[Taxacom] NZ biogeographer's exam Q3

John Grehan calabar.john at gmail.com
Sat Jan 28 18:37:00 CST 2017


But the question is why it is not necessary to assume a sea barrier for
taxa *with* a Cook Strait boundary.

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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