Feeding ecology of bonobos living in forest‐savannah mosaics: Diet seasonal variation and importance of fallback foods

Primates along with many other animal taxa are forced to cope with large shifts in basic ecological conditions because of rapid anthropogenically induced changes of their habitats. One of the coping strategies for primates is to adjust their diet to these changes, and several studies have demonstrated the importance of fallback resources for this. Bonobos, like chimpanzees, might be particularly vulnerable to habitat fragmentation because of their high dependence on fruit availability. Little is known, however, about bonobo feeding ecology in fragmented habitats and their use of fallback resources. In this study, we investigate diet seasonal variation and the exploitation of preferred and fallback foods in a bonobo population living in forest‐savannah mosaics. Results show that bonobos have adapted to this fragmented habitat by feeding on only a few fruit species, including an important number of non‐tree species (liana, herb and savannah shrub), in comparison to populations living in dense forests. These non‐tree plants have been defined as fallback and non‐preferred foods, which are most probably consumed to maintain high frugivory. Interestingly, we identified that preferred foods are all typical of mature forests while fallback resources are mainly found in forest edges or disturbed areas. This finding indicates that bonobos prefer to use mature forests when feeding, as they do for nesting, but extend their range use to forest areas in close proximity to humans when the availability of preferred fruits is low. Finally, we show that bonobo diet relies heavily on two abundant fallback fruits: Musanga cecropioides and Marantochloa leucantha. Other studies have demonstrated that the selection of abundant fallback resources enables primates to subsist at high densities and to maintain cohesive groups, as observed at this study site. Our findings suggest that bonobos living in forest‐savannah mosaics can be considered as staple fallback food consumers. Am. J. Primatol. 77:948–962, 2015. © 2015 Wiley Periodicals, Inc.

     

Chimpanzee feeding ecology and fallback food use in the montane forest of Nyungwe National Park,Rwanda

Almost all primates experience seasonal fluctuations in the availability of key food sources. However, the degree to which this fluctuation impacts foraging behavior varies considerably. Eastern chimpanzees (Pan troglodytes schweinfurthii) in Nyungwe National Park, Rwanda, live in a montane forest environment characterized by lower primary productivity and resource diversity than low‐elevation forests. Little is known about chimpanzee feeding ecology in montane forests, and research to date predominantly relies on indirect methods such as fecal analyses. This study is the first to use mostly observational data to examine how seasonal food availability impacts the feeding ecology of montane forest chimpanzees. We examine seasonal changes in chimpanzee diet and fallback foods (FBFs) using instantaneous scan samples and fecal analyses, supported by inspection of feeding remains. Chimpanzee fruit abundance peaked during the major dry season, with a consequent change in chimpanzee diet reflecting the abundance and diversity of key fruit species. Terrestrial herbaceous vegetation was consumed throughout the year and is defined as a “filler” FBF. In contrast to studies conducted in lower‐elevation chimpanzee sites, figs (especially Ficus lutea) were preferred resources, flowers were consumed at seasonally high rates and the proportion of non‐fig fruits in the diet were relatively low in the current study. These divergences likely result from the comparatively low environmental diversity and productivity in higher‐elevation environments.     

Feeding Ecology of Cross River Gorillas (Gorilla gorilla diehli) at Mawambi Hills: The Influence of Resource Seasonality

Determining the composition of primate diet and identifying factors that affect food choice are important in understanding habitat requirements of primates and designing conservation plans. We studied the diet of Cross River gorillas (Gorilla gorilla diehli) in relation to availability of food resources, in a semideciduous lowland forest site (Mawambi Hills) in Cameroon, from November 2009 to September 2011. Based on 109 d of feeding trail data, 203 fecal samples, and 22 mo of phenological monitoring, we determined that gorillas consumed a total of 242 food items, including 240 plant items from 186 species and 55 taxonomic families. Mawambi gorillas diversified fruit consumption when fruit availability increased, and consumed more fibrous foods (pith, leaf, bark) during times of fruit scarcity, consistent with results of other gorilla studies. However, fruit availability was not related to rainfall, and the period of fruit scarcity was more pronounced at Mawambi than at other gorilla study sites, due to a single long dry season and extreme rainfall at the end of the rainy season that delayed fruit production and ripening. We found no relationship between the daily path length of the gorillas and fruit consumption. We found feeding habits of Mawambi gorillas to be notably similar to those of a population of Cross River gorillas at Afi Mountain, Nigeria, although subtle differences existed, possibly due to site-specific differences in forest composition and altitude. At both sites the liana Landolphia spp. was the single most important food species: the leaves are a staple and the fruits are consumed during periods of fruit scarcity. Snails and maggots were consumed but we observed no further faunivory. We suggest that tree leaves and lianas are important fallback food sources in the gorilla diet in seasonally dry forests.     

Foraging Patterns of Sympatric Hornbills during the Nonbreeding Season in Arunachal Pradesh, Northeast India

The diet and food resource partitioning of three sympatric hornbills (Great Hornbill Buceros bicornis, Wreathed Hornbill Aceros undulatus, and Oriental Pied Hornbill Anthracoceros albirostris) during the nonbreeding season were studied relative to fruit availability in a foothill semievergreen forest of Arunachal Pradesh, northeast India. Hornbills fed on fruits of 49 plant species that comprised over 95 percent of their diet. Hornbill species partitioned food resources by varying the relative contribution of figs and non‐fig fruits in the diet. Similarity in non‐fig fruit diet was low. Ten species contributed to over 90 percent of the non‐fig diet. The availability of non‐fig fruits was much lower in the nonbreeding season than in the breeding season; however, despite lower fruit availability during the nonbreeding season, hornbills had a wide diet breadth and indirect evidence suggests that Wreathed Hornbills foraged widely in this season for fruit. Great Hornbills relied more on figs that were available year‐round. The diverse diet breadth that included rare and patchy fruit resources underscores the importance of conserving large forest tracts for hornbills.     

Diet and feeding patterns in the kipunji (<Emphasis Type="Italic">Rungwecebus kipunji</Emphasis>) in Tanzania’s Southern Highlands: a first analysis

The diet and feeding behaviour of the kipunji (Rungwecebus kipunji) was studied over 45 months, the first dietary analysis for this species. During 9498 h of direct observation of 34 kipunji groups, a list of 122 identified foodplants was recorded. The list represents 60 families, including 64 trees, 30 herbs, 9 climbers, 7 shrubs, 6 lianas, 3 grasses and 3 ferns. Kipunji were observed eating bark, young and mature leaves, ripe and unripe fruits, flowers, pith, seed pods, rhizomes, tubers, shoots and stalks. Invertebrates, fungi, moss, lichen, and soil were also eaten. Macaranga capensis var. capensis, an early successional tree, was the most commonly consumed species, with leaves, leaf stalks, pith, flowers and bark all eaten. We demonstrate that the kipunji is an omnivorous dietary generalist, favouring mature and immature leaves, ripe and unripe fruits and bark in similar proportions, with an almost comparable fondness for leaf stalks and flowers. Kipunji appear to be adaptable foragers able to modify their diet seasonally, being more folivorous in the dry season and more frugivorous in the wet. Whereas more ripe fruit is eaten in the wet season, the proportion of unripe fruit remains similar across the year. The proportion of mature leaves and pith increases throughout the dry season at the expense of ripe fruits and bark, and this may compensate nutritionally for the lack of available dry-season ripe fruits. Relatively more pith is eaten in the dry season, more stalks at the end of the dry and beginning of the wet seasons, and bark consumption increases as the rainfall rises.     

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.     

Fruit Availability and Habitat Use by Chimpanzees in the Kalinzu Forest,Uganda: Examination of Fallback Foods

We studied seasonal change in habitat use by chimpanzees in the Kalinzu Forest, Uganda. The forest comprises various types of vegetation. For each vegetation type, we compared number of chimpanzees (per km²) that used the vegetation with fruit availability in different census periods. We estimated the number of chimpanzees by nest count and fruit availability via density of fallen fruit. The mixed mature forest contained a large amount of fruit during the high-fruiting season, but it decreased rapidly in the low-fruiting season. The number of chimpanzees also decreased in mixed mature forest in approximate proportion with fruit availability. In the Parinari-dominated mature and secondary forests, both fruit availability and number of chimpanzees were very low throughout the study. In the Musanga-dominated secondary forest, the number of chimpanzees increased toward the low-fruiting season, though the fruit availability decreased slightly. A multiple regression analysis showed that various fruits had significant effects on the number of chimpanzees during the high-fruiting season, while only Musanga leo-errerae had a significant effect during the low-fruiting season. The results suggest that the fruit of Musanga leo-errerae functions as a fallback food, and a combination of different vegetation types supports the chimpanzees in the Kalinzu Forest.     

Fallback Foods of Red Leaf Monkeys (Presbytis rubicunda) in Danum Valley, Borneo

Animals in Southeast Asia must cope with long periods of fruit scarcity of unpredictable duration between irregular mast fruiting events. Long-term data are necessary to examine the effect of mast fruiting on diet, and particularly on the selection of fallback foods during periods of fruit scarcity. No such data is available for colobine monkeys, which may consume substantial amounts of fruits and seeds when available. We studied the diet of red leaf monkeys (Presbytis rubicunda, Colobinae) in Danum Valley, Sabah, northern Borneo, using 25 mo of behavioral observation, phenology and vegetation surveys, and chemical analysis to compare leaves eaten with nonfood leaves. The monkeys spent 46% of their feeding time on young leaves, 38% on seeds, 12% on whole fruits, 2.0% on flowers, 1.0% on bark, and 1.2% on pith. They spent more time feeding on seeds and whole fruit when fruit availability was high and fed on young leaves of Spatholobus macropterus (liana, Leguminosae) as fallback foods. This species was by far the most important food, constituting 27.9% of the total feeding time, and the feeding time on this species negatively correlated with fruit availability. Consumed leaves contained more protein than nonconsumed leaves, and variation in time spent feeding on different leaves was explained by their abundance. These results suggest that red leaf monkeys show essentially the same response to the supra-annual increase in fruit availability as sympatric monogastric primates, increasing their seed and whole-fruit consumption. However, they depended more on young leaves, in particular Spatholobus macropterus, as fallback foods during fruit-scarce periods than did gibbons or orangutans. Their selection of fallback food appeared to be due to both nutrition and abundance.     

Graminivory and Fallback Foods: Annual Diet Profile of Geladas (<Emphasis Type="Italic">Theropithecus gelada</Emphasis>) Living in the Simien Mountains National Park,Ethiopia

All primates show some dietary flexibility, particularly during food shortages. Foods consumed during times of scarcity (i.e., fallback foods) strongly influence the ecology and evolution of a species. Geladas (Theropithecus gelada) eat primarily graminoid leaves (i.e., grasses and sedges), but also consume other diet items (e.g., underground storage organs), especially in the dry season. We investigated the feeding ecology of wild geladas in the Sankaber region of the Simien Mountains National Park, Ethiopia across 12 mo. We asked how the gelada diet in this region, which is disturbed by livestock and agriculture, correlated with food availability and whether underground foods are fallback foods. We quantified the monthly diets of adults from eight reproductive units using instantaneous scan sampling, and seasonal aboveground and underground food availability using point-intercept transects and soil core sampling. Geladas primarily consumed graminoid leaves year-round (76.3% of the annual diet, 36.2–93.2% of the monthly diet) but spent considerable time consuming underground foods in the dry season (14.0% of the annual diet, 11.1–49.7% of the diet across dry season months). Graminoid consumption increased with graminoid availability, and underground food consumption decreased with graminoid availability. Underground food availability did not vary significantly between the dry and wet season sampling months, supporting the hypothesis that underground foods are fallback foods for geladas. We then compiled data from gelada feeding studies and found that underground foods are an important dry season diet item across study sites, but geladas rely more heavily on underground foods in habitats more heavily influenced by humans. Understanding the range and effects of primate dietary flexibility in human-modified habitats will contribute to a better understanding of how changing environments shape primate ecology and evolution.     

Habitat Exploitation by Free-ranging Saguinus niger in Eastern Amazonia

We monitored the foraging behavior of the members of a group of black-handed tamarins (Saguinus niger) at a site in eastern Amazonia. Their diet was frugivorous-insectivorous, but also included pod exudate of Parkia pendula. The focal group used all 3 types of forest—primary, logged, and secondary— in all months, but differentially between seasons. In the dry season, tamarins spent more than half of activity time in primary forest and less than a third in secondary forest whereas during the wet season, the proportions were reversed. Data on resource abundance indicated that the shift in habitat preference is related to a seasonal change in the distribution of fruit sources, with a larger number of species and individuals fruiting during the wet season. We recorded no such variation in the abundance of arthropods. While using a larger area, including more secondary forest, during the wet season, the group traveled significantly shorter distances each day, reflecting the availability of a larger number of fruit sources. Overall, the results reemphasize the ecological and behavioral flexibility of Saguinus niger and their ability to cope with habitat disturbance.     

Foraging and ranging behavior during a fallback episode: Hylobates albibarbis and Pongo pygmaeus wurmbii compared

Periodic episodes of food scarcity may highlight the adaptive value of certain anatomical traits, particularly those that facilitate the acquisition and digestion of exigent fallback foods. To better understand the selective pressures that favored the distinctive dental and locomotor morphologies of gibbons and orangutans, we examined the foraging and ranging behavior of sympatric Hylobates albibarbis and Pongo pygmaeus wurmbii during an episode of low fruit availability at Tuanan, Kalimantan Tengah, Indonesia. We found that Hylobates ranged 0.5 km day⁻¹ or 33% farther than did Pongo, but the overall daily ranging of both species did not vary as fruit availability decreased by as much as 50%. Among gibbons, we observed dietary switching to fallback foods; in particular, there was a progressively greater reliance on figs, liana products, and unripe fruit. Orangutans relied heavily on unripe fruit and fracture-resistant bark and pith tissues. Despite these divergent fallback patterns, the stiffness of fruit mesocarp consumed by Hylobates and Pongo did not differ. We discuss canine and molar functional morphology with respect to dietary mechanics. Next, to contextualize these results, we discuss our findings with respect to forest structure. The rain forests of Southeast Asia have been described as having open, discontinuous canopies. Such a structure may inform our understanding of the ranging behavior and distinctive locomotion of apes in the region, namely richochetal brachiation and quadrumanous clambering. Our approach of integrating behavioral ecology with physical measures of food may be a powerful tool for understanding the functional adaptations of primates. Am J Phys Anthropol 140:716–726, 2009. © 2009 Wiley-Liss, Inc.     

The impact of fallback foods on wild ring-tailed lemur biology: A comparison of intact and anthropogenically disturbed habitats

Fallback foods are often viewed as central in shaping primate morphology, and influencing adaptive shifts in hominin and other primate evolution. Here we argue that fruit of the tamarind tree (Tamarindus indica) qualifies as a fallback food of ring-tailed lemurs (Lemur catta) at the Beza Mahafaly Special Reserve (BMSR), Madagascar. Contrary to predictions that fallback foods may select for dental and masticatory morphologies adapted to processing these foods, consumption of tamarind fruit by these lemurs leaves a distinct pattern of dental pathology among ring-tailed lemurs at BMSR. Specifically, the physical and mechanical properties of tamarind fruit likely result in a high frequency of severe tooth wear, and subsequent antemortem tooth loss, in this lemur population. This pattern of dental pathology is amplified among lemurs living in disturbed areas at Beza Mahafaly, resulting from a disproportionate emphasis on challenging tamarind fruit, due to few other fruits being available. This is in part caused by a reduction in ground cover and other plants due to livestock grazing. As such, tamarind trees remain one of the few food resources in many areas. Dental pathologies are also associated with the use of a nonendemic leaf resource Argemone mexicana, an important food during the latter part of the dry season when overall food availability is reduced. Such dental pathologies at Beza Mahafaly, resulting from the use or overemphasis of fallback foods for which they are not biologically adapted, indicate that anthropogenic factors must be considered when examining fallback foods. Am J Phys Anthropol 140:671–686, 2009. © 2009 Wiley-Liss, Inc.     

Diet of Grauer's Gorillas in the Montane Forest of Kahuzi,Democratic Republic of Congo

We describe the diet of a semihabituated group of Grauer's gorillas (Gorilla beringei graueri) inhabiting the montane forest of Kahuzi-Biega National Park, Democratic Republic of Congo, based on direct observations, feeding remains in their fresh trails, and fecal samples collected over 9 yr. We examined fruit availability in their habitat; consumption of fruit, vegetative, and animal food; and daily intake of vegetative plant food using a transect, fruit monitoring trails, fecal analysis, and tracing of the animal's daily trails between consecutive nest sites. The fruit food repertoire of Kahuzi gorillas resembles that of western and eastern lowland gorillas inhabiting lowland tropical forests, while their vegetative food repertoire resembles that of mountain gorillas inhabiting montane forests. Among 236 plant foods (116 species), leaves, pith, and barks constitute the major parts (70.2%), with fruit making up the minor part (19.7%). About half (53.2%) of the total fecal samples included fruit remains. The gorillas used leaves, stems and other vegetative plant parts as staples. Their fruit intake was similar to that reported for mountain gorillas in Bwindi. They ate animal foods, including earthworms, on rare occasions. Variation in fruit consumption was positively associated with variation in fruit production. The gorillas ate fig fruits frequently; fig intake is positively correlated with that of other fruits, and figs were not fallback foods. They relied heavily on bamboo shoots on a seasonal basis; however, no bamboo shoots were available for several years after a major flowering event. Our results support the argument that variation in gorilla diets mostly reflects variation in vegetational composition of their habitats.     

Fallback foods of temperate-living primates: A case study on snub-nosed monkeys

Only a few primate species thrive in temperate regions characterized by relatively low temperature, low rainfall, low species diversity, high elevation, and especially an extended season of food scarcity during which they suffer from dietary stress. We present data of a case study of dietary strategies and fallback foods in snub-nosed monkeys (Rhinopithecus bieti) in the Samage Forest, Northwest Yunnan, PRC. The snub-nosed monkeys adjusted intake of plant food items corresponding with changes in the phenology of deciduous trees in the forest and specifically showed a strong preference for young leaves in spring. A non-plant food, lichens (Parmeliaceae), featured prominently in the diet throughout the year (annual representation in the diet was about 67%) and became the dominant food item in winter when palatable plant resources were scarce. Additional highly sought winter foods were frost-resistant fruits and winter buds of deciduous hardwoods. The snub-nosed monkeys' choice of lichens as a staple fallback food is likely because of their spatiotemporal consistency in occurrence, nutritional and energetic properties, and the ease with which they can be harvested. Using lichens is a way to mediate effects of seasonal dearth in palatable plant foods and ultimately a key survival strategy. The snub-nosed monkeys' fallback strategy affects various aspects of their biology, e.g., two- and three-dimensional range use and social organization. The higher abundance of lichens at higher altitudes explains the monkeys' tendency to occupy relatively high altitudes in winter despite the prevailing cold. As to social organization, the wide temporal and spatial availability of lichens strongly reduces the ecological costs of grouping, thus allowing for the formation of “super-groups.” Usnea lichens, the snub-nosed monkeys' primary dietary component, are known to be highly susceptible to human-induced environmental changes such as air pollution, and a decline of this critical resource base could have devastating effects on the last remaining populations. Within the order Primates, lichenivory is a rare strategy and only found in a few species or populations inhabiting montane areas, i.e., Macaca sylvanus, Colobus angolensis, and Rhinopithecus roxellana. Other temperate-dwelling primates rely mainly on buds and bark as winter fallback foods. Am J Phys Anthropol 140:700–715, 2009. © 2009 Wiley-Liss, Inc.     

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.     

Diet and Geophagy Across a Western Amazonian Parrot Assemblage

We identified species‐ and community‐level dietary characteristics for a species‐rich Amazonian parrot assemblage to determine relationships among dietary metrics and use of geophagy sites. Previous studies suggest that soil is consumed at geophagy sites in this region mainly to supplement dietary sodium. We accumulated 1400 feeding records for 16 parrot species over 2 yr and found that seeds, flowers, and fruit pulp featured prominently in diets, while bark, insects, and lichen were consumed in small quantities. Food availability across 1819 trees was measured, and we found that flower availability was highest in the dry season and fruit production peaked in the wet season, but that phenology patterns of the 20 most commonly foraged plant species suggest no serious food bottlenecks. Partitioning of available food resources among the 13 most commonly encountered parrots is suggested by an ordination analysis (DCA), which placed the large macaws (Ara) with the Amazona parrots at the ‘primary forest’ end of a dietary resource axis and four smaller species at the ‘successional forest’ end of the axis. Parrot species associated with successional forest also consumed less plant species overall. Furthermore, these parrot species consuming successional forest resources had higher claylick visitation rates than those consuming primary forest resources suggesting they derive the greatest benefits from soil consumption.     

Diet,Habitat Selection and Natural History of <Emphasis Type="Italic">Cacajao melanocephalus ouakary</Emphasis> in Jaú National Park,Brazil<Superscript>1</Superscript>

We studied golden-backed uacaris, (Cacajao melanocephalus ouakary) in the late-wet season of 1999 and in the mid-dry season of 2000 in Jaú National Park (JNP), Brazil. Additional observations were taken by other scientists working in JNP. Group counts range from 2 to 30 in the wet season and from 1 to > 100 in the dry. In the wet season, we recorded uacaris only in flooded forests (igapó). During the dry season they were in igapó, campinarana, and terra firme forests. We supplemented observations via interviews with local informants on seasonal use of the forest types and of particular small patches of different habitat types that exhibit high temporal patchiness in fruit availability. We recorded a total of 13 food plant species (dry season, 4; flooded season, 9), and a further 55 were provided by interviews. We noted the physical dimensions and hardness of 26 fruit species. Despite accepted specializations of the uakaris on hard unripe fruit, we recorded incidents of insectivory and folivory. Patterns of food availability, and therefore the seasonal habitat-use patterns by golden-backed uacaris, appear to be more complex than previously realized.The authors dedicate this paper to the memory of J. Marcio Ayres, the founding father of uacari field biology.     

Fragmented living: Behavioural ecology of primates in a forest fragment in the Lopé Reserve, Gabon

A 17-month study was made of the primates using a 9-ha “island” of forest, surrounded by savanna, in the northern part of the Lopé Reserve, Gabon. One group ofCercopithecus cephus (plus a young maleCercopithecus nictitans who was in permanent association with them) were resident in the fragment and groups of five other species of primates made visits during 127 days of observation:Pan troglodytes, 15 visits;Cercocebus albigena, 10;Colobus satanas, 3;Cercopithecus nictitans, 2;C. pogonias, 1. Visits were also made by lone males of three species,C. nictitans, Cercocebus albigena, andMandrillus sphinx. The eighth species of diurnal primate present at Lopé,Gorilla g. gorilla, did not visit the fragment during the study. Compared to conspecific groups in neighbouring continuous forest, primates in the fragment ate less fruit, seeds and flowers and more insects and leaves. The local population density of primates resident in the fragment was equivalent to that of the neighbouring continuous forest where all eight species occur, despite the diversity and abundance of fruit being less in the fragment. The costs imposed on the resident group by the reduced diversity and availability of preferred fruit foods appeared to be offset by a number of benefits that increased individual feeding efficiency for monkeys residing within a single fragment. These included lower travel costs, reduced feeding competition between individuals through group fission, and excellent knowledge of the location and quality of food resources in the small home range. It is also possible that the overall negative impact of inter-specific feeding competition was lower in fragments than in continuous forest and that micro-habitat differences resulted in an increased availability of palatable insect and leaf fallback foods in the fragment.     

Evolutionary Consequences of Fallback Foods

Primatologists use the term fallback foods to denote resources of relatively low preference that are used seasonally when preferred foods are unavailable. We examine the assumption that fallback foods play an important role in shaping morphological adaptations, behavior, and socioecology in primates. We discuss operational definitions of preferred and fallback foods and suggest that the evolutionary importance of fallback foods applies more to adaptations for processing than for harvesting foods. Equally, we propose that preferred resources tend to drive adaptations for harvesting foods. We distinguish 2 classes of fallback foods according to their roles in the diet and their evolutionary effects. Staple fallback foods are available year-round, tend to be eaten throughout the year, and seasonally can constitute up to 100% of the diet. Filler fallback foods never constitute 100% of the diet, and may be completely avoided for weeks at a time. We suggest that the availability of the 2 classes of fallback foods have different effects on the socioecology of primate species.     

Diet and Feeding Ecology of <Emphasis Type="Italic">Ateles chamek</Emphasis> in a Bolivian Semihumid Forest: The Importance of <Emphasis Type="Italic">Ficus</Emphasis> as a Staple Food Resource

We describe temporal patterns of food consumption by Peruvian spider monkeys (Ateles chamek) in a semihumid forest in lowland Bolivia. We assessed dietary composition in relation to temporal variation in abundance, duration, and synchrony of different food items in their home range. We collected data from September 2003 to September 2004, in the forestry concession La Chonta, Department of Santa Cruz. Throughout the period of detailed feeding data collection (February-September 2004), Ateles chamek used Ficus as a staple food resource. Figs constituted almost 50% of their diet in terms of total time spent feeding, and subjects consumed them to a great extent even during times of high overall food availability. This is contrary to the general expectation that for Neotropical frugivores, Ficus is a fallback food in times of fruit scarcity, rather than a staple food resource. Surprisingly, despite being considered ripe fruit specialists, Ateles chamek spent 18% of their feeding times eating unripe figs. Ateles chamek consumed unripe figs all through the year, including periods when ripe figs and other ripe fruit were abundant. We identify other important fallback foods for Ateles chamek in the forest, in particular the ripe fruit of Myrciaria sp.