Re: Aboriginal Overkill and Native Burning

Anj Petto (ajpetto@MACC.WISC.EDU)
Tue, 2 May 1995 13:23:53 -0600

Bret Diamond writes:

>1. The natural rate of species extinction (data extrapolated from the
>fossil record, etc.) is two species per year.

The fossil record is notoriously bad for this sort of estimate for several
reasons. First, it presumes that we "know" most of the species that exist
at any one time. Second, it presumes that most of those of which we have a
record are sufficiently preserved to reflect their comings and goings.
Think of all the plants and animals without any hard parts that are very
unlikely to fossilize. Think of all those that live in habitats that are
unlikely to allow or assist in preservation. For a good summary of these
problems with the fossil record as a chronicle of life on earth, see
something like Anna K Behrensmeyer's _Fossils in the Making_ or any more
recent text on taphonomy.

Third problem, this sort of estimate tends to smooth out what seem to be
very significant variations in the rate of extinction from one period of
time to another. Sure, habitat destruction is an important element here;
and we are doing a lot of it right now, ourselves, but it is unclear
whether we are doing any more damage than during any one of the great
extinctions periods in the fossil record -- that is, we have yet to surpass
nature's own swings in extinction rates. (The difference is, of course,
that WE can DO something about it; theoretically, we can stop, decelerate,
or otherwise modify the changes that we are making.)

So, is this really a great upswing in extinction rates, or is it merely a
reflection of better recording and more complete inventories of species
than either the fossil record or 17th Century Natural History can give us?
I think it's a fair question -- sort of in the same light as people seldom
die these days of "natural causes" because they are most likely under a
physician's care at the time of death. Therefore, they tend to die of
*something* and greatly increase the late 20th Century death rates for
certain diseases and conditions that were merely undiagnosed evern a few
decades ago.

>From 1600-1700, there were
>21 species known to have gone extinct. 1700-1800, 36 species. 1800-1900,
>84 species. 1900-1980, 104 species. Projected species loss for 1900-2000,
>185-193 species (Living In the Environment, eighth edition) Number 1
>cause of species extinction--habitat destruction. Some estimates suggest
>that we are currently loosing species at the rate of about four an
>hour-every day.


Andrew J. Petto, PhD
Coalition for Education in the Life Sciences
Center for Biology Education
675 WARF, University of Wisconsin
610 North Walnut Street
MADISON WI 53705-2397

Voice: 608.265-3497
Fax: 608.262-6801
Bitnet: ajpetto@wiscmacc