Re: Dinosaurs to birds--Survival Rates

[Philidor11@aol.com]

In a message dated 1/24/99 12:16:57 AM Eastern Standard Time,
sarima@ix.netcom.com writes:

<< If the probability of an individual surviving is, say, one in a
 >million, and the population is ten thousand, then one would expect the
entire
 >population to be destroyed. But if the population is ten million, then one
 >would expect about ten individuals to survive. >>

In a random environment such as the lottery, you'd be correct on average,
though any single trial could vary a great deal from the average.  However, in
a situation in which survival depends on conditions in a small geographic area
I expect that other factors would be involved.
For example, say a cloud of poison gas covers an entire area except for a
single sheltered valley.  If the 10,000 are herd animals and many are in that
valley, thousands would survive.  If the 10,000,000 are spread thinly over the
entire area, perhaps a few hundred might be in the valley and survive. 
The other part of the problem, for me, is breeding populations:  if a single
breeding pair survived the genetic variation would be small and, as I
understand it, the chances for survival would also be small.  The cheetahs
mentioned previously are an example.  Therefore, wouldn't a species' survival
imply that a large number of individuals had survived?