If an invasive species is introduced to a new environment, why can they outcompete local species in the same nische, if they specifically evolved in this local environment and are adapted to it, whereas the invasive species would have evolved in a similar, but not identical environment?

What factors determine wether a new species will become invasive or nor be able to survive in the new environment, and can we predict that beforehand?

What does this mean for future space exploration? Lets say, we find life on mars and bring it back (or accidentally bring it back with the sample return mission), what are the chances that it could survive on earth, and what is the probability it could pose a threat to native life?

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    $\begingroup$ one of the best examples about invasive species is iceland,it once had forrests covering large parts of the country and then sheep was introduced,you can read a bit about it here: skogur.is/en/forestry/forestry-in-a-treeless-land/… $\endgroup$ Commented Oct 27, 2023 at 3:41
  • $\begingroup$ Interesting! Thank you very much :) $\endgroup$
    – Qoray
    Commented Nov 19, 2023 at 15:03
  • $\begingroup$ In this case, the competitive advantage of sheep is obviously that they are useful to humans. But that is quite a special case. I am more interested in the general case. What determines if a species is well adapted, and why are local species not even better adapted to the local environment? $\endgroup$
    – Qoray
    Commented Nov 19, 2023 at 15:05

1 Answer 1


You are right, most species cannot invade most new environments, they have to be specially adapted to the new environment. For example, a jungle frog can't invade a desert; it'll dry out and die.

You are also right that a newly introduced (invasive) species is (almost) always going be less adapted for the new environment than the local species already living there.

So why can introduced species out-compete the locals despite not being as well adapted?
-->Most of the scientific evidence seems to point to a lack of predators in the new area for the invading species.
-->This can make some sense if you think about the power dynamic between predator and prey. If predator and prey have been living together and evolved to have relatively equal hiding and hunting ability, then they can coexist. But if a prey and predator have never encountered each other, it's possible there'll be a power imbalance. Perhaps, the predator is really good at hunting the new prey, or maybe the prey is really good at avoiding the predator. If the prey is invincible, then it becomes an invasive species in the predator's habitat. If the predator is invincible, it becomes an invasive species in the prey's habitat.

I love that you're thinking about space, but science can only really answer testable questions. -- Mars Aliens -- aren't really testable right now.

That said, probably the Mars aliens would win since their incompatible chemistry would be to their benefit. If we assume the aliens are made of weird chemicals that nothing on Earth has evolved to digest, then we wouldn't be able to eat them and derive energy, so they probably wouldn't have any predators at all. But why would they be able to eat us? Well, just like astronauts on Mars could live off the ice we find at Mars' poles, probably the Mars aliens would be able to find something similar, some of their chemicals here on Earth that they can still use for themselves to take over.
--> But I don't think they'd be eating us humans any time soon! :)

  • $\begingroup$ Oh, I was thinking about Bacteria from Mars (either by bringing back soil, or even naturally, through Panspermia). The predator-prey relationship is certainly interesting! Would it be correct to say that invasive species usually do well in environments, if those environments themselves have undergone radical changes recently (for example, certain predator species dying out, recent changes in climate, ...)? $\endgroup$
    – Qoray
    Commented Nov 19, 2023 at 15:08
  • $\begingroup$ Because what confuses me: If there is an obvious niesche, like animals that can kill turtles on an island, where before, they had no natural predator, why did no other animal evolve to fill that niesche? Is it just a question of time? (iE would there have been canivorous dodos hunting other dodos if we had left them alone for another couple million years? Or are environments like that stable without outside interference?) $\endgroup$
    – Qoray
    Commented Nov 19, 2023 at 15:10
  • $\begingroup$ And since you mentioned predictability: Is there any way to quantify what environments are "at risk" of invasive species surviving there, vs environments, where most introduced species would not pose a threat? Is there a way to quantify if a specific species would pose a threat to a local ecosystem if it was introduced there? $\endgroup$
    – Qoray
    Commented Nov 19, 2023 at 15:11
  • $\begingroup$ I don't know too much about the evidence on recently disturbed environments, but it is well studied by ecologists worried about human disturbance, I'm sure you can find lot's of information about it. Maybe even post it here as answer afterwards. I remember hearing about it once in class, and I think it depends how the environment is disturbed, some disturbances open up new niches, while others just destroy the environment, lol. $\endgroup$ Commented Nov 20, 2023 at 15:24
  • $\begingroup$ re 2nd comment: no! environments are not stable without outside involvement. Look up the experiments on trying to establish a mars or moon style colony prototype here on earth. they can't do it because inside the locked away biomes, nature does it's thing and the ecology comes crashing out of balance. Also look at the rabbit fox/wolf simulation experiments where they show the expected predator/prey boom bust cycles. all that said, yes, I do expect eventually we would see dodos evolve to eat other dodos. and then once that new animal evolves, new parasites would evolve to parasitise it... $\endgroup$ Commented Nov 20, 2023 at 15:29

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