Hydras would not compete with snakes

Most snakes eat rodents, or other small animals. Even large constrictors don't generally eat adult-human-sized prey. Assuming that hydras would be interested in human-sized or larger prey, they are no longer in competition with their mundane snake forebears. The same holds true for lizards (often eating bugs) and great wyrms.

Now, the hydras and great wyrms might threaten to wipe out your horses, but that's another question.

Horses and unicorns could coexist, the same way elk and moose, or elephants and zebras, etc, coexist. As long as you've got a rich and varied ecosystem.

Make the super animals depend on mana to live, and move the mana around. As it passes through any given area it moves slowly enough that the animals change, but fast enough that the super animals don't have time to eradicate the normal animals.

This will cause the super animals to either migrate permanently to follow the mana (assuming they can adapt to new biomes), or die out. It's no problem if the supers die out because more will arise when mana passes through the same area again.

One way to move mana around is to make it depend on some pseudoscientific thing like astrology, so the ley lines are defined by where the projected paths of the planets on the surface of the Earth get closest. Maybe the mana spots cycle through the Earth's chackras (seriously, google it up, I couldn't come up with that on my own), but with the addition that the chackras move. Or maybe they form where mana flares from the sun strike the surface, because mana flares are invisible and not deflected by the planet's magnetic field.

Or, who knows? The gods do play dice with the universe. The world is a grid and mana spots are random events.

Something many people seem to struggle with is that evolution is about survival of the fittest, not the strongest or the biggest.

The fittest individual gets to live long enough to get enough offspring that have a higher chance than their brethren to get their own offspring.

Your hydras and unicorns would require more energy than their "lesser" counterparts. They partially counter this through higher intelligence allowing them to hunt prey better, but during times of scarcity it will be the hydras, unicorns and their children that will perish first.

Also as a strategy many creatures that are larger will have fewer children per birth. This allows the "lesser" variants to compete with numbers, as they'll take up most of the food and during scarcity have more individuals that might survive.

Competition: The majority of evolutionary competition affecting predators is between the predator and its prey, not between competing predators. For example, there is an evolutionary pressure on cheetahs to run faster in order to catch their prey and a similar pressure on the prey to run faster in order to escape. A super-cheetah may find it easier to catch prey but won't compete directly with a standard cheetah so long as they don't deplete the prey animal too much. So both cheetah and super-cheetah could coexist in a similar manner to how two different predators with different hunting efficiencies often do exist in the same region.

As an alternative, perhaps super-predators naturally hunt super herbivores as they are larger (and tastier?). So normal prey animals are left for the normal predators.

Intelligence: If the super predators are smarter, they may voluntarily limit their populations to avoid killing all their normal prey - therefore there will be prey left over for normals (even if the normals find it a little harder to get a feed).

Fecundity: As an alternative, the mana might mess with ability to reproduce - or greatly increase time to reach maturity - in that case the supers population would always be small enough that they wouldn't compete for resources.

Competitive animals: There are some species that naturally compete amongst themselves, for mating privileges, leadership etc. Presumably supers would breed amongst themselves so there wouldn't be direct conflict with normals. Similarly, a super wont see a normal as a fitting opponent so wont bother fighting them for leadership - as a lion wouldn't bother fighting a cat.

In practice though, you might lose some normal species regardless of what rules you enforce. A super lion might find a normal elephant a better meal than an antelope or zebra, and they will be much easier to catch as elephants have not evolved with any defense from an extra-powerful predator. Consequences like that are the usual outcome when you add any new species to an ecosystem, and the supers are effectively equivalent to new species even in their normal environment.

If it takes multiple generations for the mutations to take hold and change the animals into a new species, the local ecosystems have time to adjust. As others have pointed out, a new species can certainly change the prey/predator balance and result in problems in obtaining food or other resources, but it isn't necessarily the new species that came from one animal competing with (and winning over) that animal.

Intelligent animals can also work to increase available food, which helps other species as well. Behaviors that do this can come from evolution itself (like how ants can herd aphids) or can be from increased intelligence (primitive agriculture or creating habitats for food animals). Depending on how intelligent these new species are. You can build this skill into your evolutions if you choose.

Any animal that doesn't have enough food, water, or safe places to create and raise their young will migrate. If the new species are happy staying put, their cousins will find better pastures, as it were.

Even if one species reduces in population due to changes from the new species, there will be other communities elsewhere. So they won't go extinct.

Given how evolution works, these creatures would eventually out compete their cousins and drive them to extinction. This would eventually lead to the world being dominated by magical beasts, eliminating all other kinds of "regular" animals.

Actually, that is not how evolution works. The basic principle is indeed "survival of the fittest", but in practice it does not come down to "biggest baddest animal wins". If you carefully consider the mathematical implications of Darwinism, and set your assumptions reasonably, you realize that in fact it's a vastly more complicated story - which is how we get our diverse biosphere on Earth. I won't go into the details of this because it's a topic that could (does!) fill whole textbooks. You'll have to take me at my word.

How can it be, you ask. How can the magnificient unicorn not dominate the horse? Well, that's all in the textbooks. But basically:

• Fitness is relative to the environment and the magical animals may be fit for the mana hot spots, but they may have very poor fitness outside. A classic fantasy staple is that magical creatures begin to weaken when not around magic. See "waning" of the Elves in Tolkien, among others -- elves are like magical, better humans, right?


• An animal maybe more bad ass, but it may need to also eat more. That's why there's more rats in the world than tigers. Fitness is not about being the most badass, but most efficient. Whoever gets the most bang for their buck proliferates the most. Buck here being food or energy, bang being, well... You know. Wizards becoming extremely hungry after casting big spells, and having to eat ridiculous amounts of calories, is another fantasy staple. It even has an analog in reality, if you look at programmers, mathematicians or students in tough exams. In fact, high caloric intake is suspected to reduce lifespan, so you could also go with that idea. So maybe unicorns can't find enough food and starve, or maybe they can but they waste so many calories on magic they rarely use that they end up dying young from heart attacks or cancer.


• This is the same as fitness being relative to the environment, but it is not a given that a magical animal will feel the same exact pressures as its mundane analog. People don't hunt horses that much, but unicorns are really cool. People might hunt them to extinction. See dodos, buffalo, and others. Same might apply to other predators, maybe wolves find unicorns really delicious.


• When you mention that "their genes are mana infused" you kind of break with any real world biology, so anything is possible. But I'm assuming this means literally that their DNA is not merely mundane nucleic acids, but has some magic in it, similar to how a magic sword is metal infused with magic. So then, if an animal eats the magic unicorn, those same molecules will be incorporated into the eater's cells, and they will likewise be just as magic.


• Predators, parasites, diseases and so on maybe somehow inhibited or killed by mana. So the unicorns do really well in the mana hot spot, but as soon as they stray too far they get exposed to all sorts of new threats they haven't adapted to. You could even play this for laughs, and make them all die from the common cold (which for some reason is cured by mana hot spots).


• In real world biology, all adaptation has a cost. Increasing your fitness with respect to one environment almost always decreases your fitness to another environment. Trivially, you cannot be both large and small. But also, it's just how physics and chemistry works - it turns out that "free lunches" are very rare in biochemistry (this may be because we're already starting with a very optimal organism) and extreme generalist, "Swiss army knife" species (eg. us) tend to not be very good at any particular thing. For example, when bacteria become resistant to an antibiotic, it usually also makes them grow slower when not exposed to that antibiotic. So your magical creatures are unlikely to be much better than their mundane cousins, and outside their original environment, might do very poorly. This is again a consequence of "fitness is relative to environment".


• Just because species A has higher fitness doesn't necessarily mean it will become the only species. When it does, that's called a selective sweep. But selective sweeps do not always happen for all sorts of reasons. The result would be a mix of the competing species in equilibrium, especially for small fitness advantages. Populations often retain a small pool of "unfit" individuals as backup for sudden environmental changes.

However, I think the main fallacy is that you assume that mundane animals are "not evolved enough", and that there could be better, "more evolved" creatures. In fact, all creatures are equally well-evolved - they have all been evolving for the exact same amount of time; which is the time since the creation of the first ever organism from which they all descend. As I noted earlier, evolution is about adaptation, not being the most badass. Therefore, in "steady-state" all species tend to be almost perfectly adapted to their environment. If you think of evolution as searching for the local minimum [of energy expenditure per offspring] of a mathematical function, most species are already in the local minimum. There's nowhere else to go.

Another way to put it is that mutation rate is not the limiting factor. It's not like these animals could explore crazy new evolutionary possibilities, if only they didn't have to sit around waiting for the odd once in a million year mutation. They are already mutating way more than enough. In fact for most things, the name of the game is to cut down on that mutation rate, both to avoid losing their "optimal" state, and also to avoid getting cancer (I think "magic gives you cancer" is a very underappreciated theme in fantasy, personally). Don't believe me? Look at Chernobyl. While there's supposedly some weird new mutants that were found there, it hasn't really created any super-animals.

So the thing you are suspecting cannot happen. Even if magic accelerates evolution, it wouldn't matter, because evolution is already fast enough and most species are already at the finish line. If magic also gives supernatural powers, that's a different story -- you have to ask why would any animal give up such awesome power, why wouldn't every animal evolve to become magical? The simplest solution is to make magical powers not work without mana, or make magical powers come with a cost.

It is true that evolution is not instant. So any a change in the environment can be too rapid for an organism to adapt. For example, even though there are bacteria that can live in scalding water, if you put an average E. Coli in a boiling pot, it will just die. You would need to raise the temperature a tiny bit in every generation. Similarly although bacteria can become resistant to antibiotics, a naive bug will not instantly resist a brand new antibiotic if it gets administered at 10x the lethal dose. You have to give it increasing, sublethal concentrations for a while. This is where mutation rate comes into play, as it can possibly accelerate the process, but not by much. This is because getting multiple mutation steps without selection acting in between is very unlikely due to the large number of probabilities involved. So if magic increases mutation rate, then it will only affect adaptation/evolution if the animals experience a sudden shift in environment, and it will only affect it briefly (until the mundane species catch up), and it will only affect it slightly.

You could just make the "magicisation" process work both ways.

After several generations of snakes/horses/lizards in a mana-rich area you get Hydras/unicorns/dragons, but after several generations hydras/unicorns in a mana-poor area you get back to snakes and horses (or perhaps some other mundane animals that lack magic but are not quite the same as the base animals were originally).

So as you move away from the mana-rich zones the abundance of magic creatures would fall, even if they are just better at everything than their non-magic relatives.

(A somewhat Tolkenesque weakening of the blood over time.)

First, a subdued rant against such terms as "hyper evolved", "more evolved", higher life form", etc.. These suggest the "ladder of life" view which is almost a defining characteristic of people who do not understand evolution.

As for your question, you seem to have almost answered it yourself. If mana is not uniformly distributed then there will be high mana areas where mana-using animals will dominate, and low mana areas where conventional animals will. In between there will be areas where they compete but because each has a safe refuge it will not be driven to extinction.

Keep in mind that mana-using organisms are not "higher" but "different". They have different needs and probably will not be competing directly with their non-mana-using progenitors.

A mana-based lifecycle.

Creatures don't consume this mana to live, but they do need it to live and they need it to produce offspring (imbuing the offspring with the mana to be magical).

Mana flows from prey to preditor, and from animal to plants when the animals die.

So unicorns have to eat grass to live, but to produce new unicorns they need to eat mana-rich plants. Similarly, Hydras have to hunt mana-saturated animals in order to reproduce.

Mana-saturated animals would learn to taste mana, smell mana, and would prefer eating from mana-saturated food stuff. They would eat some other foods, but a hydra that goes around eating horses gets fat and dies of old age and doesn't reproduce.

Mundane creatures that avoid becoming mana-saturated are low-tier food for mana-preditors. They aren't tasty.

Depending on the amount of bioavailable mana in an ecosystem would then determine the amount of magical plants, prey and preditors. The usual mass ratio would apply; plants would far outweigh prey, and prey would far outweigh preditors, as each has to work to consume the other, and if their food is rare their numbers decrease.

Have the mana "settle" in isolated locations such as an inaccessible valley or island. Something which genetic exchange is either difficult or impossible.The species in this valley would then evolve isolated from the rest of its cousin species.

Mana Affinity

There are different "flavors" of mana. The organisms capable of using mana are best at using the mana generated by others similar to them, so when they start to displace the mundanes, their supply of mana falls off accordingly. This places an upper limit on the portion of any given type of organism that can use mana, and assures there must always be some of the mundanes producing it for them to consume.

You said the magical versions of the animals have increased intelligence. Let them recognize that their survival is somehow dependent on their base form. I would suggest that the base form produces mana which is more beneficial to the higher form than other producing forms. Mana is mana, but the ones that share a heritage with the higher form are more beneficial in some way.

The higher forms could be aggressive to all other higher forms, much like in the tv show highlander where the immortals are perfectly happy to kill each other usually, but usually leave the humans alone.

The higher forms could be social with their same kind but hostile to others unless there is a beneficial relationship, like those birds that clean the teeth of predators. So grey squirrels all get along, but hate black and red ones.

So... mana helps evolve man from apes. Apes lose? Destined for extinction? Same reasons we coexist, other species can coexist. Monkeys are not disappearing any faster than other species.

We are not Pokemon! Evolution does not favor superior skills, but the ability to survive. Sharks have remained relatively unchanged since well before the dinosaurs and surviving Dinosaurs evolved into Birds (Or Crocodiles/Alligators, which are surprisingly close in relations when compared to birds and any other reptile). It's entirely possible that a hydra and it's genetic relative snake can exist in the same environment because competition edged both to survive in unique ways. Proto-Snake could retain snake like advantages because he was better at surviving with those advantages than proto-hydra snake, which faced the choice to either evolve to be better at something else or go extinct. In this case, a mana using Apex Predator role was not being fulfilled by anything better than Proto-Hydra and thus, the reproducing adults were able to pass on those advantages... but snakes remained the dominate filler of the role proto-hydra and proto-snake were competing for... though some of modern snake's advantages over Proto-Snake would occur to survive against the Hydra.

It's not that Hydra is better than snake, but Hydra is better at things the Hydra does because Proto-Hydra could not beat Proto-Snake at snake's niche, but it could beat it at another niche.

We can see this also with Birds. It's been common knowledge that Birds are the living descendants of Therapods aka Dinosaurs. Specifically certain subclasses of Dinosaurs that are mostly characterized by small bipedal builds. When the KT extinction event occurred, the sudden die off meant that for the large herbivores dinosaurs to find plant life as it wasn't growing in supplies large enough to graze upon... and the large predators had trouble finding large herbivores because, it was hard to find large sources of meat... there wasn't enough prey to sustain a large predator, smaller dinosaurs were to agile for larger predators and didn't have enough meat to offset the fuel it took to catch them, and carcasses of either were quick to rot and fester, meaning they would get sick and likely die. Being light, nimbile, and agile was an advatage in this world... one that the first mammals and proto-bird dinosaurs were better suited for than T-Rex and Triceratops... If I have a Hummer and I have a Mini, in a Mad Max style fight to the death to the nearest gas station with only enough fuel to one car to full and one car to half a tank, well the advantage is the Hummer if he can knock the Mini off the road first... but the mini is smaller and thus harder to target for the Hummer... and this also consumes more fuel for the brute with each successive attempt. The Mini is more likely to get to the gas station before the hummer... the distance over the hummer and the ever shrinking limited range before it can go no more will eventually kill the hummer in the long run... unless the hummer drive lightens the load in some fashion... or fit a more efficient method of consumption of fuel... or even finding a new mode of power... When fuel was aplety, the Hummer and the Mini could coexsist... but now that it's scarce, the Hummer needs to change how it plays the game and the next time the driver looks for a car, he's likely to take these rule in mind... or he's out of the game for good.

Evolution is all about living long enough to pass your genes along to the next generation, by any means possible. And as we know, if you want to pass your genes on, size doesn't matter, it's how you use it that counts.

High mana concentration is necessary for raising a healthy offspring.

While your magical creatures can normally roam around even in areas with low levels of mana, they need to come back to mana sources for breeding. If they don't do that, there is much higher risk that their offspring will be born dead or with some defects (like unicorn lacking a horn).

With mana sources being rare, they will become crowded with magical animals. And hydras will mostly hunt unicorns, not regular horses, to feed heir babies, because that's the type of prey that will be available close to their nests.