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Light shining through the mist : a photobiography of Dian Fossey /
Traces the adventurous life of the American woman who worked as a zoologist among the mountain gorillas of the Virunga area of central Africa.
Book
Dominance rank but not body size influences female reproductive success in mountain gorillas
According to life history theory, natural selection has shaped trade-offs for allocating energy among growth, reproduction and maintenance to maximize individual fitness. In social mammals body size and dominance rank are two key variables believed to influence female reproductive success. However, few studies have examined these variables together, particularly in long-lived species. Previous studies found that female dominance rank correlates with reproductive success in mountain gorillas (Gorilla beringei beringei), which is surprising given they have weak dominance relationships and experience seemingly low levels of feeding competition. It is not currently known whether this relationship is primarily driven by a positive correlation between rank and body size. We used the non-invasive parallel laser method to measure two body size variables (back breadth and body length) of 34 wild adult female mountain gorillas, together with long-term dominance and demography data to investigate the interrelationships among body size, dominance rank and two measures of female reproductive success (inter-birth interval N = 29 and infant mortality N = 64). Using linear mixed models, we found no support for body size to be significantly correlated with dominance rank or female reproductive success. Higher-ranking females had significantly shorter inter-birth intervals than lower-ranking ones, but dominance rank was not significantly correlated with infant mortality. Our results suggest that female dominance rank is primarily determined by factors other than linear body dimensions and that high rank provides benefits even in species with weak dominance relationships and abundant year-round food resources. Future studies should focus on the mechanisms behind heterogeneity in female body size in relation to trade-offs in allocating energy to growth, maintenance and lifetime reproductive success.
Journal Article
Positive population trends among meso‐ and megaherbivores follow intensive conservation efforts in Volcanoes National Park, Rwanda
It is unclear whether the remarkable recovery of mountain gorillas Gorilla beringei beringei in the Virunga Mountains, East Africa, that followed decades of intensive conservation efforts, is indicative of positive trends in abundance and distribution of other large mammals (meso‐ and megaherbivores). Positive population trends are particularly relevant for globally threatened elephants Loxodonta sp., as conservation and research efforts have predominantly focused on populations that range in lowland savanna ecosystems rather than the smaller but ecologically and genetically unique populations found in the Virunga montane ecosystems. We used marked pellet group counts in dung clearance plots to determine the density/abundance and distribution of three mesoherbivores (buffalo, black‐fronted duiker, bushbuck) and one megaherbivore (elephant) in Volcanoes National Park (VNP; covering part of the Virunga Mountains), Rwanda, in July–September 2008 and 2021. We estimated that elephants and duiker populations saw a minor increase between 2008 and 2021 while densities of buffalo and bushbuck increased substantially over the course of the past decade. We also found no evidence of substantial distributional shifts for elephants but observed increases in densities of the other species in the southwestern parts of the VNP. Overall, density estimates for all species were much higher in both 2008 and 2021 than in a previous survey in 2004, which suggests that meso‐ and megaherbivores have largely recovered from a steep decline in numbers towards the end of the 20th century, possibly benefitting from the same protection efforts that benefitted mountain gorillas.
Journal Article
Extreme Conservation Leads to Recovery of the Virunga Mountain Gorillas
As wildlife populations are declining, conservationists are under increasing pressure to measure the effectiveness of different management strategies. Conventional conservation measures such as law enforcement and community development projects are typically designed to minimize negative human influences upon a species and its ecosystem. In contrast, we define \"extreme\" conservation as efforts targeted to deliberately increase positive human influences, including veterinary care and close monitoring of individual animals. Here we compare the impact of both conservation approaches upon the population growth rate of the critically endangered Virunga mountain gorillas (Gorilla beringei beringei), which increased by 50% since their nadir in 1981, from approximately 250 to nearly 400 gorillas. Using demographic data from 1967-2008, we show an annual decline of 0.7%±0.059% for unhabituated gorillas that received intensive levels of conventional conservation approaches, versus an increase 4.1%±0.088% for habituated gorillas that also received extreme conservation measures. Each group of habituated gorillas is now continuously guarded by a separate team of field staff during daylight hours and receives veterinary treatment for snares, respiratory disease, and other life-threatening conditions. These results suggest that conventional conservation efforts prevented a severe decline of the overall population, but additional extreme measures were needed to achieve positive growth. Demographic stochasticity and socioecological factors had minimal impact on variability in the growth rates. Veterinary interventions could account for up to 40% of the difference in growth rates between habituated versus unhabituated gorillas, with the remaining difference likely arising from greater protection against poachers. Thus, by increasing protection and facilitating veterinary treatment, the daily monitoring of each habituated group contributed to most of the difference in growth rates. Our results argue for wider consideration of extreme measures and offer a startling view of the enormous resources that may be needed to conserve some endangered species.
Journal Article
Homosexual Behavior in Female Mountain Gorillas: Reflection of Dominance, Affiliation, Reconciliation or Arousal?
Humans are unique among primates for not only engaging in same-sex sexual acts, but also forming homosexual pair bonds. To shed light on the evolutionary origins of homosexuality, data on the occurrence and contexts of same-sex behavior from nonhuman primates may be of particular significance. Homosexual behavior involving females is poorly researched in most primate taxa, exceptions being Japanese macaques, rhesus macaques, Hanuman langurs and bonobos. We present data on homosexual behavior in female mountain gorillas in the Virunga Volcanoes (Rwanda) and test four functional hypotheses, namely reconciliation, affiliation, dominance expression and sexual arousal. Homosexual interactions between females involved both ventro-dorsal and ventro-ventral copulations accompanied by vocalizations and courtship displays. The only sociosexual hypothesis that received partial empirical support is the social status hypothesis, i.e., that mounting reaffirms the dominance hierarchy. There is also some limited evidence that same-sex behavior reflects an overall state of arousal or is triggered via a 'pornographic' effect. An adaptive function of female homosexual behavior is not readily apparent, and we tentatively conclude (until a more rigorous test becomes available) that it may simply be related to sexual gratification or that it is an evolutionary by-product of an adaptation.
Journal Article
Spatial variation in anuran richness, diversity, and abundance across montane wetland habitat in Volcanoes National Park, Rwanda
The spatial distribution of species has long sparked interest among ecologists and biogeographers, increasingly so in studies of species responses to climate change. However, field studies on spatial patterns of distribution, useful to inform conservation actions at local scales, are still lacking for many regions, especially the tropics. We studied elevational trends and species‐area relationships among anurans in wetland habitats within Volcanoes National Park (VNP) in Rwanda, part of the biodiverse Albertine Rift region. In VNP, wetlands are key sites for anuran reproduction, and anurans are likely threatened by wetland desiccation which has occurred for the last few decades. Between 2012 and 2017, we sampled anuran communities in ten VNP wetlands located along an elevational gradient of c. 600 m (from 2,546 to 3,188 m a.s.l.) and found at least eight species, including at least two Albertine Rift Endemics. We show that species richness, diversity, and abundance likely decline with a decrease in wetland size and with an increase in elevation, though additional sampling (e.g., at night) might be needed to derive definite conclusions. Larger wetlands at lower elevations contained most species and individuals, which indicates the potential threat of wetland size reduction (through desiccation) for anuran conservation. However, we also found that wetlands differed in species composition and that some species (e.g., Sclerophrys kisoloensis) were likely restricted in distribution to only a few of the smaller wetlands—suggesting that the conservation of each individual wetland should be prioritized, regardless of size. We propose that all wetlands in VNP require additional conservation measures, which should be based on knowledge gathered through long‐term monitoring of anuran communities and research on drivers of wetland decline. Only such extended research will allow us to understand the response of anurans in VNP to threats such as climate change and wetland desiccation. We found that anuran distribution in wetland habitats within Volcanoes National Park (VNP) in Rwanda, part of the biodiverse Albertine Rift, can be linked to be both altitude and wetland size, with distinct anuran communities found in different wetlands. From our findings, we draw the recommendation that all wetlands in VNP require additional conservation measures and warn that wetland desiccation, and related size reduction will have severe consequences for anuran conservation in the region.
Journal Article
Short‐term trends in great ape density in a community‐based conservation area in the eastern Democratic Republic of the Congo
The forests of eastern Democratic Republic of the Congo (DRC) constitute a biodiversity hotspot and provide habitat to two globally threatened great apes, the Grauer's gorilla Gorilla beringei graueri and eastern chimpanzee Pan troglodytes schweinfurthii. Community‐based conservation activities may provide protection to these primates and their environment, supplementing the role of protected areas. We look at spatiotemporal trends in the ape populations that inhabit a community forest, the Nkuba Conservation Area (NCA), as trends in wildlife abundances and distributions may provide a first tentative measure of conservation impact. In the absence of a single systematic approach to gauge conservation effectiveness, we explore both temporal changes in ape abundances and spatial distributions as lines of evidence. Using line transect data, we estimate that between 1000 and 2200 apes, with comparable numbers of gorillas and chimpanzees, live in the NCA. In contrast to elsewhere in eastern DRC, we found no evidence of a declining ape population or shift in their distribution after the establishment of the NCA (~2012–2013). Spatial models revealed the presence of ape hotspots that remained spatially stable across study years (2013–2020). Practical implication. That apes in the NCA do not experience rapid declines is a cautious but optimistic first sign of the conservation potential of the NCA and its associated intended (i.e. conservation activities) and unintended (e.g. researcher presence) protection interventions. Great ape populations are rapidly declining across eastern Democratic Republic of the Congo, but not in the community‐based Nkuba Conservation Area, where numbers of gorillas and chimpanzees show short‐term signs of stablisation and possible increase over a 7 year period. These trends are a cautious but optimistic first sign of the conservation potential of this community initiative.
Journal Article
Social and ecological factors alter stress physiology of Virunga mountain gorillas (Gorilla beringei beringei)
Living in a rapidly changing environment can alter stress physiology at the population level, with negative impacts on health, reproductive rates, and mortality that may ultimately result in species decline. Small, isolated animal populations where genetic diversity is low are at particular risks, such as endangered Virunga mountain gorillas (Gorilla beringei beringei). Along with climate change‐associated environmental shifts that are affecting the entire population, subpopulations of the Virunga gorillas have recently experienced extreme changes in their social environment. As the growing population moves closer to the forest's carrying capacity, the gorillas are coping with rising population density, increased frequencies of interactions between social units, and changing habitat use (e.g., more overlapping home ranges and routine ranging at higher elevations). Using noninvasive monitoring of fecal glucocorticoid metabolites (FGM) on 115 habituated Virunga gorillas, we investigated how social and ecological variation are related to baseline FGM levels, to better understand the adaptive capacity of mountain gorillas and monitor potential physiological indicators of population decline risks. Generalized linear mixed models revealed elevated mean monthly baseline FGM levels in months with higher rainfall and higher mean maximum and minimum temperature, suggesting that Virunga gorillas might be sensitive to predicted warming and rainfall trends involving longer, warmer dry seasons and more concentrated and extreme rainfall occurrences. Exclusive use of smaller home range areas was linked to elevated baseline FGM levels, which may reflect reduced feeding efficiency and increased travel efforts to actively avoid neighboring groups. The potential for additive effects of stress‐inducing factors could have short‐ and long‐term impacts on the reproduction, health, and ultimately survival of the Virunga gorilla population. The ongoing effects of environmental changes and population dynamics must be closely monitored and used to develop effective long‐term conservation strategies that can help address these risk factors. We investigated how social and ecological variation affect basal fecal glucocorticoid metabolite concentrations in wild Virunga mountain gorillas, to better understand their adaptive capacity and monitor potential physiological indicators of population decline risks. Rainfall, temperature, and exclusive home range size of a group negatively affected stress physiology of this critically endangered population. Findings indicate that effects of climate change and increasing population density must be closely monitored and used to develop effective long‐term conservation strategies that can help address these risk factors.
Journal Article