Art,
 
I think that you are on the right track--a vague general definition with
refinements for various groups of organisms. However, I don't think that
even a vague general definition of species exists that would be universally
acceptable.
 
Donald A. Levin (1979, Science 204:381-384) writes "the characteristics and
diversity of higher plant genetic systems and reproductive modes preclude
the application of a universal plant species concept." If botanists cannot
agree, certainly all biologists are not going to agree.
 
Levin states further that species concepts "are only tools that are
fashioned for characterizing organic diversity." John A. Endler (1989,
Speciation and its consequences, p. 625) expands Levin's tool analogy:
 
"Just as there are a variety of chisels made for different purposes,
different species concepts are best for different purposes; and just as it
is inadvisable to use a carving chisel to cut a mortise, problems arise when
one species concept is used when it is inappropriate. Confusion and
controversy have often resulted because different people working with
different groups of organisms mean different things by "species". There are
at least four major differences in aims of species concepts: (1) taxonomic
vs. evolutionary, (2) theoretical vs. operational, (3) contemporaneous vs.
clade, (4) reproductive vs. cohesive. These contrasts are somewhat
arbitrary, grade into each other, and give only a flavor of the various
meanings of the word "species" in the literature..."
 
I think it will be difficult to come up with a species concept that all
malacologists would agree to. May we should start there.
 
Gary
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Gary Rosenberg, Ph.D.                     [log in to unmask]
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