By the "biological species concept" that Richard describes, western &
glaucous-winged gulls should perhaps be lumped into one species. If we
wanted to be strictly faithful to this concept, we should also lump most of
the world?s gull species, most species of ducks and geese, and a great many
other types of birds that are prone to hybridize. But the biological species
concept is just one of many species concepts that biologists have proposed
and endlessly argued over. It is a frustrating yet delicious aspect of
biology that a "species" is at once something that most people feel is
undeniably real, and something that is seemingly impossible to define to
everyone?s satisfaction.

DNA analyses can be informative in many ways, including helping to delineate
cryptic species, as Richard describes with the mosquitos. However, they?re
no magic bullet, and do not fundamentally bring us any closer to resolving
the species concept debate. Where and how to draw species boundaries will
always be a subjective exercise -- a human attempt to pigeonhole natural
diversity into neat categories. But of course nature is not so neat. Rather
than view species as static entities that can be neatly categorized, it?s
probably better that we view the gulls, mosquitos, and other organisms
around us as products of speciation, the dynamic process by which species
are created and life diversifies. Because speciation, and evolution in
general, is an ongoing process, it should come as no surprise that when we
look around us in the world, we see instances of all stages of the process.
Western gulls and mallard ducks are so far diverged from each other that
they will never interbreed. However, many gulls that have more recently and
less completely diverged from a common ancestor with western gulls may still
be able to hybridize with them. Likewise, those duck lineages closely
related to mallards may still be able to hybridize with them. Once we view
the birds around us as products of a process by which lineages diverge
gradually from one another through time, all those troublesome philosophical
questions about species identity fade away. Identification challenges and
questions of hybridization still pose trouble for our lifelists, of course,
but they are a natural product -- and good illustration -- of the process
that creates them.

As a relative newcomer to the Tweeters listserv, it?s encouraging to see so
much serious discussion of identification and hybridization. It?s admirable
that so many of our community can apply so much effort, care, and hard-won
knowledge toward resolving the identity of mystifying creatures like vagrant
and/or hybrid gulls. But it?s also worth remembering that if after all our
efforts we still can?t pin a definitive ID on a particular individual,
that?s not necessarily a human failure to be ashamed of. It could just be an
unavoidable outcome of the variation resulting from natural processes. And
that, if anything, is something to celebrate.

Jay Withgott
Portland, OR
...with too much time on his hands, obviously, from not yet coming up to
chase those Renton gulls!
mailto:jwithgott at msn.com

On 1/25/04 11:50 AM, "RIsherwood at aol.com" <RIsherwood at aol.com> wrote:

> Most of the big gulls we see around Port Townsend are Glaucous winged, but
> they have rather black wingtips when seen at rest. My expert friends all tell
> me these are Glaucous winged x Western hybrids. There are lots of them and
> their population seems to be flourishing.
>
> Long ago in high school I was taught that the definition of a species is a
> population of individuals that breed among themselves to produce fertile
> offspring. If this is right then Glaucous winged and Western must be one
> species, as they are certainly achieving this. Maybe some other big gulls
> belong in this one species too....
>
> This would not be good news for the tick hunters, but there is hope.
> Entomologists studying malaria mosquitoes found that the main vector species
> in West Africa was actually six "microspecies" which were separate breeding
> populations but distinguishable only by the banding on their chromosomes.
> Perhaps we all need to buy DNA sequencers.
>
> Richard Isherwood


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