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

Colchero, Fernando; Eckardt, Winnie; Stoinski, Tara S.

doi:10.1111/1365-2656.13486

Cited by 3 publications

(7 citation statements)

References 71 publications

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“…Those previous results also resemble the effects of environmental variability, which has shown greater impact on fertility than the survival of adult females [85,86]. If so, then such results would support expectations that demographic buffering against environmental variability will be greatest for the vital rates that have the greatest influence on population growth [87][88][89]. Similarities in the effects of density dependence versus environmental variability may arise when they both reflect the same underlying factors, such as changes in the food availability per capita [90].…”

Section: Density Dependencesupporting

confidence: 59%

Population dynamics of western gorillas at Mbeli Bai

Robbins

Manguette²,

Breuer³

et al. 2022

PLoS ONE

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Long-term studies of population dynamics can provide insights into life history theory, population ecology, socioecology, conservation biology and wildlife management. Here we examine 25 years of population dynamics of western gorillas at Mbeli Bai, a swampy forest clearing in Nouabalé-Ndoki National Park, the Republic of Congo. The Mbeli population more than doubled from 101 to 226 gorillas during the study. After adjusting for a net influx of gorillas into the study population, the increase represents an inherent growth rate of 0.7% per year, with 95% confidence limits between -0.7% and 2.6%. The influx of gorillas mainly involved immigration of individuals into existing study groups (social dispersal), but it also included the appearance of a few previously unknown groups (locational dispersal). The average group size did not change significantly during the study, which is consistent with the possibility that western gorillas face socioecological constraints on group size, even when the population is increasing. We found no significant evidence of density dependence on female reproductive success or male mating competition. The distribution of gorillas among age/sex categories also did not change significantly, which suggests that the population had a stable age structure. Our results provide evidence of population stability or growth for some western gorillas (albeit within a small area). The results highlight the value of law enforcement, long-term monitoring, and protected areas; but they do not diminish the importance of improving conservation for this critically endangered species.

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Section: Density Dependencesupporting

confidence: 59%

Population dynamics of western gorillas at Mbeli Bai

Robbins

Manguette²,

Breuer³

et al. 2022

PLoS ONE

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“…We used the stochastic projection model proposed by Colchero et al . 51 , that models population dynamics for both sexes on fully age-dependent demographic rates. The model incorporates the yearly variance–covariance between demographic rates, while it accounts for infanticide as a function of the number of silverbacks (mature males > 12 years old) in the population 51 .…”

Section: Methodsmentioning

confidence: 99%

“… 51 , that models population dynamics for both sexes on fully age-dependent demographic rates. The model incorporates the yearly variance–covariance between demographic rates, while it accounts for infanticide as a function of the number of silverbacks (mature males > 12 years old) in the population 51 . Because of this relationship between infanticide and number of silverbacks, this source of mortality changes in time and cannot be assumed to be part of the infant mortality rate.…”

Section: Methodsmentioning

confidence: 99%

“…We constructed a predictive population model that combines the species’ baseline demographic rates with a model based on the susceptible-infected-recovered-susceptible (SIRS) framework. As the baseline demographic rates, we used the age-specific mortality and fecundity estimated by Colchero et al 51 for mountain gorillas (Karisoke subpopulation). We defined four epidemiological stages, namely (a) susceptible, (b) infected, (c) immune and (d) dead, each of which we further divided into a fully age-specific structure (Fig.…”

Section: Methodsmentioning

confidence: 99%

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RETRACTED ARTICLE: Exploring the potential effect of COVID-19 on an endangered great ape

Colchero

Eckardt

Stoinski

2021

Sci Rep

Self Cite

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The current COVID-19 pandemic has created unmeasurable damages to society at a global level, from the irreplaceable loss of life, to the massive economic losses. In addition, the disease threatens further biodiversity loss. Due to their shared physiology with humans, primates, and particularly great apes, are susceptible to the disease. However, it is still uncertain how their populations would respond in case of infection. Here, we combine stochastic population and epidemiological models to simulate the range of potential effects of COVID-19 on the probability of extinction of mountain gorillas. We find that extinction is sharply driven by increases in the basic reproductive number and that the probability of extinction is greatly exacerbated if the immunity lasts less than 6 months. These results stress the need to limit exposure of the mountain gorilla population, the park personnel and visitors, as well as the potential of vaccination campaigns to extend the immunity duration.

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“…Veterinary interventions in particular may explain the increased survival of the oldest females, through reducing mortality from infectious disease, to which senescing individuals are especially susceptible (Didier et al ., 2016). Adult females have particular reproductive value for population growth (Colchero, Eckardt, & Stoinski, 2021). Given that mountain gorilla females continue reproducing up until death (Robbins et al ., 2006; Alberts et al ., 2013), this increase in female life expectancy is likely to have also benefitted reproductive output.…”

Section: Discussionmentioning

confidence: 99%

Cascading effects of social dynamics on the reproduction, survival, and population growth of mountain gorillas

Morrison

Hirwa

Ndagijimana

et al. 2022

Animal Conservation

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Whilst 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.

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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

Cited by 3 publications

References 71 publications

Population dynamics of western gorillas at Mbeli Bai

Population dynamics of western gorillas at Mbeli Bai

RETRACTED ARTICLE: Exploring the potential effect of COVID-19 on an endangered great ape

Cascading effects of social dynamics on the reproduction, survival, and population growth of mountain gorillas

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