Hello J. D.; Weediness is the trait that is the worrisome one whether the species is a native or an import. In Southern California there are Opuntias that are natives that become invasive if the habitat is disturbed. The limiting factor in their invasiveness is fire. They don't recover from fire as rapidly as the competing natives.

I imagine that Opuntias in Spain behave similarly. They are interesting because they are weeds. Best regards, Jim Des Lauriers

J.D. Franco-Navarro It's rather hard to argue.

Some may say that any species becomes irrevocably an invasive species once it has been human-dispersed, and some say that, logically, any species has been an invasive species at some point (Chew MK, Hamilton AL (2010) ->The rise and fall of biotic nativeness: a historical perspective. & Vermeij GJ (2005) -> Invasion as expectation: A historical fact of life)

And there is this study by Carthey and Banks which suggest that "the logical, objective criterion that distinguishes this long-term change is the loss of ecological novelty, or in other words, the loss of naiveté of the alien species' native enemies in its new range." (Article When Does an Alien Become a Native Species? A Vulnerable Nat...

I would add that once an invasive species is now contained to a new range, and has entered some co-evolutionary mechanisms with native species, its status may be reconsidered.

Grégoire Moutardier James Des Lauriers thank you very much for your comments.

I support amnesty for non-natives that have become integrated into the food web!

Invasion or colonization is a fundamental attribute of biodiversity. Native and Non-native are constructs developed in Great Britain in the late 1800s. I live in an area that was glaciated 15,000 years ago. Virtually all of our fish, mammals (including people), plants, and invertebrates invaded this area. Dams and other infrastructure have blocked critical migratory pathways. The altered habitat of polluted reservoirs has made many of our waters unsuitable to native species while new species adapted to the new habitat are introduced (including those we don't like) are filling the void. If we care about native species, we need to repair the damaged landscape and waters, and restore the habitat, connections and resilience that they require in a changing climate.

It can be considered invasive though they stayed and adapted to the area/ecosystem for a long time if native species compete with food, survival, and reproduction to the possible predation behavior of non-native species

An invasion which already occured is still an invasion, and we still should do all we can to remove the invasive species. Saying that is an impact that already occured and we can let it be is like saying that if the plastic has already invaded the oceans it is something we should ignore. The non-native species are a form of pollution, we can call them biological pollution, and it might be the most dangereous form of pollution, because it self-replicates.

I think is is dangereous to relativize such concepts.

Amy Berkov thank you for your funny comment. I support amnesty too, do you know that Opuntia fruits are delicious? and in Mexico, the cactus blades are eaten. Delicious too.

Yum! But, for instance, the bumblebee Bombus fervidus is critically imperiled in New York State... but seems to be doing pretty well in a local NYC park: foraging often on two weedy non-natives that provide nectar from May through October. On the other hand, Doug Tallamy has compiled extensive documentation on temperate Lepidopteran host plants showing that non-native plants (even close relatives of native species) host an impoverished fauna.

Hello JD; Nopalitos are eaten by many of us in the southwestern USA. I have a nice, spineless variety in the garden. Tastes kind of like asparigus. Then, there are the tunas! Enjoy them...just don't let them escape. Jim Des Lauriers

James Des Lauriers in Cuernavaca (México) where I live for 6 months, Nopalitos are eaten as "alambres con queso", and are AWESOME. In Spain there is no tradition on eating nopalitos, but for 500 years Opuntia plants have been important as: (i) fruit harvesting (prickly pear fruit), (ii) demarcating fields and livestock properties, (iii) farm animal feed, and (iv) ornamental.

The problem is on Dactylopius coccus, a plant-parasitic hemiptera insect whose host is prickly pear cactus (Opuntia). It is also known as grana cochinilla, cochinilla grana, nocheztli (or simply cochinilla). As an ancient Mexican tradition, the carmine extracted from the females of the species has been used as a fabric dye for centuries, and even today as a colouring agent in cosmetics such as lipsticks. The Spanish conquistadors brought it to Spain to cultivate this cochineal but it did not work then, and now, 500 years later and taking advantage of climate change, the cochineal has found its perfect environment to survive and is destroying our prickly pears, but the institutions cannot do anything because it is considered an INVASIVE NON-NATIVE PLANT.

Calin Dejeu good point of view. It is true that trivialising on this subject can be dangerous, but it is undeniable that nothing is what it was, just one example: the centres of origin of domesticated plants. Tobacco was domesticated 3000 years ago and is now cultivated all over the world. It is the same with rice, potatoes, tomatoes, or even more recent crops such as mango, chia, avocado, etc. Where can we draw the line then?

I think we should stick to the issue of invasive species as regards natural and semi-natural habitats. The crops are on tilled land, which is a man-made environment. Anyway, not all the non-native species are invasive. Some of them do not multiply, so they represent a very small problem. Not all the alien species are invasive alien species:

https://ec.europa.eu/environment/nature/invasivealien/index_en.htm

Calin Dejeu yes you are right but many of them are still considered invasive, things then must be changed depending on the specie

J.D. Franco-Navarro

Dear Dr. Franco-Navarro,

You raised a very important question. My answer would be no. I do not agree that plant species that have been established and adapted to a given location for centuries should still be considered invasive species. I believe that there are many plant or animal species in the humid tropics whose exact origin is uncertain.

J.D. Franco-Navarro It is all about the concept and definition of an alien and invasive plant you would like to apply if you want to apply the concepts that are currently in use, then it is only the way of introduction to a given area that decides the status of a species: human-introduced (alien) vs. natural (native). And here is what follows: if you have an alien plant that is "naturalized and reproduce offspring in very large number at considerable distances from parent plants...etc" (see full definition in Richardson et al. 2000 Article Naturalization and invasion of alien plants: Concepts and definitions

Cuando una especie invasora lleva mucho tiempo en una área y se ha aclimatado y encajado dentro del bioma correspondiente, sin alterar el equilibrio, creo que debería dejar de ser considerada invasora. Vease la mariposa del geranio (Cacyreus marshalli), que ha invadido Europa colonizando especies ornamentales de nuestros jardines y balcones, también alóctonas. Esto no ha alterado ningún hábitat, ni afectado a la fauna o flora locales. En muchos casos la fauna invasora está asociada a plantas introducidas, y se uqedan en ellas sin afectar a la flora local.

Otra cosa es cuandoi la especie alóctona tiene un caracter invasivo que desplaza a especies autóctonas y altera el equilibrio ecosistémico, modificando la composición botánica y faunística sin posibilidad de recuperación a medio-corto plazo. La línea que separa ambas posibilidades está clara en algunos casos, pero no tanto en otros. Creo que la clave está en si se consigue un equilibrio tras la invasión que no afecte negativamente a especies autóctonas. Hay que tener en cuenta que la llegada de especies de otras áreas o continentes es un hecho que sucede de forma natural, aunque a un ritmo y con una intensidad mucho menor a la producida por la globalización de tránsito de mercancias, el principal factor desencadenante aparte de la introducción voluntaria.

Enrique Murria Beltrán that's exactly what I think! (eso mismo pienso yo)

Rosalba Tamburro

Victor B. Asio I absolutely agree with you. Thanks for your comment.

of course Dr. Pawel Wasowicz Pawel Wasowicz you are right, but my point is about alien plants that not only are fixed to a specific place for a long time, but also to plants that are naturalized but do not reproduce offspring in a very large number (maybe a regular one). I think that reproductive fitness must be an important trait for an alien species to be considered invasive. Thank for your comment.

Invasive species can cause great economic and environmental harm to the new area. Not all non-native species are invasive. For example, most of the food crops grown in the United States, including popular varieties of wheat, tomatoes, and rice, are not native to the region.

Danung Nur Adli I absolutely agree with you.

Not all alien species are capable to be invasive. There have to be some factors to make them invasive.

The Ten rules in invasion biology explains that approximately 10 % of all introduced species become established and that 10 % of those become invasive.

On the other hand, native species are able to encroach the ecosystem and can be considered invasive.

Obviously, a species should pass through different stages to become invasive. So, solely the time does not make an alien species invasive.

My answer to your question would be no.

Farzaneh Bordbar the prickly pear (Opuntia sp.) case In Spain is the perfect example of your answer. It's an alien plant, It was introduced in Spain 5 centuries ago, and It's not an invasive plant.... and on top of that the population has acquired it in its culture and folklore, and now that a plague is destroying it, we cannot protect it because the policies consider it an invasive species.

I also agree that non-native species be considered invasive when they have been established for more than a century. After a century, it could have been adapted already to the habitat, hence it is no more invasive rather a native of the area. A century is a long time which means such a plant will develop lots of interrelationships within the ecosystem and also could have become a part of the human culture.

Gibji Nimasow thank you :-) Does anyone know the case of Carpobrotus edulis and C. acinaciformis in Europe? Both are invasive species from Africa that was introduced in the 1980s in architecture and landscaping to firm up slopes and hillsides to prevent soil erosion. They unintentionally introduced species that today is "devouring" the native coastal species. That is a clear case of invasive species.

@ Farzaneh Bordbar has captured it well.

Crop production in many countries relies primarily on introduced species. In the US, bees for pollination were introduced from Europe in the early 1600's to support European crops introduced about that time.

To your point these are clearly "invasive" - but never considered as such.

"Invasive" is a modern, reactionary concept. In the broader, evolutionary biological sense - virtually all life is "invasive".

Hello all; Gibji's photos of what we call in Southern California "Iceplant" is similarly invasive in the same setting. It was in Calif at least in the early 20th century and it has had effects similar to those described by Gibji. Best regards, Jim Des Lauriers

agree with Farzaneh Bordbar

I think that the exact time (in years) is tough to establish in this case. If we look at the concept of local species, we can find genetic variations between two or more species from different regions.

We can think that: Can it be a successful invasive species are assumed local when their genetic status is most different from the original? Or: if an ancient invasive species is extinguished, do we have a critical biodiversity loss?

I believe that genomics can be a help to clarify this.

All species were "invasive" at one time. A century? Not sure the specific period of residence but agree that am arbitrtary extended time element would control application of the term.