Biogeographic memory

[P.Hovenkamp]

At 06:34 AM 9/10/01 -0400, you wrote:

>>>There was more discussion of phylogeny in Craw's earlier work, but then
>>>whether that's 'enough' for anyone I leave to individual preference.
>>If it was there, why not deal with it in the book? By downplaying the role
>>of phylogeny in the book you apparently left out an essential element of
>>the method...
>
>No, as the spatial relationships were the subject of the method the main
>massings were sufficient to illustrate the contrast with Nothofagus. The
>'phylogeny' (as biological relationships) only gives the biological
>relationships anyway.

Going back through some earlier posts I found that it was John Grehan who
came up with this as an example of how phylogeny contributes to the
identification of a main massing:

 >Designation of baselines does involve several considerations and it is
 >possible that because there is no spatiotemporally independent criteria the
 >procedure may be viewed as arbitrary. Where a distribution is adjacent to
 >more than one ocean basin it is not possible to use minimum distance alone.
 >In fig 1-10 b and c the distributions were spatially unproblematic.Two
 >other contributing elements are main massings and phylogenetic
 >relationships. This is discussed in some detail (maybe not enough for some)
 >for the ratites.
(...)
>>>>This way one runs the risk of ignoring the evidence (plainly there in the
>>>>examples) that there are different general patterns crossing the Indian
>>>>Ocean basis in different ways.
>>>
>>>Of course, and these can be recognized as different standard tracks with
>>>overlapping or nested
>>>localities - still within a common baseline with respect to a particular
>>>ocean basin. Even Croizat's (1958)
>>>map shows different tracks across common ocean basins.
>>
>>Exactly. So why restrict your interest to only 4 ocean basins?
>
>Actually there are five according to the scheme of Craw. If one is
>interested in ocean basin relationships this is the numerical limit. If one
>is interested in greater detail within a particular basin then that is the
>focus.

This seems to imply (but I may be reading too much in it) that you consider
geographic features to have some sort of hierarchical relationships. There
may be a number of features *within* an the Indian Ocean basin, but on a
lower level. Each of these is still "part" of the Indian Ocean basin.
To me, the existence of the different patterns across the "Indian Ocean
basin" suggests that this is not a unitary feature, but an combination of
two (perhaps more) features that are (at least at present) adjacent to each
other.

>>That under the name Panbiogeography you seem to be advocating an approach
>>that is both in method and in general purpose different from what Croizat
>>termed panbiogeography.
>
>In what way?

As far as I understand Croizat, he looked at the distribution patterns
first, second and third. Only when he had established general patterns he
started looking for geological or geographic correlates. But he could be
quite content if he did not find one.
I know there must be a quotation somewhere to back me up on this... Perhaps
the following will suffice (from Croizat, 1968):
"The serious student understands, of course, that it is at times very
difficult, possibly even imprudent under present conditions to effect
correlations of detail between geology and biogeography (...)"(p. 218)
"Biogeography, if correctly used, is, in sum, a primary science in its own
right" (p. 225)

>>Thus, on basis of Croizat's panbiogeography, there seem to have been two
>>developments: one towards "Panbiogeography" in the sense of Craw, Grehan &
>>Heads, the other towards vicariance biogeography, integrating Croizat's
>>approach with explicit phylogenetic data. I think the latter is the more
>>interesting development.
>
>In what way is Croizat's approach being 'integrated' with phylogenetic data
>by vicariance biogeographer - particularly as vicariance biogeography seems
>to simply be a version of Darwinian biogeography in that it cannot predict
>biogeographic history without some kind of external (non-biological)
>criterion. Usually this criterion is concordance with some hypothetical
>historical sequence from geology or paleogeography - and in this respect is
>no different from traditional Darwinian biogeography.

A fairly limited view of the developments in vicariance biogeography. Even
from reading Turner et al. it should be clear that there's more to it than
that.
I'm not going to argue whether vicariance biogeography has reached its goal
or not, but at least this line of approach tries to do two things that
Craw, Grehan and Heads' Panbiogeographys seems to have given up on:
1. It considers biological evidence independently from geological data
(treading in Croizat's steps)
2. It tries to incorporate the extra detail that resolved phylogenies
provide, especially with regard to the historical component (an expansion
of Croizat's method, which has no way to deal with historical information
of this kind).

>>I was not trying to "pick on" Croizat - merely trying to explain the
>>impopularity of and even downright hostility towards his writings.
>
>What you say doesn't seem to 'explain' anything any more than one might say
>that the hostility might stem from the fact that most biogeographers are
>Darwinian biogeographers, and the most influential biogeographers of his
>day did not appreciate having a detailed and persistent critique of what
>they took for granted.

They might not have minded so much if every point of criticism would not
have been accompanied by a sneer.
The prevailing views of biogeography were equally vehemently opposed by Van
Steenis, who
denied (like Croizat did) the role of chance in explaining currently
observed distributions.
He was quite detailed and persistent in his critique of dispersalist
scenarios, but nevertheless he was able to publish his views and was
invited to many meetings to expound them. Van Steenis first came up with
hypothetical "land bridges" (1962) to explain the observed regularities in
distribution patterns, which nobody would believe in. Incidentally, he was
quite happy when later (1979) he could replace these land bridges by
connections between shifting continental blocks (which were perfectly
acceptable by that time).

Van Steenis, 1963. The land-bridge theory in botany. Blumea 11: 235-542.
Van Steenis, 1979. Plant-geography of east Malesia. Bot. J. Linn. Soc. 79
(2): 97-178.

P. Hovenkamp
Nationaal Herbarium Nederland - Leiden
PO Box 9514
2300 RA  Leiden
The Netherlands
hovenkamp at nhn.leidenuniv.nl
http://nhncml.leidenuniv.nl/rhb