[Taxacom] Hygrobia was Eurasian-Australian distribution

Jason Mate jfmate at hotmail.com
Sun Jul 25 08:22:32 CDT 2010

OK, I´m back.

.  Hygrobia could be considered specialists if> they use the nastiest pond muck as a sanctuary.     

They don´t. This applies to the rest of the paragraph

>       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. 

If we were talking of a Central European endemic I might entertain the idea. Med doesn´t apply and it is common there too!
I think the problem as usual, is one of definitions and perspectives. On the one hand, what is meant by stagnant ponds is ponds (shallow body of water 1-20K m2) which are isolated from rivers by a significant portion of their existence. They are quite common, at least in the context of freshwater habitats.
Often they are seasonal which results in a lack of fish. No fish, lots of inverts. A large portion of dytiscids, hydrophilids, etc live in this environment and because of the fragmentation of their habitat and its short life they are good dispersers. Walk around in autumn or spring and you´ll find them even in regular puddles.Ponds can be O2 deficient but this would be worst for fish than water beetles since they are air breathers! Also the larvae of dytiscids have to contend with the same conditions yet they do not have these strange gaps.If Hygrobia depended on acidic bog ponds, thermal pools or saline puddles I would grant that these are marginal or at least rare habitats. Regular ponds are not. And if you want a contrasting example you have Helophorus, which is also quite partial to ponds and stagnant water bodies like these and like Hygrobia they are poor swimmers. Yet they are extremely common, diverse and ubiquitous throughout the Holarctic.Hygrobia is common (where it occurs), a good disperser, ecologically flexible and tolerates potential competitors. So it begs the question, why not in much of Russia, Central Asia and China?

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