Panbiogeography of the Americas

[John Grehan]

>After reading Croziat, who as others have also noted could have greatly
>benefited from the assistance of an editor and peer review, I could never
>figure
>out exactly how tracks are to be drawn (defined, identified) nor have
>practioners, to my knoweledge, ever been precise in describing this proceedure.

Since there was no mention of what was read its difficult for me to
understand how Stuart Poss never found the information. Page (1987)
for one gave some detailed attention to the proceedures.

>There has been much discussion of tracks, but these always seem to be described
>as some relatively vague association between two or more non-contiguous
>distributions of presumtive sister-taxa.

What paper are being refered to that substantiates this characterization?

>
>Does one connect each locality collected with all others via a line to form the
>track as the work of some authors seems to imply, or is the mean position or
>some other geometric or statistical measure of cluster density of a set of
>points used to define the track geometry?

The principal method is to link nearest neighbors

Does it even need to be a line (arc)?
>If not, how much curvature over the surface (wiggle or deviation from a true
>arc) is permissible and by what criteria does one decide?

There is a formula by Phipps that can be used should one so desire.

If it is not a line
>or curve does it have width?

no

If so, what criteria are used to establish how
>much?  What about disjunct distritibutions?  Does one draw separate tracks for
>each segment, when connecting it to that of its presumptive
>sister-species?  How
>are outliers, "odd" vagrants, or potential locality record errors addressed by
>this technique when establishing the intial tracks?

All disjunctions are connected by the track.
>
>How does the technique for track deliniation (?definition) take into account
>distributional (latitudinal or positional) shifts in distributions through time
>when "drawing" and comparing tracks based upon contemporary distributions?

If this is perceived to be important for a particular analysis, then the
track would
have to be specified with respect to a particular time.

How
>does the technique account for seaonal or temporal variation in range
>boundaries?

One could draw tracks with respect to particular patterns at particular times.


 How does the methodology for establishing  track geometry account
>for extinction over a portion of the geographic range?

The track line implies an "extinction" in the sense that it bridges the spatial
connection that is not expressed biologically by the presence of actual
organisms.

Obviously, extinction
>can result in certain "track geometries" characterizing extant distributions
>being simply methodological artifacts unrelated to the historical processes
>responsible for producing the observed distributions.  How does one distinguish
>"true tracks" from those that are simply the result of chance associations?

This is where the development of statistical techniques is desirable. Craw
has applied
compatibility analysis to answer this kind of question.

>There was a paper discussing the inability of track analysis to address last
>issue, I believe by Simberloff and colleagues, but I can't remember the exact
>citation.

Simberloff just pointed out the absence of statistical tests for track
analysis. At
the time there were none. Now there are.


 Perhaps someone can refresh my memory.  I do not recall seeing a
>presentation rebutting these objections, except for a few vauge pontifications
>that they were somehow irrelevant to track analysis.

Read papers by Craw, Page, Henderson. The panbiogeography book should
give an adequest general overview of these issues.
>
>Some authors, including Croizat, seem to like to use a sort of "inferred or
>approximate" convex hull around extant distributions, crudely drawn to describe
>(deliniate? define?) tracks.

Please give a specific map example and I will comment.

What is the methodological and emperical basis for
>use of such a "track geometry" for a given set of species?  Clearly, such a
>methodology would be inappropriate in the case where just one or a few
>vagrant/imigrant individuals from only a portion of the former range were able
>to get from point A to point B, as we now know is often the case for many
>non-indigennous species now living in the US and whose presumtive track is a
>reflection of the route taken by the airplane or ship bearing the
>founder(s) and
>which could not be inferred by simply looking at the extant distribution (track
>geometry) alone (molecular and morphometric analysis are, however, often useful
>in confirming that these routes "tracks" were the ones taken and accounting for
>the extant distribution).

One can draw tracks of dispersal routes. Panbiogeographic analysis has
generally been
focused on distributions involving differentiated relatives. Croizat did apply
panbiogeography to the origin of American Indians, and made a number of
predictions
that are only now being corroborated by anthropologists.
>
>Given a track, however drawn, how does one distinguigh among the many potential
>historical mechanisms that might be drawn with the same track (ie disperal
>along
>the track as in many pan-austral distributions of marine organisms vs.
>continental drift [see, as an example, arguments between Rosen and McDowell
>regarding distribution of the Galaxiidae)?

Panbiogeographic analysis is not primarily about dispersal vs vicariance.

 How does one distinguish among
>mechanisms (tracks?) with the same track track geometry that may be
>separated in
>time?

These are issues that can be investigated once the patterns are recognized.
Track analysis provides the patterns of geographic relationships that allows
such considerations to be examined with respect to a general knowledge of
spatial geometry. Many biogeographers discuss such questions and come to
conclusions about individual groups without seeming to know how similar
or different a particular distribution is in relation to distributions in
general.
Panbiogeography offers a method to remidy that problem.

 Given a spheroidal earth, how does one decide, which direction (ie
>over/through what intermediate geographic regions) to draw the connection
>(association)?

Minimum distance, main massings.


>Perhaps with answers to such questions, the value of Croziatian biogeographic
>analysis can be better appreciated.  Are there any references which provide
>criteria for precisely establishing track geometry?  Remarkably, these do not
>seem to be cited in most works utilizing this approach, but intead often cite
>Croizat, who to my knowledge, provided none.

Again, what papers were read? The characterization is not substantiated by the
actual number of papers that have delt with these specific issues.

The issues raised here cover a great deal of biogeography, and my comments
are necessarily brief (I am leaving the office for a couple of days), but I
think
that much of it is covered by the panbiogeography book as well as earlier
publications.