I know that for two populations A and B, there are situations in which there is a two way exchange of individuals between the populations, and there are situations in which there is no exchange of individuals between the populations. I have thought before of a situation involving one way isolation between two populations, in which it's easy for individuals from population A to immigrate to population B, but impossible for members of population B to immigrate to population A.

I tried searching to see if I could find any examples of one way isolation between populations, and couldn't find any examples, although I don't know if this is from not using the correct keywords to find it, not knowing where to look, or there being no known examples of it.

Are there any real world examples of the one way isolation I mentioned between populations?

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    $\begingroup$ pit caves come to mind. $\endgroup$
    – John
    Jun 25, 2020 at 15:46
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    $\begingroup$ Fishes leaving on both sides of a waterfall too high to climb up. Sunflowers living along rivers and that reproduce clonaly through cutting, where cuts gets transported by the water stream. Plants reproducing with seed flying in the air and living on a windy sea shore. Plancton living in a water stream. $\endgroup$
    – Remi.b
    Jun 25, 2020 at 15:46
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    $\begingroup$ @Remi.b Do you know the names of any of the specific species that would be examples of this? $\endgroup$ Jun 25, 2020 at 17:17
  • $\begingroup$ Are you thinking of modern-day politics e.g. it was easy to go from one side of the iron curtain to the other, but a lot harder for the reverse? $\endgroup$
    – Allure
    Jun 26, 2020 at 0:26
  • $\begingroup$ livescience.com/nuclear-bunker-cannibal-ants.html $\endgroup$
    – filo
    Jun 26, 2020 at 14:23

1 Answer 1


You might want to look for asymmetric dispersal.

Asymmetric dispersal has been found in many freshwater fishes (such as bullhead; Junker 2012), freshwater mussel (Terui et al., 2014) and in marine kelp (bull kelp; Collins et al., 2010).

That being said asymmetric dispersal does not mean that dispersal goes exclusively one way. Maybe Blondel et al. (2020) reporting asymmetric isolation caused by waterfalls in guppies can be helpful to you.

I am also thinking of polyploid and invasive lines of sunflowers that often live along rivers and reproduce clonally through cutting, where cuts gets transported by the water stream. I co-authored a paper on the evolution of these invasive sunflower lines (Bock et al., 2018) so I should know the literature well but I don't and I am not able to cite a paper that really describes the dispersal and population structure of these sunflower lines. Such patterns might be found in Mimilus as well.

Planctons follow water streams and can therefore have very asymmetric dispersal too (Pringle and Franks, 2001).

I am also thinking of plants reproducing with seed flying in the air and living on a windy sea shore or in windy wide open plane (e.g. tumbleweed). But I cannot give you a reference.

  • $\begingroup$ Thank You! I liked reading about how in the case of guppies, natural selection would tend to favor traits that would make the guppies less likely to go through the waterfall in guppies living above the waterfall, which makes sense seeing as how a guppy going past the point of no return would be equivalent to dying with respect to the above waterfall population. $\endgroup$ Jun 26, 2020 at 21:39

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