Mario Schweiger wrote:Looking on nautical charts, Cres-Losinj seems, it has been longer connected to the mainland (Istria) than Krk island.
Sea depth between Istria and Cres has a maximum of 52 meters, mostly between 46 and 48 meters, nearly over the full length.
Sea depth between Cres and Krk is at lest 68 meters and between Krk and the mainland in the east at least 58 meters.
40 meters depth for less than 1 km east of Voz (NE Krk).
Therefore, ammodytes reached the area to late after the last glacial, is no good explanation.
Don't see why it shouldn't be. Imagine the following scenario, in full accordance with the (present) sea depths
and what (very little!) we know about the
dynamics of the "flooding" of the Adriatic basin after the latest
(actually quite puny!) glacial maximum:
Vammo advances/spreads to the northwest from its South Balkan refugium, along the eastern Adriatic coast,
while at the same time the sea floods the Adriatic basin... In a quite real sense, it's kind of a race - who gets
first to particular sites, Vammo or the sea? (And remember, Vammos are rather slow when it comes to moving
anywhere around, let alone migrating large distances...)
Around 11 000 years before present (b. p.) the sea level was about -50 m (with respect to the present one),
Cres/Lošinj and Krk had already been separated by a sea channel, but Krk was still attached to the nearby
mainland, and Cres/Lošinj as well (to Istria). Both were still
peninsulas.
Vammo reaches Krk "in the last moment", just before it separates from the mainland and becomes an island.
Vammo proceeds spreading further to Istria and reaches its northern parts. It's quite a long way, all around
the northern part of the Adriatic basin - now already "flooded", and it takes time... Too much time to reach
Cres/Lošinj still as a peninsula of Istria, instead of newly-born islands...
Cres/Lošinj separate from Istria and become islands
before Vammo reaches
those parts. (Actually they had
detached slightly
before Krk did, but it doesn't matter, as all this happened within a (relatively) very short
time, maybe just some 500 years. The rate of "flooding" - the increase of the sea level - was at its maximum
at the time, it was quite a "dramatic" period of rapid change...)
BTW, at around 11 000 years b. p. Rab was already an island, while Pag and Krk were still peninsulas. So, no
Vammo on Rab... On its spreading towards the north it inhabited the
peninsula of Pag, skipped the
island of
Rab (what else could it have done...) and reached the
peninsula of Krk just in time. But for the Cres/Lošinj
peninsula, so far away, it was already too late... For Istria it was not, as it has remained a peninsula till the
present day.
And that's just what one observes today - both the islands and the distribution of
V. ammodytes on them.
So, what should be so wrong with an explanation like that?
Of course the "model" is
extremely crude - it relies just on the sea depths encountered today and doesn't take
into account the possible changes of the sea bed itself. At least the mighty river Po with its sand deposits could
have either "sank" or "raised" the sea bed, at least in the Northern Adriatic, and the river Neretva could have done
an analogous mischief in the Central Adriatic... But let's leave that to the dedicated experts who earn their daily
bread solving "additional complications" like that... making their doctoral dissertations, scientific papers,... Let
them live. (After having spent almost a month trying to understand all these "additional complications", I decided
to just give it up and leave all that to THEM. Maybe one day someone writes a "definitive" and clear review paper
on "all that"... Till then, I'll just stick to this oversimplified hypothesis of mine.)
Maybe, it is the presence of Malpolon on Cres island.
As far as I know,
Malpolon insignitus and
Vipera ammodytes do not exclude each other anywhere else.
On the contrary.