[Taxacom] NZ biogeographer's exam Q3

[Stephen Thorpe]

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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