[Taxacom] Reproducibility of descriptive data

[Richard Pyle]

DAMN!  After writing the message below, I just now saw Michael Heads'
beautifully concise statement of basically the same thing (I should learn to
read my entire inbox before responding).  Now the conundrum....should I just
delete this message, and thereby effectively waste the last 15 minutes of my
life?  Or should I click "send"?  Hmmm....decisions, decis...  [oops!]

Stephen,

You seem to be heavily invested in the idea that "natural" boundaries exist
between what we should all (eventually) recognize as "species", and that
these boundaries are somehow more "real" (Sharp? Discernable? Objective?)
than boundaries between, say, genera, or between subspecies.

Let's explore this idea a bit.  I'll leave the "asexual" issue to Paul,
Brian, and others, and I'll focus on the sexually-reproducing beasties (and
weeds).

If I understand you correctly, in the world of sexually reproducing
organisms, you believe a "real" boundary exists between species-entities in
nature (independent of whether or not we humans have figured out where those
boundaries are), and those boundaries are fundamentally more definitive
(Australia-like) than the boundaries between things we humans call "genera"
(and other higher ranks of classification). I'm not exactly sure where you
stand on the "realness" of the boundaries between subspecies and other
lower-rank taxa, but I'll go out on a limb and assume you think those
gaps/boundaries are also not as "real" as the ones between species.  And
further, you believe that the basis for this natural "species" boundary is
somehow directly related to reproductive potential.  Are these fair and
accurate representations of your opinion on this matter?  

The crux, then, for discovering/recognizing these boundaries seems to boil
down to something like the probability that two given organisms can produce
viable offspring.  If the probability is very high, then we would say that
the two organisms are the same species.  If the probability is very low,
then we would regard the two organisms as belonging to different species.
If we select our two organisms from what a population geneticist would
regard as the same population, then the probability of reproductive
compatibility is very high.  On the other hand, if the two organisms were
selected from what most taxonomists would treat as different genera
(animals) or families (plants), then the probability of reproductive
compatibility is very low.

The problem is, there is a continuum of examples in nature between what we
would call "populations", and what we would call "genera"/"families".  If
there was some fundamental "natural" process that delineated "these two
organisms are the same species" from "these two organisms belong to
different species", then we wouldn't expect a single continuum; we would
expect a bi-modal sort of pattern.  In other words, we would expect a
continuum of examples between kin-groups on up through subspecies; then some
sort of demarcation or inflection or discontinuity at the species boundary;
then another continuum from species complexes on up to Kingdoms.  The
existence of a demarcation/inflection/discontinuity along the spectrum of
possible scenarios between "same population" and "different genera/families"
would be your smoking gun for the "naturalness" or "reality" of the species
boundary.  

When I was a student, I used to believe that such natural boundaries
existed. But after a couple decades traveling the Pacific and seeing
variation in my group of interest (coral-reef fishes), I can't seem to find
it.  All I see is many different examples that fall at all points along the
continuum.  And that's among vertebrates -- which tend to "follow the rules"
more closely than other groups (such as -- Egad! -- plants).

I'm not the only one who has arrived at this same basic conclusion after
many years observing nature.  I'll repeat the quote I sent you off-list a
few days ago, from that clever bloke Darwin:

"No one definition [of species] has as yet satisfied all naturalists; yet
every naturalist knows vaguely what he means when he speaks of a species."
[...] "Hence, in determining whether a form should be ranked as a species or
a variety, the opinion of naturalists having sound judgment and wide
experience seems the only guide to follow. We must, however, in many cases,
decide by a majority of naturalists, for few well-marked and well-known
varieties can be named which have not been ranked as species by at least
some competent judges."

In other words: A species is what a taxonomist says it is, and a good
species is what a community of taxonomists say it is. (As has been echoed on
this list by several different people on multiple occasions over the years).

Aloha,
Rich

Richard L. Pyle, PhD
Database Coordinator for Natural Sciences
  and Associate Zoologist in Ichthyology
Department of Natural Sciences, Bishop Museum
1525 Bernice St., Honolulu, HI 96817
Ph: (808)848-4115, Fax: (808)847-8252
email: deepreef at bishopmuseum.org
http://hbs.bishopmuseum.org/staff/pylerichard.html