[Taxacom] Reproducibility of descriptive data

[Stephen Thorpe]

>Genera can have moats at their boundaries, too
This is the nitty-gritty "nub of the jist"
Yes, genera can have real gaps (=moats) between them and all other genera - most do!
The point though is that you can be a lumper or a splitter regarding genera, and it is purely subjective
Example: A, B, and C are three distinct species
There is a gap between A and B, and a bigger gap between (A, B) and C
All three of the following possibilities are equally valid (let square brackets [ ] enclose genera):
(1) [A], [B], [C]
(2) [A, B], [C]
(3) [A, B, C]
Only convenience/taste/... can decide between them
BUT, if A, B, C are individuals (or populations), and [ ] enclose species, then the correct option above is determined by facts of reproductive integrity. Even if reproductive integrity is vague and a definite exact level of it must be (subjectively) chosen, there is still a HUGE difference in what is going on here as opposed to the generic case above, where our choice of option (1, 2 or 3) was entirely unconstrained by objective facts. So people, like Richard Pyle, who seem to think that a gap is a gap is a gap, regardless of taxonomic level, and that there is nothing "special" about species, are quite wrong! 

Another analogy: statistics is all about discovering objective facts about the world, given a chosen significance level. The fact that the significance level is chosen doesn't make the results any less objective! A chosen level of reproductive integrity doesn't make species any less objective! But there is no level of anything IN THE WORLD (=no level of anything OBJECTIVE) that you can choose to find out anything about genera. Maybe ... :)

Stephen
________________________________________
From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Mike Dallwitz [m.j.dallwitz at netspeed.com.au]
Sent: Friday, 11 September 2009 5:13 p.m.
To: TAXACOM
Subject: Re: [Taxacom] Reproducibility of descriptive data

Stephen Thorpe wrote:

> Robust! Another way of saying that species have a real, natural
> boundaries! Absolutely, yes! :)

The principles I'm writing about have nothing to do with taxonomic levels,
as I tried to make clear by writing "a class ... (such as a subspecies,
species, or genus)". Indeed, they apply to classes of non-living things
too, e.g. books.

By 'robust description' or class definition, I mean one such that it will
usually be fairly obvious whether or not a new specimen belongs to the
class. If a new specimen matches the definition fairly well, we can assign
it to the class (and, if we can be bothered, adjust the definition as
necessary), without agonizing over it too much.

(Note that this is not, by any means, the detailed discussion that I
threatened to give!)

Of course, if the class has a 'natural' boundary, with a moat or wall
separating it from other classes (for whatever reason), making a robust
description will tend to be easier. Genera can have moats at their
boundaries, too.

>> Which comes first, the concept or the inclusions (exemplars)?
>
> Actually, you mean which defines the concept, the description or
> the inclusions (exemplars)?

No, Jim and I were both talking (I think!) about the mental process of
forming classes - which everyone does, not just taxonomists. The process
of making definitions for communicating the class concept to others comes
later, if it's done at all.

--
Mike Dallwitz
Contact information: http://delta-intkey.com/contact/dallwitz.htm
DELTA home page: http://delta-intkey.com

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