[tdwg-content] tdwg-content Digest, Vol 20, Issue 17

[Nico Cellinese]

Thank you Rich for saying what I want to say (well...almost) so much better than I can.  

Just want to add a couple of things:

>> I also question the utility of analyzing 
>> occurrence records at clades higher than species.

So you are assuming that species are clades.  I agree, but that is a very controversial statement.  Pretty much the reason why the PhyloCode doesn't extend to cover species. Species are not clades to many of us. So, that is to say that many would argue that analyzing occurrence records within/between clades may exclude species altogether.

In very practical terms, when you look at a clade and attach the "species" label to it, you overlay a ranking system to a clade system.  That is completely arbitrary, and that is why the species rank is absolutely not different than any of the higher ranks. 

>> Species are assumed to be made up of population 
>> of interbreeding individuals,

Well, again that very much depends on who you talk to. As Rich said, there is another forum where these things are discussed ad nauseam. We will never agree of what species are, maybe because we are talking about fiction.

>> But what is a genus vs, a subgenus, vs a tribe?

Fiction, vs fiction vs fiction. 

>> If these higher clades were somewhat stable and 
>> had some agreed on understanding then this might
>> make sense.

A clade is not more stable than a "genus" or "family" or "tribe".  Every time we add a species to a genus, or a genus to a family, etc. we change the original taxon concept.  That's certainly not stability.  Every time we add a taxon to a clade we may change the ingroup content but we do not change the reference to the ancestor.  In that regards, clades are much more stable.

>> There is no clear reasoning behind why one clade 
>> is a family in Mammals and a clade of similar 
>> age is a genus in Beetles.

Absolutely correct.  Ranks are not comparable so two families or genera can't be compared, in fact two species can't be compared. Hennig suggested to start ranking from a specific age, e.g. Cretaceous or so, and that would make ranks more comparable but the entire exercise would not be practicable and we would keep arguing endlessly anyway.

> Perhaps not.  But within Mammals, or within Beetles, or within fishes, they
> might have more useful meaning.

Actually, I disagree with Rich on this one.  Ranks are useful to the extend that they are compatible (they go well) with any hierarchy, but they do not add any value to our knowledge, e.g. what we really know of a group and its descendants.

Nico