[Taxacom] Fwd: complete list of all species

Paul van Rijckevorsel dipteryx at freeler.nl
Fri Feb 15 10:52:39 CST 2008


> Paul van Rijckevorsel wrote:
>> * the type determines what the name is attached to
>> * the circumscription defines the taxonomic boundaries
>> * a description (or a set of descriptions) of a taxon is only possible
>> and meaningful when its circumscription is established.

From: "Mike Dallwitz" <m.j.dallwitz at netspeed.com.au>
> In a sense, descriptions must come first. The taxonomist derives the
> circumscriptions by analyzing descriptions of lower taxa or specimens.
> This may be done in the mind, or with aids such as a computer.

***
In practice making descriptions and making decisions on circumscription will
often go either hand in hand or will alternate until a stable situation has
been reached. From a theoretical viewpoint this need not be so: a taxonomist
can view the material, make decisions on circumscriptions (in his head) and
only then start drawing up descriptions. Of course, how realistic this is
will depend rather on the kind of person the taxonomist is and on the nature
of the available material.
* * *

> However, this is irrelevant to the point I was trying to make. If others
> are to make use of the concept and the associated name, the taxon must be
> adequately, accessibly, and reproducibly described. The type is a
> legalistic concept of little or no scientific value.

***
Indeed the type is of little scientific value, although it may be of
enormous practical value. And indeed it is of great value if "the taxon
[is] adequately, accessibly, and reproducibly described." However, from a
theoretical point of view this is not a requirement: nothing stops a
taxonomist from describing reproductively isolated groups as taxa, even if
they are poorly distinguishable to most users, who lack the sufficient
apparatus to make the distinction. This too is, or can be, science. It will
not necessarily be universally accepted as good science, but maybe it will
be.

However, the point I was trying to make is that unless you include making
decisions on circumscription it is wrong to speak of science, no matter how
fine the descriptions themselves may be.

Paul
* * *

>> I would guess that the main reason for failing identifications would
>> be the absence of good pictorial material.

> The failures are due to characters that are poorly defined and/or poorly
> communicated. Illustrations are often important, but their absence is not
> necessarily the main problem.

> One problem is character 'states' that are not mutually exclusive. No
> matter how well you communicate the meaning of such 'states', they will
> inevitably lead to errors in identification.

> Explanatory notes and images should be prepared, and the characters
> tested, _before_ substantial amounts of data have been recorded, not as an
> afterthought just before publication. The testing should be done by having
> several people record data for the same taxa, either by recording all the
> data again, or by doing identifications from the data. Students might
> benefit from participating in this, and volunteers might find it
> interesting.

> Testing by identification should continue throughout the development of
> the data. Checking descriptions generated from the data is not sufficient
> to ensure reproducibility: you might be confident that the description is
> correct, but be unable to reproduce it independently, which is what is
> needed.

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