A Viable Ecology?

[ùìéè äîáåê]

In my never-ending quests to create a consistent world, I constructed the following and would very much appreciate any comments on it. Notice my intention is not to provide a true ecologically-sound world, that's way out of my league - and not very interesting, to me. My goal here is to create a system that will allow me to rationalize how come there are X monsters of type Y in that place - I mean, they have to eat, right?

I have done so by assuming each creature requires to eat food with a total weight of a creature two size categories smaller than him per day (I dervied this from the Size comparison picture in the PHB ).
I derived the following population densities, based on the assumption of 1 sq. mile producing enough food to support 180 Medium-sized herbivores.
The densities are given per sq. mile.

Density:_________Herbivores________Carnivores
Size
Fine____________37773 1/4_________who cares?
Dimunitive________7554 2/3_________who cares
Tiny_____________1259 1/9_________126
Small____________251 5/6__________25 1/5
Medium__________18 8/9___________4 1/5
Large____________1 1/5____________5/6
Huge____________5/953____________1/16
Gargantuan_______0_______________3/746
Collosal__________0_______________1.74876E-05

Does this seem reasonable? Useful? Pathetic? Useless? A mad undertaking only a fool would undertake, that risks undermining all that is good and proper?

 

[drowdude]

A mad undertaking only a fool would undertake, that risks undermining all that is good and proper?

Indeed

 

[Elder-Basilisk]

A worthy attempt

I'm not going to evaluate your math but I have a few comments.

Conceptually, I like it when my DMs try to present a consistent world where NPCs, ecologies, etc. make sense. It's hard to know how a character could react to unusual situations or develop suspicions about odd things if 30 foot tall, 10 foot wide monsters are regularly found in rooms with 5 foot high entrances or herds of tyrannosaurusses attack the party in the middle of a desert.

On the other hand, I don't think that one equation would be sufficient to give you a balanced ecology. Deserts, jungles, tundra, and marshes would all have different densities of population.

Furthermore, overpopulation in certain segments is a regular occurance in nature--particularly where people are around. A campaign to erradicate medium and larger predators (which often feed on livestock) would most likely result in more herbivores than usual around developed lands. On the other hand, those might lose numbers to habitat destruction or deliberate hunting too (most farmers don't like rabbits or gophers eating their crops after all). Perhaps, even more to the point, most of the time adventurers are involved in combat with animals it will be because the numbers are out of whack. For example, if adventurers are attacked by starving wolves, it's probably because there are more carnivores in the area than the number of herbivores can support. Otherwise, the wolves wouldn't be starving and they probably wouldn't attack the adventurers. Unless your PCs are really odd, they probably won't be counting the number of wolves in non-combat encounters.

Another fact to consider is that some animals in the monster manual are noted for being destructive to the ecology. Bullettes, for instance, typically eat everything there is to eat in a territory and then move on. If a territory has a Bullette in it and very little stuff to eat it's probably because the Bullette already ate it. If there's not enough to sustain a Bullette for very long, that's to be expected too--they hunt an area until it's not worth hunting and then move on.

On the whole, I think you're better off just adjudicating on a case by case basis as your stories require than trying to come up with a formula that won't be applicable in most cases anyway.

 

[willpax]

What might be more interesting is to consider how population patterns would be changed with the addition of some of these monsters into the mix. For example, there are a number of large, flying predators in the Monster Manual. I would think that herd animals in grassland areas would have to adapt in significant ways to cope with griffons and so on. Some of the slower herd animals (such as cows) might have been hunted to extinction, leaving only the quick (such as gazelles).

If you've read Jared Diamond's _Guns, Germs, and Steel_, then you may remember his arguments about the central importance of domesticated animals in human development. Without cows as a significant source of nutrition and labor, humanity would have had a much harder time advancing. This in turn might explain the slow development of many D&D worlds.

Just a musing that follows your own train of thought. I'm not sure I would bother counting the mosquitoes, however.

 

[Fenris]

Do the densities represent a specific species or "all" of the medium herbivores in a given area? In regards to the effects of particular monsters on domesticated animals, most monsters and other beasties are located well into the wilderness. Of which in most fantasy and medieval settings there is an abundance of. Why would a Griffin attack a cow if it has to fight off dozens of villagers? In any case a cow or a gazelle would feed a Griffin for about a week. Most large predators eat off a single large kill for several days. That combined with a nessesarily low population of Griffins (large range, solitary habits) leads to the conclusion that cows would not become extinct.