Long-term collapse in fruit availability threatens Central African forest megafauna.

Afrotropical forests host much of the world's remaining megafauna, although these animals are confined to areas where direct human influences are low. We used a rare long-term dataset of tree reproduction and a photographic database of forest elephants to assess food availability and body condition of an emblematic megafauna species at Lopé National Park, Gabon. Our analysis reveals an 81% decline in fruiting over a 32-year period (1986-2018) and an 11% decline in body condition of fruit-dependent forest elephants from 2008 to 2018. Fruit famine in one of the last strongholds for African forest elephants should raise concern about the ability of this species and other fruit-dependent megafauna to persist in the long term, with potential consequences for broader ecosystem and biosphere functioning.

Gorilla diet in the Lopé Reserve, Gabon: : A nutritional analysis.

The results of an analysis of gorilla diet in the Lopé Reserve, Gabon are presented. Samples were assayed for nutrients and plant secondary compounds (total phenols, condensed tannins and alkaloids) in an attempt to explain gorilla food choice. The diet is the most diverse so far analysed for gorillas; it seems to be a balance between sugary fruit, proteinaceous leaves, and relatively fibrous stems. Most fruits and herbaceous stems are succulent, but some drier, fibrous fruit and bark is also consumed. Seeds are another component of the diet, including unripe ones. Fruit, seeds, leaves and bark may all contain very high levels of total phenols and condensed tannins; but all herbaceous stems assayed contain low levels of these compounds. Alkaloids are not apparently a significant component of gorilla foods, and may be avoided. Gorillas at Lopé tend to avoid fatty fruit, and select leaves which are high in protein and low in fibre compared to the general vegetation. When fruit and preferred young leaves are scarce, proteinaceous barks and mature leaves, and sugary pith, are important sources of nutrients. We conclude that gorillas exploit the broad frugivore niche in West African lowland forests, and are part of the frugivore community there. What distinguishes them is their ability to eat large fibrous fruit, mature leaves and stems, and to overcome high levels of phenolics (we use "phenolics" as an umbrella term for both total phenols and condensed tannins). Gorilla diet at Lopé overlaps greatly with that of sympatric, frugivorous, primates, and resembles more closely that of chimpanzees than it does gorilla diet studied elsewhere in Africa.

Composition of the diet of chimpanzees and comparisons with that of sympatric lowland gorillas in the lopé reserve, gabon.

Over an eight-year period, a total of 174 food items were recorded for chimpanzees (Pan t. troglodytes) in the Lopé Reserve in central Gabon. Plant foods, principally fruit, dominated the diet but insects were eaten regularly, and predation on at least three species of mammal occurred infrequently. The diversity of the vegetative component of the diet (leaves, stems, and bark) was probably underestimated by fecal analysis. Comparison of chimpanzee diet at Lopé with that of sympatric lowland gorillas showed the majority of foods were eaten by both species (73% of chimpanzee food items and 57% of gorilla food items). The overlap of fruit species was greater (82% and 79%, respectively) than that of other food classes. Both chimpanzees and gorillas harvested the majority of their plant foods arboreally (76% and 69%, respectively). The high degree of dietary overlap suggested that ecological competition between these two closely related species might exist. Few overt signs of competition for food either between or within species were observed but when fruit was scarce, the diets of the two species showed greatest divergence. The major differences between chimpanzee and gorilla diet at Lopé were the larger quantities of vegetative foods regularly eaten by gorillas and their ability to resort to a diet dominated by vegetative foods when fruit was scarce. In these respects, chimpanzees at Lopé resembled populations of Pan troglodytes studied elsewhere while Lopé gorillas resembled mountain gorillas (Gorilla g. beringei) and bonobos (Pan paniscus) in their greater dependence on vegetative foods. © 1993 Wiley-Liss, Inc.

Insect-eating by sympatric Lowland gorillas (Gorilla g. gorilla) and chimpanzees (Pan t. troglodytes) in the Lopé Reserve, Gabon.

Sympatric populations of lowland gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes troglodytes) in the Lopé Reserve in central Gabon consumed insects at similar average frequencies over a 7-year period (30% versus 31% feces contained insect remains). Data came mostly from fecal analysis supplemented by observation and trail evidence. The weaver ant (Oecophylla longinoda) was the species eaten most frequently by both gorillas and chimpanzees. Other species of insects wore eaten but there was virtually no overlap: Chimpanzees used tools to eat Apis bees (and their honey) and two large species of ants; gorillas ate three species of small ants. Thus, despite their shared habitat, the esources utilized were not identical as gorillas do not show the tool-use "technology" of chimpanzees. The frequency of insect-eating by both species of ape varied seasonally and between years but in different ways. This variation did not seem to be related to the ratio of fruit to foliage in their diets. Gorillas of all age-classes ate insects at similar rates. Comparisons with insectivory by other populations of gorillas indicate differences exist. Mountain gorillas (Gorilla g. beringei) in the Virunga Volcanoes, Rwanda, consume thousands of invertebrates daily, eating them inadvertently with handfuls of herbaceous foods but they deliberately ingest insect-foods only rarely. Lowland gorillas at Lopé habitually ate social insects, and their selective processing of herbaceous foods probably minimizes inadvertent consumption of other invertebrates. Gorillas at Belinga in northeastern Gabon, 250 km from Lop6, ate social insects at similar rates but ignored weaver ants in favor of Cubitermes sulcifrons, a small species of termite that occurs at Lopé but was not eaten by gorillas. This indicates that local traditions similar to those reported for chimpanzees also exist amongst populations of gorillas. © 1992 Wiley-Liss, Inc.

Composition of the diet of lowland gorillas at Lopé in Gabon.

This report describes the composition of the diet of lowland gorillas, Gorilla gorilla gorilla, at Lopé in central Gabon. This population inhabits mature evergreen tropical forest and is not habituated to human observers. Data were collected during 6 years of an ongoing long-term study, from feeding-trails and by direct observation, but mostly by fecal analysis. Gorillas ate 182 plant foods from 134 species and 36 families. The fruit diet was diverse: 95 species were consumed, most with succulent pulp, and some immature seeds were eaten. Fruit remains were recorded in 98% of dung. Vegetative parts of Aframomum and Marantaceae formed staple foods, as they were abundant, accessible, and available year-round. Soil and social insects were also ingested; remains of weaver ants were recorded in one third of feces. More foods have been recorded for gorillas at Lopé than elsewhere and this is the most frugivorous population studied so far.

Ten days in the life of a mandrill horde in the Lopé Reserve, Gabon.

Mandrills have long been known to form large aggregations in the wild, but it has proved difficult to obtain detailed information on the socioecology of these groups. An unusually large (>600) horde of mandrills was followed for ten days during the 1995 dry season in Central Gabon, and data were collected on group composition and ecology while the mandrills were in an area of forest-savanna mosaic habitat in the north of the Lopé Reserve. Three separate counts of most of the group showed that fully coloured "fatted" adult males were present throughout the horde at a mean ratio to other individuals of 1:21. Paler "non-fatted" adult and sub-adult males were also distributed throughout. Mandrill diet over the ten days consisted mainly of insects, seeds from forest trees, and leaves or stems of understory herbaceous plants. Feeding was extremely selective, with most food items consumed in a much higher proportion than would be predicted from their relative availability. Ranging data also showed that the mandrills foraged preferentially in certain forest types within the forest-savanna mosaic, namely in Marantaceae and Rocky Forest. It is suggested that one reason why mandrills pass through gallery forests and forest-savanna mosaic in the dry season in the Lopé Reserve is because they find fruit there from preferred species, which are no longer fruiting in the main forest block, thus allowing them to maintain the fruit component of their diet at a time of fruit shortage. © 1996 Wiley-Liss, Inc.

Chimpanzees (Pan troglodytes verus) and their mammalian sympatriates: Mt. Assirik, Niokolo-Koba National Park, Senegal.

In intact, mosaic ecosystems, chimpanzees are sympatric with a wide range of other mammals, which may be predators, prey, or competitors. We delve beyond the nominal data of species lists to interval-level data on 35 medium-bodied and large-bodied mammals encountered at a hot, dry, and open field site in far West Africa. Frequency of encounter, habitat where found, and number of individuals encountered are analysed for species for which enough data were accumulated. Further, we compare findings over three periods (1976-1979, 2000, 2012). Species most often encountered were those normally classed as typical savanna forms. Even a crude classification into forest, woodland, and grassland ecotypes yields differences in species likely to meet apes. Comparison of encounter rates over time was surprisingly congruent, although not all species seen in the 1970s survived to the 2000s. Overall, Assirik's mammalian fauna is comparable to palaeo-faunal guilds sympatric with various extinct hominins.

Who killed Porthos? Genetic tracking of a gorilla death.

We describe a novel application of "forensic" genetics to study a key demographic event in a population of wild gorillas. We used microsatellite genotyping and non-invasively collected DNA samples to identify one individual western lowland gorilla as being most likely to have caused the death of another in Lopé National Park, Gabon. Data from relatively few genotypes permitted the identification of female transfer events and the interpretation of individual behavior that was previously impossible using observational methods, thus providing rare behavioral data on an elusive forest-dwelling species. Importantly, this study highlights the need for future studies of dispersal and local population structuring in forest populations, and more accurate population census methods. Genetic studies focusing on individual identification may play a valuable role in future gorilla conservation efforts.

Western gorilla diet: a synthesis from six sites.

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.

Mitochondrial DNA phylogeography of western lowland gorillas (Gorilla gorilla gorilla).

The geographical distribution of genetic variation within western lowland gorillas (Gorilla gorilla gorilla) was examined to clarify the population genetic structure and recent evolutionary history of this group. DNA was amplified from shed hair collected from sites across the range of the three traditionally recognized gorilla subspecies: western lowland (G. g. gorilla), eastern lowland (G. g. graueri) and mountain (G. g. beringei) gorillas. Nucleotide sequence variation was examined in the first hypervariable domain of the mitochondrial control region and was much higher in western lowland gorillas than in either of the other two subspecies. In addition to recapitulating the major evolutionary split between eastern and western lowland gorillas, phylogenetic analysis indicates a phylogeographical division within western lowland gorillas, one haplogroup comprising gorilla populations from eastern Nigeria through to southeast Cameroon and a second comprising all other western lowland gorillas. Within this second haplogroup, haplotypes appear to be partitioned geographically into three subgroups: (i) Equatorial Guinea, (ii) Central African Republic, and (iii) Gabon and adjacent Congo. There is also evidence of limited haplotype admixture in northeastern Gabon and southeast Cameroon. The phylogeographical patterns are broadly consistent with those predicted by current Pleistocene refuge hypotheses for the region and suggest that historical events have played an important role in shaping the population structure of this subspecies.

Catastrophic ape decline in western equatorial Africa.

Because rapidly expanding human populations have devastated gorilla (Gorilla gorilla) and common chimpanzee (Pan troglodytes) habitats in East and West Africa, the relatively intact forests of western equatorial Africa have been viewed as the last stronghold of African apes. Gabon and the Republic of Congo alone are thought to hold roughly 80% of the world's gorillas and most of the common chimpanzees. Here we present survey results conservatively indicating that ape populations in Gabon declined by more than half between 1983 and 2000. The primary cause of the decline in ape numbers during this period was commercial hunting, facilitated by the rapid expansion of mechanized logging. Furthermore, Ebola haemorrhagic fever is currently spreading through ape populations in Gabon and Congo and now rivals hunting as a threat to apes. Gorillas and common chimpanzees should be elevated immediately to 'critically endangered' status. Without aggressive investments in law enforcement, protected area management and Ebola prevention, the next decade will see our closest relatives pushed to the brink of extinction.