semi-paraphyletic taxa: a new paradigm?

Doug Yanega dyanega at MONO.ICB.UFMG.BR
Wed Jan 6 18:47:36 CST 1999


Curtis Clark wrote:

>I agree that enforcing coordinate ranks is an unnecessary purism, but when
>I see people comparing the number of families in two different communities
>or geological epochs, I wonder if we aren't being misleading to
>non-systematists (or at the very least not doing an adequate job of
>educating them).

I'm with you on this. Frankly, I have an even less charitable opinion of
any study that considers numbers of higher taxa as a valid parameter rather
than just a gross *index* of diversity (and one with VASTLY unequal
weighting - which is not specified anywhere in the paper, inevitably). Just
consider a family like Scarab beetles; some people consider it to be as
many as 20 separate families. It makes a huge difference in one's diversity
analyses, which shows just how little such analyses can be trusted. Such a
study is more influenced by the taxonomy than by the actual diversity being
studied.
        As far as I'm concerned (and here comes the contentious part), the
fault lies not in the taxonomy, but the people doing the studies, and the
referees who give them their grants and approve their papers for
publication with little or no thought to how arbitrary the basis is for the
fragile edifice they're presenting in the end; if you want to say anything
fundamental about diversity, you really shouldn't be looking any higher
than (morpho)species. This SHOULD be so obvious that no one would touch a
family-level study with a ten-foot pole, but they're out there in print. If
I compare the bee fauna of Sonora with Florida, there are the same number
of families (heck, in some classifications, there's only one bee family!),
but five times as many species in the former area! Heck, even at the genus
level, the differences aren't nearly so substantial (it's simply that some
genera in the southwestern deserts are incredibly speciose). The higher you
go, the more information you lose, until the comparison, as in this case,
can become worthless if not utterly misleading - to *everyone*, not just
non-systematists. I have little doubt, though, that just such a comparison
would fly past a grant committee and reviewers. That's probably more a
matter of the pressure for immediate results than anything else - it's HARD
to do morphospecies-level work, and it's time-consuming (as well as
impossible in most paleo studies), so people accept short cuts as a
necessary evil, even though they should know better. I don't know how else
to explain it, since it really doesn't seem like solid, justifiable
science.

Peace,

[NOTE THAT I WILL BE LEAVING BRAZIL ON FEB 13]

Doug Yanega    Depto. de Biologia Geral, Instituto de Ciencias Biologicas,
Univ. Fed. de Minas Gerais, Cx.P. 486, 30.161-970 Belo Horizonte, MG   BRAZIL
phone: 31-499-2579, fax: 31-499-2567  (from U.S., prefix 011-55)
                  http://www.icb.ufmg.br/~dyanega/
  "There are some enterprises in which a careful disorderliness
        is the true method" - Herman Melville, Moby Dick, Chap. 82




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