Bioregionalisation Track Analysis Reading The Biogeography Part 4

Bioregionalisation Track Analysis Reading The Biogeography Part 4

I was wondering with two papers left, whether there would still be any point to going on. The last two use track analysis and area cladograms, respectively, and those were already used by the first and second paper, so would there be any new insights into the methodology of pan- and vicariance biogeography?

However, the next paper,

Martinez et al., 2017. Biogeographical relationships and new regionalisation of high-altitude grasslands and woodlands of the central Pampean Ranges (Argentina), based on vascular plants and vertebrates. Australian Systematic Botany 29: 473-488.

... uses track analysis at least partly to do something different than the previous instance. There is the question of the "relationship" of a biome, but then there is also bioregionalisation. So that is a new angle.

The idea seems to be relatively simple. As before, the panbiogeographer looks at the occurrences of species, draws minimum-distance lines ("tracks") between them, and then identifies areas where the tracks of several species overlap as "generalised tracks". In the present case, a very short generalised track is then "used to recognise natural areas in terms of their biota because they result from more or less consistent overlapping distributions of two or more endemic taxa".

Okay, same question as always: does this make sense?

Well, more than the claim that generalised tracks are always evidence of vicariance, which this paper kind of only makes in passing (while, weirdly, explaining the panbiogeographic reasoning in words so identical to those used in the Romano et al paper that I wonder if they were in both cases copy-pasted from Croizat). To me the approach just seems part unnecessarily complicated, part not data-rich enough.

As for the first, yes, an area with several endemic taxa may well deserve recognition as a natural unit, a vegetation zone, a biome (whatever) in some area classification. But if the idea is to identify areas defined by endemic species, why do we need a track analysis as an intermediate step? Why not simply plot the occurrences of endemic species? At that point all the information is there, and tracks, generalised or not, do not add anything.

As for the second, as I mentioned before there are several other methods available for bioregionalisation. Some use clustering approaches to group grid cells or other small areas into larger areas based on shared species content or even the relatedness of those species. The newest ones use modularity or map equation analyses to examine networks of species and the grid cells they occur in; in contrast to clustering, where it is the researcher's somewhat subjective choice how many clusters to accept, these network approaches have algorithms for deciding more objectively how many truly distinct units there are.

In other words, in my eyes track analysis seems to be superfluous to requirements if we are merely interested in the simple measure of shared endemics, and it is unable to provide the depth of information that could be obtained from examining other shared distribution patterns.