The means by which different species are kept reproductively isolated. These may be: (a) chromosomal (if cross-mating occurs, the incompatibility of the karyotypes makes any hybrid inviable or sterile); (b) mechanical (the two species cannot mate because they are of different sizes, or because the genitalia are shaped differently); (c) ethological (the courtship rituals of the two species diverge at some point so that an incorrect response is given and the sequence is brought to a stop); or (d) ecological (the two species occupy different microhabitats and normally do not meet). Other mechanisms include the breeding seasons being out of phase, or members of one species being unattractive to members of the other. Many RIMs, especially ethological ones, amount merely to mate preference, so that in the absence of a preferred partner (of the same species) a member of a different species will be accepted. In this way hybrids between different species may be bred in captivity and may even be found to be fully fertile.
Subjects: Ecology and Conservation — Zoology and Animal Sciences.