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RE: Extinction scenarios




-----Original Message-----
From:   Jonathon Woolf [SMTP:jwoolf@erinet.com]
Sent:   Monday, August 17, 1998 5:14 AM
To:     TomHopp@aol.com
Cc:     dinosaur@usc.edu
Subject:        Re: Extinction scenarios

<<Laurie Bryant's study of Montana nondinosaur vertebrates found a total of 
more
than forty species that occur on both sides of the K-T boundary: 10 fish, 7
salamander, 3 frog, over a dozen turtle, 1 champsosaur, 4 lizard, 1 snake, 
3
crocodilian.  Exactly how many turtle taxa survived is unclear because 
turtle
fossils are extremely common in the study area, and their taxonomy is 
somewhat
muddled.  I submit that while the replacement scenario may explain one or 
two or a
few species appearing both before and after, it does not explain the 
reappearance
of a combination of forty different species.  Were _all_ of these species 
so
cosmopolitan that they occured both in Montana and in a refugium half a 
world
away?  Rather unlikely, I think.>>

This feeds into a speculation I had the other day.  The question I was 
trying to address is how we can sort out the effects of the killing agent 
from the effects of post-apocalyptic competition.

Years ago I was involved in a study of ecological succession on spoil 
islands left by channel dredging in Florida.  One of the interesting 
conclusions we reached was that the mature community on a spoil island, at 
least on scales of 10-20 years, was not  necessarilly the same as the 
surrounding ecosystem.  Perhaps conditions had changed somewhat since the 
native turtle grass - mangrove - palmetto series had been established.  For 
whatever reason, these new, completely barren islands seemed headed for a 
rather different ecological fate.  The native group, while quite capable of 
sustaining itself in undisturbed areas, was no longer capable of 
re-establishing itself through succession.

Now multiply that study by a factor of millions.  That is, suppose the 
surface of the earth is largely barren and that 99.5% of *everything* has 
been wiped out.  Even if not a single species is made actually extinct by 
the catastrophe, the ecological picture has been fundamentally changed. 
 First, for a good many years, the system will be one of constantly 
changing succession.  Second there is no guarantee that the climax 
conditions would be the same as the original, pre-apocalyptic community, 
particularly since recruitment from undisturbed areas would be unimportant.

These factors, rather than selective killing, could be responsible for 
virtually all of the extinction which occurred.  The study you cite 
suggests that this speculation may not be too far-fetched.

  --Toby White