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RE: Extinction scenarios
From: Jonathon Woolf [SMTP:email@example.com]
Sent: Monday, August 17, 1998 5:14 AM
Subject: Re: Extinction scenarios
<<Laurie Bryant's study of Montana nondinosaur vertebrates found a total of
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,
crocodilian. Exactly how many turtle taxa survived is unclear because
fossils are extremely common in the study area, and their taxonomy is
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
of a combination of forty different species. Were _all_ of these species
cosmopolitan that they occured both in Montana and in a refugium half a
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.