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Linda Vigilant - One of the best experts on this subject based on the ideXlab platform.
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The geographic distribution of genetic diversity within Gorillas.
American journal of primatology, 2015Co-Authors: Tillmann Fünfstück, Linda VigilantAbstract:Gorillas, like all non-human great apes, are endangered. Understanding the distribution of genetic diversity across their range is important because low diversity may arise in small populations through increased inbreeding, and, by reducing reproductive fitness, may lead to decreased chances of persistence of a given population. Previous studies found higher genetic diversity in the Western (Gorilla Gorilla) than in the eastern Gorillas (Gorilla beringei), but rarely employed individuals of known geographic origin to investigate the distribution of diversity across multiple populations. The present study fills that gap by analyzing 1,161 individuals from nine sites across all four currently recognized Gorilla subspecies. Genetic diversity at each site was estimated using published data from seven highly-variable microsatellite loci. We found that the small and fragmented populations of Cross River Gorillas, eastern lowland Gorillas and mountain Gorillas were less diverse than any of the five analyzed Western lowland Gorilla populations. The higher levels of genetic variation within the Western lowland Gorillas might be best explained by the facts that they (i) exhibit larger present and past effective population sizes than the other subspecies and (ii) maintain higher rates of gene flow through the existence of largely continuous habitat within their range. With regard to conservation, the high genetic diversity within Western lowland Gorillas is encouraging and retention of dispersal corridors between already protected areas is essential. Am. J. Primatol. 77:974-985, 2015. © 2015 Wiley Periodicals, Inc.
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historical sampling reveals dramatic demographic changes in Western Gorilla populations
BMC Evolutionary Biology, 2011Co-Authors: Olaf Thalmann, Mimi Arandjelovic, Katerina Guschanski, Daniel Wegmann, Marie Spitzner, Christoph Leuenberger, Richard A Bergl, Linda VigilantAbstract:Background: Today many large mammals live in small, fragmented populations, but it is often unclear whether this subdivision is the result of long-term or recent events. Demographic modeling using genetic data can estimate changes in long-term population sizes while temporal sampling provides a way to compare genetic variation present today with that sampled in the past. In order to better understand the dynamics associated with the divergences of great ape populations, these analytical approaches were applied to Western Gorillas (Gorilla Gorilla) and in particular to the isolated and Critically Endangered Cross River Gorilla subspecies (G. g. diehli). Results: We used microsatellite genotypes from museum specimens and contemporary samples of Cross River Gorillas to infer both the long-term and recent population history. We find that Cross River Gorillas diverged from the ancestral Western Gorilla population ~17,800 years ago (95% HDI: 760, 63,245 years). However, gene flow ceased only ~420 years ago (95% HDI: 200, 16,256 years), followed by a bottleneck beginning ~320 years ago (95% HDI: 200, 2,825 years) that caused a 60-fold decrease in the effective population size of Cross River Gorillas. Direct comparison of heterozygosity estimates from museum and contemporary samples suggests a loss of genetic variation over the last 100 years. Conclusions: The composite history of Western Gorillas could plausibly be explained by climatic oscillations inducing environmental changes in Western equatorial Africa that would have allowed Gorilla populations to expand over time but ultimately isolate the Cross River Gorillas, which thereafter exhibited a dramatic population size reduction. The recent decrease in the Cross River population is accordingly most likely attributable to increasing anthropogenic pressure over the last several hundred years. Isolation of diverging populations with prolonged concomitant gene flow, but not secondary admixture, appears to be a typical characteristic of the population histories of African great apes, including Gorillas, chimpanzees and bonobos.
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Effective non-invasive genetic monitoring of multiple wild Western Gorilla groups
Biological Conservation, 2010Co-Authors: Mimi Arandjelovic, Martha M Robbins, Christophe Boesch, Josephine Head, Hjalmar S. Kühl, Fiona Maisels, Linda VigilantAbstract:Obtaining reliable population size or abundance estimates of endangered species is critical for their conservation and management. Genotyping non-invasively collected samples is an effective way to gain insights into the number and grouping patterns of rare or elusive animals. In this study we used genetic capture–recapture estimators to obtain a precise estimate of the size of a Western Gorilla population inhabiting an intensely sampled 101 km 2 area in Loango National Park, Gabon. Using 394 putative Gorilla samples collected opportunistically over a 3 year period, we identified 83 unique genotypes. We used a rarefaction curve, Bayesian estimator and two maximum-likelihood methods to estimate that between 87 and 107 individuals used the study area between February 2005 and September 2007. The confidence interval surrounding the genetic estimate was smaller than that obtained using traditional ape survey methods. In addition, genetic analysis showed that Gorilla and chimpanzee faeces were identified with 98% and 95% accuracy in the field, respectively. Patterns of co-occurrence of individual Gorillas suggest that at least 11 Gorilla social groups and five lone silverback males lived in the study area and that several individuals transferred between groups during the 3-year study period. When properly designed and implemented as part of a long-term biomonitoring program, genetic capture-recapture should prove an invaluable tool for evaluating, even on a large-scale, the population size and dynamics of apes and other elusive species.
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Genetic identification of elusive animals: re‐evaluating tracking and nesting data for wild Western Gorillas
Journal of Zoology, 2008Co-Authors: Brenda J. Bradley, Diane M. Doran-sheehy, Linda VigilantAbstract:Western Gorillas Gorilla Gorilla have been exceedingly difficult to habituate to the presence of human observers. Nevertheless, researchers have amassed a wealth of information on population densities and group structure for this ape species by locating and counting the sleeping nests of wild individuals. Such nest-count studies have suggested that Western Gorilla groups often have multiple silverbacks and these multimale groups occasionally divide into smaller subgroups. However, observational data from forest clearing sites and from a few recently habituated Western Gorilla groups show no evidence of multimale family groups or of subgrouping. This discrepancy underscores a long-standing question in ape research: How accurately do nesting sites reflect true group compositions? We evaluated these indirect measures of group composition by using DNA from faeces and hair to genetically identify individual Gorillas at nesting sites. Samples were collected from unhabituated wild Western Gorillas ranging near Mondika Research Center in the Central African Republic and Republic of Congo. DNA extracted from these samples was genotyped at up to 10 microsatellite loci and one X–Y homologous locus for sex identification. Individuals were then identified at nesting sites by their unique multilocus genotypes, thus providing a ‘molecular census’ of individual Gorillas. Results confirm that Western Gorillas often build more than one nest at a nesting site and, thus, nest counts can be highly inaccurate indicators of group size and composition. Indeed, we found that nest counts can overestimate group size by as much as 40%, indicating that true Gorilla population numbers are probably lower than those reported from census surveys. This study demonstrates how genetic analysis can be a valuable tool for studying and conserving elusive, endangered animals.
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RESEARCH ARTICLE Effects of Habitat Fragmentation, Population Size and Demographic History on Genetic Diversity: The Cross River Gorilla in a Comparative Context
2008Co-Authors: Richard A Bergl, Brenda J. Bradley, Anthony M. Nsubuga, Linda VigilantAbstract:In small and fragmented populations, genetic diversity may be reduced owing to increased levels of drift and inbreeding. This reduced diversity is often associated with decreased fitness and a higher threat of extinction. However, it is difficult to determine when a population has low diversity except in a comparative context. We assessed genetic variability in the critically endangered Cross River Gorilla (Gorilla Gorilla diehli), a small and fragmented population, using 11 autosomal microsatellite loci. We show that levels of diversity in the Cross River population are not evenly distributed across the three genetically identified subpopulations, and that one centrally located subpopulation has higher levels of variability than the others. All measures of genetic variability in the Cross River population were comparable to those of the similarly small mountain Gorilla (G. beringei beringei) populations (Bwindi and Virunga). However, for some measures both the Cross River and mountain Gorilla populations show lower levels of diversity than a sample from a large, continuous Western Gorilla population (Mondika, G. Gorilla Gorilla). Finally, we tested for the genetic signature of a bottleneck in each of the four populations. Only Cross River showed strong evidence of a reduction in population size, suggesting that the reduction in size of this population was more recent or abrupt than in the two mountain Gorilla populations. These results emphasize the need for maintaining connectivity in fragmented populations and highlight the importance of allowing small populations to expand. Am. J. Primatol. 70:848‐859, 2008. � c 2008 Wiley-Liss, Inc.
Christophe Boesch - One of the best experts on this subject based on the ideXlab platform.
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Contextual correlates of syntactic variation in mountain and Western Gorilla close-distance vocalizations: Indications for lexical or phonological syntax?
Animal Cognition, 2015Co-Authors: Daniela Hedwig, Martha M Robbins, Roger Mundry, Christophe BoeschAbstract:The core of the generative power of human languages lies in our ability to combine acoustic units under specific rules into structurally complex and semantically rich utterances. While various animal species concatenate acoustic units into structurally elaborate vocal sequences, such compound calls do not appear to be compositional as their information content cannot be derived from the information content of each of its components. As such, animal compound calls are said to constitute a form of phonological syntax, as in the construction of words in human language, whereas evidence for rudimentary forms of lexical syntax, analogous to the construction of sentences out of words, is scarce. In a previous study, we demonstrated that the repertoire of close-distance calls of mountain and Western Gorillas consists of acoustic units that are either used singularly or non-randomly combined. Here, we investigate whether this syntactic variation provides indications for lexical or phonological syntax. Specifically, we examined the differences between the potential information content of compound calls and their components used singularly through investigating the contexts in which they are used. We found that the Gorillas emitted compound calls in contexts similar to some but not all components, but also in a context rarely found for any of their components. As such, the investigated compound calls did not appear to be compositional as their information content cannot be derived from the information content of each of their components. Our results suggest that combining acoustic units into compound vocalizations by Gorillas constitutes a form of phonological syntax, which may enable them to increase the number of messages that can be transmitted by an otherwise small repertoire of acoustic units.
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acoustic structure and variation in mountain and Western Gorilla close calls a syntactic approach
Behaviour, 2014Co-Authors: Daniela Hedwig, Kurt Hammerschmidt, Martha M Robbins, Roger Mundry, Christophe BoeschAbstract:Our understanding of the functioning of a species’ vocal repertoire can be greatly improved by investigating acoustic variation and using objective classification schemes based on acoustic structure. Here we used a syntactic approach to investigate the acoustic structure of the Gorilla close distance vocalizations (‘close calls’), which remain as yet little understood. We examined 2130 calls of 10 mountain Gorillas (Gorilla beringei beringei) from Bwindi Impenetrable National Park, Uganda, and 5 Western lowland Gorillas (Gorilla Gorilla Gorilla) from Bai Hokou, Central African Republic. We segmented calls into units using distinct acoustic features and employed model-based cluster analyses to define the repertoire of unit types. We then examined how unit types were combined into calls. Lastly, we compared unit type use between age–sex classes and the two study groups. We found that the Gorilla close calls consist of 5 intergraded acoustic unit types which were flexibly but yet non-randomly concatenated into 159 combinations. Our results are in line with previous quantitative acoustic analyses demonstrating a high degree of acoustic variation in a variety of animal vocal repertoires, particularly close distance vocalizations. Our findings add on to (1) the recent argument that the common practice of describing vocal repertoires as either discrete or graded may be of little value as such distinctions may be driven by human perception and non-quantitative descriptions of vocal repertoires, and (2) recent studies indicating that flexibility in close range social calls can come about through combinatorial systems, which previously have been studied primarily in long distance vocalizations. Furthermore, our study highlights differences in the vocal repertoire of Western and mountain Gorillas, as expected given differences in environment and social behaviour. Our results offer opportunities for further in-depth studies investigating the function of the Gorilla close calls, which will contribute to a more comprehensive understanding of ape vocal communication in general.
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Effective non-invasive genetic monitoring of multiple wild Western Gorilla groups
Biological Conservation, 2010Co-Authors: Mimi Arandjelovic, Martha M Robbins, Christophe Boesch, Josephine Head, Hjalmar S. Kühl, Fiona Maisels, Linda VigilantAbstract:Obtaining reliable population size or abundance estimates of endangered species is critical for their conservation and management. Genotyping non-invasively collected samples is an effective way to gain insights into the number and grouping patterns of rare or elusive animals. In this study we used genetic capture–recapture estimators to obtain a precise estimate of the size of a Western Gorilla population inhabiting an intensely sampled 101 km 2 area in Loango National Park, Gabon. Using 394 putative Gorilla samples collected opportunistically over a 3 year period, we identified 83 unique genotypes. We used a rarefaction curve, Bayesian estimator and two maximum-likelihood methods to estimate that between 87 and 107 individuals used the study area between February 2005 and September 2007. The confidence interval surrounding the genetic estimate was smaller than that obtained using traditional ape survey methods. In addition, genetic analysis showed that Gorilla and chimpanzee faeces were identified with 98% and 95% accuracy in the field, respectively. Patterns of co-occurrence of individual Gorillas suggest that at least 11 Gorilla social groups and five lone silverback males lived in the study area and that several individuals transferred between groups during the 3-year study period. When properly designed and implemented as part of a long-term biomonitoring program, genetic capture-recapture should prove an invaluable tool for evaluating, even on a large-scale, the population size and dynamics of apes and other elusive species.
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Dispersed Male Networks in Western Gorillas
Current biology : CB, 2004Co-Authors: Brenda J. Bradley, Christophe Boesch, Diane M. Doran-sheehy, Dieter Lukas, Linda VigilantAbstract:Abstract Although kin-selection theory has been widely used to explain the tendency of individuals to bias beneficial behaviors towards relatives living within the same social group [1], less attention has focused on kin-biased interactions between groups. For animal societies in which females emigrate, as is the case for mountain Gorillas ( Gorilla beringei beringei ), encounters between males in different groups often involve aggressive displays that can escalate to physical violence and fatal injuries [2, 3]. However, recent findings on the little-studied Western Gorilla ( Gorilla Gorilla ) indicate that interactions between social groups occur more frequently than they do in mountain Gorillas and are often [4, 5], although not always [5, 6], surprisingly nonaggressive. We investigated the pattern of genetic relationships between individuals of different groups and found evidence suggesting a previously unrecognized "dispersed male network" social structure in Western Gorillas in which the single males leading social groups were usually related to one or more nearby males. We propose that this provides a basis for extra-group, kin-biased behaviors and may explain the reported peaceful intergroup interactions. Furthermore, these results suggest that a patrilocal social structure, in which males remain in their natal region and potentially benefit from kin associations, is a feature unifying African apes and humans.
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Behavioral ecology of Western Gorillas: New insights from the field
American journal of primatology, 2004Co-Authors: Diane M. Doran-sheehy, Christophe BoeschAbstract:The papers in this issue are from a conference held in May 2002 at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. This conference brought together researchers from all current Western Gorilla sites for the first time with the aim of synthesizing the most current information available on Western Gorilla behavioral ecology. Our goal was to assess the degree of behavioral diversity in Gorillas in light of our current understanding of social evolution. The articles include 1) synopses of the current information on Western Gorilla foraging strategy, social behavior, life history, and genetic variation; 2) more-detailed descriptions of home-range use and intergroup encounters across sites; and 3) the first description of the social behavior of Western Gorilla females.
Diane M. Doran-sheehy - One of the best experts on this subject based on the ideXlab platform.
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Individual distinctiveness in call types of wild Western female Gorillas.
PloS one, 2014Co-Authors: Roberta Salmi, Kurt Hammerschmidt, Diane M. Doran-sheehyAbstract:Individually distinct vocalizations play an important role in animal communication, allowing call recipients to respond differentially based on caller identity. However, which of the many calls in a species' repertoire should have more acoustic variability and be more recognizable is less apparent. One proposed hypothesis is that calls used over long distances should be more distinct because visual cues are not available to identify the caller. An alternative hypothesis proposes that close calls should be more recognizable because of their importance in social interactions. To examine which hypothesis garners more support, the acoustic variation and individual distinctiveness of eight call types of six wild Western Gorilla (Gorilla Gorilla) females were investigated. Acoustic recordings of Gorilla calls were collected at the Mondika Research Center (Republic of Congo). Acoustic variability was high in all Gorilla calls. Similar high inter-individual variation and potential for identity coding (PIC) was found for all call types. Discriminant function analyses confirmed that all call types were individually distinct (although for call types with lowest sample size - hum, grumble and scream - this result cannot be generalized), suggesting that neither the distance at which communication occurs nor the call social function alone can explain the evolution of identity signaling in Western Gorilla communication.
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Western Gorilla Vocal Repertoire and Contextual Use of Vocalizations
Ethology, 2013Co-Authors: Roberta Salmi, Kurt Hammerschmidt, Diane M. Doran-sheehyAbstract:Despite considerable interest in the vocal communication of non-human primates and its possible relevance to theories of language evolution, we know surprisingly little about how vocal communication varies between closely related species inhabiting differing environments. Here, we provide the first quantitative description of the vocal repertoire, calling rates, and call usage in wild Western Gorillas and compare it to the previous work on mountain Gorilla vocal behavior. During 1572 h of focal follows (n = 533), we collected behavioral data on and recorded vocalizations (n = 2163) of eight individuals in one group at Mondika Research Center (Republic of Congo). We supplemented these data with opportunistic recordings of an additional adult male in a second group. We used discriminant function analysis to test how well calls can be categorized by their acoustic structure and used behavioral data to determine the typical usage of Western Gorilla call types. The vocal repertoire comprised of 17 call types. Twelve of 17 call types were given primarily in a single context. Our results were similar to previous studies of mountain Gorillas in that grunts, and grumbles were used most frequently and the silverback male vocalized more frequently than other group members. However, compared to mountain Gorillas, Western Gorillas used an additional call type (sex-whinny), used a second call type (hoot series) in a completely different context and by all age–sex classes, and used many more call types in a more context-specific fashion. Our study suggests that although vocal production is highly constrained by morphology and phylogeny, differing social and ecological conditions can yield differences in the use and function of calls, even between two closely related species such as Western and mountain Gorillas.
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Male and female Western Gorilla diet: preferred foods, use of fallback resources, and implications for ape versus old world monkey foraging strategies.
American journal of physical anthropology, 2009Co-Authors: Diane M. Doran-sheehy, P. Mongo, Jessica L. Lodwick, Nancy L. Conklin-brittainAbstract:Most of what is currently known about Western Gorilla (Gorilla Gorilla) diet is based on indirect studies using fecal samples and trail signs rather than measures based on direct observations. Here we report results on adult male and female Western Gorilla foraging behavior, based on systematic focal observations and nutritional analyses of foods. We found that Western Gorillas, like other apes, are highly selective ripe fruit specialists, seeking fruit high in energy, low in antifeedants, and rare in the environment. During seasonal fruiting peaks, fruit accounted for up to 70% of feeding time. When ripe fruit was scarce, Gorillas increased time spent feeding on leaves and nonpreferred fruits and herbs. Leaves were the major fallback food, accounting for up to 70% of feeding time in males and 50% in females during periods of fruit scarcity. In spite of large differences in body size, the sexes were remarkably similar in their overall diet, not differing in time spent feeding on fruit or preferred herbs. However, the male consistently fed more often and on a greater variety of leaves than did females, whereas females fed more often on fallback herbs and termites. Our findings, when considered in light of previous findings on sympatric mangabeys, indicate that the foraging strategy of Western Gorillas is broadly similar to that of chimpanzees and orangutans, and distinct from that of old world monkeys.
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Genetic identification of elusive animals: re‐evaluating tracking and nesting data for wild Western Gorillas
Journal of Zoology, 2008Co-Authors: Brenda J. Bradley, Diane M. Doran-sheehy, Linda VigilantAbstract:Western Gorillas Gorilla Gorilla have been exceedingly difficult to habituate to the presence of human observers. Nevertheless, researchers have amassed a wealth of information on population densities and group structure for this ape species by locating and counting the sleeping nests of wild individuals. Such nest-count studies have suggested that Western Gorilla groups often have multiple silverbacks and these multimale groups occasionally divide into smaller subgroups. However, observational data from forest clearing sites and from a few recently habituated Western Gorilla groups show no evidence of multimale family groups or of subgrouping. This discrepancy underscores a long-standing question in ape research: How accurately do nesting sites reflect true group compositions? We evaluated these indirect measures of group composition by using DNA from faeces and hair to genetically identify individual Gorillas at nesting sites. Samples were collected from unhabituated wild Western Gorillas ranging near Mondika Research Center in the Central African Republic and Republic of Congo. DNA extracted from these samples was genotyped at up to 10 microsatellite loci and one X–Y homologous locus for sex identification. Individuals were then identified at nesting sites by their unique multilocus genotypes, thus providing a ‘molecular census’ of individual Gorillas. Results confirm that Western Gorillas often build more than one nest at a nesting site and, thus, nest counts can be highly inaccurate indicators of group size and composition. Indeed, we found that nest counts can overestimate group size by as much as 40%, indicating that true Gorilla population numbers are probably lower than those reported from census surveys. This study demonstrates how genetic analysis can be a valuable tool for studying and conserving elusive, endangered animals.
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Dispersed Male Networks in Western Gorillas
Current biology : CB, 2004Co-Authors: Brenda J. Bradley, Christophe Boesch, Diane M. Doran-sheehy, Dieter Lukas, Linda VigilantAbstract:Abstract Although kin-selection theory has been widely used to explain the tendency of individuals to bias beneficial behaviors towards relatives living within the same social group [1], less attention has focused on kin-biased interactions between groups. For animal societies in which females emigrate, as is the case for mountain Gorillas ( Gorilla beringei beringei ), encounters between males in different groups often involve aggressive displays that can escalate to physical violence and fatal injuries [2, 3]. However, recent findings on the little-studied Western Gorilla ( Gorilla Gorilla ) indicate that interactions between social groups occur more frequently than they do in mountain Gorillas and are often [4, 5], although not always [5, 6], surprisingly nonaggressive. We investigated the pattern of genetic relationships between individuals of different groups and found evidence suggesting a previously unrecognized "dispersed male network" social structure in Western Gorillas in which the single males leading social groups were usually related to one or more nearby males. We propose that this provides a basis for extra-group, kin-biased behaviors and may explain the reported peaceful intergroup interactions. Furthermore, these results suggest that a patrilocal social structure, in which males remain in their natal region and potentially benefit from kin associations, is a feature unifying African apes and humans.
Martha M Robbins - One of the best experts on this subject based on the ideXlab platform.
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Variation in the social organization of Gorillas: Life history and socioecological perspectives
Evolutionary anthropology, 2018Co-Authors: Martha M Robbins, Andrew M. RobbinsAbstract:A focus of socioecological research is to understand how ecological, social, and life history factors influence the variability of social organization within and between species. The genus Gorilla exhibits variability in social organization with Western Gorilla groups being almost exclusively one-male, yet approximately 40% of mountain Gorilla groups are multimale. We review five ultimate causes for the variability in social organization within and among Gorilla populations: human disturbance, ecological constraints on group size, risk of infanticide, life history patterns, and population density. We find the most evidence for the ecological constraints and life history hypotheses, but an over-riding explanation remains elusive. The variability may hinge on variation in female dispersal patterns, as females seek a group of optimal size and with a good protector male. Our review illustrates the challenges of understanding why the social organization of closely related species may deviate from predictions based on socioecological and life history theory.
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Contextual correlates of syntactic variation in mountain and Western Gorilla close-distance vocalizations: Indications for lexical or phonological syntax?
Animal Cognition, 2015Co-Authors: Daniela Hedwig, Martha M Robbins, Roger Mundry, Christophe BoeschAbstract:The core of the generative power of human languages lies in our ability to combine acoustic units under specific rules into structurally complex and semantically rich utterances. While various animal species concatenate acoustic units into structurally elaborate vocal sequences, such compound calls do not appear to be compositional as their information content cannot be derived from the information content of each of its components. As such, animal compound calls are said to constitute a form of phonological syntax, as in the construction of words in human language, whereas evidence for rudimentary forms of lexical syntax, analogous to the construction of sentences out of words, is scarce. In a previous study, we demonstrated that the repertoire of close-distance calls of mountain and Western Gorillas consists of acoustic units that are either used singularly or non-randomly combined. Here, we investigate whether this syntactic variation provides indications for lexical or phonological syntax. Specifically, we examined the differences between the potential information content of compound calls and their components used singularly through investigating the contexts in which they are used. We found that the Gorillas emitted compound calls in contexts similar to some but not all components, but also in a context rarely found for any of their components. As such, the investigated compound calls did not appear to be compositional as their information content cannot be derived from the information content of each of their components. Our results suggest that combining acoustic units into compound vocalizations by Gorillas constitutes a form of phonological syntax, which may enable them to increase the number of messages that can be transmitted by an otherwise small repertoire of acoustic units.
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acoustic structure and variation in mountain and Western Gorilla close calls a syntactic approach
Behaviour, 2014Co-Authors: Daniela Hedwig, Kurt Hammerschmidt, Martha M Robbins, Roger Mundry, Christophe BoeschAbstract:Our understanding of the functioning of a species’ vocal repertoire can be greatly improved by investigating acoustic variation and using objective classification schemes based on acoustic structure. Here we used a syntactic approach to investigate the acoustic structure of the Gorilla close distance vocalizations (‘close calls’), which remain as yet little understood. We examined 2130 calls of 10 mountain Gorillas (Gorilla beringei beringei) from Bwindi Impenetrable National Park, Uganda, and 5 Western lowland Gorillas (Gorilla Gorilla Gorilla) from Bai Hokou, Central African Republic. We segmented calls into units using distinct acoustic features and employed model-based cluster analyses to define the repertoire of unit types. We then examined how unit types were combined into calls. Lastly, we compared unit type use between age–sex classes and the two study groups. We found that the Gorilla close calls consist of 5 intergraded acoustic unit types which were flexibly but yet non-randomly concatenated into 159 combinations. Our results are in line with previous quantitative acoustic analyses demonstrating a high degree of acoustic variation in a variety of animal vocal repertoires, particularly close distance vocalizations. Our findings add on to (1) the recent argument that the common practice of describing vocal repertoires as either discrete or graded may be of little value as such distinctions may be driven by human perception and non-quantitative descriptions of vocal repertoires, and (2) recent studies indicating that flexibility in close range social calls can come about through combinatorial systems, which previously have been studied primarily in long distance vocalizations. Furthermore, our study highlights differences in the vocal repertoire of Western and mountain Gorillas, as expected given differences in environment and social behaviour. Our results offer opportunities for further in-depth studies investigating the function of the Gorilla close calls, which will contribute to a more comprehensive understanding of ape vocal communication in general.
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Effective non-invasive genetic monitoring of multiple wild Western Gorilla groups
Biological Conservation, 2010Co-Authors: Mimi Arandjelovic, Martha M Robbins, Christophe Boesch, Josephine Head, Hjalmar S. Kühl, Fiona Maisels, Linda VigilantAbstract:Obtaining reliable population size or abundance estimates of endangered species is critical for their conservation and management. Genotyping non-invasively collected samples is an effective way to gain insights into the number and grouping patterns of rare or elusive animals. In this study we used genetic capture–recapture estimators to obtain a precise estimate of the size of a Western Gorilla population inhabiting an intensely sampled 101 km 2 area in Loango National Park, Gabon. Using 394 putative Gorilla samples collected opportunistically over a 3 year period, we identified 83 unique genotypes. We used a rarefaction curve, Bayesian estimator and two maximum-likelihood methods to estimate that between 87 and 107 individuals used the study area between February 2005 and September 2007. The confidence interval surrounding the genetic estimate was smaller than that obtained using traditional ape survey methods. In addition, genetic analysis showed that Gorilla and chimpanzee faeces were identified with 98% and 95% accuracy in the field, respectively. Patterns of co-occurrence of individual Gorillas suggest that at least 11 Gorilla social groups and five lone silverback males lived in the study area and that several individuals transferred between groups during the 3-year study period. When properly designed and implemented as part of a long-term biomonitoring program, genetic capture-recapture should prove an invaluable tool for evaluating, even on a large-scale, the population size and dynamics of apes and other elusive species.
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Social structure and life-history patterns in Western Gorillas (Gorilla Gorilla Gorilla).
American journal of primatology, 2004Co-Authors: Martha M Robbins, Magdalena Bermejo, Chloé Cipolletta, Richard J. Parnell, Florence Magliocca, Emma J. StokesAbstract:Life-history traits and ecological conditions have an important influence on primate social systems. Most of what we know about the life-history patterns and social structure of Gorillas comes from studies of eastern Gorillas (Gorilla beringei sp.), which live under dramatically different ecological conditions compared to Western Gorillas (Gorilla Gorilla sp.). In this paper we present new data on Western Gorilla social structure and life histories from four study sites, and make comparisons with eastern Gorilla populations. Data were obtained from two study sites with Gorilla groups undergoing the habituation process (Lossi, Democratic Republic of Congo and Bai Hokou, Central African Republic) and two "bai" studies (Maya Nord and Mbeli Bai, Republic of Congo). The size and structure of these groups were similar to those seen in eastern Gorillas. However, differences in the occurrence of various group transitions (group formations, changes between one-male and multimale composition, and group disintegrations) exist, and Western Gorillas notably exhibit much higher rates of male emigration and correspondingly fewer multimale groups compared to mountain Gorillas. Certain phenomena have been observed only rarely, including predation by leopards. The preliminary data show no significant differences in birth rates between Western Gorillas and mountain Gorillas. The ecological variability across Gorilla habitats likely explains the flexibility in the social system of Gorillas, but we need more information on the social relationships and ecology of Western Gorillas to elucidate the causes for the similarities and differences between Western and eastern Gorillas on the levels of individuals, social groups, and population dynamics.
Magdalena Bermejo - One of the best experts on this subject based on the ideXlab platform.
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Western Gorilla space use suggests territoriality.
Scientific reports, 2020Co-Authors: Robin E. Morrison, Jacob C. Dunn, Germán Illera, Peter D. Walsh, Magdalena BermejoAbstract:The evolutionary origins of how modern humans share and use space are often modelled on the territorial-based violence of chimpanzees, with limited comparison to other apes. Gorillas are widely assumed to be non-territorial due to their large home ranges, extensive range overlap, and limited inter-group aggression. Using large-scale camera trapping, we monitored Western Gorillas in Republic of Congo across 60 km2. Avoidance patterns between groups were consistent with an understanding of the “ownership” of specific regions, with greater avoidance of their neighbours the closer they were to their neighbours’ home range centres. Groups also avoided larger groups’ home ranges to a greater extent, consistent with stronger defensive responses from more dominant groups. Our results suggest that groups may show territoriality, defending core regions of their home ranges against neighbours, and mirror patterns common across human evolution, with core areas of resident dominance and larger zones of mutual tolerance. This implies Western Gorillas may be a key system for understanding how humans have evolved the capacity for extreme territorial-based violence and warfare, whilst also engaging in the strong affiliative inter-group relationships necessary for large-scale cooperation.
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home range use and intergroup encounters in Western Gorillas Gorilla g Gorilla at lossi forest north congo
American Journal of Primatology, 2004Co-Authors: Magdalena BermejoAbstract:I present data on home-range use and types of intergroup encounters for one group (Apollo) of Western Gorillas (Gorilla Gorilla Gorilla) from a new study site in the Republic of Congo. The total home-range size of the focal group, which I calculated by superimposing a 100 m × 100 m grid over the mapped daily path traveled, was 11 km2. The majority (73%) of the group's home range was used exclusively, although at the periphery it overlapped with the ranges of three other groups. Most encounters (86%) with other groups (n = 14) took place in the periphery of the home range, and appeared to involve access to fruit trees. The focal group silverback's encounters with solitary silverbacks occurred throughout the focal group's home range, did not involve access to fruit, and typically resulted in aggressive or avoidance behavior. The focal group silverback's response to other group males was more varied: it included tolerance (64%), avoidance (14%), and aggression (21%), and was dependent upon the identity of the extragroup male. The focal group exhibited an unusual form of tolerant behavior toward some other groups by occasionally forming “nesting supergroups” (two groups nested together overnight at distances of 30–50 m). The Western Gorillas at Lossi were somewhat fluid in their grouping. Subgrouping and supergrouping occurred, although more infrequently than reported previously, and with a new twist: subgrouping did not necessarily require a silverback's presence. I stress the need for intraspecific comparisons and more complete data sets on Western Gorilla social organization. Am J Primatol 64:223–232, 2004. © 2004 Wiley-Liss, Inc.
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Western Gorilla diet: a synthesis from six sites.
American journal of primatology, 2004Co-Authors: M. Elizabeth Rogers, Katharine Abernethy, Magdalena Bermejo, Chloé Cipolletta, Diane M. Doran, Kelley Mcfarland, Tomoaki Nishihara, Melissa J. Remis, Caroline E. G. TutinAbstract:The objective of this paper is to collate information on Western Gorilla diet from six study sites throughout much of their current range, including preliminary information from two sites (Afi and Lossi), where studies of diet have begun only recently. Food lists were available from each site, derived from indirect signs of Gorilla feeding (such as feces), with some observational data. Important staple, seasonal, and fallback foods have been identified, and a number of striking similarities across sites have been revealed based on a much larger data set than was previously available. It was confirmed that the Western Gorilla diet is always eclectic, including up to 230 items and 180 species. The greatest diversity is found among the fruit species eaten, fruit being included in Western Gorilla diets from all sites and throughout most or all of the year. Eight plant families provide important foods at five, or all six, sites, suggesting that it may be possible in the future to predict which habitats are the most suitable for Gorillas. Gorillas exploit both rare and common forest species. Similarities and differences among sites can be explained superficially on the basis of geography and the past history of the forest. Gorilla density across sites appears to be most affected by the density of monocotyledonous bulk food plants, but its relationship to the density of important tree food species has yet to be tested.
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Social structure and life-history patterns in Western Gorillas (Gorilla Gorilla Gorilla).
American journal of primatology, 2004Co-Authors: Martha M Robbins, Magdalena Bermejo, Chloé Cipolletta, Richard J. Parnell, Florence Magliocca, Emma J. StokesAbstract:Life-history traits and ecological conditions have an important influence on primate social systems. Most of what we know about the life-history patterns and social structure of Gorillas comes from studies of eastern Gorillas (Gorilla beringei sp.), which live under dramatically different ecological conditions compared to Western Gorillas (Gorilla Gorilla sp.). In this paper we present new data on Western Gorilla social structure and life histories from four study sites, and make comparisons with eastern Gorilla populations. Data were obtained from two study sites with Gorilla groups undergoing the habituation process (Lossi, Democratic Republic of Congo and Bai Hokou, Central African Republic) and two "bai" studies (Maya Nord and Mbeli Bai, Republic of Congo). The size and structure of these groups were similar to those seen in eastern Gorillas. However, differences in the occurrence of various group transitions (group formations, changes between one-male and multimale composition, and group disintegrations) exist, and Western Gorillas notably exhibit much higher rates of male emigration and correspondingly fewer multimale groups compared to mountain Gorillas. Certain phenomena have been observed only rarely, including predation by leopards. The preliminary data show no significant differences in birth rates between Western Gorillas and mountain Gorillas. The ecological variability across Gorilla habitats likely explains the flexibility in the social system of Gorillas, but we need more information on the social relationships and ecology of Western Gorillas to elucidate the causes for the similarities and differences between Western and eastern Gorillas on the levels of individuals, social groups, and population dynamics.
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Home‐range use and intergroup encounters in Western Gorillas (Gorilla g. Gorilla) at Lossi forest, North Congo
American journal of primatology, 2004Co-Authors: Magdalena BermejoAbstract:I present data on home-range use and types of intergroup encounters for one group (Apollo) of Western Gorillas (Gorilla Gorilla Gorilla) from a new study site in the Republic of Congo. The total home-range size of the focal group, which I calculated by superimposing a 100 m × 100 m grid over the mapped daily path traveled, was 11 km2. The majority (73%) of the group's home range was used exclusively, although at the periphery it overlapped with the ranges of three other groups. Most encounters (86%) with other groups (n = 14) took place in the periphery of the home range, and appeared to involve access to fruit trees. The focal group silverback's encounters with solitary silverbacks occurred throughout the focal group's home range, did not involve access to fruit, and typically resulted in aggressive or avoidance behavior. The focal group silverback's response to other group males was more varied: it included tolerance (64%), avoidance (14%), and aggression (21%), and was dependent upon the identity of the extragroup male. The focal group exhibited an unusual form of tolerant behavior toward some other groups by occasionally forming “nesting supergroups” (two groups nested together overnight at distances of 30–50 m). The Western Gorillas at Lossi were somewhat fluid in their grouping. Subgrouping and supergrouping occurred, although more infrequently than reported previously, and with a new twist: subgrouping did not necessarily require a silverback's presence. I stress the need for intraspecific comparisons and more complete data sets on Western Gorilla social organization. Am J Primatol 64:223–232, 2004. © 2004 Wiley-Liss, Inc.
