On 28/07/2006, at 10:26 AM, [EMAIL PROTECTED] wrote:
Another problem is that members of a species may never have an
opportunity
to interbreed.
That's not so much of a problem - if there are two distinct breeding
groups that are separated, they can be considered separate species
even if they could successfully reproduce if mingled. But yes, it
does show another grey area that must be considered when deciding on
species status.
A ring species where there are variations in a geographically
continuous members who can interbreed with their "next door
neighbor but not
with individuals at the other end of the ring (be it around the
world or around
a geographic barrier.)
For everyone else, in case you're not aware, the classic example is
usually given as various gulls around the Arctic Circle. The Lesser
Black-Backed Gull and the Herring Gull are two common gulls seen in
the UK, two very distinct species. But the Herring Gull could
interbreed with the American Herring Gull, and the Black-Backed with
its Russian cousins. And those relatives interbreed with others
further round, and *those* breed with each other. So it shows that
small variations that characterise only sub-species or close species
relationships can lead to a wide gulf across a long geographic range.
Of course, science being science, it's recently been shown that while
the concept is sound, the classic example might not actually be a
true ring species as the Herring Gull and American Herring Gull's
ranges are distinct, and they both evolved from a common ancestor.
D'oh. :) But it also seems like the range of the Lesser Black-Backed
is expanding across the Atlantic, so the ring may yet be closed...
Charlie
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