Monsters and Ecology

[BOZ]

my sister was once bit by a moose.

 

[mythusmage]

Getting back on track (if only for this one post) ...

The first question to ask yourself regarding any terrestrial location is, how wet is it? That is, how much precipitation does it get on an annual basis?

Other than the eastern coastal plain and the far north Australia is dry. Not terribly dry, but dry enough that plant life is sparse and scattered. Means animal life lives on the thin edge most of the time. With few herbivores to predate it pretty much precludes large predators. Even at best Australia has only dingos and thylacines as predators, and they are small animals with a limited range. Get out to the really dry parts and you're limited to goannas and other small lizards.

Once you've learned how wet a place is, you need to determine such things as physical geography, soil chemistry, plant cover, and animal life. The Amazon basin gets a lot of rain every year. But that same rain leeches away at the soil. Plant life has to grow fast to sequester minerals; without this fast growth Amazonia would erode away into the Atlantic.

In contrast Central Asia around Mongolia gets nowhere near as much precipitation. But what it does get is sufficient to support some of the richest grasslands in the world. And it is these grasslands that in turn supports herds of wild and domestic grazers of such a size that it makes the fabled herds of the Serengeti look pitiful.

Now consider the Olympic Penninsula in Washington State. A locale with a combination of conditions that can support an amazing mix of plant and animal life. Including (quite possibly) a few hundred (at least) 800 pound bipedal primates.

Of course, most folks aint gonna be bothered by a little climatological inconsistency as long as the adventurin's good.

 

[Yair]

This Site looks at prey/predator ratio's amongst Dinosaurs and suggests that large dinosaur predators (and Sabre tooth cats) had a ratio of 3.5% to 5%, going to less than 1% in sub-optimal conditions (like Creatceous Mongolia). So we can probably presume that this range is standard across most mammals with a 3.5% ratio being average.

Interesting. Taking weight into account, the predator/pray ratio (assuming a moose weighs 4 times as much as a wolf) is about 1.1%. That coincides with lions in the modern Savannah too, apparently.

I can't get consistent data on real-world weights by googling, it seems about 500 kg for mooses and about 20 for red wolves (the common variety at Isle Royale); x25 rather than the x4 that D&D assumes. This implies a real predator/prey weight ratio of only 0.18%.
Even assuming gray wolves (less common at the park) at around 45 kg and smaller moose (one site lists the average at 427 kg), the ratio is still x9. This implies a predator/prey weight ratio of 0.47%.
In D&D terms, weight-wise, if a wolf is Medium than the moose is Huge.

So taking a 3.5% ratio for Temperate environments I'd then assign different values to the other environments (eg Desert, Arctic 1%, Tropic 5%). I'd also presume that unusually large predators (like Griffons, Wyverns and of course Dragons have Reptile-like metabolisms and thus low ratios ie 1/10 of mammals)

Yes, this seems like a good estimate.
I would put the carrying capacity of mammal prey at around 5%, i.e. I'll have about 5% of the population's weight in supported predators, each with a 1-5% allotment. That's too high by Isle Royal data, which suggests only a 1% carrying capacity (or 0.2 to 0.5% with real weights), but it seems plausible enough.
I'll also put large predators like Griffons, Wyverns, Frost Worms, Dragons, Vermin, and so on at increased efficiency, probably even more than x10 for dragons.

Good.

 

[Tarril Wolfeye]

Just one little thing: If you look at the table of monster weights in MM, you'll see that a Large monster weighs 8x as much as a Medium monster. (It's because doubling in length will get you a 2 x 2 x 2 factor on weight based on the volume)

 

[Yair]

Just one little thing: If you look at the table of monster weights in MM, you'll see that a Large monster weighs 8x as much as a Medium monster. (It's because doubling in length will get you a 2 x 2 x 2 factor on weight based on the volume)

Doh!
That makes things make a bit more sense. Not much, but still.

 

[fusangite]

Here's the basic problem you are confronting:

The rules of ecology that exist for our world won't work for the D&D world because
(a) They are premised on our world's physics, chemistry and biology. We know for a fact that these things are not true in D&D. D&D has four elements, not 100+. D&D physics can sustain creatures made out of elements, devoid of circulatory systems and individual organs. The list can go on ad infinitum.
(b) If one looks at the Monster Manual and contemplates the attributes of the various creatures contained therein, there is just no way to shoehorn this number of massive predatory creatures into a single global ecosystem.

So, the sensible question to ask is not: how can I create a D&D environment that complies with real world physics/ecology -- because we know no D&D environment is going to do this, what with spells going off, undead walking around, etc. The sensible question to ask is: what set of ecological rules need to be true for the environment I am building to make sense?

I recommend you look at some pre-modern theories of ecology that are likely to be compatible with a world containing a four element system, dragons, elementals and spells. Aristotle is, in my opinion, where it's at; Pliny the Elder may also be a help, although his theories are not as explicit.