[Taxacom] NZ biogeographer's exam Q3

John Grehan calabar.john at gmail.com
Sat Jan 28 19:34:01 CST 2017


Far fetched or not is not the issue. It's a might or might not be that has
no informative content. It might be the kupe discovered the South Island
rather than the North. Inventing might be's to explain away tectonic
correlation is like saying that there is no informative content to
correlation just because the correlation may not mean anything. It might be
sheer coincidence that marine taxa conform to the same distributional
boundaries as terrestrial and certainly one might prefer that view. It
might be sheer coincidence that species disperse by chance only to make
sure somehow (teleology?) to avoid overlap with sister taxa - time and time
again, taxon after taxon. The alternative explanation raises no such
paradox.

John Grehan

On Sat, Jan 28, 2017 at 8:02 PM, Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
wrote:

> Chance dispersal is not far fetched. It is very mundane. Therefore, it is
> a priori very likely to be a big factor for species distributions,
> particularly for close adjacent landmasses.
>
> Stephen
>
> --------------------------------------------
> On Sun, 29/1/17, John Grehan <calabar.john at gmail.com> wrote:
>
>  Subject: Re: [Taxacom] NZ biogeographer's exam Q3
>  To: "Stephen Thorpe" <stephen_thorpe at yahoo.co.nz>
>  Cc: "taxacom" <taxacom at mailman.nhm.ku.edu>
>  Received: Sunday, 29 January, 2017, 1:49 PM
>
>  As a
>  separate response to Stephen suggesting patterns either
>  side of the Strait "might" be the result of chance
>  dispersal, I would fully agree that it might be the case,
>  just as all the tectonically bounded distributions within NZ
>  might be the result of chance dispersal and have no causal
>  relationship, or that the biogeographic boundary at the
>  MacPherson/MacLeay overlap is just the result of chance
>  dispersal and has no causal relationship with the tectonic
>  correlation, or that the the movement of planets might be
>  the result of chance rather than Newtonian laws. I agree
>  that anything might be possible, even that moas swam to New
>  Zealand after the (non-existent) drowning of NZ. But
>  'might be" is just a 'might be" which also
>  means "might not be" and does not seem to get
>  anyone very far very fast. Of course, I might be wrong
>  :)
>  John Grehan
>  On Sat, Jan 28, 2017 at
>  7:17 PM, Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
>  wrote:
>  On the
>  other hand, the sea barrier might be the primary factor,
>  followed by chance dispersal over the strait to the adjacent
>  land on the other side (followed by limited spreading).
>
>
>
>  Stephen
>
>
>
>  ------------------------------ --------------
>
>  On Sun, 29/1/17, John Grehan <calabar.john at gmail.com>
>  wrote:
>
>
>
>   Subject: [Taxacom] NZ biogeographer's exam Q3
>
>   To: "taxacom" <taxacom at mailman.nhm.ku.edu>
>
>   Received: Sunday, 29 January, 2017, 12:37 PM
>
>
>
>   NZ biogeographer’s exam Q3
>
>
>
>   Why is it not necessary to assume that a Cook Strait
>
>   boundary in a
>
>   terrestrial group is the result of the sea barrier?
>
>
>
>   “It is natural to assume that a Cook Strait boundary in
>  a
>
>   terrestrial group
>
>   is the result of the sea barrier. Yet many southern
>  groups
>
>   reach their
>
>   northern limit at the *northern* side of the strait
>  (e.g.,
>
>   the cicada
>
>   *Amphipsalta
>
>   strepitans*; Marshell et. al., 2012). In a similar way,
>  many
>
>   northern
>
>   groups have their southern limits at the southern side
>  of
>
>   the strait. For
>
>   example,* Hebe parviflora* (PLantaginaceae) is
>  widespread in
>
>   the eastern
>
>   North Island and has its southern limit along the
>
>   northeastern shores of
>
>   the South Island (Marlborough Sounds, Cape Campbell)
>  (Bayly
>
>   and Kellow,
>
>   2006). These distributions indicate that it is the Cook
>
>   Strait region – not
>
>   the strait itself – that marks the phylogenetic
>  break.
>
>
>
>   In a similar pattern to that of these last, terrestrial
>
>   groups, Ross et a.
>
>   (2012) reported a Cook Strait break in the estuarine
>
>   bivalve, *Austrovenus
>
>   stuchburyi*, but noted that the break does not coincide
>
>   exactly with the
>
>   modern strait. Instead, northwest Nelson specimens belong
>  to
>
>   the North
>
>   Island clade, and Wellington specimens are in the South
>
>   Island clades.
>
>   Again, the pattern suggests that the modern topography
>  of
>
>   the Cook Strait
>
>   region is not relevant to the biogeographic
>  break."
>
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>
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>
>   1987-2017.
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