The rise of the hominids as an adaptive shift in fallback foods: plant underground storage organs (USOs) and australopith origins.

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.

Western gorilla diet: a synthesis from six sites.

Part I Introduction.- The Values and Challenges of Long-Term Field Studies.- Part II Madagascar.- Berenty Reserve, Madagascar: A Long Time in a Small Space.- Beza Mahafaly Special Reserve: Long-Term Research on Lemurs in Southwestern Madagascar.- Long-Term Lemur Research at Centre Valbio, Ranomafana National Park, Madagascar.- A 15-Year Perspective on the Social Organization and Life History of Sifaka in Kirindy Forest.- Part III America.- The Northern Muriqui (Brachyteles hypoxanthus): Lessons on Behavioral Plasticity and Population Dynamics from a Critically Endangered Species.- The Lomas Barbudal Monkey Project: Two Decades of Research on Cebus capucinus.- Tracking Neotropical Monkeys in Santa Rosa: Lessons from a Regenerating Costa Rican Dry Forest.- The Group Life Cycle and Demography of Brown Capuchin Monkeys (Cebus [apella] nigritus) in Iguazu National Park, Argentina.- Part IV Asia.- Social Organization and Male Residence Pattern in Phayre's Leaf Monkeys.- White-Handed Gibbons of Khao Yai: Social Flexibility, Complex Reproductive Strategies, and a Slow Life History.- V Africa.- The Amboseli Baboon Research Project: Forty Years of Continuity and Change.- The Thirty Year Blues: What We Know and Don't Know About Life History, Group Size, and Group Fission of Blue Monkeys in the Kakamega Forest, Kenya.- Long-Term Research on Chimpanzee Behavioral Ecology in Kibale National Park, Uganda.- Long-Term Field Studies of Chimpanzees at Mahale Mountains National Park, Tanzania.- Long-Term Studies of the Chimpanzees of Gombe National Park, Tanzania.- Long-Term Research on Grauer's Gorillas in Kahuzi-Biega National Park, DRC: Life History, Foraging Strategies, and Ecological Differentiation from Sympatric Chimpanzees.- Long-Term Studies on Wild Bonobos at Wamba, Luo Scientific Reserve, D.R. Congo: Towards the Understanding of Female Life History in a Male-Philopatric Species. VI Summary.- A Comparative Perspective on Long-term Field Studies.

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Long-term field studies of primates

This paper describes the size and structure of western lowland gorilla groups visiting Mbeli Bai, a swampy forest clearing in northern Congo. An observation platform at the edge of the clearing was used over a 3-yr period, with gorillas visible for 1,681 hr. Data are presented on 14 groups and seven solitary males. Mean group size (excluding solitary males) was 8.4 ± SD 4.3, and did not differ significantly from most other gorilla studies. All groups at Mbeli contained only one fully mature male and did not show evidence of fission-fusion or regular subgrouping. All emigrating males that remained in the population became solitary, and “bachelor” groups were not observed. Methodological issues are raised, including the classification of multi-male groups, and the demographic profiles of other populations are discussed in the light of results from Mbeli. Am. J. Primatol. 56:193–206, 2002. © 2002 Wiley-Liss, Inc.

Group size and structure in western lowland gorillas (Gorilla gorilla gorilla) at Mbeli Bai, Republic of Congo.

Via a field study of chimpanzees (Pan troglodytes schweinfurthii) and gorillas (Gorilla gorilla beringei) in Bwindi Impenetrable National Park, Uganda, we found that their diets are seasonally similar, but diverge during lean seasons. Bwindi chimpanzees fed heavily on fruits of Ficus sp., which were largely ignored by the gorillas. Bwindi gorilla diet was overall more folivorous than chimpanzee diet, but was markedly more frugivorous than that of gorillas in the nearby Virunga Volcanoes. During 4 mo of the year Bwindi gorilla diet included more food species than that of the chimpanzees. Three factors in particular—seasonal consumption of fibrous foods by gorillas, interspecific differences in preferred fruit species, and meat consumption by chimpanzees—contributed to dietary divergence between the two species. When feeding on fruits, gorillas ate Myrianthus holstii more frequently than chimpanzees did, while chimpanzees included more figs in their annual diet. Chimpanzee diet included meat of duikers and monkeys; gorilla frequently consumed decaying wood.

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Behavioral Ecology of Sympatric Chimpanzees and Gorillas in Bwindi Impenetrable National Park, Uganda: Diet

A census of the eastern lowland gorillas Gorilla gorilla graueri in Kahuzi-Biega National Park with reference to mountain gorillas G. g. beringei in the Virunga Region, Zaire

A population census of chimpanzees (Pan troglodytes schweinfurthil) was conducted in the original part of Kahuzi-Biega National Park. Zaire. The census provides the first estimate of the density of chimpanzees in montane forests of Equatorial Africa. At least three unit groups of chimpanzees were identified in the census area during the 1990 bamboo season. The estimated density (0.13 chimpanzees/km2) falls within the range of densities in savanna. the driest chimpanzee habitat. The estimated density was far lower than the density of gorillas that sympatrically inhabit this montane forest, even though the two apes have been found at almost equal density in tropical forests in other areas. Chimpanzees were typical forest-dwellers, but goriiias ranged over various types of vegetation, including the open vegetation and the swamp. The low diversity and availability of fruits in the montane forest are responsible for the low density of chimpanzees who are frugivorous in various habitats. At least five out of eight primate species raided crops around the borders of the park. Chimpanzees raided maize and plantain bananas. The hostility of the local people towards these primates has recently become heightened in this area. More international attention is needed to augment conservation activities and to protecl. these primates . from the hazards of human disturbances in this area.

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Andrea Spangenberg

Papers

A census of the eastern lowland gorillas Gorilla gorilla graueri in Kahuzi-Biega National Park with reference to mountain gorillas G. g. beringei in the Virunga Region, Zaire

Population Density and Ranging Pattern of Chimpanzees in Kahuzi-Biega National Park, Zaire: A Comparison with a Sympatric Population of Gorillas