[Taxacom] NZ biogeographer's exam Q3

John Grehan calabar.john at gmail.com
Sat Jan 28 17:37:14 CST 2017


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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