more on species

[warrena at bcc.orst.edu]

Thanks to Chris Durden for a different perspective!

Chris starts by providing various definitions for 
species (a good idea!), and clearly illustrates 
that "species" has different meanings in the worlds of 
geology and biology.  "Species" in geology 
and "species" in biology are similar only in that they 
they are a "kind"; beyond this the similarities fade.  

Asexual organisms are only considered to be species 
under some species concepts (they are usually called 
lineages under species concepts that don't recognize 
asexual "species.").  This is a minor point, but 
illustrates how different species concepts view the 
terminology in different ways.  

Chris demonstrates that "subspecies" in mammals are not 
equivalent to subspecies in corals or subspecies in 
butterflies (must be allopatric in mammals but can can 
have narrow zones of overlap in insects and broad zones 
of overlap in corals).  

So if the species (subspecies) problem is so simple, 
why is there no standard definition of subspecies that 
can be applied to species in these different groups?  
Having one group of animals where subspecies are 
allopatric populations, but having another where 
subspecies meet and blend is not a simple solution to 
the problem (how about bacteria, viruses, plants?).  

Note that the use of niches as characters we can use to 
define species or subspecies is linked to a certain 
species concept (they would be irrelevant to some 
species concepts). 

The real problem seems to be exactly how to describe 
and communicate geographical variation.  Everyone 
agrees on the use of species, but that is where the 
agreement ends.  I don't claim to have the answers but 
hope these posts cause us to think about this and 
evaluate how we deal with this in our everyday lives...

I recently read about several salamanders that exist as 
asexual lineages but are placed in genera with sexually 
reproducing species (like Ambystoma jeffersonianum- 
apparently a product of a hybridization event; 
reproductive females mate with A. platineum but the 
sperm does not fertilize the egg- it only stimulates 
egg development).  It is in cases like this, in my 
opinion, that challenge species concepts and force us 
to take a philosophical look at the meaning 
of "species" in the biological sense.  

Andy




 
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