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Thursday, October 8, 2009

Re: BRYONET: local endemics


The word "species" is used in many ways by biologists, and it pays to
be sensitive to the different meanings. There are alternative words
one can use if one is trying hard to be understood, but it adds some
awkwardness to the language.

In a local community, the things we call "species" are not
necessarily very close relatives, and the representation of diversity
is not comprehensive. Many of us as local naturalists delight in
recognizing the "species" in our area, the habitats that they occur
in and don't occur in, and which other "species" they occur with or
seem to avoid. I have spent a great deal of time studying
interactions between "species," such as pollination interactions and
interactions between plants and their insect parasites (you probably
call them herbivores). But, when I use the word "species" to talk
about those entities that have a local ecology and morphology, I am
not comparing one to the next in the same way that I would be if I
were trying to treat the diversity in (say) a genus of mosses as they
vary geographically and non-geographically throughout the world. Both
the local naturalist and the geographically-sensitive systematist use
the word "species," and the nexus is a thrilling one, but no one
should think that there is only one usage for the word "species" when
we talk of all of this. An endemic species is not a species in the
same way that a species in a local community is a species.

There is a huge literature on this topic that people who have come to
biology via mosses might not be as aware of as Brent, Dave, and me.
It might help to introduce some other words to the dialog, if not to
banish the word "species" at least to clarify its many meanings. What
Brent is talking about are clades, and real clades are manifest at
every gradation of level imaginable (crudely and violently rank-able
as subspecies, species, subsections, sections, subgenera, genera,
etc.). When I am studying the "species" in a local community, I am
generally interested in entities called avatars. An avatar is an
actor on the ecological stage. It is avatars whose population size
grows or diminishes in a landscape, who do better than other avatars
in dry spots or in wet spots, who are eaten preferentially over other
avatars by a certain kind of beetle, and more generally who divvy up
the niches in Sequoia National Park ;-} The word avatar was brought
into the biological literature to contrast it to the word deme, demes
being the things that are variously related to other demes, usually
in at other places. As evolution proceeds, often but not always in a
geographic context, demes have diverged by gradual changes in
genetics, shifts from one life-style to another in a punctuated
fashion, secondarily interbred with other demes that might be close
relatives or fairly distant relatives, and in many other ways come to
be peculiar. A deme may graduate into a clade. The grouping above
avatar is a guild. I think you get my drift.

Meanings corresponding to "avatars" versus "demes" or "clades" versus
"guilds" are not the only meanings that are conveyed when one uses
the word "species" in various conversations. For example, biologists
will often tell you that such-n-such is species-specific, but how
specific is that? Very often it is well above the level that any
systematist would call a species. Mistletoes that mostly occur on
oaks, mistletoes that mostly occur on sycamores, and mistletoes that
mostly occur on conifers could more accurately be said to be clade-
specific, but even that is not quite right. Another big
terminological train wreck is that around 1940 the word "speciation"
came to mean the acquisition of reproductive isolating barriers
between evolving entities, these entities being spoken of as
biological species (very often leaving off the adjective
"biological"). But it is clear that speciation in this sense can
happen long after the entities have diverged to be dramatically
distinct, or in other instances long before. The word "speciation" is
so entrenched in describing a subject of great interest in
evolutionary biology that there is no chance of getting rid of it,
but one has to be clear-headed enough to realize that there's no
close correspondence between biological species and avatars or
coalescent clades or nominal species like Pseudoleskeella tectorum
and Pseudoleskeella catenulata. You have to know what I'm talking
about from context.

I agree with Brent that clades are real but ranking them can only be
done crudely and the ranking is misleading if treated as meaning much
of anything more than a way of keeping track of biodiversity.
Actually, I doubt this is all that controversial among people in the
business, if they could only all agree to use my semantics. True,
some people working with some organisms can make a case that the
lowest rank of species in ideal circumstances is different, but that
is almost never the case because real organisms are related to other
organisms that live in different places, and the whole thing has come
to be the way it is historically. I am not as eager as Brent,
however, to abandon our vague and slippery usage. I think this is
because I'm pretty sure I wouldn't be able to get my students to use
words like avatar if their lives depended on it. We are going to keep
on using the same word for several different but not-entirely-
different meanings, just like democrat and Democrat.

Respectfully my 2 cents,
Paul Wilson
California State University

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