  Demographic stochasticity is important in determining extinction risks of
small populations, but it is largely unknown how its effect depends on the life
histories of species. We modeled effects of demographic stochasticity on
extinction risk in a broad range of generalized life histories, using matrix
models and branching processes. Extinction risks of life histories varied
greatly in their sensitivity to demographic stochasticity. Comparing life
histories, extinction risk generally increased with increasing fecundity and
decreased with higher ages of maturation. Effects of adult survival depended on
age of maturation. At lower ages of maturation, extinction risk peaked at
intermediate levels of adult survival, but it increased along with adult
survival at higher ages of maturation. These differences were largely explained
by differences in sensitivities of population growth to perturbations of
life-history traits. Juvenile survival rate contributed most to total
demographic variance in the majority of life histories. Our general results
confirmed earlier findings, suggesting that empirical patterns can be explained
by a relatively simple model. Thus, basic life history information can be used
to assign life-history-specific sensitivity to demographic stochasticity. This
is of great value when assessing the vulnerability of small populations.
