[Taxacom] NZ biogeographer's exam Q3

[Stephen Thorpe]

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

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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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