Growth  of the Yellowstone grizzly bear
   population,  as  indicated by the number of females observed with cubs
   and the number of cubs.

   The  effective population size (Ne) is based on the breeding potential
   of  a  population,  incorporating  information  about the sex ratio of
   breeding individuals.
Ne = 4NfNm / (Nf + Nm)

   Nf  and  Nm  are  the  numbers  of females and males that successfully
   breed.

   Ne  is  also  affected  bylife  history  traits  such  as family size,
   maturation  age,  genetic  relatedness  among population members, gene
   flow, and population fluctuations.

   Shaffer  estimated  that  a  total grizzly bear population of 70 to 90
   individuals would have a 95% chance of surviving for 100 years. 1