Abstract
AbstractWhilst the conservation impacts of density‐dependent population effects have been well studied, the impact that socially‐driven changes (e.g. group fissions that increase group density) can have on population growth in social species have only recently come to light. An increase in group density and intergroup encounters in a subpopulation of mountain gorillas Gorilla beringei beringei was shown to have driven a more than fourfold increase in infanticide, slowing population growth. In this study, we delve deeper into the consequences of these socially‐driven changes in group density, examining how patterns of reproduction and survival have changed in this subpopulation across more than 50 years. We show that adult female survival increased with strengthening conservation efforts early in the study, then remained stable, while age at first birth remained stable across the entire study. Interbirth intervals and female reproductive success did not vary significantly across time overall. However, socially‐driven increases in group density since the mid‐2000s appear to have had a cascade of effects. In addition to the increase in infant and adult male mortality from violence during intergroup encounters, higher encounter rates, and mortality were likely responsible for an increase in female transfers, which delayed reproduction. Females faced a 7.5‐month delay when transferring once and a 1.5‐year delay when transferring twice or more between births. We show these changes correspond with a 26.63% reduction in female reproductive success in 2007 to 2018, compared to 1994 to 2006, with females taking more than 2 years longer to produce an offspring that survived infancy. These findings demonstrate that social dynamics can have consequences for population growth beyond the immediate mortality effects of violent encounters. This further highlights the critical importance of social dynamics in the conservation of social species, particularly when populations are restricted to small or fragmented regions of habitat.
Published Version
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