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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
> Even if one factor only weakens a species, the more bad luck you stack
> more likely you are to reduce numbers even more.
Exactly. A species already damaged by one cause is more susceptible to
[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)].
The peace of God be with you.