species/subspecies query

Don McAllister mcall at SUPERAJE.COM
Wed Nov 15 07:58:12 CST 2000


Jorge Chiapella wrote:

> Mark, it depends on which species concept you believe.
> . There is
> a similar situation I heard about with the pumas in America (not the USA, I
> mean the whole continent!) animals from Patagonia do not produce viable
> offspring when breed with animals from Alaska. But they certainly produce
> viable little pumas when breed with animals of other parts of South America.

I have heard of a similar case for salmanders around the Sacramento-San Joaquin
Valley in California. The species occurs in a ring around the valley,
interbreeding along the ring-like range. But where they finally came together
again they act like species and fail to interbreed.  I would suppose that one
would conclude that this is one continuous monotypic species.

In the case of A, B & C, one could liken this to a ring like the salamanders, or
a lengthy more or less linear pattern of the puma.  The exception being that the
former continuous range has become broken up into three parts. In both of these
cases, ring or linear, there is continuous exchange, or the potential, of
genetic information between the populations, hence there is a single species,
only broken up if there are strong stepwise changes in characteristics that meet
some rule, like the 75% or 93% rule used by some taxonomists.

In  allopatpric populatons, using the biological species concept one judges,
often from morphological or other data whether the species would interbreed or
one can combine this with the presence or absence of breeding times, ecological
preferences, etc. to arrive at a conclusion.  One can judge if the allopatric
populations are as distinct as other sympatric pairs of species or not, as a
"ruler" to make the judgement more quantitative.  In the two case allopatric
pair the case is simple, one can conclude whether or not the allopatric
populations meet the criteria or not.

In the three case example problem posed, there is the potential, should the
three populations ranges expand to meet one another for genetic information to
be passed along between the three, through the compatible pair. That would
suggest that the three are a broken ring or linear range and that the three
should be treated as one species.  If the distinctions between them are
sufficient, one might, depending on the criteria applied, recognize them as
three subspecies or not.

Of course a cladist might evaluate the situation differently, unless she or he
was a biological cladist!

don
Don McAllister




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