04
Mar
10

Biogeography

On the face of it, this subject seems like a rather straight-forward case of population distribution. That would be incredibly wrong. Biogeography incorporates a wide range of subjects such as genetics, paleontology, geology, and ecology to model the historical population distributions.

How the hell is this done? It was done for humans: by looking for areas with the greatest genetic diversity, the locations from which range expansion originated can be deduced with some confidence. Human Y-chromosome genetic diversity radiates from Africa with additional major radiations in the Middle East. It can also be done through “ecological niche models” (which are abbreviated “ENMs”) which seeks to model a population distribution given the environmental factors, competing species, and geological history. These two models are independent of one another, and both have some advantages and disadvantages. An additional source of biogeographical data include fossils of all kinds (both the organisms and their tracks, nests, or other signs). ENMs have several drawbacks, though. Among them is the coarse nature of the grid cells (250 square kilometers each) and the lack of implementing additional compounding factors such as competitive exclusion of one species by another which occupies a similar niche. Phylogenetic biogeography models (PBMs) have their own drawbacks, namely an even larger size of the historical range estimates (“West Coast of North America,” “northern Pacific rim”) and the unknown time at which this restricted range occurred.

A combination of a PBM and ENM can alleviate many of these issues. This is what makes this paper so very fascinating. By using separate models to verify the results of each, it is possible to get a much higher degree of accuracy in the overall model. ENMs can provide a time, PBMs can demonstrate if a compounding issue (such as competition or migration barriers) were present which the ENM does not account for. It may be possible to create a hybrid model in the future based upon some of the work here.

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