Pacific land snail phylogeography - grad student project

john grehan jgrehan at ADELPHIA.NET
Wed Dec 4 22:21:59 CST 2002

Ken Kinman wrote:
>     I don't see how favoring one particular geo-narrative necessarily
>REQUIRES one to ignore other geo-narratives.

Agreed. In the case cited I was referring to the apparent exclusion of
alternative geonarratives as the presumption of overwater dispersal into
and across the Pacific ocean was based on a particular geonarrative. The
geological nature of the Pacific was asserted to be the formation of
islands in situ
by "hot spot" volcanism. It was not asserted as one particular conjecture
among others.

>And besides, it seems to me
>that the main purpose of this project is to discern patterns, and that such
>patterns would be grist for your mill (as well as theirs).

Its quite possible that I misunderstood the main purpose of the project. I
had the impression that the main purpose was to chart routes of overwater
dispersal (perhaps according to some kind of progression rule or other
dispersal/vicariance argument). I agree that the empirical data - the
geographic locations and the postulated biological relationships provide
information for mapping the tracks for this group that can be compared with
the tracks of other groups.

>     If Pacific dispersal of Succineids is mainly by rafts of vegetation,
>that might yield a different pattern than if dispersal is mainly by hitching
>a ride on birds (especially birds that can fly longer distances).

It might, or it might not. Some people, Blair Hedges for example, believe
that different means of dispersal can result in the same geographic
patterns (i.e. a snail and a bird might have the same dispersal route).

>If it is
>the latter, the particular geo-narrative would not be as critical.  Right?

The geo-narrative appears to be the context by which Darwinian
biogeographers generally decide how to invoke centers of origin and routes
of dispersal.

John Grehan

>        ----- Cheers,
>                Ken Kinman
>>From: john grehan <jgrehan at ADELPHIA.NET>
>>Reply-To: john grehan <jgrehan at ADELPHIA.NET>
>>Subject: Re: Pacific land snail phylogeography - grad student project
>>Date: Tue, 3 Dec 2002 22:17:09 -0500
>>Robert Cowie wrote
>>>Because of the geological nature of the Pacific - islands formed in situ
>>>by "hot spot" volcanism - the evolution of Pacific island biodiversity
>>>is dominated by dispersal followed by intra-island radiation. Given this
>>>general scenario, we will address several questions, based on hypotheses
>>>we have generated from preliminary study, including:
>>>1) How frequent is dispersal between islands and archipelagos?
>>>2) What are the routes of colonization into the Pacific?
>>>3) What is the pattern of intra-archipelago diversification?
>>>4) What are the taxonomic (generic) affiliations of the Pacific island
>>This seems to be a good example of the Darwinian model of biogeography
>>where biogeography is treated as being independently uninformative of the
>>past. Instead one relies on a selected geohistorical narrative as the basis
>>for biogeographic narrative constructions. In this case the chosen
>>geo-narrative is that of isolated island hotspot formation which requires
>>one to ignore other geo-narratives (e.g. former island arcs) that might
>>provide an alternative geohistory to that of colonization routes into the
>>Pacific as proposed by Cowie. Biogeography is rendered methodologically
>>incapable of providing explanations that exceed the boundaries of current
>>'knowledge' (the 'knowledge' being the selected geological story).
>>The stated goal of the project is said to be "To develop a hypothesis of
>>the phylogenetic and geographic origins and diversification of Pacific
>>island succineid land snails." Perhaps it should be reworded as "To develop
>>a dispersal hypothesis of the phylogenetic and geographic origins and
>>diversification of Pacific island succineid land snails according to the
>>geo-narrative of isolated hotspot formation."
>>John Grehan
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