[Taxacom] How to generate biogeographic and ecological nonsense

[Stephen Thorpe]

One certainly cannot uncritically accept anything by those authors! Mind you, one should not uncritically accept anything by any authors!

Stephen

--------------------------------------------
On Thu, 29/12/16, John Grehan <calabar.john at gmail.com> wrote:

 Subject: [Taxacom] How to generate biogeographic and ecological nonsense
 To: "taxacom" <taxacom at mailman.nhm.ku.edu>
 Received: Thursday, 29 December, 2016, 12:46 PM
 
 As most list members no doubt
 appreciate, one cannot use the geological
 ages of mountains or islands to uncritically make up maximum
 divergence
 dates. A good example of the biogeographic mess that is
 otherwise created
 (and remains a heavy burden on the scientific integrity of
 many New Zealand
 studies) is illustrated by Heads for *Maoricicada* in New
 Zealand as
 follows:
 
 
 “Buckley et al. (2001) calibrated the timeline for
 phylogeny in*
 Maoricicada* *campbelli* by assuming that *Maoricicada* was
 no older than
 the current alpine habitat (~ 5 Ma), as the genus is mainly
 alpine. This
 makes the assumption that taxa currently located in the
 alpine zone require
 alpine habitat, and this is not necessarily correct. In any
 case, *M.
 lindsayi* occurs at 0-500 m elevation, and *M. campbelli*
 itself is
 recorded from 10 to 1580 m (Buckley and Simon, 2007). In
 fact, most of the
 “alpine” species of *Maoricicada *are known from some
 localities below the
 alpine zone; 10 out of 14 have populations at less than 1000
 m (around the
 level of the tree line) and several have populations in the
 lowlands
 (Dugdale and Fleming, 1978). These records suggest that
 *Maoricicada* and
 at least some of its diversity existed before the present
 alpine
 environment developed, surviving in lowland areas of open
 vegetation. The
 diverse ancestral complex would have been inherited by the
 mountains of the
 Kaikoura orogeny, as they rose. If this was the history, it
 would undermine
 a habitat calibration based on the age of the mountains.
 
 
 Based on the “mountain age” *habitat *calibration,
 Buckley et al. (2001)
 calculated that the earliest divergence within *M.
 campbelli* occurred at
 2.3 Ma, and they concluded: “We cannot reconcile the
 earliest date of
 divergence within M. campbelli with rifting along the Alpine
 Fault, a
 process that began to accelerate 10 million years ago.”
 Yet the young age
 they calculated for divergence in *M. campbelli* is based on
 the doubtful
 assumption they made about the age of the genus.
 
 
 Buckley et al. (2001) assumed that alpine taxa in
 Maoricicada could be no
 older than their alpine habitats. In a subsequent study of
 the genus,
 Buckley and Simon (2007) abandoned this method. Instead,
 though, they
 calibrated a molecular clock for *Maoricicada *by assuming
 that related
 cicadas, endemic on Norfolk Island and Kermadec Islands,
 could be no older
 than their current *islands*. But islands are just another
 habitat type
 within a region, as are mountains, leaf surfaces, or
 puddles. The existence
 of *prior* islands in the region means that calibration
 using island age,
 will, as will calibration using habitat age, give dates for
 clades that are
 too young by an indeterminate amount. Buckley and Simon
 (2007) found that
 *Maoricicada* diverged only in the mid-Miocene. This date is
 too young (by
 how much is not known), but at least it confirms that
 *Maoricicada* existed
 before the origin of high montane habitats.
 
 
 Hill et al. (2009) carried out further studies on
 *Maoricicada campbelli*
 and confirmed that the main break in *M. campbelli* is
 between a Central
 Otago clade and the rest. They wrote “we can only
 speculated as to what
 process initiated both the divergence of *M. campbelli *from
 the rest of
 Maoricicada at <2.6 Ma, and the main *M. campbelli* split
 at 1.5-2.1 Ma”
 (p. 13). As discussed, the “island age” calibration
 (from Buckley and
 Simon, 2007) that these dates depend on is flawed.
 
 
 
 The authors based their conclusions on these dates, but they
 did not refer
 to major geological features at the boundaries, such as the
 Moonlight
 tectonic zone, and instead suggested that increased
 sedimentation of river
 gravel caused by rising mountains produced habitat “into
 which *M.
 campbelli *evolved” (p. 14). The new sedimentation and new
 habitat might
 explain local range expansion or contraction in the group
 during the
 Kaikoura orogeny, but they do not account for the *location*
 of the mean
 break in the species.”
 
 
 
  John Grehan
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 Injecting Intellectual Liquidity for 29 years.