[Taxacom] Examples for Eurasian-Australian distribution

[John Grehan]

Why should the absence of Hygrobia from all the rest of the world be a
problem since all taxa are absent from somewhere eles.

John Grehan

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Oliver
Hawlitschek
Sent: Thursday, July 22, 2010 4:12 AM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Examples for Eurasian-Australian distribution

As stated by Ken, our problem is in fact the current absence of Hygrobia
from all the rest of the world, which probably means that today's
Hygrobia species show a relic distribution. Of course there may be other
species yet to be found. I should note that the Chinese Hygrobia davidi
Bedel, 1883 is known from the type specimen only and has never been
found afterwards.

In: Benton, M.J. (1993) The fossil record 2, a Miocene fossil of
Hygrobia is mentioned, but with no further information. Does anybody
know more about this?

Best regards


Oliver




-------- Original-Nachricht --------
> Datum: Wed, 21 Jul 2010 20:03:31 -0500
> Von: kennethkinman at webtv.net
> An: taxacom at mailman.nhm.ku.edu
> Betreff: [Taxacom] Examples for Eurasian-Australian distribution

> Hi Oliver,
>       I don't really understand John's response that there are
> "innumerable" such cases.  My understanding of your question would be
> cases where a taxon has a disjunct distribution in Europe, China, and
> Australia, but NOT elsewhere.  If so, such cases would probably be
> relatively small in number.  The European species of Hygrobia is
> apparently also found in North Africa, which might tend to restrict
such
> cases even further.   Off hand, I don't know of any other such cases,
> but I will give it more thought.             
>       Anyway, I would agree with you that this distribution is not the
> result of recent dispersal.  Since Hygrobia is a relatively primitive
> taxon, it most likely had a wider distribution in the past and many
> intermediate populations of Hygrobia (species or subspecies) simply
went
> extinct due to (1) competition with certain (presumably more derived)
> taxa, and/or (2) loss of habitat which offered their particular
> requirements.  I would also add that it is perhaps possible that some
> intermediate species still exist, especially in southeastern Asia,
which
> have simply not yet been discovered.  
>           ---------Cheers,
>                            Ken
> ------------------------------------------------------------
> Oliver Hawlitschek wrote:
> Dear all, 
> I have a biogeographical question: the aquatic beetle genus Hygrobia
> (Dytiscoidea) is present with one species in Europe, one in China and
> four in Australia. 
> Does anybody know any other group of organisms showing a similar
> distribution? Probably, it is not the result of recent dispersal. 
> Thanks 
> Oliver Hawlitschek 
> 
> 
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