<One problem with a discussion of the word "rare" is that it has more
than one meaning. One person can make a convincing argument using one
meaning of the word, and another can make an equally convincing argument
using a different meaning.>
Thank you Andrew.  So often, we seem to be tripping up over semantics
(ie, how terms are defined and used) here on the old list, and the the
current debate is unfortunately not one of the "rare" exeptions!!  One
must be quite careful to define one's terms when there is room for
ambiguity: our language is annoyingly imprecise at times ( my favorite:
the super-complete version of the Oxford English dictionary gives over
200 usages of the word "run"!).
Also, as Frank has pointed out, opinions are sometimes presented as more
factual than they actually are. However, sometimes a statement of fact
is taken as an opinion, which is just as confusing for the reader.
Personally i try to avoid giving opinions at all in situations where
empirical evidence and logic (two of the cornerstones of the scientific
method)  are more appropriate.  For example, it is not a matter of
"opinion" that rare and very rare molluscan species do undoubtedly exist
- it is a simple matter of definition, as per my previous message:
"rarity" is a term which is useless unless operationally defined, and
when the term IS defined, then  BY DEFINITION, there will be species
which fall within the parameters used to define the term: for example,
if we operationally define a "rare" molluscan species as one which falls
into the bottom  5 percent of number of specimens found so far, then by
definition, 5% of all molluscs will be "rare", using that definition.
That said, any definition should be apprpriate for the taxa and
environments involved:  it is difficult to compare different phyla and
land vs sea-dwelling organisms, for example : an absolute number of 500
living specimens may cause a vertebrate such as a whale or tiger to be
considered  extremely rare,  whereas a molluscan species with very low
densities over a  very wide geographic distribution may be considered
"extremely rare" even if the estimated global population is many
thousands  or tens of thousands! (or even millions: if a  molluscan
species occurs at a density of less than ten individuals per sqare km
over an area of a million square km, it will still very very seldom be
sampled, and wil thus fall into most definitions of "rare" (also, think
of the difficulties of mating at that sort of density, for an organism
say, 10mm in size!!), even though there are 10 million of them.
'nuff said. goodnite fellow Conchlers!
-Ross M.
--
Ross Mayhew:    Schooner Specimen Shells:    Http://www.schnr-specimen-shells.com
"We Specialize in the Unusual"
Phone: (902) 876-2241     Snail Mail; P.O Box 20005, RPO Spryfield,
Halifax, N.S., Canada, B3R 2K9.
But try to find "something for Everyone"!!