[Taxacom] Shorter trans-oceanic dispersal of Nothofagus

Michael Heads michael.heads at yahoo.com
Wed Jul 28 00:51:25 CDT 2010


Dear Ken and colleagues,
 
It is not too difficult to think up possibilities for trans-oceanic dispersal in Nothofagus. As suggested, the trees may have floated with their seeds held above sea-level. Floating islands are often proposed for trans-Atlantic affinities and might have been involved here. Or Nothofagus may formerly have had means of dispersal that were subsequently lost. The taxonomy might be wrong and Nothofagus may actually be polyphyletic. Ancient Polynesians, unknown in the fossil record, may have transported the plants  Seeds may have been caught in a freak hyper-hurricane, lodged under the toe-nail of  a migrating pterosaur... etc. Stranger things than all of these have happened.  
   But there is no need to speculate, as there are plenty of facts to work with. As Edgar Poe observed, 'the ingenious are always fanciful, and the *truly* imaginative never otherwise
than analytic'. 
  Some relevant facts are: Nothofagus grows down to sea-level in SW New Zealand, and this area has one of the highest rainfalls in the world. Flooding, landslides, storms that break off large branches etc. happen all the time. And yet on Stewart Island (the third main island of New Zealand), just 25 km away across Foveaux Strait, Nothofagus is absent and probably never grew there (McGlone & Wilson, New Zealand J Botany 34: 369. 1996). The whole island comprises excellent Nothofagus habitat. If trans-oceanic dispersal is the key process, why has it not worked here?  
  As I noted in my last post, Nothofagus is also absent from the high mountains of Borneo, mainland Asia and most of the Andes, where there is also excellent habitat for the genus. How does a dispersal explanation account for these absences? Why bring in a completely theoretical process such as trans-oceanic dispersal in Nothofagus when it is not needed and does not actually explain the observed data? 

Michael Heads

Wellington, New Zealand.

My papers on biogeography are at: http://tiny.cc/RiUE0

--- On Wed, 28/7/10, Kenneth Kinman <kennethkinman at webtv.net> wrote:


From: Kenneth Kinman <kennethkinman at webtv.net>
Subject: [Taxacom] Shorter trans-oceanic dispersal of Nothofagus
To: taxacom at mailman.nhm.ku.edu
Received: Wednesday, 28 July, 2010, 2:03 PM


Dear All,
      I can totally understand the reluctance to accept a very long
trans-oceanic dispersal of Nothofagus from Chile to New Zealand (or even
vice versa).  It seems unnecessary given most present data, but new data
and reinterpretations of old data may eventually change things.  Time
will tell.       
      In the meantime, I wonder if this reluctance also applies to
shorter distance trans-oceanic dispersal of Nothofagus, particularly
between Australia and New Zealand (either way).  I wouldn't be surprised
if panbiogeographers would poo-poo even that idea, but what about you
non-panbiogeographers?  Is the trans-oceanic dispersal of whole
Nothofagus trees (fruit plus ectomycorrhiza) that difficult to swallow?
Sure, you put Nothofagus seeds in salt water and they don't sprout, but
what about seeds transported within the fruit (husk).  How vulnerable
are they to the salt water, especially if the branches they are hanging
from are floating well above the ocean waves?  And if such trees were
washed out to sea by a massive flood, the fruits would be saturated by
fresh water during the initial part of the journey (which would help to
dilute any salt water trying to penetrate the fruit further out to sea.
The journey between Australia and New Zealand (or vice versa) is much
shorter, and therefore seems far more immune to the objections voiced
against a South America to New Zealand dispersal.
           -------Cheers,
                       Ken Kinman


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