a question about speciation?

Question

let us say there is a population of fish and they some how become separated into two populations, after awhile the two fish populations become one again. is speciation a necessary consequence of those events? why or why not?

Answer 1

speciation is not a necessary consequence in this case...species must be able to breed and produce viable offsrping.....some members separated may come back together and still be able to breed....The other thing however is if there are enough features different to be considered a different species EVEN if they still interbreed and produced offspring. THese would then be called hybrids.
Often allopatric speciation often occurs more with species nearby than with those a considerable distance away....the closer species may not be able to interbreed anymore, but those further away may still be able to, even if they are less closely related..its just they have not needed to have isolating mechanisms in place. Its just how things work out I guess.

Answer 2

If the two populations are seperated in different environments, that give them the need for different adaptations, allopatric speciation may occur. Speciation is not necessary because there may not be any significant mutations that cause differences during the time of seperation the change the generations ability to produce offspring.

Answer 3

A major stipulation to say that two populations has speciated is that they cannot produce viable offspring when crossed (meaning offspring that can also reproduce).

If they came back together again, then they did not speciate.

Answer 4

Look up cichlids of lake tanganyika. They have become separated and come back together several times over millions of years, due to the lake partially drying and refilling, with the result that there are now nearly 200 different species. See the link below for an article.