Dan,

You say "populations" are "difficult to define" but also precisely
defined." Is there a paradox here? How can one precisely define a
population that extends throughout an extensive habitat, e.g., Song
Sparrows around here, with no clear habitat divisions to isolate breeding
populations? Do populations then vary in size from a few pairs that nest
in an isolated patch of riparian woodland to nearly continent wide
extensions of species such as robins? Is there an arbitrary statistical
watershed with respect to rates of gene exchange?

Gene Hunn.

On Sun, 4 Feb 1996, Dan Stephens wrote:

> In message <Pine.ULT.3.91.960204142913.10036D-100000 at elwha.evergreen.edu>
> Burton Guttman writes:
> >
> > Maureen Ellis asked for "the standardized correct use for the following
> > terms in differentiating birds: Race, morph, phase, population,
> > subspecies, variant, form." I'll reply to the whole gang, in case some
> > people disagree with me.
> >
> > _Population_ refers generally to all the individuals of one species living
> > in one area, but it is vague because "area" has no set limits. If the
> > area has a distinct boundary, as an island does, the limits are more
> > obvious, but since birds are so mobile one can rarely set definite limits
> > on a population.
> >
>
> > If anyone disagrees with these definitions, let's meet in a marsh
> > somewhere and have a good knock-down, drag-out argument.
> >
> Burt, I am not looking for a knock-down, drag-out (and certainly not one
> in a marsh). However, "Where all men think alike, no one thinks very much".
> For a population biologist your definition of a population is wholly inadequate.
>
> A population includes all members of a species living in a particular
> geographical area *and making up one breeding group*. Sometimes this
> clumping or aggregation is easily seen such as in a colony of seabirds on
> an island as you mentioned. Other times these aggregations are due to
> favorable hatitat intermixed with unfavorable areas. For example I show
> my students a population of Yellow-breasted Chats at my banding station.
> They can't see the entire population at once, but they can "see" the riparian
> zone they use for breeding in the summer, extending for about 6 miles along
> the creek.
>
> A population is a specific "step" in the levels of biological organization-
> between an organism and a species. Organisms are organized into populations
> which are organized into species. Populations are immersed in the landscape,
> they interact with their environment in complex and subtle ways. In fact,
> populations can not be separated from their landscapes without destroying them.
>
> Populations, like ecosystems, are difficult to define due to their conceptual
> nature, and geographical nebulousness. I like MacArthur's analogy: 'Populations
> are the actors, ecology is the stage, and evolution is the play'. Populations
> are the units that evolve, they are quite precisely defined, and understanding
> them is essential for biologists studying above the organismal level.
>
> To change the subject slightly: Maureen mentioned that she had learned to use
> the terms juvenile, immature and subadult. I would be interested in her
> definitions. Juvenile/Juvenal is commonly missused: we refer an individual that
> is between its natal down and its first basic plumage (first winter plumage) as
> a juvenile (a noun). This bird is in its juvenal plumage (an adjective). This
> plumage is almost always seen in the late summer and fall. Immature usually
> refers to any plumage that is not adult. Subadult to the plumages between
> juvenal and adult in those species that take several molts to reach their
> definitive adult plumage (e.g. Gulls, Eagles).
>
> Well, back to grading papers.
>
>
>
>
>
>
>
> Dan Stephens (509) 662-7443
> Dept. of Biology fax: (509) 664-2538
> Wenatchee Valley College e-mail: dstephen at ctc.edu
> 1300 Fifth Street
> Wenatchee, WA 98801
>
>