Diet and seasonal changes in sympatric gorillas and chimpanzees at Kahuzi–Biega National Park

Based on 8 years of observations of a group of western lowland gorillas (Gorilla beringei graueri) and a unit-group of chimpanzees (Pan troglodytes schweinfurthii) living sympatrically in the montane forest at Kahuzi–Biega National Park, we compared their diet and analyzed dietary overlap between them in relation to fruit phenology. Data on fruit consumption were collected mainly from fecal samples, and phenology of preferred ape fruits was estimated by monitoring. Totals of 231 plant foods (116 species) and 137 plant foods (104 species) were recorded for gorillas and chimpanzees, respectively. Among these, 38% of gorilla foods and 64% of chimpanzee foods were eaten by both apes. Fruits accounted for the largest overlap between them (77% for gorillas and 59% for chimpanzees). Gorillas consumed more species of vegetative foods (especially bark) exclusively whereas chimpanzees consumed more species of fruits and animal foods exclusively. Although the number of fruit species available in the montane forest of Kahuzi is much lower than that in lowland forest, the number of fruit species per chimpanzee fecal sample (average 2.7 species) was similar to that for chimpanzees in the lowland habitats. By contrast, the number of fruit species per gorilla fecal sample (average 0.8 species) was much lower than that for gorillas in the lowland habitats. Fruit consumption by both apes tended to increase during the dry season when ripe fruits were more abundant in their habitat. However, the number of fruit species consumed by chimpanzees did not change according to ripe fruit abundance. The species differences in fruit consumption may be attributed to the wide ranging of gorillas and repeated usage of a small range by chimpanzees and/or to avoidance of inter-specific contact by chimpanzees. The different staple foods (leaves and bark for gorillas and fig fruits for chimpanzees) characterize the dietary divergence between them in the montane forest of Kahuzi, where fruit is usually scarce. Gorillas rarely fed on insects, but chimpanzees occasionally fed on bees with honey, which possibly compensate for fruit scarcity. A comparison of dietary overlap between gorillas and chimpanzees across habitats suggests that sympatry may not influence dietary overlap in fruit consumed but may stimulate behavioral divergence to reduce feeding competition between them.     

Diet composition of chimpanzees inhabiting the montane forest of Kahuzi,Democratic Republic of Congo

The diet of chimpanzees was investigated by direct observations, feeding remains, and fecal analysis from January 1994 to December 2000 in the montane forest of Kahuzi-Biega National Park. A total of 171 food items were identified, among which 156 items were plant materials belonging to 114 species from 57 taxonomic families. Chimpanzees consumed 66 species of fruits (62 species of pulps and four species of seeds). Results of fecal analysis showed that fig fruits were the most frequently eaten. Their seeds occurred in 92% of a total of 7212 chimpanzee fecal samples. The chimpanzees changed their diet according to seasonal and annual variations in both abundance and diversity of fruit species. However, they are very selective frugivores. Only a few pulp-fruit species are regularly identified in their fecal samples. During the rainy season, when ripe fruit was scarce, chimpanzees relied heavily on piths and leaves. They swallowed leaves of two species of Commelinaceae without chewing, probably for medical purposes. Animal foods were eaten infrequently. The montane forest of Kahuzi, where chimpanzees range up to 2600 m above sea level, may be the highest altitudinal limit ever recorded for their distribution. Compared to other chimpanzee habitats, Kahuzi has a low diversity of fruit species and the availability of a few pulp-fruit species may be critical to the survival of Kahuzi chimpanzees.     

Chimpanzee oil-palm use in southern Cantanhez National Park, Guinea-Bissau

Cantanhez National Park in southern Guinea-Bissau is a mosaic of forest, mangrove, savanna, and agricultural fields, with a high prevalence of oil-palm trees (Elaeis guineensis). It hosts many different animal species, including the chimpanzee (Pan troglodytes verus). Very little is known about the ecology of chimpanzees inhabiting this area. The main aims of this study were to evaluate chimpanzee nesting behavior, define trends of habitat use, and estimate chimpanzee density in four separate forests by applying the marked nest counts methodology. From the 287 new nests counted, 92% were built in oil-palm trees with a significantly higher frequency of nests in the forest edge than in forest cores. Differences in nest detection rates were observed in the four monitored forests, with two forests being more important for chimpanzee's nesting demands. The number of nests documented in the forests seemed to be correlated with the frequency of other signs of chimpanzee activity. Although chimpanzees selected nests on the forest edge, they were most frequently observed in forest core areas. Constraints associated with estimating chimpanzee density through oil-palm nest counting are discussed.     

Temporal Variation in Insect-eating by Chimpanzees and Gorillas in Southeast Cameroon: Extension of Niche Differentiation

I studied insect-foraging strategies of great apes and aimed to define niche differentiation in their insect diet. I investigated seasonality in fruit-, foliage-, insect-, and meat-eating by great apes in southeast Cameroon via indirect methods and measured activity and nest densities of insect prey. I used a multinomial logistic regression to analyze the data. Gorilla and chimpanzee insect-, ant-, and termite-eating does not correlate with rainfall. Ant- and nonwinged termite-eating by chimpanzees increased in periods of succulent fruit scarcity and provided protein and energy, which might have compensated for the protein-low foliage eaten then. The apes ate winged termites when succulent fruit was abundant. Ant and winged termite consumption by gorillas correlates positively with that of chimpanzees. Ant-eating by gorillas increased when fruit was scarce, but was also associated with temporal ant activity and nest density. Both ape species also encountered more ant nests and trails in that period, as they predominantly foraged for herbs in vegetation types with high ant availability. In contrast, fruit-eating correlates positively with nonwinged termite-eating by gorillas, but again temporal prey availability is also associated. Termites might have provided 1) supplemental iron when tannin-rich fruits were eaten or 2) antidiarrheal properties when gorillas ate too much laxative fruit. Termite-eating by both ape species is not associated with spatial termite availability. In conclusion, there is niche differentiation in their insect diet. Based on the trade-off between foraging effort and nutritional gain, chimpanzees use a high-energy and gorillas a low-energy strategy when feeding on termites, but both use a low-energy strategy when feeding on ants. However, more information on the consumption of ant larvae is necessary to define niche differentiation in their ant diet.     

Nest groups of wild bonobos at Wamba: selection of vegetation and tree species and relationships between nest group size and party size

We examined the location of nest groups, spatial distribution of nests within a nest group, and attributes of individual nests of wild bonobos at Wamba, Democratic Republic of Congo. We also examined the seasonal factors influencing nesting behavior and compared the nest group size with the 1 hr party size during daytime. We defined a nest group to be a cluster of nests that were built in the same evening and found within 30 m from the other nearest nest. Examination of the largest gap within a nest group suggested that 30 m was an acceptable cutoff value. Monthly rainfall or fruit abundance did not significantly influence the monthly mean nest group size. Nests were built in the swamp forest for as many as 13% observation days, suggesting the need for reevaluation of the use of swamp forest by bonobos. The use of swamp forest was influenced not by seasonal rainfall or fruit abundance, but by the fruiting of specific species. Preferred tree species for building nests accounted for 19.8% of standing trees, which suggested that the selection of sleeping sites was not largely restricted by the distribution of specific species. The mean 1 hr party size was almost identical through the day and was similar to the mean nest group size. Parties of bonobos sometimes split into smaller nest groups, especially when feeding on non‐preferred fruits during fruit scarcity. By contrast, when feeding on preferred fruits while ranging in large parties, they often aggregated to form even larger nest groups. When sleeping in small‐ or middle‐sized nest groups, they tended to aggregate the next morning. These tendencies may reflect the gregarious nature of bonobos who prefer to range or sleep together as far as circumstances allow. Am. J. Primatol. 72:575–586, 2010. © 2010 Wiley‐Liss, Inc.     

Nest-Building by Chimpanzees (Pan troglodytes verus) at Seringbara, Nimba Mountains: Antipredation, Thermoregulation, and Antivector Hypotheses

The construction of nests (or beds) for sleeping is a chimpanzee universal, yet little is known about the adaptive function of nest-building. We present an in-depth study of nest-building by unhabituated chimpanzees at the Seringbara study site in the Nimba Mountains, Guinea, West Africa. We recorded 1520 chimpanzee nests over 28 mo during three study periods between 2003 and 2008. We investigated where chimpanzees built their nests, both across the home range and in nest trees, and assessed how altitude and habitat type affected nest site selectivity. We examined whether or not chimpanzees were selective in nest tree choice regarding physical tree characteristics and tree species and assessed plant species preference for both tree- and ground-nesting. We tested three, nonmutually exclusive, hypotheses for the function of arboreal nest-building. We assessed whether selectivity for nest tree characteristics reflected an antipredator strategy, examined whether nesting patterns (both arboreal and terrestrial) and nesting height were influenced by variation in climatic conditions (temperature, humidity, wind), and measured mosquito densities at ground level and in trees at 10 m and related mosquito densities to nesting patterns. Chimpanzees preferred to nest above 1000 m and nested mainly in primary forest. They preferred relatively large trees with a low first branch, dense canopy, and small leaves and showed preference for particular tree species, which was stable across years, whereas plant choice for ground-nesting was largely based on plant availability. We found no support for the antipredation hypothesis, nor did mosquito densities explain arboreal nest-building. The thermoregulation hypothesis was supported, as both nesting patterns and nest-height variation across seasons reflected a humidity-avoidance strategy. Chimpanzees nested higher in trees and at higher altitudes in the wet season. In sum, chimpanzees were selective in their choice of nest sites, locations, and materials, and tree-nesting patterns at Seringbara were best explained by a thermoregulation strategy of humidity avoidance.     

Feeding ecology of western lowland gorillas in the Nouabalé-Ndoki National Park,Congo

The feeding ecology of western lowland gorillas (Gorilla gorilla gorilla) living in the Nouabalé-Ndoki National Park, northern Congo, was surveyed for one full year. This is the first record to make clear the seasonal changes in the feeding habits of gorillas in a whole year, living in the primary lowland forest almost completely undisturbed. Fecal contents, feeding traces, and direct observation were analyzed with reference to a fruit availability survey. Although the gorillas fed largely on fruits in the forest, their basic diet was fibrous parts of plants, including shoots, young leaves, and bark. Terrestrial herbaceous vegetation, such as monocotyledons of the Marantaceae and aquatic herbs having much protein content and minerals, were frequently eaten even in the fruiting season. As these highly nutritious fibrous foods were superabundant all year, the major foods of the Ndoki gorillas seemed to be those plants. However, they selected fruits as their alternative food resources in the fruiting season. Gorillas foraged on many fruit species, while showing strong preferences for some particular species. The swamp forest, including marshy grasslands, was an important and regular habitat for the Ndoki gorillas.     

Fruit availability, chimpanzee diet, and grouping patterns on Rubondo Island, Tanzania

We examined seasonal patterns of fruit availability, dietary quality, and group size in the descendants of an introduced chimpanzee population on Rubondo Island, Tanzania. The site has supported a free-ranging population without provisioning for 40 years. Our goals were to determine whether Rubondo chimpanzees experience periods of fruit shortage, and whether they respond to changes in fruit availability similarly to chimpanzees at endemic sites. We indexed the fruit availability of tree and liana species on transects stratified across three chimpanzee ranging areas. We used fecal analyses to evaluate seasonal changes in diet, and used data on party size and nesting group size to examine seasonal patterns of grouping. Tree fruit availability was positively correlated with rainfall, with a period of relative tree fruit scarcity corresponding with the long dry season. Liana fruit availability was not related to rainfall, and lianas exhibited less variable fruiting patterns across seasons. Fruits made up the majority of the chimpanzee diet, with lianas accounting for 35% of dietary fruit species. Fruits of the liana Saba comorensis were available during all months of phenological monitoring, but they were consumed more when tree fruit was scarce, suggesting that Saba comorensis fruits may be a fallback food for Rubondo chimpanzees. There were no increases in consumption of lower-quality plant parts between seasons, and there were no changes in group size between seasons. These results contrast with evidence from several endemic chimpanzee study sites, and indicate that Rubondo chimpanzees may have access to abundant and high-quality foods year round.     

Fruit availability and chimpanzee party size at Kahuzi montane forest,Democratic Republic of Congo

The effect of fruit availability on chimpanzee party size was investigated in the montane forest of Kahuzi. Seasonal variation in both fruit availability and party size was examined. Fruit abundance per se does not affect chimpanzee party size. However, seasonality and distribution patterns of fruits are both determinant ecological factors that control the size of chimpanzee parties at Kahuzi. There was no correlation between fruit abundance and the spatial distribution of fruits. When fruits were clumped and available in large amounts for a long period, chimpanzee party size increased, or otherwise decreased when fruits were highly available for only a limited period. Tree species that produced only a small amount of ripe fruit throughout the year did not affect the foraging party size of chimpanzees. Temporal and spatial variability in fruit abundance seems to constrain grouping patterns of chimpanzees at Kahuzi more so than in other chimpanzee habitats previously described.     

Fallback foods and dietary partitioning among Pan and gorilla

Recent findings on the strong preference of gorillas for fruits and the large dietary overlap between sympatric gorillas and chimpanzees has led to a debate over the folivorous/frugivorous dichotomy and resource partitioning. To add insight to these arguments, we analyze the diets of sympatric gorillas and chimpanzees inhabiting the montane forest of Kahuzi-Biega National Park (DRC) using a new definition of fallback foods (Marshall and Wrangham: Int J Primatol 28 [2007] 1219–1235). We determined the preferred fruits of Kahuzi chimpanzees and gorillas from direct feeding observations and fecal analyses conducted over an 8-year period. Although there was extensive overlap in the preferred fruits of these two species, gorillas tended to consume fewer fruits with prolonged availability while chimpanzees consumed fruits with large seasonal fluctuations. Fig fruit was defined as a preferred food of chimpanzees, although it may also play a role as the staple fallback food. Animal foods, such as honey bees and ants, appear to constitute filler fallback foods of chimpanzees. Tool use allows chimpanzees to obtain such high-quality fallback foods during periods of fruit scarcity. Among filler fallback foods, terrestrial herbs may enable chimpanzees to live in small home ranges in the montane forest, whereas the availability of animal foods may permit them to expand their home range in arid areas. Staple fallback foods including barks enable gorillas to form cohesive groups with similar home range across habitats irrespective of fruit abundance. These differences in fallback strategies seem to have shaped different social features between sympatric gorillas and chimpanzees. Am J Phys Anthropol 140:739–750, 2009. © 2009 Wiley-Liss, Inc.     

The fruit phenology of Musanga leo-errerae and its importance for chimpanzee diet in Kalinzu Forest Uganda

This study reports the rate of fruit phenological pattern of Musanga leo-errerae and how it sustains the chimpanzee population better than other fruits in Kalinzu Forest Reserve. We analysed 2635 faecal samples to determine the proportion of M. leo-errerae by composition of fruit diet compared with other fruits eaten by chimpanzees. Musanga leo-errerae trees were monitored for fruit production between November 2002 and December 2004. Musanga leo-errerae fruit production did not vary significantly between months (ANOVA, F  = 2.0, d.f. = 11, P  = 0.13). The size of fruit and rate maturation varied with seasons, although fruit production was synchronous and available all year round. From the 2635 faecal samples analysed, 79.2% contained M. leo-errerae fruit seed. Chimpanzee diet in Kalinzu is 75% frugivorous, 37.2% of which is solely contributed by M. leo-errerae fruit. The continuous availability of M. leo-errerae fruit makes it the most important food for chimpanzees in this forest, especially during general fruit scarcity there by joining figs in importance for chimpanzee survival in tropical Africa.     

The behavioral ecology of sympatric African apes: implications for understanding fossil hominoid ecology

The behavioral ecology of the great apes is key evidence used in the reconstruction of the behavior of extinct ape and hominid taxa. Chimpanzees and gorillas have been studied in detail in the wild, and some studies of their behavioral ecology in sympatry have also been been carried out. Although the two ape species have divergent behavior and ecology in important respects, recent studies have shown that the interspecific differences are not as stark as previously thought and subsequently urge new consideration of how they share forest resources when sympatric. These new data require re-examination of assumptions about key aspects of chimpanzee-gorilla ecological divergence, such as diet, ranging and nesting patterns, and the mating system. Diet is a key component of the species adaptive complexes that facilitates avoidance of direct competition from the other. While the nutritional basis for chimpanzee food choice remains unclear and no doubt varies from site to site, this species is a ripe fruit specialist and ranges farther during periods of ripe fruit scarcity. Gorillas in the same habitat also feed on ripe fruit when widely available, but fall back onto fibrous plant foods during lean periods. The inclusion of animal protein in the diet of the chimpanzees and its absence in that of the gorillas also distinguish the species ecologically. It may also offer clues to aspects of ecological divergence among early members of the hominid phylogeny. The paper concludes by suggesting likely characteristics of sympatric associations of Pliocene hominids, based on field data from extant sympatric apes.     

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

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.     

Selective logging, habitat quality and home range use by sympatric gorillas and chimpanzees: a case study from an active logging concession in Southeast Cameroon

We examined range use by great apes during logging activities and investigated associations between local variations in ape abundance and changes in the structure of the habitat or in the availability of fruits after disturbances. We carried out two annual censuses of western lowland gorilla (G. g. gorilla) and chimpanzee populations (Pan t. troglodytes) in an active logging concession in Southeast Cameroon. The results suggest that gorillas may adapt their range use to avoid most recently logged compartments, while chimpanzees appear to be more spatially resilient to logging. In our study site, selective logging affected 10% of the forest. After logging, gorillas nested in all types of vegetation, while chimpanzees nested exclusively in mixed mature forest. Fruit availability was not affected by logging and did not explain the distribution of ape nests in the study area.     

Chimpanzee seed dispersal quantity in a tropical montane forest of Rwanda

We describe chimpanzee seed dispersal in the tropical montane forest of Nyungwe National Park (NNP), Rwanda, for a total of three years from January 1998 through May 2000 and May 2006 through March 2007. Relatively few studies have examined chimpanzee seed dispersal in montane communities where there are generally fewer fruiting tree species than in lowland forests. Such studies may reveal new insights into chimpanzee seed dispersal behaviors and the role that they play in forest regeneration processes. Chimpanzees are large‐bodied, highly frugivorous, and tend to deposit the seeds of both large‐ and small‐seeded fruits they consume in a viable state. We found that chimpanzees dispersed a total of 37 fruiting species (20 families) in their feces, 35% of which were large‐seeded trees (≥0.5 cm). A single large‐seeded tree, Syzygium guineense, was the only species to be dispersed in both wadges and feces. Based on phenological patterns of the top five large‐seeded tree species found in chimpanzee feces, our results indicate that chimpanzees do not choose fruits based on their availability. There was, however, a positive relationship between the presence of Ekebergia capensis seeds in chimpanzee feces and S. guineense seeds in chimpanzee wadges and their respective fruit availabilities. Our data reveal that proportionately fewer chimpanzee fecal samples at NNP contained seeds than that reported in two other communities in the Albertine Rift including one at mid‐elevation and one in montane forest. As in other chimpanzee communities, seeds of Ficus spp. were the most common genus in NNP chimpanzee feces. Our data do not support previous studies that describe Ficus spp. as a fallback food for chimpanzees and highlights an intriguing relationship between chimpanzees and the large‐seeded tree species, S. guineense. Am. J. Primatol. 71:901–911, 2009. © 2009 Wiley‐Liss, Inc.     

Variation in behavioral traits of two frugivorous mammals may lead to differential responses to human disturbance

Human activities can lead to a shift in wildlife species’ spatial distribution. Understanding the specific effects of human activities on ranging behavior can improve conservation management of wildlife populations in human‐dominated landscapes. This study evaluated the effects of forest use by humans on the spatial distribution of mammal species with different behavioral adaptations, using sympatric western lowland gorilla and central chimpanzee as focal species. We collected data on great ape nest locations, ecological and physical variables (habitat distribution, permanent rivers, and topographic data), and anthropogenic variables (distance to trails, villages, and a permanent research site). Here, we show that anthropogenic variables are important predictors of the distribution of wild animals. In the resource model, the distribution of gorilla nests was predicted by nesting habitat distribution, while chimpanzee nests were predicted first by elevation followed by nesting habitat distribution. In the anthropogenic model, the major predictors of gorilla nesting changed to human features, while the major predictors of chimpanzee nesting remained elevation and the availability of their preferred nesting habitats. Animal behavioral traits (body size, terrestrial/arboreal, level of specialization/generalization, and competitive inferiority/superiority) may influence the response of mammals to human activities. Our results suggest that chimpanzees may survive in human‐encroached areas whenever the availability of their nesting habitat and preferred fruits can support their population, while a certain level of human activities may threaten gorillas. Consequently, the survival of gorillas in human‐dominated landscapes is more at risk than that of chimpanzees. Replicating our research in other sites should permit a systematic evaluation of the influence of human activity on the distribution of mammal populations. As wild animals are increasingly exposed to human disturbance, understanding the resulting consequences of shifting species distributions due to human disturbance on animal population abundance and their long‐term survival will be of growing conservation importance.     

The Influence of Seasonal Variation on Chimpanzee (Pan troglodytes schweinfurthii) Fallback Food Consumption, Nest Group Size, and Habitat Use in Gishwati, a Montane Rain Forest Fragment in Rwanda

The increased number of primates living in fragmented habitats necessitates greater knowledge of how they cope with large-scale changes to their environment. Chimpanzees (Pan troglodytes) are exceptionally vulnerable to forest fragmentation; however, little is known about chimpanzee feeding ecology in fragments. Although chimpanzees have been shown to prefer fruit when it is available and fall back on more abundant lower quality foods during periods of fruit scarcity, our understanding of how chimpanzees use fallback foods in forest fragments is poor. We examined how chimpanzees cope with periods of fruit scarcity in Gishwati Forest Reserve, a disturbed montane rain forest fragment in Rwanda. We assessed seasonal changes in chimpanzee diet and the use of preferred and fallback foods through fecal and food site analysis. We also examined seasonal variation in nest group size and habitat use through marked nest censuses. We found that chimpanzees experienced a seasonal reduction in preferred fruit availability, which led to a seasonal diet shift to more fibrous foods, including several that functioned as fallback foods. Our results suggest that during periods of fruit scarcity the chimpanzees also reduced nest group size. However, we found that the chimpanzees did not alter their habitat use between high- and low-fruit seasons, which suggests that the small size of the forest limits their ability to change their seasonal habitat use. Consequently, fallback foods appear to be particularly important in small food-impoverished habitats with limited ranging options.     

Dietary Response of Chimpanzees and Cercopithecines to Seasonal Variation in Fruit Abundance. I. Antifeedants

In order to understand dietary differentiation among frugivorous primates with simple stomachs, we present the first comparison of plant diets between chimpanzees and cercopithecine monkeys that controls for food abundance. Our aim was to test the hypothesis that monkeys have a more diverse diet as a result of their dietary tolerance for chemical antifeedants. Our study species are chimpanzees, blue monkeys, redtail monkeys, and gray-cheeked mangabeys living in overlapping ranges in Kibale National Park, Uganda. We indexed food abundance by the percentage of trees having ripe fruit within the range of each group; it varied widely during the year. Chimpanzees spent almost 3 times as much of their feeding time eating ripe fruits as the monkeys did and confined their diets almost exclusively to ripe fruits when they were abundant. Monkeys maintained a diverse diet at all times. When ripe fruit was scarce chimpanzee and monkey diets diverged. Chimpanzees relied on piths as their main fallback food, whereas monkeys turned to unripe fruits and seeds. For each primate group we calculated the total weighted mean intake of 5 antifeedants; condensed tannins (CT), total tannins assayed by radial diffusion (RD), monoterpenoids (MT), triterpenoids (TT), and neutral-detergent fiber (NDF). Monkeys had absolutely higher intakes of CT, RD, MT, and TT than those of chimpanzees, and their intake of NDF did not differ from that of chimpanzees, appearing relatively high given their lower body weights. However contrary to expectation, dietary divergence during fruit scarcity was not associated with any change in absolute or relative intake of antifeedants. For example, fruit scarcity did not affect the relative intake of antifeedants by cercopithecines compared to chimpanzees. Our results establish chimpanzees as ripe-fruit specialists, whereas cercopithecines are generalists with a higher intake of antifeedants. The low representation of ripe fruits in the diets of cercopithecines has not been explained. An important next step is to test the hypothesis that the difference between Kibale chimpanzees and cercopithecines represents a more general difference between apes and monkeys.     

Water and fish select for fleshy fruits in tropical wetland forests

Adjacent floodplain and upland tropical forests experience the same temperature and precipitation regimes, but differ substantially in plant species composition and biotic interactions because of extensive flooding. We hypothesize that flooded forests filter fruiting traits linked to seed dispersal by water and fishes, such that selection by water and fish led to (1) trees that synchronize the timing of fruiting with annual floods, and (2) the evolution of fleshy tissues on fruits to improve buoyancy and increase fruit consumption rates by fish. To test this hypothesis, we compared plant communities in seasonally flooded forests and adjacent upland forest in terms of fruiting phenology, the frequency of trees bearing fleshy fruit, and the role of fleshy tissues in buoyancy and seed viability. Beta‐diversity in this system is high, with significant differences in species composition across habitats. As predicted, the production of ripe fleshy fruits was significantly greater in flooded than upland forests during the flood season. Furthermore, we found that trees with fleshy fruit were significantly more abundant in flooded forests even though species richness of fleshy fruit‐bearing trees was proportionally similar in flooded and upland forests. Additionally, fleshy pulp increased buoyancy. Likewise, time afloat decreased for denser fruit and those with high seed to pulp ratios. In concert, these results suggest that fleshy fruits in Neotropical floodplain forests facilitated hydrochory and ichthyochory. Once established, water and fish became important agents of selection on fruiting traits.     

Foods consumed by sympatric populations ofGorilla g. gorilla andPan t. troglodytes in Gabon: Some preliminary data

Data on foods consumed by gorillas and chimpanzees living in primary forest in Gabon were collected, mainly by examination of the contents of feces. Gorillas ate fruit very regularly (some fruit remains were present in 97.6% of 246 fecal samples examined), in addition to leaves, stems, pith, and bark. Some fruit remains were present in all chimpanzee fecal samples examined. Mean numbers of fruit species per fecal sample were 2.5 for gorillas and 2.1 for chimpanzees. Sixty percent of all identified foods recorded for gorillas were recorded for chimpanzees as well. Our results indicate that important differences in diet exist between western lowland gorillas and the eastern gorilla populations of Kahuzi-Biega and the Virunga Volcanoes. It is now clear that western gorillas cannot be accurately classed as folivores.