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Re: dino extinction



From: Jeffrey Martz <martz@holly.ColoState.EDU>
 >      In regard to the "coincidental multi-causal" idea, what are some
 > opinions and critiques of D. Raup's kill curve of extinctions?  He plotted
 > all extinctions on a graph (with number of species going extinct on the
 > Y axis, I can't remeber waht the x-axis was) that made a nice, smooth
 > curve.  In other words, ...
 > but rather that there are all sizes of extinctions
 > and the larger the extinction, the more rare it is.

This is pretty much what one would expect for multicausal models.

It also fits with what I know of the fossil record (there are rather
many of mid-sized mass extinctions, and *some* species go extinct in
every geological interval).

The curve he probably gets is something like an exponential probability
distribution, or at least that would be my expectation.

 >  He likened it to how
 > people generally have averge days, with occaisional bad days, and rarely
 > real bad days, just on the likelyhood of a certain NUMBER of crappy
 > things happening to you coincidentally in the course of 24 hours (at
 > least, thats what I think he meant-its been a while since I read his book).

Quite so.  And this model does indeed produce an exponential probability
distribution.

 > ...
 > Even if one factor only weakens a species, the more bad luck you stack
on, the
 > more likely you are to reduce numbers even more.

Exactly.  A species already damaged by one cause is more susceptible to
others.

[For instance, part of the reason that the California condor is
threatened today is that the current climate is not really well-
suitee to it to begin with - it might well be on its way to extinction
even without our influence (though this is hard to determine)].

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

The peace of God be with you.