[Taxacom] Sampling/ Pseudoreplication in Morphometric Taxonomy

[Richard Zander]

These are good questions. A reviewer recently asked how I could have had the gall to describe a new species based on only one specimen. After a moment of entirely justified rage, I actually thought about it and replied to the editor:

"Although this species is recognized from only one specimen, some traits are qualitative, not quantitative; the range of variation in all related species is such that there is no overlap of traits; and distinctiveness is greater between the new species and related species than between each of those related species."

Thus OTHER species matter in delimiting a new species. 

Also, regarding general rules for sampling, the heavy-math book Mathematical Taxonomy by Jardin and Sibson has nothing much about sampling.

The book Sampling by S. K. Thompson has much on biology but little on taxonomy. Apparently we are truly isolated as scientists. The Chapter 4 on Sample Size is interesting. Formulas are available for estimating needed sample size depending on the expected distribution of the data points. If a simple distribution is expected, then sampling can be sparse. But if there might be two or more peaks, or considerable asymmetry, lots of sample points are needed. Lots and lots. 

In my opinion, because distributions of somewhat variable plants within a species are expected to be similar to those of related species, and if you have some crowding of related species but no real overlap, then your sample size can be low, i.e., you expect a certain level of stenomorphism. The new species fits in. 

 If there are no closely related species and the new species could be rather variable, well, describe it anyway and let future experts with more data deal with it. Putting it in the literature is important. Thus, no, a single specimen does not capture the full range of morphological variation, but there is no need or requirement for it to do so. The full range of variation of all species is not yet captured, and won't be since plants with unusual morphology are selected against, or are named as new species by such as we.

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Richard H. Zander
Missouri Botanical Garden – 4344 Shaw Blvd. – St. Louis – Missouri – 63110 – USA
richard.zander at mobot.org Ofc: +1 314 577-0276
Web sites: http://www.mobot.org/plantscience/bfna/bfnamenu.htm and http://www.mobot.org/plantscience/resbot/ 


-----Original Message-----
From: Taxacom [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Thomas Murphy via Taxacom
Sent: Thursday, October 17, 2019 4:10 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Sampling/ Pseudoreplication in Morphometric Taxonomy

I'm wondering if anyone has any literature recommendations pertaining to sampling methods in morphometrics studies (to delineate species). I realize sampling more than one individual from a population meets the criteria for pseudoreplication. Should we be overly concerned with pseudoreplication in multivariate analyses if our ultimate goal is capture variation that
(hopefully) resembles biological reality? Wouldn't a taxonomic treatment based on morphometric data benefit from within and between population variation.

Those who sample more than a single individual of a population, in my opinion, have to options:
1) Average all measurements between individuals (subsampling), treating the averaged values as a single sample.
2) Treat all individuals, within and between, as different samples.

The problem I see with option #1 is that the averaged values do not represent a  single individual and therefore could be misleading. The problem with option #2 seems to be the pseudoreplication argument (as outlined above). Of course, the other option is to just measure a single "representative" individual from a population- does this capture the necessary morphological variation for a diagnosis?

I have seen all of these applied to morphometric methods of taxonomic research. I'd be interested in what anyone thinks about this issue, as I have not been able to locate literature that directly addresses this in systematics.

Thanks,

Thomas Murphy
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