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In my setting Dragons evolved on a n isolated continent far from where man evolved. But in the past thousand years dragons have been introduced to the human inhabited continent, which is filled with real world Eurasian and North American wildlife as opposed to the fantastic.

Introduced species have a habit of cashing native ones to go extinct or be vastly reduced in numbers, but I still want predators like wolves and bears to exist.

How could an ecosystem withstand the introduction of a new apex predator, or is the logical conclusion of any introduction the extinction of many native species?

Dragons are animals and not sentient in this setting. They are not magic, they’re a 100 kilogram dromeosaur descendent that lives alone and reproduces slowly. They are carnivores and have to eat their body weight in food per week. This question could even be rephrased as “would tigers cause ecosystem collapse if you placed them in Alaska?” It’s honestly more about introducing large predators than anything else

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    $\begingroup$ You need to tell us a lot more about these dragons. How big are they? How SMART are they? If this is fantasy, are they partially magical, or completely non-magical. Can they fly? Can they breathe fire? What do they eat? How OFTEN do they eat? How often do they mate? How many eggs do they lay? How long do the parents care for the baby dragon? What's the infant mortality like? All of that stuff defines what your answer will be. Without it, we're just pulling stuff out of our butts here, which by definition makes this Opinion Based. $\endgroup$
    – Morris The Cat
    Commented Mar 6, 2020 at 2:42
  • $\begingroup$ @Morris The Cat I will edit to add better details $\endgroup$
    – user71781
    Commented Mar 6, 2020 at 2:53
  • $\begingroup$ Congrats for posting the 25000th question. $\endgroup$
    – L.Dutch ♦
    Commented Mar 6, 2020 at 7:32

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It's probably not a problem at all.

OK, so it actually depends entirely on what the EXISTING predator/prey relationship is like. Your Tiger/Alaska scenario is actually a really good one because introducing Siberian Tigers to Alaska wouldn't make that much of an impact at all, because alaska already has Polar Bears, Mountain Lions, and Wolves. The Tiger would be competing directly with those and sure it might win, but as far as the rest of the ecological system is concerned, that wouldn't make any difference. The Caribou doesn't care if it's getting eaten by a Wolf or a Tiger, and there's only so much food around for a hypercarnivore anyway.

Where ecological collapse comes in is in scenarios where an apex predator is introduced that is feeding on things that never HAD a predator before, like the introduction of house cats all over the South Pacific. Where animals are subject to predation that never were before, they get wiped out because there are no controls on the new predator and they just kill everything till there's no more food.

This wouldn't be the case for your dragons becase, again, they're competing directly with existing predators, and all the existing prey species are just as able to defend themselves against the Dragons as they are against bears, wolves, mountain lions, and depending on how far south we're talking about, crocodiles and alligators.

So, TLDR, new apex predator that takes over for an existing apex predator, or predators, doesn't create a problem. If your dragons were either fast enough that deer and smaller game can't outrun them like they can wolves or mountain lions, or large enough that they could take down full grown and healthy caribou or bison or elk with impunity, THEN you would have a threat of collapse because your dragons would eat themselves to death, and wipe out all their prey species, and then die out.

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  • $\begingroup$ @AdrianColomitchi The specific scenario you imply is covered in the last TLDR paragraph. If dragons can eat all the food, they would wipe themselves out. $\endgroup$
    – Shadowzee
    Commented Mar 6, 2020 at 5:45
  • $\begingroup$ @AdrianColomitchi did you read the OPs edits? these 'Dragons' don't breathe fire. Likewise, a predator that breeds slowly and eats rarely as the OP described aren't going to cause an ecological collapse regardless because unlike your rabbits, their population can't increase rapidly enough. You're making a lot of assumptions about what these dragons are capable of that aren't actually supported by what the OP wrote. $\endgroup$
    – Morris The Cat
    Commented Mar 6, 2020 at 14:13
  • $\begingroup$ @MorrisTheCat missed them, thanks. $\endgroup$
    – Adrian Colomitchi
    Commented Mar 6, 2020 at 14:16
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They are territorial.

Do you know what kills most tigers (after humans)? Other tigers.

This is a similar situation: males and females do not tolerate their own gender in their home range and will cheerfully fight to the death over it.

Similarly, mating time is a time fraught with danger and very careful woo-ing by the males.

The hatchlings similarly face a time of danger when they first fledge: they have to find empty space to live before the adults start to see them as competition.

in this way, other dragons are a bigger source of competition than a shortage of food could ever be.

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They are enlightened environmentalists

In many setting, dragons are smarter than humans. Your dragons recognize that destroying the natural order will result in less food, in the long run. As a result, they select their food sources carefully. They'll focus on sickly creatures, carrion, and the like at first (their distance in the evolutionary tree renders them immune to most mammalian diseases).

As they become familiar with the human-populated areas, they will make the following observations.

  • Humans are unnaturally endemic to the area, and causing ecological harm

  • Humans don't seem to have any natural predators, and are in fact the most effective killers of other humans

So, they will also focus on eating human peasants. They will avoid eating Nobles and Knights, due to the tendency of those types of humans to organize and participate in large scale human population reduction events.

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  • $\begingroup$ Cool idea and answer, but these dragons definitely aren’t smart enough for that. I edited accordingly $\endgroup$
    – user71781
    Commented Mar 6, 2020 at 2:20
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    $\begingroup$ Alternatively, they focus on eating particularly disliked nobles in order to gain a following of peasants... $\endgroup$
    – user20574
    Commented Mar 6, 2020 at 17:24
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Semiframe challenge: do you need dragons to survive in the wild? If you introduce a foreign species to a new environment there are two directions of possible outcomes. The one you describe is ecological collapse. It is also possible that the new species just can't survive in the wild in the new habitat. The most obvious reason for that is temperature. If you were to put lions into a Canadian forest, they would quickly die out in the first winter, their ability to kill deer doesn't help at all. So if you don't need wild dragons in Eurasia, you can just claim that they can't survive there on their own for some reason (climate, lack of suitable prey, lack of suitable habitat, some nutrient is missing in the local fauna, some local fauna like a virus or fungus just easily kills them off, etc).

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    $\begingroup$ Eurasia includes lots of warm places too. Italy, Greece, Southern China. Large reptiles do very well in many parts of Eurasia. Extremely large, in some cases. $\endgroup$
    – Morris The Cat
    Commented Mar 6, 2020 at 14:35
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They sleep. A lot.

These dragons split off from the main dinosaur lineage before the shift towards a completely warm-blooded lifestyle was complete. Instead of being fully warm-blooded or cold-blooded, they went a different route of "switching" between warm-blooded and cold-blooded biology depending on the local abundance of food. This makes them capable of a high-energy lifestyle when in "hunting mode", but also able to go for extremely long periods without food, like a crocodile.

In many ways, these dragons are similar to bears, but leaning more heavily towards the "hibernation" side. Like bears, they naturally regulate their own reproduction, only able to conceive when resources are abundant. This keeps them from overpopulating and wiping out their resources.

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The food chain just regulates itself

Introduction of a new apex predator is common in nature, they follow the rules of everything else, if there are food sources, they thrive, if there are no food sources, their offsprings die young, therefore reducing their numbers and allowing the rest of the chain to jump up again. Since your dragons are nonmagical and behalve like any other animal, there's no problem in it.

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I'll divide what I think the dragon would eat into these categories:

Large land predators (like bears): They specialize in tough terrain, where the dino has a hard time maneuvering around obstacles.

Medium land predators (like mountain lions): They learn to be stealthy, but end up with significantly reduced numbers (ignore the last three words if it's more convenient to do so).

Social land predators (like wolves): They outsmart the dragon, possibly find a way to take it down.

Birds of prey: They fly away, besides, they aren't worth the effort to eat.

Snakes: They're hard to find.

My questions to you that would help improve my answer:

Are the eggs easy to find and swallow?

Can the dragons fly?

How smart are the dragons compared to wolves?

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