Re: Help my foggy memory please!

[Stan Friesen <swf@tdat.ElSegundoCA.NCR.COM>]

  >
 > The possibly overblown claim was that we have (in the
 > recent past, I said since the Industrial Revolution) had
 > killed off and were still killing off about the same number
 > of species (I meant in percentage terms, I guess) as when
 > the dinosaurs died out; in other words, we are artificially
 > creating one of the great biological extinction events that
 > some think happen every 26 million years ago.
 >
 > So, exactly what is the scoop?  Have we already done so?
 > Are we going to do so in a mere couple of years?

At least so far, the total number of extinctions just
qualifies as a *minor* extinction event - *even* if you
count all of the Late Pleistocene extinctions.

Now, it *is* true that if we continue this rate of extinction
for a great many more years we will have reached a level of
extinction matching the 5 biggies (of which the dinosaur extinction
was the last).
 >
 > I also have read/heard claims that something like half of
 > the land species exist in the Amazon basin and the claim is
 > we'll wipe most of it out in a couple more decades of slash
 > and burn agriculture.  Is the 50% number (or something very
 > like it) true?  Have we already wiped out a large number of
 > species there?

Probably and yes.

That is, the number of species is *vastly* higher in a given
area of tropical rain forest than in any other habitat.  By
extrapolating from known censuses, estimates of the total
diversity in the tropics all cluster around 50% or *higher*.
 >
 > Can anyone cite some sources that either confirm it or
 > semi-confirm it?

Almost any good *scholarly* work on either biogeography
or tropical rain forests will do.  Try a *university*
library near you for the best references.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.