DOI: 10.5061/dryad.b2rbnzsdx
title: 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

description: 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.
description: The study was carried out in Volcanoes National Park in Rwanda,
 on the groups of habituated mountain gorillas monitored by the Dian Fossey
 Gorilla Fund’s Karisoke Research Center, often referred to as the Karisoke
 subpopulation. Since 1967, groups in this subpopulation have been
 monitored and protected on a near daily basis. Through the mid 2000s, the
 Karisoke groups generally numbered three but over the last decade, group
 fissions and new group formations resulted in an average of 10 groups in
 the region (see Caillaud et al, 2014). During daily observations, detailed
 demographic data were recorded, such as dates of birth and death, dates
 and types of individuals’ entry (immigrants) and departure (emigrants)
 from the study population, group composition, and maternal relatedness
 (for further details see Strier <i>et al</i>. 2010 and Granjon
 <i>et al.</i> (2020). In particular, groups were frequently
 monitored (daily between 2010-2016), and the arrival of a new individual
 to a monitored group was recorded as immigration. When individuals were
 lost to follow, depending on age, sex, health and group movement
 individuals could be classified as emigrated. However, when in doubt, the
 fate was recorded as unknown (Granjon <i>et al.</i>
 2020).
description: The Survival data consist of the number of individuals per age
 and sex (F = female, M = male, U = unknown), and per detection class.
 These are: a) 'Alive' when individuals entering the age interval
 survived until the end of the interval; b) 'Died' when
 individuals entering the age interval died during the interval; c)
 'Censored' individuals known to have survived but were then not
 seen again (e.g. out-migration); and d) 'Disapeared' individuals
 that were not detected but their fait was unknown (i.e. they could have
 out-migrated or die). The reproduction data consist of
 the number of females of a given age present at the study population
 within the study period, as well as the total number of infants produced
 by females of that age.  The data consist of three
 columns: Age, Females, Infants. The Age column starts at the age at sexual
 maturity for mountain gorillas until the last age a female was present in
 the study. Columns Females and Infants depict the total number of each
 category for each female age.