Rare species????
Look how many new species are named from a single unit, gastropod or
bivalve and then look at subsequent collecting and publications which
extend the distribution of that species.
A species is only rare when it is difficult to find but when the habitat
is found and numerous specimens become available the values are anly in
the dealers mind, probably because he or she has paid some outrageous
price for the "rare specimen", the penalty of being a dealer.
 
Kev
 
 
Ross Mayhew wrote:
>
> < The speculation has been made that it is safe to say there are rare
> shells, yet no scientific evidence that I am aware of, was offered to
> support this statement. As such it becomes an opinion, no better or
> worse than those offered by others, but just an opinion.>: this quote is
> selected because it is the most concise utterance of one line of thought
> on this topic.
>         Several possible reasons for species being "truly rare" were put forth
> : 1) the "evolutionarily declining" species Hans Turner wrote about
> (which if evolution is truly the way species develop, most probably
> exist, perhaps in large numbers!),  ( some species  have developed
> methods for breeding even though they may have extremely low densities,
> so spp "at the end ot their time" could hold out for protracted periods
> in some cases!!) 2) species which live only in extremely uncommon
> habitats, 3) spp which have a very limited geographical distribution  ,
> and 4) species which are becomming endangered by non-evolutionary
> influences (such as human) - i am sure several other categories can be
> postulated also.
>         It is an established fact that a good number of species are known from
> only a handful of specimens, often despite heavy sampling by various
> methods in the areas where they are found.   While this does not
> nessessarily mean ALL such spp are in fact "truly rare", as many of the
> species falling into the above categories may be expected  to be, taken
> as a global fact it is a strong indicator that there are indeed species
> which are just not at all common in nature, independant of their
> representation in collections, scientific or private.
>           On a strictly common-sense note, it seems likely that total,
> planetary populations of species fall along some sort of distributional
> curve, with abundant spp such as Cypraea moneta on one end, and extreme
> examples of the type of categories mentioned above being more likely to
> fall towards the other ("numerically low global population") end of the
> curve.  **By definition**, the species on the extreme ends of such a
> distibutional curve could be designated "abundant" and "rare".  It must
> be noted, however, that it is seldom possible to identify which species
> probably belong to the "extremely rare" category (based upon this
> particular difinition of rarity, ie - other operational definitions
> could include spatial distribution, range, the total number of local
> populations, etc.), given our often limited information-base at present.
>   What is certain, however, is that no matter HOW one defines rarity, a
> certain percentage of species WILL fall into this category, simply "by
> definition".  The "rarer" a species actually is, the more data will be
> required to determine its actual status, hence the more difficult it
> becomes to make an accurate designation, ie. to attatch numerical
> estimates with acceptable statistical confidence levels.  Thus, no
> matter how defined operationally, some species will truly be "rare" and
> "extremely rare", but determining which spp actually fall into these
> categories is often quite difficult, given the resources typically
> avaliable for this type of enquiry.
> -Ross M.