[Taxacom] Clade age (was: Taxacom Digest)
jfmate at hotmail.com
Sat Nov 12 04:41:27 CST 2011
> > There is a variety of definitions to choose from and every single one fails in some case or another. JFM
> And every single one succeeds in some case or another. CURTIS
Agreed, but definitions are limited by the biased view of their creators. As much as we would like to think otherwise we are the ´wise´ blind men and either because of laziness, lack of time, resources or simply specimens, we mostly make calls based on gut feeling (our experience, which maybe be analytical if we wrote down the thought process, but most of the time is just ´knowing´when something is different). But if the means are available, using several definitions (and their inherent tests) should be preferred. I was sent last night an article (on Scambus wasps) that amply demonstrates this idea, if one has the means. However most of the time we even lack material, hence gut calls (typological concept) is the most commonly used. Nothing wrong with it, but on occasion it will fail. Personally the typological +biological or phylogenetic concept is my favourite choice simply because it works in my group and I can get my mind around it.
This takes me to John. A species´s subdivision is a matter of curtailing gene flow. It can coincide with a physical breakdown due to emerging barriers (as in Lynn´s organisms) but it could equally be due to assortative mating due to differences in phenologies, sexual selection, host choice or distance slowing down flow between the extremes of a range. You see, presently most researchers accept vicariance as well as dispersal as well as sympatric/parapatric/allopatric speciation. So in my closet there are many boxes and one has a label and it says ´Vicariance´. I have it right next to ´Dispersal´.
Finally I would point out that De Queiroz´s lineage-as-species definition has its own inherent problems. At what level do we call a lineage a species? What level of branching can we assume to be part of the lineage´s own ´fuzziness´? Species tend to behave more like networks than lineages so I can only see it working on physically isolated groups. A population on a mountain top or an island may be its own lineage, isolated (in this case physically) from other lineages but can one be certain that it is sufficiently distinct? The addition of other data, such as synapomorphies (phylo concept) would certainly help, but are the differences significant? What can we call significant?. I think that they all fail because it is a gradual process, and only time/extinction makes the cuts.So in the end if you feel comfortable that it works on your group then go for it.
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