How many species concepts are there?

Do you remember the definition of species from your high school or college biology class?  Me neither -- but worry not!  Even if you remembered it word for word, there's a good chance it's not the same definition your friends and co-workers learned and it's certainly not the only definition floating around out there.  So how many species concepts are there?

According to John S. Wilkins in his recent guest post over at Punctuated Equilibrium (also here on John's blog) there are either 26-27, 7, 2, 1 or 0.  The article is well worth the read as John gives a nice, brief overview of the many different definitions of a biological species, their similarities and differences, and the key concepts behind those definitions. 


If you don't mind my giving away the punchline, here's what it all boils down to:

Final score: 26-27, 7, 2, 1 or 0.

What to think? My solution is this:

There is one species concept (and it refers to real species).

There are two explanations of why real species are species (see my microbial paper, 2007): ecological adaptation and reproductive reach.

There are seven distinct definitions of "species", and 27 variations and mixtures.

And there are n+1 definitions of "species" in a room of n biologists.

For a more detailed treatment of the idea of biological species, see John's book 'Species: A History of the Idea'.

[Hat tip to John Hawks and GrrlScientist]