Real biogeography problem

[Fred Rickson]

Maybe a real biogeographic problem would be enjoyable and helpful to the
current discussion.  I would love to have some help/discussion/brainpower
thrown at a current biogeographic situation I am working with
.so here is a
REAL problem.

Humboldtia is a genus of small legume trees with 4 species distributed
along the Western Ghats of south India (moist areas).  Individuals are
quite gregarious often forming small area of 10s to 100s of trees.  Two
species have special morphological structures which facilitate occupation
by ants and other invertebrates.  Two species do not have most of these
special traits.  Now, a fifth ant-associated species exists in Sri Lanka
(same moist requirement) and forms dense little areas of many, many trees
(very common).  DNA analysis shows the Sri Lankan tree sister to the most
eastern of the Indian species, also an ant form.  On the basis of
morphology the Sri Lankan species is also the most advanced of the five.
No other species of this genus exist.

So, it seems to me as if the south Indian area is ancestral and Sri Lanka
is derived.  If any of the Indian species ever occurred in Sri Lanka, or
vice versa, I would think the species would still be around given the
gregarious and successful nature of all of the species within their home
range.  Now, do I draw a track from the Indian sister species to Sri Lanka
and claim vicariance across the former, but now submerged, land bridge, or
do I just do the botanical thing and suggest a wanton seed sometime after
the Eocene became established, and subsequently evolved into the Sri Lankan
species?  I really don't have any idea of an answer to this distribution
question.

Now that is a tight little story and there is still no easy answer.  I may
have some help because a proposed comparison of the invertebrates living in
association with each species (within swollen, hollow, self-opening stems)
might shed some light on whether whole plants and there pals marched across
the land bridge, or seed arrived and the plants have picked up a new,
unrelated set of friends.  Any comments appreciated, biogeographical or
otherwise.


Fred R. Rickson
Professor of Botany
Department of Botany
Oregon State University
Corvallis, Oregon
USA  97331

Tel: (541) 737-5272
Fax: (541) 737-3573
email: ricksonf at bcc.orst.edu

----------
> From: Thomas Schlemmermeyer <termites at usp.br>
> To: TAXACOM at USOBI.ORG
> Subject: Re: Panbiogeography of the Americas
> Date: Thursday, September 30, 1999 7:58 AM
>
> Let me, just for the fun of it, throw in my impression while reading
Croizat.
> Croizat's problem apparently were not marine organisms, it were plants.
> Much can be said and done about exact mathematical procedures, such as
the
> question wether great circle or straight line distances should be taken.
> But it seems that Croizat's problem was a roughly logical one. And this
is also
> my impression I gained in discussion with other panbiogeographers.
> They do not think in exact continuous distance measures, rather they seem
to
> make rough logical connections of the kind: If group X is present on
> Madagascar, Sri Lanka, Oceanic Island and Northwest-South-America, than
this
> organism is pacific (whatever this means), if group Y is present in
Africa and
> Southeastern Brazil, than it is atlantic (whatever this means), and so
on.
> As the Croizat machine is an enormous data file of monographies,
check-lists
> and so on, the task to reinvent it seems to me rather the task to check
these
> logical connections above mentioned and how they tie in with overall
observed
> diversity.
> Of course, marine organism are a special case, but no coriolis-force can
take
> them from the Pacific to the Atlantic and vice versa.
> But if I recall correctly, the late (in this case the use of the word
"late"
> seems to be justified) Rosen worked with this problem
>
>   Cheers   Thomas
>
>
>
> >If this is the case, ocean currents will largely confound the usefulness
of
> this
> >technique for marine biogeography..  Because of the Coriolis force and
because
> >continental margins create obstacles around which fluids and the
organisms in
> >them
> >must flow, they seldom travel in straigh lines of minimum distance.
Likewise
> >non-linear coastal margins will confound the approach when dealing with
coastal
> >species.  Perhaps this was a problem with Rosen's analysis.  He used the
> >"approximate convex hull" technique for defining tracks as opposed to
the
> >"minimum
> >distance approach."
> >
> >--
> >_____________________________________________________________________
> >Stuart G. Poss                       E-mail: Stuart.Poss at usm.edu
> >Senior Research Scientist & Curator  Tel: (228)872-4238
> >Gulf Coast Research Laboratory       FAX: (228)872-4204
> >P.O. Box 7000
> >Ocean Springs, MS  39566-7000
> >
>
>
>
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> Thomas Schlemmermeyer
> Museu de Zoologia, Universidade de São Paulo
> Caixa Postal 42694
> CEP 04299-970
> São Paulo, SP, Brasil
>
> Residência:
> Thomas Schlemmermeyer
> Caixa Postal 00276
> CEP 14001-970
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>
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