I’m wondering to how new forms of an invasive species are viewed in conservation.
If given enough time, an organism will evolve into multiple species or subspecies. As this process, speciation, continues, the effected species will become more and more different from its ancestors. Speciation is largely dependent on geography and the unique challenges the area brings. The species adapts.
An extreme example of changing geography to an organism is to introduce it to a completely foreign environment, such as bringing a European species to North America. The species will change due to the differing habitat, resources, competition, predation, weather, etc.
So here’s my question, what is done about an invasive species that is different (visually, structurally, in niche, etc) from the original introduced specimens? Would it still be considered invasive? It isn’t the species from Europe anymore, it evolved in North America and is therefore a North American species.
I’d like to hear the community’s thoughts.
It would take a long, long time for that happen, many centuries and likely thousands of years. We don’t have to worry about it for the next few millennia.
Species are often distinguished based on weather or not they can produce fertile offspring, so given enough time for evolution to genetically distinguish the invasive species from it’ original ancestor I don’t see why that wouldn’t be possible. However, it would still be considered an invasive species as long as it poses a net detriment to the invaded ecosystem(s) - other species in said ecosystem(s) would have to evolve to prey or parasitize on the invasive species in order to control its population and at that point we may consider the species to be exotic/non-native but no longer invasive.
I think @raymie has it right. The time it would take for an introduced species to differentiate from its parent species is so long that none of us here need worry about it.
Evolution and even speciation can happen quite quickly given the right set of conditions. A study published just a week or two ago showed seasonal evolution (that is, within one year!) in fruit flies: https://www.the-scientist.com/news-opinion/fruit-flies-evolve-in-time-with-the-seasons-study-69816
This isn’t speciation, but it only takes one change (depending on what it is) for a new species to be created (such as a change in ploidy), so I wouldn’t discount that invasive species could evolve to be distinct from the populations in their native ranges.
That said, I think that the lineage (whether it is the same species or not) could still be considered invasive. What really defines an invasive species is a lack of evolutionary history with the organisms in the area where it is new (its invasive range). It hasn’t evolved with them, and they haven’t evolved with it. So an invasive species evolving in its new range is part of the process of it becoming “more native.” If in time many native organisms also evolve in response to the invader and it no longer has a strong/disproportionate impact on that ecosystem, I think it would be fair to remove the label of “invasive”. This is indeed likely to take hundreds or thousands of years because it would involve the evolution of many species. However, it has likely happened already with species that humans introduced to new places tens of thousands of years ago. I don’t know of any specific examples, but it would be cool to know some!
Going off your comment, it seems that the invasive title is only temporary given enough time. And that once other species evolve to to deal with the introduced species, it becomes native.
To me, invasive species are often given the title due to a human influence. However, plenty of species could have been considered invasive at one point in their history. The camelids, for example, first evolved in North America but have since migrated to Asia, South America, and Africa. Mass migration and competition are a natural part of nature (though I’m not saying we should continue to introduce species into new environments).
In the long-term, being invasive is only one part of their evolutionary history.
I think there already are examples of this, for example the dingos in Australia, descending off domestic dogs introduced by men and now considered a separate subspecies (and I think not considered invasive?)
I don’t think anyone has discounted that. It is mostly a matter of time. Fruit flies are short lived and evolve quickly but how many new species have been evolved in a lab? How many new ones have evolved outside the lab while we’ve been alive? How many of those have had an impact on the environment?
To put it another way I’m not going to hold my breath until a potential new Scots broom (Cytisus scoparius) species or subspecies is no longer considered to be invasive. We are changing the natural world faster than ever before.
The first example I thought of was the Dingo. I think they haven’t been in Australia long enough to be considered non-invasive. Plus, most of the Australian wildlife haven’t adapted to the predator.
They still pose a bug threat to the native ecosystem, something a native species doesn’t usually do.
I think the big failure of the invasive-vs-exotic-vs-native trichotomy is our current era of rapid anthropogenic climate change.
Is a species still native to a region if a new and unsuitable climate has invaded it?
Sometimes ecological communities can evolve gracefully, or can migrate along with the climate as it shifts. But where there are barriers to migration, or when phenotypic mismatches disrupt interactions between different parts of original ecosystem … I think we’ve going to need to come up with better ways of thinking about all this.
Cardamine pratensis var. palustris could be an interesting and confusing example of an invasive becoming naturalized. I’m not sure what the current consensus is, but depending on who you ask it’s endangered or invasive in Illinois, a completely unique species, a subspecies, a variant, or a synonym of European C. p. ssp. paludosa. It’s also threatened in Minnesota, according to the MN Dept. of Natural Resources. It’s morphologically recognizable, but frequently lumped with the invasive northern European species. Some believe it’s entirely native, some think it’s a naturalized and speciated rare exotic, and others think it’s just invasive.
Many of the worst invasive plants have an annual life cycle, and produce thousands of seeds per generation. And they are invasive generally because they arrived in their new home without their co-evolved pathogens and predators. On the face of it, the combination of short generation time and sudden release of selective pressure from co-evolved species could result in rapid divergence and speciation. I’m pretty sure there are documented instances of this for at least North American invasives over the past 100-200 years, but I don’t have citations ready at hand.
Given the right circumstances it can happen quickly, over the span of a few decades rather than centuries.
A case in point is the introduction of Italian Wall Lizards (Podarcis sicula) to the island of Pod Mrčaru, Croatia in 1971. Over the next 30 years they underwent enough significant changes that if they’d been discovered in the 2000s without knowing their history and point of origin they’d very likely have been classed as a separate species.
Here’s a write-up on them I did a while back, with internal links to sources.
This is not correct; they are considered non-invasive in Australia, and our other wildlife has indeed adapted to them as a predator
I often think about the common Starling, introduced to NA in the later 1800’s. The population (gene pool) was fairly small - has there been any work done on comparing the genome of Starlings in, say Winnipeg, to the European ones? I’m not particularly fond of them, but I do respect such a tenacious organism!
A few of the island fox subspecies in southern California may have been introduced by humans several thousand years ago, which might be another example.
Not the starling but I recall a paper that looked at either morphological or genetic divergence in introduced populations of house sparrow. Apparently there was detectable variation in New World populations although not enough to consider them new species or subspecies.
I agree with the comments that it would require a very long time for many taxa groups to go through that process, and that if it did happen they’d still be considered invasive and associated with the original invasive species. Although, this topic also brings to mind the fact that scientists originally define species as native or introduced in part based on the length of time that passes, not only on the location a lineage originated in. For example, Hylaeus masked bees are considered native to Hawaii in Oceania despite that the lineage was introduced from Asia long ago.
I live in Singapore. Some examples of Invasive species in America, horses, snakeheads, mitten crabs, hybrid cichlids, pythons, lionfish, Kudzu, big head carp, asian giant hornets, asian longhorn beetle…
Evolution is generally a very slow process. We do not see new species appear in our lifetime. Although new species can be discovered deep in some jungles.
Different countries have different methods regarding conservation. If small exotic populations are sighted at an area, there can be an effort at eradication. Once the population has become endemic, they go into control rather than elimination. Different species are view differently. Example, if there are rats on an island full of seabirds, they might make a great effort to take out the rats. If an organism has much appeal to people, such as cats or horses, these organisms in a feral state may be viewed differently.
There hasn’t been much examples of species which has diverged alot. I guess hybrid cichlids in the ornamental fish trade, such as flowerhorn and South american cichlid hybrids may be an example. There are some stories of salmon, trout hybrids. Hybrids can sometimes have hybrid vigour that give them an advantage over comparable native wildlife. However, scientists have records of their genes, and they will not be classified as new species.
Procambarus virginalis or *Procambarus fallax f. virginalis is still treaten as invasive and probably evolved in Europe.