Do you think species extinct in an area should be reintroduced?

In my opinion, animals should not be reintroduced if they are extinct by a long time, as it could cause harm to other animals and plants in the area because they are adapted to living without them. For example, if the animal that was going to be introduced was a herbivore, it could cause harm to other plants nearby. But if the animal was only extinct by a few years, it would be fine to reintroduce the animal because the animals and plants living in the area would still probably be adapted to be living with the animal.

Historically, when humans introduce species to an area where they are not typically found, the outcomes have been of an unforeseen, often disastrous result. However, I am an advocate for restoration of natural habitat or substitution of cultivars with native species. Often we see that the once encountered species return by their own migratory natures. An example of this is the extensive conservation efforts by dedicated naturalists in Ohio. Wildlife – Raccoon Creek and Arc of Appalachia | Savings Ohio’s Wildlands and Putting You in Them


Introduction should be managed according to current state of the place, if herbivore is missing you should make sure there’s a predator to eat it or humans should shot down or relocate excessive animals. No adaptation could undergo in a hundred years or less that most species are missing from somewhere.


Absolutely yes. An ecosystem can’t function correctly without all of its parts.


what’s too long for you? realize that what feels like too long for you, individually, might be irrelevant for humans (or any other species) as a whole. timescales relevant to entire species differ enormously to timescales relevant to an individual with a lot of behavioral plasticity.

intentional reintroductions of extirpated species do need to take a lot of factors into consideration (and typically, they ACTUALLY take a lot of factors into consideration). oftentimes, ecosystem restoration to something more similar to a past condition is a major objective. some species provide outsized ecosystem services, and some species are much less obvious. reintroduction of keystone species is often a larger priority when larger scale ecological restoration is the objective.

since humans are most likely the reason that the species were extirpated in the first place, then we absolutely should strive to repair things when we can.

now, the calculus is a little different if you’re referencing efforts to clone wooly mammoths from DNA found frozen in glaciers and/or permafrost.


“An ecosystem can’t function correctly without all of its parts.”

That assumes there is a correct way for an ecosystem to function and the rest are incorrect. I’d say if you take away one of its species it will function differently. You might decide it is a different ecosystem. But it will still function and who is to decide which version is correct?


I am never convinced by this kind of argument, as I feel that too often weasel words are used to justify their viewpoint.

  • What is meant by long time? 100 years? 1,000 years? One million years?
  • What is harm meant in this instance? Any kind of change? Disturbance that we would see in the reintroduced organism’s existing range with similar effects? Or actual detriment directly contributing to the irreversible decline of native species?
  • What is meant exactly by “adapted to living without them”? Adapted in how and what way? Is there a specific time limit in which organisms are able to adapt, then suddenly unable to adapt? Why would the organisms be unable to re-adapt to the reintroduced species, especially if they coevolved with the same species in the past?

if you take away one of its species it will function differently.

Technically correct. The only caveat is that the ecosystem will not function as it did before and it will, more often than not, take thousands to millions of years for the ecosystem to naturally replace that organism, especially if it was a keystone species: a species that has a disproportionately large effect on its natural environment relative to its abundance.

who is to decide which version is correct?

It is often the case that is it us humans who is the cause of that’s organism’s extirpation from the specific ecosystem. In such cases, who are we to say that the ecosystem is “correct”? Especially when we can see negative effects from that’s organism’s absence in the ecosystem?

This would apply equally to species that humans extirpated thousands of years ago as it does to species we drove extinct within the past few decades.


There are well-established IUCN guidelines for reintroductions and other forms of translocation, which can help groups of people to come to a well-informed decision in specific contexts:

The guidelines are also available in a range of languages other than English.


Personally, I’m hoping they keep the dinosaurs out of my neighborhood.


Oh, but birds are beautiful.(


The answer to the topic question varies a lot depending on what kind of organism you’re talking about and how long it’s been gone from that location. Reintroducing an extirpated plant into a small refugium is going to be very different from reintroducing a large wide-ranging carnivore. There are political, practical, as well as biological reasons for whether to do it or not.

As for the time since the species went extinct, in most cases we’re talking about decades rather than centuries or millennia. But there’s actually an introduction project underway for putting Bolson Tortoises in New Mexico where they have not existed since the Pleistocene. But tortoises in a remote area aren’t much threat to human development and they don’t eat livestock so that one may not be very controversial.

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I am concerned, but not necessarily opposed to reintroduction of genetically modified, blight resistant American Chestnut back into its native range in the eastern US, where it was a domiinant species a century ago.There is much talk of restoring the “primeval” forest, but in the mean time other species including oak, maple, beech, etc. have established a new equilibrium. What impact might reintroduction have on forest ecosystems?


I personally don’t think that “Pleistocene rewilding” is a good idea in any form. Simply put, what worked in the Pleistocene probably won’t work now.

I like the idea of reintroducing locally-extirpated species, but I also think it is one that needs to be approached with some degree of caution. I have a lot of questions that I’d like to ask, and some general guidelines. Also, I’d always rather make the reintroduction one that “works with nature” rather than one that is mechanistic.

I am less concerned with how long a species is absent and more concerned with a variety of other factors.

Questions I would ask:

  • Did the species go extinct due to habitat loss?
  • Is the species found in adjacent or nearby areas? If so, how are those populations faring?
  • Are there any barriers to dispersal or establishment into the area where it has been extirpated?

First, you need to make sure that suitable habitat exists, because otherwise, the effort will likely fail, wasting effort. In most cases, if you address other conservation issues, such as creating habitat, ensuring nearby populations are healthy, and creating corridors for dispersal, the species will re-establish itself on its own. This would be my preferred course of action. These things are all important to do anyway, and will have cascading benefits for many species.

If a species cannot re-establish on its own, such as if nearby populations are faring poorly, or if there are no nearby populations, it then becomes trickier. A big question I have is, which source populations are you going to take from, to re-establish it?

If you take from a population too far away, there are several ways harm could come. One, it might fail to establish because it may be poorly-adapted to local conditions. However a second problem is that, if it does establish and spread far enough to come into contact with other regional populations, it might be genetically distinct from these other populations that it could cause outbreeding depression, which in the short-term could harm both populations. If both are shaky, this could be dangerous. (This scenario seems unlikely because it would only occur in the case that the new population expanded enough to come into contact with another, so presumably it wouldn’t be too vulnerable but I would still want to think about it. Outbreeding depression is a common problem in certain plant species that have very large ranges, and it can happen in animals too.)

And yet another problem with introducing new genetic material from far away is the opposite: “hybrid vigor” or added vigor from genetic diversity. There could be a risk that if the species interbreeds with other regional populations, it could become invasive. An example of a species doing this would be the common reed, Phragmites australis, where there is evidence of “hybrid vigor” from introduced and native populations cross-breeding.

I tend to work more with plants than animals. One issue that seems critically important with plants, but is also true of animals, is the relationships between the species and other species that eat it, are preserved. This typically happens if the reintroduction is adjacent to its current range, but it may not happen if there is a large geographic divide, because the animals or pathogens that eat the species cannot travel over a large gap without host plants. Insects can travel surprisingly far to find host plants, like tiny flying insects can pass over gaps of many counties to find preferred host plants, in large part because many insect adults can eat nectar from many plants, and they only need the special host to lay eggs and feed larvae. So this is how you have the Ailanthus webworm moth skipping over large gaps in the introduced range of Ailanthus altissima, to expand from southern Florida where it has a native host plant, and it is now found in much of North America. But insects won’t necessarily cross the rocky mountains or the great plains or other huge geographic divides.


I also wanted to separately reply, I think there are relatively low risks when these reintroductions are carried out on a micro-scale, and I have actually done dozens of such reintroductions in the ecological restoration work I do.

I.e. when there are small islands of isolated and/or highly fragmented, highly degraded wild habitats, as is the case in most wild areas, there are a lot of areas where the habitat might be suitable for a variety of plant species, but they’re not found there simply due to accident, the history of the site, and isolation from nearby populations. Like, as an example, small woodlands surrounded by suburbs, in my region, often grow up with invasive species like English ivy, Norway maple, tree of heaven, Japanese honeysuckle, and Amur honeysuckle. All of these are highly problematic species ecologically, and many of them are planted in people’s yards.

I’ve found a tremendous benefit to seeding native plants into these small fragmented habitats.

And, doing this, in a few cases, I have actually reintroduced some locally-extirpated plants, talking a level of moving a distance of about 1 county over (about 20-50 miles) to the closest wild populations of certain plants.

For example I got Chasmanthium latifolium, which was locally extirpated in New Castle County, DE, established in some of these degraded woodland fragments at many sites in the county.

In an overwhelming majority of cases though, I’m not ever introducing things over such distances, it’s more like moving seeds over distances of 1-2 miles, maybe sometimes 5 miles, to establish new plant populations in suitable habitat.

I don’t worry at all when I do such introductions. Like these ecosystems are all so incredibly overrun with highly-damaging invasive plants, the status quo is actively causing damage because these habitats are breeding grounds for these invasives, from which they can colonize other areas.

I also have seen real transformations of some areas. Like I’ve seen areas where there is not only an increase in insect populations, but a big increase in populations of birds, and then predators like hawks and foxes, following some of the work I’ve done. It’s really exciting to watch. All I ever did was move some plant seeds and pull out some invasives, and the animals all came in on their own.


Depends. The Bolson Tortoise experiment might actually work and provide an assurance population for this species which is declining in its limited range in Mexico. Some other proposals I’ve seen, such as releasing modern Cheetahs in the North American grasslands to chase our lazy Pronghorns, I’m not so enthusiastic about.


Outbreeding depression can be a problem, but sometimes the genetics work the other way. For example, the native grass Festuca roemeri used to be a community dominant on upland prairies all around Oregon’s Willamette Valley and into the mountains. It was abundant. Like all abundant species (including humans) it carried a load of genetic defects that were unimportant in a population biology sense (however tragic they may be for the human family involved). Now, however, the species has been vastly reduced by conversion of its habitat for farms and town, by grazing, and by succession to forest (favored both by planting and by fire suppression). Some population can be counted on your fingers – tiny. Such populations are inevitably inbred, becoming homozygous for defective genes that would have been hidden in the more diverse larger population that once existed. Revegetation should be done using seed from multiple populations (not just the closest one) to introduce healthy versions of the genes and establish a form of hybrid vigor that will continue for generations (though it will decrease somewhat after the F1 generation).


I think it depends hugely on the species, and relevant experts should be asked about individual cases. There’s no one-size-fits-all for this sort of thing.

One thing to keep in mind is that not all extinctions are human-induced. Sometimes a natural shift in the ecosystem puts one species out of favor. If that’s the case, we should probably stick to maintaining a captive population (if it’s dwindling everywhere), or just let it live in fewer places than it used to. Unless it’s a one-time thing, like if a volcanic eruption puts a species in serious danger, since that’s not the same as conditions slowly shifting too far away from what that species favors.

And, sadly, there’s currently a question of where to put the limited time and funds; what’s better, reintroducing one species or using that time and money to help several others?

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I was reminded of this by the tortoises. There is a place in Hawaii called the Makauwahi Cave Reserve where they use unwanted pet tortoises as placeholders for giant Pleistocene ducks that went extinct once humans arrived to the islands. The tortoises prefer to eat invasive plants and recycle nutrients into the soil, which allows native plants to regenerate and bring the ecosystem to a more natural state. Their grazing habits also prevent the area from being too homogenized and ultimately boosts biodiversity.

Now I’m not saying that we should introduce tortoises everywhere, but Pleistocene rewilding does have a basis in reality and should not be discounted just because people want to put elephants in Texas or whatever.