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I bow to Tom Hopp's expertise on viral epidemiology but I'm not sure that
anyone on the list is ecologically unsophisticated enough to think that
such epidemics often cause extinction (there are numerous examples of
balances being struck between infector and infectee once the infectee has
declined in number and/or been split up inyo isolated populations). The
point is that diseases may cause massive population decline and extinctions
are *always* preceeded by massive population decline which, for the
unfortunate, and for whatever reason, happens to progress all the way to
zero. Raup has made this point repeatedly in the context of palaeontology
and it is universally accepted in ecology that extinction is more likely in
small populations than large ones, and particularly in populations that
once were large and have now become small.

I'm afraid I missed the original e-mail from Jaime but if this is all about
faunal mixing at the end of the Cretaceous as a possible extinction
mechanism, then disease would only have been one of a complex of problems
that occur when previously isolated communities collide. Disease would
probably not have been the ultimate mechanism of extinction but it
certanily could have been a primary factor in population decline and thus a
contributory factor in eventual extinction.

Chris Lavers