Please have a look at this link and PDF attachment.

http://dnr.wi.gov/topic/invasives/what.html

https://www.researchgate.net/publication/259258596_Invasive_Species_in_a_Changing_World

Book Invasive Species in a Changing World

Invasive species do not begin by displacing but there are sequential stages to the last one where they displace. The aggressiveness in growth among other characteristics could be the initial phases

In my understanding invasive species allways compete against the native species. Maybe this rivalrs does not allways imply displacement and life is just harder for the native species :-).  Or in your literature they mistook invasive species with Neobiota.

Hi.

About invasive plants may be good to read this important reference, which link is:

http://onlinelibrary.wiley.com/doi/10.1046/j.1472-4642.2000.00083.x/abstract 

Sometimes there is confusion with the concepts "invasive", "naturalized", etc.

Best regards. 

Invasive species are plants and animal species that possess competitive habits which allows them to dominate and sometimes displace certain  native species.The common characteristics include prolific seeding,allelopathy for plant species.The net effect of those plant traits is native species displacement in severe situations,but sometimes dominate the native plant species.

An invasive species is now at the step 3 (1=Introduction; 2=Naturalization) and thus multiply and colonize its new habitat faster than in its native one. No needs to ecological ravage in the definition however by ecological principles, adding this new organism in the system --> ecological change did often occur (species removal, physicochemical changes, etc.) 

There is a confusion of technical terms in the answers to this question. Good definitions of the terms concerning this theme you can find in the article presented by Rubén Barone (above):

http://onlinelibrary.wiley.com/doi/10.1046/j.1472-4642.2000.00083.x/abstract

If the terms get swapped this will be an endless discussion without a valuable result.

Favourable environmental conditions may promote the migration in sequences that lead to displacement and settlement of the newcomers in the new habitat. 

Thanks for post, 

Introduced species can be invasive, naturalized or neutralized

there are plenty examples for flora, but less for fauna 

Invasive species - species which is not native for this country, landscape, habitat etc.

Maybe not necessary to replace other (native) species. Some invasive species just compete with native ones and thus influence the native environment negatively.

Dear Gloria,

As there is a great diversity of the life forms, delineation of the term is troublesome. For plants, there is bunch different terms like archeophye ets as they have longer history of displacement.

See EU's latest regulation on the prevention and management of the introduction and spread of invasive alien species, Article no 3 for the current definiton: 

http://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1417443504720&uri=CELEX:32014R1143

Dear Jonathan,

I agree and I think the reason why we are not in the worst 100 is simply the monstrosity of the effect not comparable to all combined.

Dear Gloria, I recommend this books or papers

Duncan, R.P., T.M. Blackburn, and D. Sol, 2003.The ecology of bird introductions. Annual Review of Ecology, Evolution and Systematics 34:71–98.

Simberloff, D., and M. Rejmánek (Eds.). 2011. Encyclopedia of Biological Invasions. University of California Press, Berkeley, California, USA.  It is free in internet

Simberloff, D. 2013. Invasive species. What everyone need to know. Oxford University Press. 329 pp.

Be careful with the wrong conceptualization.

Invasive species are for definition harmful. If the specie is not harmful, it is introduced species or naturalized, etc. Exist several terms.  However two principal concepts for biological invasion: the biological and biogeography without connotation to the impacts, and the concept implicating impacts.

The definition supported by the World Conservation Union (IUCN), the Convention on Biological Diversity and the World Trade Organization explicitly assumes that invasive species cause impacts to the economy, environment or health (see IUCN 2000 ).

[Downloaded from http://issg.org/is_what_are_they.htm 9/15/ on 15 September 2015]: “The International Union for Conservation of Nature, (IUCN) describes invasive species as animals, plants or other organisms introduced by man into places out of their natural range of distribution, where they become established and disperse, generating a negative impact on the local ecosystem and species. Invasive species can negatively impact human health, the economy (i.e. tourism, agriculture), and native ecosystems. These impacts may disrupt the ecosystem processes, introduce diseases to humans or flora and fauna, and reduce biodiversity. Invasive species are organisms that have been transported from their native environment to a new environment”.

However it is a limitation because not all invasive species is knows the real impacts and the assessment are pendent.

Follow to Duncan et al (2003) the biological invasion concept as …… exotic species that have been deliberately or accidentally transported by humans to a new location beyond their normal geographic range limits.

 Like other important authors the definition explicitly excludes any connotation of impact, and is based exclusively on ecological and biogeographical criteria.

But As I began my comment, there are many literatures with wrong conceptualization. I recommend you follow the classics….

Hi Gloria

There is also the issue that an invasive species may not be entirely "invasive" throughout it's new range. For instance, I am aware that Decsurainia sophia is regarded as a trouble-some invasive plant in the states, but here in the UK it is an ancient introduction and has never become truly invasive. Furthermore, work has been undertaken to try and protect it. Indeed plenty of native species can be regarded as invasive. I have heard it said that rosebay willowherb was quite scattered and not very common until the railways developed across Britain.

 Dear Rafael,

It writes free on internet. Please, where can we download 'Encyclopedia of Biological Invasions' from?

Hi again.

In the case of the Canary Islands we have some endemic species that can be invasive outside our area, due to their high potential to colonize degraded and disturbed areas, like Rumex lunaria and Echium simplex. In fact, this last species has been found in South Africa invading natural vegetation. Sometimes endemic island species can be very invasive in continental areas...

Best regards. 

Dear Colleagues,

Thank you very much for your responses. I did not reply earlier because I was checking on the suggested literature before I could contact all of you again. From your messages and what I read it seems to me that the concept of “invasive species” has some different usages depending on authors and/or studied organisms. Certainly, it is not possible to have “standard” definitions for all, but apparently, the use of the term “invasive” is too broad and open to discussion. For instance, is it possible to consider a fish native species living in a certain basin as “invasive” when it has been reported in a ‘new location’ in the same basin? For me the fish is not invasive, simply it is moving in its natural geographical territory; the problem is the researcher who has not seen it before. Independently of this, is it correct to identify as “invasive” a species in its natural environment and territory?

Thanks again,

Gloria Arratia

Dear Gloria, fish are maybe a bit specific case. We consider already "invasive" species of fish, if it came to our waters (eider naturally or artificially) to Central Europe even from another (distant) part of Palearctic region, or from the Nearctic region and especially when it is competing with native species of fish.

Dear Samuel,

Thank you very much for providing me with information about interperatations of freshwater fishes/invasive/no invasive in Europe and other parts of North Hemisphere.

Gloria 

Dear Gloria, I suggest you follow the concept from Biological Invasions papers and books, from the classic researchers of the topic. Your examples is not the case of invasive fish. For definition an invasive fish must be transited for the steps of the biological invasion process: transporte, introduction, established and invasive and this fish must be out of thier original distribution. In many cases the invasion is product of the artificial introduction by human and could be intencional or unintencional.

Dear Rafael,

Thank you for your comments that confirms my doubts on the topic of freshwater fishes vs interpretation on invasive species. My questions arose when I read in an important journal a paper with the given example, that was followed by another similar paper on the matter.  But in this case, definitively is not human action.

Gloria

Hi Gloria, Almost always the action of humans is present. For example in Cuba a pigeon S. decaocto arrived , suppose as ¨natural way¨, however this species was introduced before in Bahamas and form those island arrive to Cuba . The same with Bubulcus ibis from South America. In the case of birds some time the human intervention is not direct and is hide in the history, We have cases of introduction in the first year of colonization that now look as native species.

Hi Rafael, we have also the Streptopelia decaocto pigeon (or dove) species in Central Europe, but it came here naturally from the Balkans in the 1950-ies. Now it become an established member of our fauna and nobody calls it (in Slovakia) an invasive species, even if everybody is aware, that it is not native for Central Europe. Maybe the case of the Caribbean is different, but to Central Europe it arrived in a completely natural way, without any human contribution.

Dear Samuel, sometimes the process of invasion is a cryptic process that is not easely determined. Sometime the modification of habitat by men facilite the invasion of some species that like approach habitat with human construction, garbage, and dont care the human presence, etc. Sometime action or transformation of habitat will create condition for the life of alien species.  Will be interesting analyses if the ¨naturally arriving in the Barkans ¨was facilited by human transformation or something push out the species from the original distribution urbanization, tourism, wars, agriculture expansion, etc.

However the case of Islands is different.

Dear Colleagues,

This is a very interesting exchange of ideas, especially when we are talking about three different continents. The fish example that I mentioned is from South America, a fish with a family history at least 65 Ma in the its natural habitat, living in a place still not contaminated by humans or at least no one is known to live in such unfriendly environment! Thus, we are dealing here with interpretation of fishes and birds from Central Europe, the Caribbean and the case of island (migrations and invasions), and an "old", endemic  inhabitant of a freshwater basin. Can we apply the same concept of "invasive" to the examples that we have under discussion?

Dear Gloria, in the case of your fish is not correct apply the invasive term because the fish was not move from the original distribution to a new one with the human intervention. In the case of Balkans I would like consider all possible historical conditions. In the case of Cuba, yes, the species is invasive, although some ornithologist consider the contrary. because they said that arrived in natural way.

Dear Rafael and Gloria,

I try to summarize at least the case of Streptopelia decaocto. It is obviously a case of an invasive species. It invaded from the Balkans penninsula most of Europe some decades ago. For me it was interesting to learn, that it arrived already to North America (probably naturally) and that it had been introduced to the Bahamas and from there already invaded Cuba. (Our interpretation in Central Europe, that this species we do not consider to be invasive, is maybe scientifically not correct, because this species behaves as an invasive one).  Simply, it is well established already in Central Europe, it occupies a species - specific niche , not occupied in this part of the world before by any other dove species, and it does not compete really with other Streptopelia species in central Europe).  The already mentioned Bubulcus ibis is another good example of an invasive species, now occupying already all of the continents except the Antarctic, and it spread completely naturally, without human intervention. It is a tricky question, what is the reason of these invasions. Probably some answer exists, but it can be very different , depending on species of area, I think...

Hi again.

In my opinion Streptopelia decaocto is not an invasive species in the strict sense of the term, as an invasive taxon must be introduced directly by man and this species has expanded over the Western Palearctic naturally. A different question may be its presence in the American continent. We have big populations of this dove in the Canary Islands from the 90s, and the species arrived here by its own, not introduced by man, and the same process is being occurred in the Cape Verde Islands, Madeira asnd the Azores at this moment. On the contrary, the related Streptopelia risoria has been introduced by man and its presence in the Canaries is due to the human activities, as this species is frequently maintained in captivity. So, we can consider this last taxon as a full invasive species. 

Hi again, also if invasive species should compete with native ones, at least in central Europe the Collared dove Streptopelia decaocto do not compete really with any native species. (So maybe it is correct opinion, at least locally for central Europe, that this species is not invasive).

Dear Samuel, but some research have been realized to check competition of Sd? The species must be feeding, flying, using perch, reproducing etc. Something is doing with respect to interaction with other native birds. Sometime the lack of information is the reason to consider that a specie is no competing? It is a question

the species must be using resources that are used by other native species or not?

The case of Streptopelia decaocto, and several birds nowadays, should be accepted as a special case of human aided dispersal. These are not technically introduced, but dispersed following changes in human habitats. These days, several bird species only marginally or accidentally recorded from Turkey in the past are expanding their ranges into the Syrian bordering regions of Turkey, due to war. First record of urban established populations of Ps. krameri (many previous occasional sights exist) in Turkey coincides with Gulf War I.

I agree with Rafael though. The only possibility to argue of no conflict will be case of totally empty niches, which is not the case for urban birds. As long as they eat what other urban birdies have to eat, there is for sure competition. This competition is not always supposed to be destructive/obvious. Not all the invaders are aggressive. But we can say that collared dove has the same attitude of expanding its nonnative range and endevouring new challenges. Non agressive invaders can be responsible for parasite or disease outbreaks, not to forget, as in the case of Pseudorasbora parva. 

Ümit KEBAPÇI, from the native distribution area of the collared dove.

Dear Rafael, Ümit and others, I agree with everything what Ümit and Rubén has written on Collared dove Streptopelia decaocto. In my opinion this species is a nonaggressive species , I leave open the question if it is invasive or not, but rather I support an opinion that it is probably a nonivasive species in ares, where it has been distributed without human intervention. According to its competition with native species: I agree, that there is some competition in urban environment, e. g. with feral pigeons, house sparrows, urban populations of blackbirds, etc. But the species is not aggressive and it did not cause a decline of any other bird species directly, as far I know (at least in Central Europe).

Dear Samuel,

Let me tell another one. When I first heard Carpinus orientalis termed as an invasive species, I was stunned. It was a native species! For an organism, invasiveness may not require a nonnative origin. Wikipedia page of the species even count it as a native species for its Palearctic range, leaving out Nearctic range which is 100% known to have invaded by escapees. So there is not a consensus. The matter of distinction between natural dispersal and others is the human intervention. If the dispersal is triggered or aided by roads, farms, nomads, clearings, fires and wars, then we can clearly talk about human intervention and this is the case in general. Whether active or passive, human aided dispersal is utilized by only some of the species from a group for some reason and they become invasives. Since there was no record a century ago, in your area, it is not native but naturalized (like Cyprinus carpio and Opuntia ficus-indica). An invasive, again saying, may not be harmful, even it can be beneficial. But, with certainty, it will change its environment forever as it will be a new gear in the system.

However an Invasive Species by definition is harmfull as Simberloff. The problems is that not all invasive species have been assessed by the impact or effect over other species and nature. In other case when the impact is no known the especies could be considered Established or introduced with the potencial to become invasive.

You are right. However, bright side of invasiveness is a brand new topic with regards to ecosystem services. Especially in the collapsed ecosystems and the ones with depleted resources, while they are disasterous elsewhere invasives can be the only things you get. As you see, this too is a commonly observed everywhere.

Thank You for Your new example, Ümit. The example of Carpinus orientalis demonstrated the complexity of the term. The same species in some parts of its range can behave differently as in other part of its range. As generally animals, and especially birds are able to move on long distances easier than plants, human intervention in case of birds, when they expand their range, has maybe not as high importance as in case of plants.

Hi again.

Apart from some invasive birds (introduced by man and spreading over the archipelago, e.g. several Psittacidae species), in the Canaries we have some very dangerous, invasive vascular plants, like Pennisetum setaceum. I don't know at this moment any other introduced plant with such high potential for invasion in natural habitats of our archipelago, apart from Opuntia maxima. On the other hand, another problematic species is Ailanthus altissima. For the moment this last species is present only in a few areas of natural vegetation, but it's growing in road margins and old cultivated fields, spreading from there to new sites. And one of the classic examples of invasion by an introduced mammal in an oceanic island is Atlantoxerus getulus, a ground squirrel from NW Africa, which is abundant on Fuerteventura, the easternmost island of the Canaries. It was introduced there (a single pair) in 1965, in 1980 the species occupied about 20% of the island's surface, and now has colonized more than 80-90%...

Best regards. 

Atlantoxerus getulus is a good match for a what happens when you put a nonnative warm blooded animal to a similar climatic and geographic area question. Ailanthus altissimus is another example for what can happen when you put a rapid growing nonnative tree from a different climatic zone into generous Mediterranean climatic zone.

Two questions and their clear answers may tell a lot for some Homo brains. But just not for many of ours, THEREFORE our administors'.  

PS: It's a pity to see how we are losing a paradise, underappreciated even to have called as 'island of dogs' at first embrace. A. altissimus can indeed be more agressive in our area to replace natural upper vegetation to some extend. You should be happy with the stage of ruderal extensions.

Hi again.

Thanks for your comments, Ümit.

Fortunately, there has been some action against Ailanthus altissima on Tenerife, Canary Islands, developed by local authorities. These actions were centred in two "dangerous" populations, which are (or were) invading natural vegetation, but the species continue to spread in other areas, normally close to roads and in old cultivated fields. 

With regards to the squirrel Atlantoxerus getulus, there are some people studying this mammal on Fuerteventura, but the degree of expansion there is so high that at this moment is impossible to control it. In any case, it's very important to assure they are not introduced in other islands of the archipelago. 

Best regards.