[Taxacom] Definitions was Clade age
jfmate at hotmail.com
Mon Nov 14 14:59:56 CST 2011
> > Well, it can happen. That is the basis for concepts such as ring species. The breakdown> > of panmixis can happen in a variety of ways.> > So there is the point, that species can comprise non-interbreeding elements.
Yes, worded like that you are correct, the question is why they are not interbreeding. As Ken pointed out American (introduced) Passer domesticus is not breeding (not really sure but I´ll assume it isn´t) with their European cousins, yet I wouldn´t call them different species. On the other hand some cryptics species coexist and don´t mix. So the biological concept sensu Mayr works when applied in context (when given a choice they do/don´t), and the same can be said about all other concepts. So in my mind concepts are guidelines or scorecards. It is a lot easier to communicate with others what commonly accepted definitions and it also keeps the process from sliding into I-know-best. > What I mean is that in usual practice vicariance and dispersal are overlain according to some preconceived notion rather than being discovered through biogeographic evidence.> > > They all 'fail' because they are attempts at defining species when they are really attempts to define species boundaries using criteria that cannot apply to all species. What they are really doing is identifying parameters that are spatiotemporal (and therefore biogeographic) by which a species entity is predicted for a given time and place. Species, like any other taxonomic level, can be diagnosed. But as for 'defining' one ends up just tying oneself in obscure metaphysical knots.....> > As for species´ definitions, they are necessary not because they are real but because > > they force us to analyze our ideas and the reasons why we choose to do what we do, as > > well as allowing others to tear holes in them, a painful but necessary process. > > But as above, people are in practice not defining species, but specifying parameters for their recognition in space and time.
I can also define a population or an individual, it is just a matter of collecting the necessary characters (morphological, molecular, ecological...). The point is that when you are pondering the question yourself you don´t go throughdefinitions yourself, you dig in and see if it somehow clicks, but you still need a concept so that you can communicate your opinions to others.
> > so by definition their geographical location is part of the issue. > I said sptatiotemporal, not geographical.> > > Of course there are other equally important factors as well without which biogeography alone cannot work. > ???? Explain
Sorry I was lazy and I assumed that somehow we where talking about the same thing. I mean that without phylogenies, some form of dating and other data the only thing biogeography (tracks or something else) will tell you is that Aus bus is in area A and Gus hus in area B, i.e. you will be mapping and that´s it. In fact dispesal and vicariance will leave the same biogeographic pattern many times, how to tell (or at least try?): Firstly, are these taxa each others closest relatives (phylogenetics) or they just look similar (convergence)? Is their split oldish or youngish (I´d be more assertive but I don´t feel like starting yet another thread)? Can this "dated" split be explained best by X or Y (geological evidence, ecological, currents, etc).
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