Centre of origin digression

John Grehan jgrehan at SCIENCEBUFF.ORG
Mon Apr 4 09:10:32 CDT 2005


Blimey, Don puts up a challenge too hard to resist! I don't know about
'explaining' a distribution, but one might wonder about Croizat's slogan
"dispersal forever repeats'. The question that one might first ask about
the examples given by Don is whether they are 'exceptional' in some way,
or run of the mill. To Don the distributions 'make no sense
geographically' This is a common kind of refrain in biogeography - that
people working with particular groups cannot make sense of their
geography and it seems that this problem arises from not being aware of
the geography of life in general or in having an adequate geographic
framework for comparing distributions. 

We draw attention to this in our 1999 book were we draw attention to
examples (p. 67) such as Jeffrey (1988) noting the "astonishing
geographical disjunction" of Dactyliandra welwitschii between SW Africa
and India, or the astonishment of Touw (1993) in finding a continental
Asian moss on Madagascar. We point out that such disjunctions (centers
of astonishment) are remarkable only for their lack of geographic
continuity, and so it goes for the Norway-New Zealand disjunction
mentioned by Don. As a connection, however, this pattern is entirely
normal and run of the mill - common enough to be boring. There are many
distribution connections (tracks), for example, between various parts of
Europe and New Zealand that track, to a greater or lesser extent, the
Tethyan geosyncline. Perhaps the Norway-New Zealand disjunction is just
a subset distribution of a very common and boring biogeographic
relationship. One might, for example, see the mosquito subgenus as an
element of the connection shown by the admiral butterfly distribution
that also includes Norway and New Zealand. 

As for the bibionid fly in north Queensland and New Guinea with several
others in central America (I would be grateful for the citation), it is
a perfectly good example of a central trans-Pacific track. There are
innumerable examples in the literature. Although different in geographic
detail, the bibionid biogeography is replicated in the distribution of
Playroptilon (Matile 1990) present in Queensland and New Guinea as well
as South East Asia, and Central-Northern South America. Similarly, the
distribution of dibamid snakes disjunct between South East Asia and
eastern Mexico is different in geographic detail, but has the same
biogeographic orientation.

Geographic disjunctions are geographic artifacts that can overwhelm the
individual systematist if they are not aware of geographic patterns in
general. It is this generality of biogeography that is usually missing
in the quest for centers of origin holy grail.

John Grehan



> -----Original Message-----
> From: Taxacom Discussion List [mailto:TAXACOM at LISTSERV.NHM.KU.EDU] On
> Behalf Of Don.Colless at CSIRO.AU
> Sent: Sunday, April 03, 2005 12:53 AM
> To: TAXACOM at LISTSERV.NHM.KU.EDU
> Subject: Re: [TAXACOM] Centre of origin digression
> 
> Robert quoted Tom diBenedetto: "I actually do not think that there is
> phylogenetic evidence in spatial distributions". In a narrow sense,
yes.
> But surely a phylogeny (cladogram) that makes no sense geographically
> needs close attention; e.g.,(an actual case) a mosquito subgenus
> distributed only in Norway and New Zealand. No doubt a more modern
study
> would find (maybe has already found) extensive homoplasy at work and
the
> taxon a non-starter phylogenetically. But the model remains. And I
> remember a colleague's delight when an ordination put all his putative
> genera into geographically sensible clusters. There IS information
there
> that relates in some way to the evolution of a group.
> 
> That isn't to say that distribution can provide a definite rejection.
A
> perfectly good genus of bibionid fly, as monophyletic as you could ask
> for, has one species in north Queensland and New Guinea and several
others
> in central America. But no doubt John Grehan will explain that one.
> 
> Don Colless,
> Div of Entomology, CSIRO,
> GPO Box 1700,
> Canberra. 2601.
> Email: don.colless at csiro.au
> Tuz li munz est miens envirun
> 
> 
> 
> 
> -----Original Message-----
> From:   Taxacom Discussion List on behalf of Robert Mesibov
> Sent:   Sat 4/2/2005 9:48 PM
> To:     TAXACOM at LISTSERV.NHM.KU.EDU
> Cc:
> Subject:             Centre of origin digression
> "I cannot agree with Robert that we systematists exclude geographical
> information.  We need it, and we use it.  In fact, some of us use it
in
> keys.
> Robin Leech"
> 
> Do you _define_ your taxa with the help of geography? Or do you define
> them
> with inherent characters alone? Does the geographical information in
your
> keys tell people anything more than where your character-based taxa
can be
> found? There are very, very few papers in the taxonomic literature in
> which
> names are given to what one brave specialist has explicitly called
> "pheno-geographic units".
> 
> Check the TAXACOM archives in mid-2002 for an illuminating discussion
on
> how
> systematists use or don't use geographical information. The hard-nosed
> position was very ably put by Tom diBenedetto in a series of posts,
> finishing with:
> 
> "I actually do not think that there is phylogenetic evidence in
spatial
> distributions. There is geopgraphic evidence - there is biogeographic
> data,
> but I don't think it rises to the level of phylogenetic evidence. To
be
> evidence, particular data must have a well-understood set of
implications
> relative to phylogenetic conclusions (as in character evidence -
matching
> states indicate common descent). The problem with spatial data is not
> extracting the evidence, it is meeting the basic requirements of
> evidence."
> 
> I don't argue against the objections to putting geographical
information
> into the character mix when doing phylogenetic analysis. I'm just sad
(all
> right, grumpy) that so many systematists do so little biogeography in
> parallel with character-based analysis. For those systematists "centre
of
> origin" means nothing. They've got their tree and they're happy. The
tree
> shows character-based ancestor-descendant relationships, based
exclusively
> on living forms in the many groups where fossils or their use is
> problematic. The tree doesn't show times and it doesn't show places,
so
> it's
> certainly _not_ an evolutionary history.
> 
> Getting those times and places requires accepting and working with
> non-character-based evidence. The results are often messy and
> inconclusive,
> as indicated by the ongoing discussion here about "centre of origin"
of
> archaeopterygids.
> 
> I'm way out of my depth here, but do I understand that these bird-like
> fossils come from what's NE China today? And wasn't that area one of
the
> terranes that docked with the Eurasian core fairly late, like
mid-Jurassic
> or early Cretaceous? Suggesting the beasts originated somewhere else
and
> got
> rafted to "Asia"?
> ---
> Dr Robert Mesibov
> Honorary Research Associate, Queen Victoria Museum and Art Gallery
> and School of Zoology, University of Tasmania
> Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
> (03) 6437 1195
> 
> Tasmanian Multipedes
> http://www.qvmag.tas.gov.au/zoology/multipedes/mulintro.html
> Spatial data basics for Tasmania
> http://www.geog.utas.edu.au/censis/locations/index.html
> ---




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