[Taxacom] Examples for Eurasian-Australian distribution

Kenneth Kinman kennethkinman at webtv.net
Thu Jul 22 17:09:39 CDT 2010


Hi Jason,
      It seems to me that the muck layer of a stagnant pond can be quite
marginal.  It is likely to be relatively hypoxic.  And depending on
soils around the pond, all kinds of bad stuff (including heavy metals,
high acidity, and even dangerous bacteria, etc.) could make it even more
marginal.  
      I think it would be interesting to study the particular kind of
pond muck that Hygrobia species generally live in.  If they can tolerate
the worst pond muck (which might tend to be in the deeper central parts
of the pond), that might provide a sanctuary where they have little
competition from Dytiscids that can't tolerate those levels of hypoxia
or contamination.  Furthermore, it would be a sanctuary away from
predators that would rather hunt Dytiscids in cleaner parts of the pond.
Flamingos often have no predators or competition because they can live
in extremely nasty water.  Hygrobia could be considered specialists if
they use the nastiest pond muck as a sanctuary.     
       I don't know if some chironomids might be enjoying the same sort
of benefits, but I will check out that possibility.  My point is that
the worst pond muck in an acidic, stagnant, pond might not be marginal
for Hygrobiids, but it could be marginal for most Dytiscids.  That could
give Hygrobiids just enough of an edge to co-exist with Dytiscids.
Hygrobiids inefficient swimming could require less oxygen, and hypoxic
conditions could be less of a problem for them (than for more active
swimmers).  However, if conditions don't exist to produce this nasty
sanctuary, Hygrobiids eventually die out.  
      If so, I can't help but wonder if the Industrialization of Europe
might have sometimes helped the Hygrobiids out with mining activities
and a lot of other pollutants pouring into ponds.  But all of this is
admittedly a "just-so story", and it would take further research to
evaluate it scientifically.  But then again, a meteor stiking the Earth
and wiping out dinosaurs was once a "just-so story".  
           --------Ken





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