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Re: Extinction scenarios

In a message dated 8/19/98 7:07:26 PM, Betty Cunningham wrote:

<<So what about factors that are not dependant on the animal host such as
Histoplasmosis or Valley Fever, which are nice desease-like fungii?
Could these have a bearing on this discussion?  They aren't true
deseases in that a person inflicted with one (probably?) could not
transmit it.
All you would need in the cases of these is to drive a population into
an area seeded with the fungus.  It might not 'infect' every individual
but it could decimate a population undefended.>>

Nice term, decimate.  This is what virulent organisms often do, take nine-out-
of-ten individuals out of a populate (as smallpox did to the Native
Americans).  Still, the ever-variable immune system is prepared for this, and
the remaining one-in-ten proliferate to produce a disease-resistant
population.  Still no extinction.

Furthermore, environmental pathogens like fungi are notoriously poor killers,
because they are not adapted well to the new environment within the infected
host.  The notion that they could kill even one-in-ten, let alone nine-in-ten,
is unheard of.

Then PTJN wrote:

< as someone with some background in Anthropology, I will note that viral
pandemics have been identified as _stong_ and _ contributing_ factors to
massive populations declines of Paleo-Indian populations in the North America
in the 16th and 17th centuries.  Perhaps those diseases would not, by
themselves, have delivered a death blow to those cultures, but by eliminating
a substantial percentage of the population they certainly dramatically
increased their susceptibility to outside influences that they may otherwise
have been able to resist. 
    The corollary here is that some type of pandemic disease among the
Dinosaurs may have left survivors, for the reasons Tom articulates, but they
would have been few and far between.  Pandemic disease would have left
individual survivors who may have been able to sustain the population in
normal times, but in extraordinary times--such as those that witness a huge
bolide impact--those populations may not have been vigorous or numerous enough
to survive.
    So . . . . is it the disease or the bolide that "caused" the extinction?>

The bolide.  The scenario above is not realistic.  Its analogy breaks down as
follows:  while diseases did indeed decimate Native Americans, those diseases
did not decimate ALL AMERICAN MAMMALS.  Your concept only gets rid of one
species of dinosaur, not all.  This is true because highly lethal
microorganisms are always highly adapted to their hosts, flourishing in
humans, say, but harmless to mice or chimpanzees.
    Tom Hopp