Dear Alex,
what's with the ZIP-disc.
Helmut
Helmut "Helix" Nisters
Franz-Fischer-Str. 46
A-6020 Innsbruck / Austria / Europe
phone: 0043 / 512 / 57 32 14
e-mail: [log in to unmask]
web: www.netwing.at/nisters/
(please visit it and sign guestbook)
always looking for shellgrit from all over the world
for my nearly 89 years aged mother Irmgard
to makes happy and to keep up her health
office:
Natural History Department of the
Tiroler Landesmuseum Ferdinandeum Innsbruck
Feldstrasse 11 a
A-6020 Innsbruck / Austria / Europe
phone: 0043 / 512 / 58 72 86 - 37
web: www.tiroler-landesmuseum.at
(specimen donations to the
Tiroler Landesmuseum molluscs collection
are always appreciated)
----------
Hi
This could be the start of an interesting line of discussion. The concept of
species rarity, and what constitutes rarity, is a central one in ecology. It is
recognized that species abundance matrices have a number (dependent on many
factors) of species with low abundance. In many instances this number maybe
one. There are many models that seek to explain this. It is also the case that
re-visits to a site may throw up other, previously unrecorded species. But it
is necessary to see whether these newly recorded species are of low abundance
or not. If they are, then inadequate sampling would be my first assumption.
This is why its necessary to look at sampling efficacy at sites (cumulative
number of species vs. time, or area). If the newly recorded species is present
in large abundance I would want to look at population demographic processes,
and possible changes in abiotic (and possibly biotic) variables to help explain
it.
Other ways to look at communities include biomass and biovolumes. Sometimes,
but by no means always, species present at low abundance usually have high
biomass. We need also to look at habitat structure and influences on local
populations from a regional perspective. This leads onto metapopulation
dynamics. A very interesting subject and one that may interest others in
discussion.
Alex
"Harry G. Lee" wrote:
> Dear Liz et al.,
>
> The distribution of species collected at a single station by their
> frequency, given a good measure of biodiversity, always has a bunch of
> "stragglers" (only one or two examples of certain species). A typical
> example (and one in which human selective factors had been minimized) is
> Charlotte Lloyd's report discussed recently in this forum
> <http://home.sprynet.com/~wfrank/remarkab.htm>. Look at all the species
> preceded by a "1"!
>
> Corollary to this pattern, which I have witnessed in fossil and Recent
> land, marine and aquatic field collections over 50 years of noodling for
> shells and their contents, is the fact that there WILL be additional taxa
> (given a diverse and robust regional fauna) on a revisit to the same
> collecting site.
>
> The numbers-crunchers can model this frequency distribution into some kind
> of chi-square or asymptotic transmogrification, but the "straggler" concept
> is good enough for me. I think this experience is a paraphrase of Andy R's
> hypothetical melange of field trips to the Cretaceous pit and Liz's posting
> below.
>
> Now to tackle that recommended reading of high specific gravity prose (vide
> infra)!
>
> Harry
>
> At 06:26 PM 6/21/00 +0100, you wrote:
> >Dear all,
> >
> >As Andrew points out, the expectation is a curve which rises sharply
> >and then tails off. Since there is rarely enough time to exhaustively
> >collect and identify every specimen it is not surprising that
> >ecologists have devised various ways of estimating species diversity.
> >If anyone is interested, the friendliest book on the subject I know
> >is:
> >
> >Magurran, A.E. (1988) Ecological Diversity and its Measurement.
> >Chapman & Hall.
> >
> >From the replies coming in, it looks as if conch-l collectively has
> >some interesting data on the subject.
> >Liz
> Harry G. Lee
> Suite 500
> 1801 Barrs St.
> Jacksonville, FL 32204
> USA 904-384-6419
> <[log in to unmask]>
> Visit the Jacksonville Shell Club Home Page at:
> http://home.sprynet.com/~wfrank/jacksonv.htm
>
> oo .--. oo .--. oo .--.
> \\(____)_ \\(____)_ \\(____)_
> `~~~~~~~` `~~~~~~~` `~~~~~~~`
ÿ
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