This situation is perhaps akin to some phenomena during a species invasion of new habitat. In such cases, small founding populations may be able to adapt to a new area or habitat unlike that (to greater or lesser degrees) of the parent population and successfully persist over time (establish). Selection can be intense, and adaptive variations in a small population could increase in frequency relatively quickly. In the insect biocontrol field, there are examples of purposive releases of exotic biocontrol agents that fail to establish. Then, after many tries, suddenly a release "takes" -- the population establishes and begins to spread -- in a few cases becoming an invasive itself (e.g., Harmonia axyridis, an introduced ladybird beetle in North America). The reason for this, in part, is probably getting a founding population with the right combination of pre-adaptations to make establishment and persistence possible. So possible key terms: colonization, founder population, invasion genetics, population establishment, genetic revolution, bridgehead effect. I recommend you take a look at Lombaert et al. (2010) PLoS ONE 5(3):e9743.

Working on the similar subject with mammals I think "peripheral population" seems to be a proper definition. "Peripheral " both in terms of position to the core of the geographical range and ecological requirements which (to our best knowledge) are "typical" for the given species. I do not know how good is this defintion from native speakers' point of view, but I hope you understand what I mean.

Daniel, could you please give me references to the publications on "non-typical" fish populations, that you've mentioned in tour post? thanks advanced

I forgot to mention in the original question that I was interested in populations which become established in habitats or ecosystems within their natural range, but those that are not typical of their ecological niche.

I think the case of deliberate introductions of exotic species is a very good example and an opportunity to perhaps understand the mechanisms that allow non-native species which originated in a completely different environment to establish themselves in atypical or novel ecosystems.

Although, as far as I understand, most non-native, exotic species have become established in environments or habitats that are typical or similar to their place of origin. Furthermore, invasive or non-native species are often ecological generalists, but those are not the species I am interested in. I am more interested in species that have done this, which are ecological specialists.

And Thomas, I will have a look at that paper you suggested. At this stage, I am looking for any sort of examples that can explain "ecological mutations" or "niche mutations" as opposed to genetic ones.

With regard to your definition, Nickolay, I am referring to populations that are peripheral in terms of ecological requirements, which is what I am talking about. After another discussion this week, I was reminded of the concept of novel ecosystems, which I mentioned above. This describes the nature of atypical habitats for a species, but not the phenomenon of populations establishing themselves in such habitats.

I suppose there are not many examples of this, and so the phenomenon may not have a widely recognized definition or proper name. I am aware of several species that experience this situation in Australia, such as the Eastern Barred Bandicoot, a species of bell frog, and some kind of aquatic snail.

Thank you for your suggestions! Let me know if you think of anything else. I will continue to update this post as I progress.

Nickolay, I will send you the document of the fish example I am talking about soon. At the moment, I do not have it, because it is not publicly available and I have to contact the university which holds the thesis.

@Nikolai, peripheral population could really be a good term. But - I am not native speaker.

According to the dictionary, periphery (which is an adjective or describing word) means:

1. pertaining to, situated in, or constituting the periphery

2. concerned with relatively minor, irrelevant, or superficial aspects of the subject in question.

In our case, I would say that the first definition is most applicable. This means that you are quite accurate, Nickolay. The population of native fish I am talking about in this question, has occurred on the other side of a large mountain range, where it cannot physically occur because of geographical constraints.

It only occurs there, because it was translocated to a reservoir in the area, by humans at the start of the 20th century. The reason it is believed to be an unusual case, is because this species cannot naturally reproduce in still water such as a lake or reservoir. However, in this case, that is exactly what is happening.

So, geographically and ecologically, "peripheral population" would be an accurate term.

Niche / habitat shift? I googled it and it works. It's very used for species that are forced to "move" their niche when they share the habitat with another member of the same guild, either native or invasive species. There are lots of papers on Google scholar with both entries (niche shift and habitat shift)

Thank you Jorge, that is actually useful to another part of my literature review, which is about intra-specific variation in widely distributed species.

It does not quite capture the concept I'm talking about. The problem is, that the situation I am talking about is such an extreme shift. It is not something that happened gradually. In 1905, several species of these riverine fish were introduced to this dam outside of their natural range (and not to mention, on the other side of a mountain range) and they are now self-sustaining there.

This is strange because these species are generally accepted as being exclusively riverine species, and attempts to induce spawning among some of them, in captivity using reconstructed, riverine environments (mesocosms), have failed over several years.

It would seem that this is a rather novel idea and perhaps may require further investigation, although there may be a possibility (now that I think of it) of some sort of genetic variation harbored within some portions of these riverine populations which are adapted to more lentic habitats (e.g. deep pools, slow flowing sections) in some of the rivers where they occur.

Perhaps, this introduction of these species has triggered some short term evolutionary change, that has previously only been expressed under conditions of extended drought when their home rivers are only a series of static, deep, disconnected pools.

I think this discussion has really ignited my thought process and I really appreciate the advice that everyone has offered.

Dear Daniel, if you are dealing with species of riverine fish that were introduced to a dam outside of their natural range, I think we may be talking about some sort of invasion. The term (ecological-) invasion (and unfortunately so the discipline) is rather vague, in part because it requires an unknown long-range dispersal distance to occur. So how long should this distance be? Thousands or hundreds of km? Inter-continental or inter-regional? In my view, what really defines an invasion is how new the invaded environment is for the invading species, i.e. how many new interactions is it going to encounter in the context of new levels of resources. On the other hand, if most of the invaded environment is not really new, then we may be facing a successional process, where the species "colonise" an environment where it could have been before (and gone extinct, and so on). So I'd say it would be a colonization-invasion continuum depending on the novelty (and not the dispersal distance) of the colonized/invaded environment. Forest expansion is often put in the colonization pigeon-hole, because it usually occurs after grasslands or savannas are somehow modified and forest trees are able to establish in these new (although neighbouring) environments.

Having said that, my advice would be not to pigeon-hole you study case in an ecological-jargon category. If you are trying to construct your theoretical framework for studying these fish, it would be good to keep it simple, go to the basics and try to depict the river and the lacustrine environments in terms of ecological interactions, and try to figure out what the differences would be. Here is a good paper that may guide you in this process:

Gurevitch, J., Fox, G.A., Wardle, G.M., Inderjit, y Taub, D. 2011. Emergent insights from the synthesis of conceptual frameworks for biological invasions. Ecology Letters 14:407-418.

All the best

I'm not sure whether a plant analogy will help with fish, but here goes: For plant populations that establish outside their original range or ecological niche, we typically use the word "naturalized". For example, red pine (Pinus strobus) is native to the cool, dry northeastern mountains in my state, but has been planted outside this range and is now naturalized in some locations. In other words, the planted populations are self-sustaining with healthy regeneration. Naturalized populations may or may not become invasive. All non-native invasive plants are naturalized, but only a few naturalized plants, regardless of origin, become invasive.

I really like Andres' thoughts on this. There may not be an exact descriptive word for the exact case you are describing. But phenomenologically, the fundamental processes involved seem to be related to the fundamental dynamics of a species' invasion of novel habitat. And I agree that invasion (in its broad sense) of new territory that is essentially the same ecologically is more toward the colonization end of the spectrum, and less relevant. Your example would be toward the other end of the continuum characterized by novelty of interactions at the interface of the organism with its new environment. And if you approach the invasion literature in that light, you may find examples that are directly relevant to your fish story.

That's a nice perspective. I suppose colonization is a different kind of invasion, because the latter normally refers to something undesirable or negative. Actually, after discussing this case with some fellow students of mine, I've come to realize that this is quite simply a case of a species expanding beyond the limits of it's realized niche (after an instance of human intervention).

The only reason that some of these species may not be able to colonize still waters, is because of the lack of fluvial and thermal dynamics that trigger spawning events.

I guess what is becoming clear to me now that what I am looking for, is not necessarily the term or label for these range or niche shifts, but rather, what one would call such a dramatic change in the fundamental life-history of species. In that case, it's something that (as I've already discovered) one would call a dichotomous life-history. Perfect examples are some species of pacific salmon, which have both anadramous (migrating) and non-anadramous (non-migrating) variants which remain resident in their home rivers, occurring in the same population.

So now that I think about it, perhaps colonization would best describe the phenomenon (ecologically) but biologically, it's simply an instance where a species or several species have developed a dichotomous life-history.

That seems like a far out idea, considering it's almost certainly an isolated incident. It's highly unlikely that over the space of 130 years, since we first translocated our native fish species here in Australia from rivers to artificial dams, that they would developed dichotomous life-histories so fast.

But what is more likely is that, as my fellow students pointed out to me, perhaps it means that we have failed to appreciate the possibility that our native fish species have a wider niche or more flexible life-history than we first thought.

I will go down the colonization path in my literature search and see what I come up with. Thanks again everyone, really appreciate it!

'Pioneer species' might also help with your search terms.

Colonization is definately a good name for the process of establishing the population in the novel habitat, and I agree that novetly of habitat could be the decisive factor affecting this process. But I'm still thinking of "peripheral" being a good name for the population itself, though probably there isn't plently of literature on this subject.