[Taxacom] NZ biogeographer's exam Q3

John Grehan calabar.john at gmail.com
Sat Jan 28 18:49:45 CST 2017


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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