Data from: Evidence of demographic buffering in an endangered great ape: Social buffering on immature survival and the role of refined sex-age-classes on population growth rate

Theoretical and empirical research has shown that increased variability in
demographic rates often results in a decline in the population growth
rate. In order to reduce the adverse effects of increased variability,
life-history theory predicts that demographic rates that contribute
disproportionately to population growth should be buffered against
environmental variation. To date, evidence of demographic buffering is
still equivocal and limited to analyses on a reduced number of age-classes
(e.g. juveniles and adults), and on single sex models. Here we used
Bayesian inference models for age-specific survival and fecundity on a
long-term dataset of wild mountain gorillas. We used these estimates to
parameterize two-sex, age-specific stochastic population projection models
that accounted for the yearly covariation between demographic rates. We
estimated the sensitivity of the long-run stochastic population growth
rate to reductions in survival and fecundity on ages belonging to nine
sex-age-classes for survival and three age-classes for female fecundity.
We found a statistically significant negative linear relationship between
the sensitivities and variances of demographic rates, with strong
demographic buffering on young adult female survival and low buffering on
older female and silverback survival and female fecundity. We found
moderate buffering on all immature stages and on prime-age females.
Previous research on long-lived slow species has found high buffering of
prime-age female survival and low buffering on immature survival and
fecundity. Our results suggest that the moderate buffering of the immature
stages can be partially due to the mountain gorilla social system and the
relative stability of their environment. Our results provide clear support
for the demographic buffering hypothesis and its predicted effects on
species at the slow end of the slow-fast life history continuum, but with
the surprising outcome of moderate social buffering on the survival of
immature stages. We also demonstrate how increasing the number of
sex-age-classes can greatly improve the detection of demographic buffering
in wild populations.