What about separated populations that enjoy sex with each other but turn out to be nearly always infertile?
That would be considered complete speciation since there is still no gene flow between the populations.
What about ring species?
That is considered incipient speciation. Wiki has a decent page:
Incipient speciation - Wikipedia, the free encyclopedia
What about parthenogenic species, that are all female and have no interbreeding ever?
The same would apply for bacteria and other asexual species. Species in this case are defined as a population that undergoes the same selective pressures and fills the same niche.
What about long extinct species, for which we cannot derive DNA results or mating habits, but only ancient fossils?
They are defined by morphology using multivariate analyses. In other words, a group of fossils that are statistically more alike than other fossils.
Upvote
0