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Western Gorillas (western + gorilla)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

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, Issue 4 2009
D. Doran-Sheehy
Abstract 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. Am J Phys Anthropol 140:727,738, 2009. © 2009 Wiley-Liss, Inc. [source]

Using behavior to determine immature life-stages in captive western gorillas

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 6 2010
J.E. Hutchinson
Abstract Ontogenic development is divided into infant, juvenile, adolescent and adult life-stages. Although the developmental trajectory of an individual is a flexible entity, which differs within species, environment and sex, life-stage classifications are generally structured, age-based systems. This invariably leads to rigidity within a dynamic system and consequently hampers our understanding of primate life history strategies. We propose that life-stage classifications should be quantitative, flexible entities, which use a reliable measurement of development. Here, we provide a methodological example where placement into a life-stage is based upon behavioral variance between other similar-aged individuals. Behavioral data were collected from 12 male (3,11 years old) and 9 female (3,8 years old) captive immature western gorillas (Gorilla gorilla gorilla) housed in five family groups, using continuous focal sampling; 900,hr of data were collected over 131 days. Data were applied to four published life-stage classifications for mountain gorillas (Gorilla beringei beringei), which showed variable ability to determine life-stage in western gorillas. A new life-stage classification (Hutchinson & Fletcher) was proposed specifically for western gorillas, whereby multiple co-varying behavior provided a robust measure of linear development across immaturity. Each life-stage was found to be a distinct ontogenic phase and the classification discriminated life-stage with a high level of accuracy. Using the Hutchinson & Fletcher classification we provide evidence for disparity in developmental trajectories between the sexes from the juvenile period onwards. To expand the understanding of primate life histories, we propose that flexible classifications should be used to enable comparison of allometric life history traits within and between species, from birth onwards. Am. J. Primatol. 72:492,501, 2010. © 2010 Wiley-Liss, Inc. [source]

The strategic use of sex in wild female western gorillas

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 12 2009
Diane M. Doran-Sheehy
Abstract Human females, unlike most mammals, are sexually active outside of fertile periods. This decoupling of sexual behavior from its conceptive function has had an enormous impact on human social relationships, and yet we know little about why there was selection for nonconceptive mating. Here we examine one form of nonconceptive mating, the mating that occurs during pregnancy or post-conceptive (PC) mating, in wild western gorillas (Gorilla gorilla). Using a near complete mating record for five females during gestation, we show that pregnant females varied in the timing and frequency of mating, and used PC mating conditionally, synchronizing copulations to occur on days when other females mated, and refraining from mating for lengthy periods when no other females mated. As pregnant females mated exclusively with the same male before and after conception, and mated in response to group female (and not male) behavior, we conclude that western gorillas used PC mating as a form of female competition, and not to confuse paternity or to obtain immediate benefits from the male, as suggested earlier. The male initiated copulations preferentially with females of high rank, rather than distinguishing between pregnant and cycling females. Therefore, PC mating appears to be a strategy by which high-ranking pregnant females attempt to minimize male interest in other females, while reinforcing their own status and potentially delaying conception in others. These findings indicate that female-mating competition is more important than considered earlier, and may be a factor in the evolution of nonconceptive mating in humans. Am. J. Primatol. 71:1011,1020, 2009. © 2009 Wiley-Liss, Inc. [source]

Physical maturation, life-history classes and age estimates of free-ranging western gorillas,insights from Mbeli Bai, Republic of Congo

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 2 2009
Thomas Breuer
Abstract Physical maturation and life-history parameters are seen as evolutionary adaptations to different ecological and social conditions. Comparison of life-history patterns of closely related species living in diverse environments helps to evaluate the validity of these assumptions but empirical data are lacking. The two gorilla species exhibit substantial differences in their environment, which allows investigation into the role of increased frugivory in shaping western gorilla life histories. We present behavioral and morphological data on western gorilla physical maturation and life-history parameters from a 12.5-year study at Mbeli Bai, a forest clearing in the Nouabalé-Ndoki National Park in northern Congo. We assign photographs of known individuals to different life-history classes and propose new age boundaries for life-history classes in western gorillas, which can be used and tested at other western gorilla research sites. Our results show that western gorillas are weaned at a later age compared with mountain gorillas and indicate slower physical maturation of immatures. These findings support the risk-aversion hypothesis for more frugivorous species. However, our methods need to be applied and tested with other gorilla populations. The slow life histories of western gorillas could have major consequences for social structure, mortality patterns and population growth rates that will affect recovery from population crashes of this critically endangered species. We emphasize that long-term studies can provide crucial demographic and life-history data that improve our understanding of life-history evolution and adaptation and help to refine conservation strategies. Am. J. Primatol. 71:106,119, 2009. © 2008 Wiley-Liss, Inc. [source]