[Taxacom] Examples for Eurasian-Australian distribution

Jason Mate jfmate at hotmail.com
Thu Jul 22 14:35:12 CDT 2010

But, it coexists with many Dytiscids! In fact the habitat that it favours (ponds) is a favorite of a large proportion of water beetles. I agree that its current environment (bottom feeding) is probably due to being outcompeted by better swimmers in open water (unlike Dytiscids it has a primitive alternating stroke: thus it is a poor swimmer). Alas the bottom of a pond is not a marginal environment; plenty of ponds and chironomids are doing pretty well!. As for Amphizoa, yes, it is relictual. However it is a specialist, usually of mountain springs and rivers. Species that live in these environments tend to be poor dispersers.(rivers are fairly permanent).



> From: kennethkinman at webtv.net
> Date: Thu, 22 Jul 2010 13:29:52 -0500
> To: taxacom at mailman.nhm.ku.edu
> Subject: [Taxacom] Examples for Eurasian-Australian distribution
> Dear All,
>        Last night I surmised that the relic distribution of Hygrobia was
> probably due to competition or habitat loss.  I am now leaning more
> towards competition, specifically with members of Family Dytiscidae
> (apparently its sister group).  
>        Dytiscidae is a relatively large family and probably outcompeted
> related families (such as Hygrobiidae and Amphizoidae).  So I would
> hypothesize that Hygrobiids escaped total extinction by surviving in
> marginal habitats that most Dytiscids perhaps don't tolerate very well
> (particularly stagnant water that is acidic).  Amphizoidae also has a
> relic distribution and may have survived in a similar manner.
>            ---------Ken
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