[Taxacom] Dispersal... again

[Karl Magnacca]

On Wed, October 26, 2011 2:11 pm, Michael Heads wrote:
> Hi Karl,
>
> You don't need continuous land (e.g. a lost continent) for
> vicariance. For example, two metapopulations on an active island
> arc (surviving in situ on individually ephemeral islands) can be
> separated by rifting.

They can be, but it depends on the organism.  For many things that
have speciated on islands, even crossing a 50-mile channel between
islands is such a rare event that they don't exist as
metapopulations between oceanic islands.

> The dispersal model for Hawaii relies entirely on the suggestion
> that there was a period (33-29 Ma) in which no islands (Clague et
> al, 2009:1) or no high islands (Clague et al., 2009: 10) were
> emergent, but the calculation this was based on is dubious.

No, this is an interesting part of the story but irrelevant.  Even
granting the most wildly optimistic past scenario of islands
scattered across the Pacific, you're still left with having things
cross 500 miles of ocean from the nearest seamounts that could
possibly have ever been high islands with any significant diversity.
 By my definition, that still counts as long-distance dispersal.

Also, the 2009 paper was based on coral growth, not the approximate
calculated height.  On top of that, even that number is the maximum
height attained, which doesn't take into account what is removed by
erosion.  Oahu and Kauai have a long way to go before submergence,
but they've already had most of their tops removed so that only the
core of the volcanic pipes remain at the highest points.  So if
anything, Clague's 1996 underestimate is probably an *overestimate*
of the relative height between the original shoreline and the peak
at submergence.

Karl