Author Abstract: Misconceptions arising from efforts to translate panbiogeography into terms used in other biogeographic and evolutionary theories are discussed with respect to Cox's (1998, Journal of Biogeography, 25, 813-828) critique of panbiogeography. Croizat's rejection of 'Darwinian dispersal' applies only to efforts to utilize this concept as a general explanation for biogeographic patterns. The conceptual difference between distribution and panbiogeographic dispersal maps is illustrated to show that Croizat did not synonymize distribution and dispersal. Croizat's position on continental drift and plate tectonics does not support Cox's (1998) claim that Croizat 'for long time' refused to accept the theory of plate tectonics. The methodological relationship between panbiogeographic analysis and geology suggests an independence of methodology that prevents geological theory from falsifying panbiogeographic predictions. Panbiogeographic predictions for the eastern Pacific are shown to be in agreement with current historical geological models. Claims by Cox (1998) that the panbiogeographic method is variable and questionable are evaluated with respect to the biogeographic homology of primitive frogs, ratite birds, and southern beeches to demonstrate the consistent application of minimal distance, main massing, phylogenetic affinity and baseline criteria. Panbiogeographic classification concepts are contrasted with the Darwinian system (supported by Cox) utilizing a concept of unitary geographical area based on the language of Roman military rule. Inconsistent positions expressed in recent critiques of panbiogeography may indicate an underlying and implicit acceptance of the empirical and theoretical progress generated by panbiogeography within modern biogeography. 'The formation of groups has an invigorating effect in all spheres of human striving, perhaps mostly due to the struggle between the convictions and aims represented by the different groups' (Einstein, 1938. Collier's, 26 November).
Note to Readers: Follow links above for author email, full article text, or the publishing scientific journal. Author notes in my review are in quotes.
Review: We will continue our examination of panbiogeography this week with a more updated paper from Grehan (the author of our first review this week). Like Grehan's first paper we reviewed, we'll continue our definition of panbiogeography.
As the author notes, "panbiogeography is the only research program in historical biogeography based on the analysis of spatial or geographical relationships [and] it is perhaps for this reason more than any other that panbiogeography remains so controversial among biogeographers."
What we hope to achieve with paper 2 is to build on the foundation of understanding of panbiogeography that we covered on February 28 with the first paper. As such, I won't go into a big discussion of reiterating facts or arguments or points by this author (the same author as our first paper this week) that were already covered with the first paper. I'll only bring up new points or facts that I feel can help clarify an understanding of panbiogeography.
While spatial relationships are integral to all biogeography analyses, what the author means is that "with most historical biogeographers trained as biologists and having a primary interest in biological systematics [how organisms are related to each other], a fundamental shift in perspective is required to accept geography as an integral element of biogeographic analysis."
In other words, our training and preconceptions can affect how we interpret biological data in a geographical context. When approaching panbiogeography, one must be interested more in the geographical connection of areas than merely the similarity of species checklists. For panbiogeographers, Darwinian evolution alone is insufficient to explain the "many facts of world biogeography."
In a Darwinian context, speciation occurs through isolation of individuals and populations sexually to the point where one original population or species becomes several populations of the same species, that when exposed to various environmental factors, makes it favorable from a reproductive standpoint for certain features of the original population to perpetuate through the generations while other features are lost. When enough divergence of features occurs, and where the two (or more) populations are no longer reproducing together naturally, then the populations are considered by taxonomists to be separate species.
What panbiogeography emphasizes is how geographic separation is often paramount in speciation and therefore, to determine ancestral source populations, one must consider the geographic history and connectivity of various populations.
As we discussed last week, when the various populations are plotted on a map and connected by minimum-spanning trees, it is possible to create a map of a most conservative dispersal route, illustrated by the author below.
As an example illustrating the above figure, the author uses the case of the eastern Pacific ocean and how Baja (Mexico) was once separate from North America, and how the Caribbean plate (in plate tectonic theory) helped form Central America through compression during the movement of North and South America towards each other. The author points out how Croizat's original theory of panbiogeography as it relates to the formation of the Americas has, in recent years, been supported by plate tectonic theory.
The rest of the paper is concerned with how panbiogeography evolved after its foundation by Croizat. The greatest contribution to panbiogeography occurred in 1987 with the "introduction of graph theory [a branch of mathematics] by Page providing a new analytical context for tracks, nodes and baselines that was compatible with Croizat's earlier definitions and applications."
Two new terms in panbiogeography were introduced by Craw in 1988: "orientation" and "ocean baseline." Orientation refers to "the origin and direction of flow of migration with respect to a baseline" and includes "arrows on figures [of tracks] to designate directionality to the tracks." The term "ocean baseline" was introduced to emphasize "Croizat's assignment of major global baselines to ocean basins." A third new term was introduced by Henderson in 1990: "antinode." Antinodes "identify geographical centers of significant absence of taxa that may also be informative for track analysis." Sometimes, the absence of species or groups is just as important as the presence of species or groups. As we'll see in the future in another paper of Pacific Island biogeography, biogeographical regions were discovered when one ignored the floras and faunas of atolls compared to larger, "high" islands.
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