When should a taxon be considered to be a subspecies of a certain species, and when as a different species? Are there some general guidelines how to assign a specific taxonomic status to a taxon?


Generally speaking, different species can't interbreed. For example, a giraffe can't mate with a gorilla.

Occasionally, very closely related species do interbreed - e.g. lions and tigers breeding in zoos. But the offspring are generally infertile.

Subspecies can interbreed, but they seldom do simply because they're separated from each other.

For example, consider the brown bear and the wolf, each of which have vast ranges embracing a wide variety of habitats. A subspecies adapted to a montane environment isn't likely to breed with a subspecies adapted to a desert environment. Of course, it would have been virtually impossible for a Eurasian wolf subspecies to interbreed with the wolf subspecies that lived in Newfoundland prior to its eradication.

The separation doesn't have to be geographic. Subspecies can sometimes evolve physical or behavioral differences that inhibit them from breeding with other subspecies.

  • $\begingroup$ At least in case of physical or behavioural separation, we should call it different species, or am I wrong? $\endgroup$ – Rob Jan 14 '16 at 8:56
  • $\begingroup$ By physical separation, I mean geography. Imagine if there was a huge earthquake, and a giant crevasse suddenly appeared in the middle of a species' territory. Animals on one side of the crevasse couldn't mate with animals on the other side - but they'd still be the same species. A more familiar example is animals that migrate to islands. An animal living on the island of Newfoundland can't mate with a member of its own kind living in Japan. $\endgroup$ – David Blomstrom Jan 15 '16 at 0:05
  • $\begingroup$ Behavior is more complex, but here's a theoretical example... Imagine an animal that's genetically programmed to mate with individuals that are approximately its own size. Now, think about brown bears, which range from 500 lb. inland grizzlies to coastal giants that can weigh 1,500 pounds or more. IF size was a factor in their mating ritual, then they might be expected to mate only with similar-sized subspecies. (This is just a hypothetical example, as I don't have a clue about brown bear reproduction.) $\endgroup$ – David Blomstrom Jan 15 '16 at 0:08
  • $\begingroup$ Please could you add some supporting scientific material that reinforces your answer and allows further reading. $\endgroup$ – rg255 Mar 8 '16 at 7:28

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