[Taxacom] Polar bears as a subspecies or species

Kenneth Kinman kennethkinman at webtv.net
Thu Jan 22 10:11:53 CST 2009


Hi Jody,
      No, I don't think it would "necessitate" a wholesale reduction of
species to subspecies status, and in fact such a move would be
ill-advised.  Big pendulum swings of lumping and splitting are not
helpful in the long run.  I advocate evaluating each case carefully, so
sometimes I lump and sometimes I split.     
                                     
        First of all, the best species concept for any given taxon
should be tailored and tweaked to that taxon.  A species concept that
works for many land mammals will often not work well for various other
animal taxa, plant taxa, etc.  And secondly, even among mammals, there
are varying mixes of factors which resulted in reproductive isolation,
some of which can be reversed (loss of ice in the case of polar bears),
while others are more permanent.  It is all those other factors that
will determine if there will be successful interbreeding between polar
and grizzly bears on a large scale.  For instance, intrinsic differences
in reproductive biologies (and chemistries), and slightly more extrinsic
factors like behavior (would it be mostly male grizzlies impregnating
polar females, rather than a more general mixing?).  

         It's sad that many polar bears will have to endure this
unintended "science experiment", but it looks like it is now going to
happen to some degree, and we should learn a lot from the results.  The
results will be similar for some other taxa, but no doubt quite
different for other taxa.  That's why just a single species concept
doesn't work a lot of the time, and why there is so much debate on the
subject.  And  much speciation is so gradual and "fuzzy", its total
completion is uncertain and often contingent on future events, so that
just adds more fuel to the debates.  In mammals, I think there is enough
fuzziness and possible resumption of gene flow in the future that I
think more lumping of species is warranted.  However, I don't think
there is yet enough evidence to advocate lumping polar bears and brown
("grizzly") bears into a single species.                  
         --------Ken Kinman
                                 
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Jody wrote:
We must keep in mind that the manner in which hybrids are treated
taxonomically depends in large part on the species concept being
employed by individual taxonomists. If you adhere to Mayer's Biological
Species Concept, then Steve's and Ken's points below are certainly
valid. But there are plenty of other species concepts that do not
require complete reproductive isolation. Right now there are literally
thousands of validly published and widely recognized species -- of both
animals and plants -- that have the ability to successfully interbreed
with other equally valid and recognized species and produce fertile
offspring. Based on the argument below, would this, then, necessitate
that all of these "species" should now be considered "subspecies?"





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