A continuation of the previous section and the previous pests section, which is detailed enough to warrant a section of its own.
This thread in particular caught my eye as a reference, but I believe we need to work with a more complex model for what animals will eat than simply using a broad-stroke "Vermin-hunter" token, especially for as long as that means that a bat that eats insects will have to have the behavior model of a cat.
Instead, I believe we need to work out a system for creating broad predatory behaviors, and allowing the game to proceedurally generate the exact food webs from these. This means that we start from the plants (or other energy-producers), work out what eats those plants, and then what are the predators of these "herbivores", and the predators of those predators.
Some sort of nod towards energy loss needs to be made - real food chains rarely go beyond three links on land or five in the water, since a predator needs about ten times its mass (not population number, mass) of prey species to feed itself, and keeping a stable population requires a certain minimum number of a species just for having genetic diversity. This could be a part of the previously discussed population models for pests, as well. The mass of the vermin being eaten instead of pure number of vermin in existence can be part of the calculation taking place. (The number of "links" is based upon the total amount of resources, especially energy, in the ecosystem - a highly energetic ecosystem, such as a world with a more powerful sun, or a highly magical ecosystem with xenosynthetic plants, could potentially support more links in the food chain. An odd number of links in the chain help support more producers, since a food chain with only producers with no predators leads to overpopulation, a food chain with only plants and herbivores leads to overgrazing, but a predator reduces herbivore populations, and helps raise more producers in the system.)
Note that this means that creatures like amethyst men might become "producers" (in that they do not eat other creatures, but produce their own energy, presumably through being xenosynthetic), with predators of their own, provided they can digest something like an amethyst man's magical energy. (Maybe that's the ecological role of a Forgotten Beast - eater of the craziest crap you can imagine. Of course, how do you work that into an ecosystem, do they excrete slade or something?)
So, instead of having a "vermin-hunter" tag per se, we could use more specific criteria. A web-spinning spider and a jumping spider are both insectivorous predators, but the web-spinner can only attack creatures that are stuck in its webs, which basically means they only prey upon flying insects (and will eat even small birds or bats that get caught in their webs if they are capable), while jumping spiders can't usually catch flying prey, but pounce upon crawling insects (or anything small enough they could take it in a fight and be capable of eating it later). A wolf is a carnivorous preditor, of course, but it probably won't hunt anything the size of a mouse or smaller, since it's just not worth a wolf's time to try to eat it. A wolf in a pack will hunt a large herbivore like a bison, but won't be foolish enough to attack a tiger unless the tiger is either on the verge of death, or the wolves are desperately hungry. This means that what we need is a set of tokens for predators to choose their prey based upon their size, motive habits, capacity to defend itself, and the specializations of the predators in particular.
Pack or solitary predators like wolves would also change what they hunt based upon how large a pack they have with them at the moment. Solitary wolves eat smaller prey like rabbits, but larger packs of wolves will attack deer or larger herbivorous creatures that are too dangerous to take on alone.
The game itself just semi-procedurally determines at the start of the world what animals eat what. (With some way of manually overriding whether or not certain creatures eat other specific creatures for the purposes of modding.) This would help prevent having to come up with a giant list of everything a wolf might possibly eat when it gets hungry enough - it just tries to hunt something that is of a certain percentage of its own size, and adjusts that based upon the size of the pack, and how many mouths it has to feed with a single kill, and how likely they are to be able to win the fight in the first place.
As a part of the previously mentioned nutritional model that simply uses "food groups" as a means of balancing nutrition, we could have a set of tokens for every plant that includes some guidelines on what kind of food the plant might provide - a grassy plant and a woody tree-like plant would have different kinds of creatures consuming them (if anything consumes trees at all), while fuits and vegetables and grains and seeds could be distinguished. Flowering plants (including trees like apple trees) that have nectar that attracts insects (like bees) before they bear fruit would require a token, and possibly a nectar type associated with them (which would again relate back to the
buzzing bee thread), and then have their fruit or vegetable as a separate set of tokens. The form the plant's seeds take can be another matter. Creatures may select to only eat fruits, eat fruit and vegetable matter, eat grassy matter, or even eat woody material, as well as having a capacity to drink nectar from a flower. The ability to crack open nuts in nut-bearing plants can be another matter. This can give us a somewhat more diverse base of herbivorous and omnivorous creatures by placing more specific food-type tokens on the plants themselves.
This means we need to get into the degree of specialization of predators, since there needs to be something between "attacks anything of this size range" and "attacks only this specific named creature". We could use some of the tokens, like the previously mentioned flier token to change what predators will attack them. Cats, after all, may potentially be aggressive enough hunters to kill a bug for fun, but they can't subsist on a diet of flies, no matter how good a hunter Scamps may be.
(While we're at it, making orb-weaver spiders (web spiders) that do not aggressively attack prey by spitting webs at them, but by spinning a web, and waiting for prey to come to them would be a good thing to put in eventually, as well. "Ambush predator" should mean more than just being hidden while they behave like every other ambulatory creature, it should also imply lying in wait.)
This could mean something like having jaws that are specific to certain types of tasks, like nut eating or grazing or predatory behavior. (No more crocodile jaws that are exactly the same as a cow's jaws.) If we start having creatures like turtles with serious ability to use their shells, then only creatures with shell-cracking capacities will be able to be their predators. Taking a page of Darwin's, and nut-cracking beaks on a bird would have implied nut-eating ability, but preclude some forms of insectivorous feeding. Longer beaks that are meant for preying upon insects that are tree parasites preclude nut eating. This would allow for both the purposes of differentiating what sort of prey species any given creature eats, as well as making animals have bodies differentiated by more than number of limbs and general size.
Also possible is using a less concrete set of tokens for what a creature eats, instead using something like a "Hyperpredator" or "mesopredator" or "hypopredator" type of token, which indicates how much of each type of "food group" that a creature must eat. (This would work well in conjunction with a dwarven nutrition model based upon food groups as a bonus.)
Magical ecosystems may also bring in very odd ecosystems, as some creatures may prey upon the magical nature of other creatures, being either magical parasites or carnivores - leading to that "eating" of an amethyst man either by disabling it (or somehow making itself a parasite the amethyst man itself cannot remove), and consuming some of its xenosynthetic organs or stored energy, or just consuming the creature outright.
This also can potentially serve as a basis for "Procedural Evolution", a commonly postulated idea in the suggestions forums. If we have a decent model of the costs of adaptations, in terms of how much mass they need to eat to stay alive, and development cycle time, we can actually have the basis for calculating some basic form of evolution.
In talking to The Phoenixian, he was mentioning the difference that something like a rainforest has upon its ecology, and I think this could be broaded into talking about a
Keystone Species. I'm not quite sure how to specifically model this on purpose as of yet, but it gives a good idea of how
a creature can have a dramatic impact on its environment. Having something like elk that graze differently based upon the presence of a predator species, hence
allowing different forms of trees to grow would be a serious power goal, but might be possible. If we can get more advanced animal behavioral models, then having behavioral models that change based upon the presence of predators could be possible.