Date: Sun, 16 Jul 2000 12:42:21 +0200 From: strega@split.it (Tassara) To: cp@opus.hpl.hp.com Message-Id: <aabcdefg2128$foo@default> Subject: Re: Bird Dispersion
Hi John,
>Why would the bird eat the Aldrovanda seed? Is it contained in a fruit? (I
>don't know but I'm guessing it isn't).Is the seed resistant to stomach acids?
>etc etc
>From what I could observe, they are contained inside a fruit while ripening
and they stay there (ripe and floating) until it dissolves, eaten by small
crustacea.
When they sink to the bottom of the lake they have of course no more chance
to be eaten by birds.
Birds often eat floating plants, and so probanly also Aldrovanda, and also
fruiting Aldrovanda with ripe seed.
About the seed resistance to stomach acids, I have no data.
However, often seeds are: so why not Aldrovanda's ones?
Also, it is difficult to think of different systems of seed dispersal in
Aldrovanda: they are surely not carried by wind and in the water they sink,
so they can't float away.
>By your own arguments, a lot of plant species should be far more widespread
>than they actually appear to be (for instance why aren't Sarracenia spread
>out in the entire USA. Why didn't Sarracenia make it to Europe or S.
>America?).
Birds do not eat Sarracenia seeds, from what I know.
Sarracenia is not so widespread because there are natural barriers which
prevent this: deserts and high mountains between E and W USA; a tropical
area between N and S America; and some salt water between America and Europe.
In the far past, however, some of these barriers have been crossed:
Darlingtonia in California and Heliamphora in S. America descend from the
same plants from which also Sarracenia descend, and these old plants
colonized almost the entire American continent.
Spread of plants depends much, of course, also on their adaptability to new
environments.
> Yes there is the argument that intervening populations between Europe
> and
>Australia (if we take Aldrovanda as an example) could have died out
>since, but there should be small populations dotted inbetween (now I'M
>guessing!!!!).
In fact some of these populations still exist: Africa, India, Manchuria,
Timor island...
Very interesting is the case of Utricularia australis, which almost never
produces seeds, but can be found growing in Europe and New Zealand and in
almost the entire zone between these two locations.
Of course I can't know what really happened, but bird dispersal (combined
with other local phenomena) seems a reasonable explanation for such
distributions.
Kindest regars
Filippo Tassara
Genoa, Italy
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