[Taxacom] NZ biogeographer's exam Q3

Stephen Thorpe stephen_thorpe at yahoo.co.nz
Sat Jan 28 19:02:44 CST 2017

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.


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>
 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).
 ------------------------------ --------------
 On Sun, 29/1/17, John Grehan <calabar.john at gmail.com>
  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
  terrestrial group
  is the result of the sea barrier. Yet many southern
  reach their
  northern limit at the *northern* side of the strait
  the cicada
  strepitans*; Marshell et. al., 2012). In a similar way,
  groups have their southern limits at the southern side
  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)
  and Kellow,
  2006). These distributions indicate that it is the Cook
  Strait region – not
  the strait itself – that marks the phylogenetic
  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
  the North
  Island clade, and Wellington specimens are in the South
  Island clades.
  Again, the pattern suggests that the modern topography
  the Cook Strait
  region is not relevant to the biogeographic
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