibility too much, leading to an alternate table layout as such:

• 1% to 3%: Apex Predator
• 3% to 18%: Level 4
• 19% to 93%: Level 3
• 94% to 100%: everything else

DMs may find this layout is more congenial to gameplay while still preserving the same general ratios.

Notes:

• The strength of the apex predator can be a guide as to whether the land is ripe for settlement or destined to remain wilderness for the foreseeable future. It should be assumed that humans in a fantasy setting will, as they were in the real middle ages, attempting to clear land into which they hope to expand. In fantasy settings, however, there are things which can easily repel even determined groups of humans, and if the apex predator in a given environment is sufficiently difficult to kill, certain areas may remain uncleared and unused regardless of the wishes of the local civilization! For instance, a region where the apex predator is the lion may present danger, to be sure, but can eventually be cleared for use by determined humans. Compare this to a forest where the apex predators are phase spiders!"everything else" is a useful catch-all for the rare, miscellaneous encounters from levels 1 or 2 that might actually prove dangerous to PCs. For instance, AD&D has numerous dangerous plants, like whipweed or yellow musk creepers. These plants cannot be exceedingly common, however, or there'd be no creatures from level 1 left to eat the plants! Putting such encounters in "everything else" is a good way to model this.
  
  
• Placement of intelligent humanoids requires some judgment. If the area is truly wilderness, the humanoids must either be non-cultivators (like ogres) or exceedingly rare. For instance, if the DM wants to include human bandits in the woods, it's probably best to list them as an option under "apex predator," since if humans were in the woods in any greater abundance, they'd have cleared out the other apex predators and started to tame the land. Goblins, however, who avoid the larger creatures and mostly live by trapping herbivores and small predators actually qualify for level 4!
  
  
• The level of the encounter is a fine guide to the behavior of the creature encountered.
• Creatures in level 3 are non-confrontational unless desperate or frightened - they will fight if their homes are invaded, their young threatened, or they are backed into a corner, but that's it. It may be that characters experienced in woodscraft can "defuse" an encounter with a creature at level 3.
• Creatures at level 4 will only attack with an advantage - if the target is smaller and weaker, if the target is injured, or if the target is outnumbered. Again, goblins make a fine level 4 creature, don't they?
• Apex predators can and will attack anything they choose, and are frequently good at stalking prey and assessing the danger they present. Apex predators may hunt singly or in groups, depending on type and, if semi intelligent or intelligent, may present a massive threat to PCs.

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Delta back here again -- Personally, I think that's pretty nifty, and the solid real-world math being used as a foundation is the kind of thing that gives me really good results in the past. Would you consider using that as a basis for your tables?