[Taxacom] Examples for Eurasian-Australian distribution

[Kenneth Kinman]

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