Taxacom S/N Ratio (3)

Peter Rauch peterr at VIOLET.BERKELEY.EDU
Wed Feb 15 08:10:41 CST 1995

Date:         Tue, 14 Feb 1995 15:17:17 -0800
Subject:      Re: Splitting/lumping
To: Multiple recipients of list BIRDCHAT

Byron Butler asked "Are species real?"  It depends on what you mean by
"real."  Just about everyone would agree that species are evolutionarily
independent lineages of ancestors and descendants.  There are two aspects
of evolutionary independence, however -- divergence from other lineages
and reproductive isolation from other lineages.  Different species
concepts emphasize these aspects to different degrees and, to the extent
that these do not occur simultaneously, different species concepts will
sometimes diagnose the same set of populations as one or multiple species,
depending on where the emphasis lies.

Much of the current interest in The Species Problem has resulted from the
realization that the BSC quite simply makes some unfounded assumptions.
The criterion of "potential interbreeding" is a blatant one.  Another one
is the significance attributed to hybridization.  When this topic came up
last fall I offered two examples (Bullock's/Baltimore orioles and
Black-capped/Carolina chickadees) of populations that hybridize but are
nevertheless *not* sister groups -- in each case, one of the populations
in question is the sister group of another popluation (or set of
populations) that does not hybridize with the others.  In a nutshell, the
BSC was formulated at a time when mainstream evolutionary biologists
simply were not paying much attention to evolutionary patterns of descent
(phylogenetic relatedness among taxa).  It would be naive to expect that
the explosion of interest in genealogic relationships of the past 20 years
(i.e., the cladistic revolution -- or paradigm shift, if you prefer) would
*not* result in reappraisal of how we draw lines between species.

As Byron Butler mentioned, many of the species being "split" today were
previously recognized as distinct but were lumped in accord with the
tenets of the BSC.  Perhaps it would be more accurate to think of these
species as being "un-lumped."  At any rate, given the arbitrariness of
species concepts, the ESA should seek to preserve biological diversity
regardless of the "rank" a diagnosably distinct population is currently
accorded by systematists.  And "species" is a *rank* just as "genus,"
"family," etc., are.  Splitting and lumping are artifacts of a
classification based on ranks; again, those interested in this topic might
want to read this short essay: DeQueiroz & Gauthier 1994. Trends in
ecology & evolution 9:27-31.

David Wright
dwright at

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