>I keep hearing people throwing around terms like "sustained population". Is
>there a certain time frame that is accepted by the scientific community? 100
>years? 1 million years?
>500 generations?
 
 
Often sustainable population refers to a certain population size necessary
to prevent problems due to extreme inbreeding.  There is not a direct
reference to time; indirectly, the relevant time would depend on the time
required for a new generation.
 
To determine if a population is declining, we can only rely on the amount
of time during which we have records.  The fossil and subfossil record
gives some indication, but shells last a long time and can be redeposited.
We do not have a good way to determine the precise rate at which shells
accumulate (except possibly for shells that were alive during atmospheric
nuclear bomb tests and thus can be precisely dated).
 
David Campbell
 
"Old Seashells"
 
Department of Geological Sciences
CB 3315 Mitchell Hall
University of North Carolina at Chapel Hill
Chapel Hill NC 27599-3315
USA
 
919-962-0685
FAX 919-966-4519
 
"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
Gold Bug