On rarity
Our forthcoming exhibit 'Rare Shells' examines the nature of rarity. There are few inherently rare animals or plants, as in order to achieve reproduction a certain population of partners must exist. Nature is sufficiently harsh and competitive that its inhabitants cannot evolve into unviable forms and thus extinguish themselves - as long as the environment does not change.
The most common kind of rarity results from forced interaction with other beings. Species become rare as their habitat is destroyed (tigers, pandas etc), or through the ascendence of competitors. In nature, it is rare for a competitor to suddenly achieve a major advantage, to the extent that it threatens or eradicates another species. This is the famous 'balance of nature'. What often happens, however, is that external interference results in a species suddenly appearing in an environment where it can be the dominant predator. Euglandina snails introduced to Pacific islands or rats in New Zealand are typical examples.
Another kind of 'rarity' is a function of sampling. Some species are 'rare' simply because only a few examples have yet been seen by those of us who record such things. A few years back, golden cowries were just one example - scarce and expensive, right until someone found where they live and made the effort to collect them. Now they're a $50 shell, if that.
Finally, there is the rarity of declining groups. Pleurotomariids (slit shells) were once hugely abundant in world oceans, with hundreds of genera and thousands of species in the fossil record. Though new living species continue to be found here and there (or not, depending on how much phenotypic variation you admit), the Recent Pleurotomariidae still comprise just three or so genera and about 28 species. Nevertheless, if you take the trouble to visit their habitat there are plenty of them - at 2800 feet off the Bahamas, for example, slit shells are not rare at all.
PC.
Paul Callomon
Collections Manager
Malacology, Invertebrate Paleontology and General Invertebrates
Department of Malacology
Academy of Natural Sciences
1900 Parkway, Philadelphia PA 19103-1195, USA
Tel 215-405-5096
Fax 215-299-1170
Secretary, American Malacological Society
On the web at www.malacological.org
>>> [log in to unmask] 02/08/06 01:14AM >>>
"Rare shells are rare only because their habitat is relitively unknown."
Perhaps so in some cases; but not in others - looking at better-known groups
of plants and animals, like orchids, birds and mammals, some species are
genuinely rare and vulnerable for a variety of reasons - some are losing out
to competition from newer models, some are dependent on very small habitats
or niches that are disappearing, some are being picked on by a particular
pathogen or predator (sometimes that means us ...).
The risk in making this statement is that it gets to be used to justify
collecting - and over-collecting - vulnerable species. Species do get wiped
out by overcollecting - there are plenty of examples among birds and
orchids. It's possible to wipe out very common species very fast if you
don't think about and keep an eye on impact.
If there's any doubt, surely the golden rule is to wait before you collect
any live shells until you've seen plenty of specimens at that time and in
that locality, and then to be restrained in the number you take. Do you
want to be the person who shot the last passenger pigeon?
Bas
----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, February 01, 2006 4:02 AM
Subject: Re: Rarities
> . In order to be a living creature at all, there have to be enough of you
> to reproduce. Once it is discovered where you live, frequent, or hang out,
> you are no longer as rare as once thought. I believe it was Norm Pashible
> (sp) who tracked down the once rare Gloria Maris. I once tracked down a
> racoon---but ended up feeding him day-old bread.
> Art
>
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