[Taxacom] NZ biogeographer's exam Q3

John Grehan calabar.john at gmail.com
Sat Jan 28 20:05:29 CST 2017


Of course everything is a mixture of vicariance and dispersal. No argument
there. Issue is how do the two work in relation to each other. Competitive
exclusion might work as a maybe for species, but vicariance also applies to
genera, families etc. - do these levels of organization competitively
exclude each other also? If so, what is the empirical evidence? And how
does it 'explain' the tectonic correlations?

To get to the empirical on Cook Strait, how does invocation of chance
dispersal either side of Cook Strait predict endemism?

John Grehan

On Sat, Jan 28, 2017 at 8:53 PM, Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
wrote:

> "avoiding overlap with sister taxa" could be the result of competitive
> exclusion. Anyway, all I'm saying is that a mixture of vicariance and
> dispersal is pretty obviously what actually happens.
>
> Stephen
>
> --------------------------------------------
> 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, 2:34 PM
>
>  Far
>  fetched or not is not the issue. It's a might or might
>  not be that has no informative content. It might be the kupe
>  discovered the South Island rather than the North. Inventing
>  might be's to explain away tectonic correlation is like
>  saying that there is no informative content to correlation
>  just because the correlation may not mean anything. It might
>  be sheer coincidence that marine taxa conform to the same
>  distributional boundaries as terrestrial and certainly one
>  might prefer that view. It might be sheer coincidence that
>  species disperse by chance only to make sure somehow
>  (teleology?) to avoid overlap with sister taxa - time and
>  time again, taxon after taxon. The alternative explanation
>  raises no such paradox.
>  John
>  Grehan
>  On Sat, Jan 28, 2017 at
>  8:02 PM, Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
>  wrote:
>  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.
>
>
>
>  Stephen
>
>
>
>  ------------------------------ --------------
>
>  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>
>
>   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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