Fallback Foods Research Articles

Surviving at the highest and coldest: Nutritional and chemical components of fallback foods for Yunnan snub-nosed monkeys.

Fallback foods (FBF), categorized into staple and filler types, are suboptimal food sources chosen by animals in response to a scarcity of preferred food items during specific periods. Using lichens as FBF by Yunnan snub-nosed monkeys (Rhinopithecus bieti) represents a distinctive ecological adaptation and evolutionary development within nonhuman primates. This study delves into the annual dietary choices of the species to address issues, elucidate the nutritional value, and understand the ecological significance of lichens for this primate species, which resides at the highest altitudes and experiences the coldest weather among global primates. The findings reveal that the lichens consumed by the monkeys serve as the staple FBF, with Bryoria spp. and Usnea longissima being the primary dietary species. The former is the preferred choice, providing higher digestible fiber (neutral detergent fiber) levels but lower tannin, fat, ADF, and energy levels. During the dry season, lichens dominate as the monkeys' primary food and nutritional resources. In the wet season, they act as a fundamental food selection rather than an ideal dietary choice, substituting nutrients from fruits, seeds, and leaves. Compared to other Asian colobine counterparts, this species exhibits the highest lichen consumption but the lowest proportions of leaves, flowers, and seeds. This study provides valuable evidence and information for developing or amending conservation strategies and guidelines for the dietary management of captive breeding of monkeys, one of the world's critically endangered primate species.

Linking diet switching to reproductive performance across populations of two critically endangered mammalian herbivores

Optimal foraging theory predicts that animals maximise energy intake by consuming the most valuable foods available. When resources are limited, they may include lower-quality fallback foods in their diets. As seasonal herbivore diet switching is understudied, we evaluate its extent and effects across three Kenyan reserves each for Critically Endangered eastern black rhino (Diceros bicornis michaeli) and Grevy’s zebra (Equus grevyi), and its associations with habitat quality, microbiome variation, and reproductive performance. Black rhino diet breadth increases with vegetation productivity (NDVI), whereas zebra diet breadth peaks at intermediate NDVI. Black rhino diets associated with higher vegetation productivity have less acacia (Fabaceae: Vachellia and Senegalia spp.) and more grass suggesting that acacia are fallback foods, upending conventional assumptions. Larger dietary shifts are associated with longer calving intervals. Grevy’s zebra diets in high rainfall areas are consistently grass-dominated, whereas in arid areas they primarily consume legumes during low vegetation productivity periods. Whilst microbiome composition between individuals is affected by the environment, and diet composition in black rhino, seasonal dietary shifts do not drive commensurate microbiome shifts. Documenting diet shifts across ecological gradients can increase the effectiveness of conservation by informing habitat suitability models and improving understanding of responses to resource limitation.

How mangabey molar form differs under routine vs. fallback hard-object feeding regimes

Background Components of diet known as fallback foods are argued to be critical in shaping primate dental anatomy. Such foods of low(er) nutritional quality are often non-preferred, mechanically challenging resources that species resort to during ecological crunch periods. An oft-cited example of the importance of dietary fallbacks in shaping primate anatomy is the grey-cheeked mangabey Lophocebus albigena. This species relies upon hard seeds only when softer, preferred resources are not available, a fact which has been linked to its thick dental enamel. Another mangabey species with thick enamel, the sooty mangabey Cercocebus atys, processes a mechanically challenging food year-round. That the two mangabey species are both thickly-enameled suggests that both fallback and routine consumption of hard foods are associated with the same anatomical feature, complicating interpretations of thick enamel in the fossil record. We anticipated that aspects of enamel other than its thickness might differ between Cercocebus atys and Lophocebus albigena. We hypothesized that to function adequately under a dietary regime of routine hard-object feeding, the molars of Cercocebus atys would be more fracture and wear resistant than those of Lophocebus albigena. Methods Here we investigated critical fracture loads, nanomechanical properties of enamel, and enamel decussation in Cercocebus atys and Lophocebus albigena. Molars of Cercopithecus, a genus not associated with hard-object feeding, were included for comparison. Critical loads were estimated using measurements from 2D µCT slices of upper and lower molars. Nanomechanical properties (by nanoindentation) and decussation of enamel prisms (by SEM-imaging) in trigon basins of one upper second molar per taxon were compared. Results Protocone and protoconid critical fracture loads were significantly greater in Cercocebus atys than Lophocebus albigena and greater in both than in Cercopithecus. Elastic modulus, hardness, and elasticity index in most regions of the crown were greater in Cercocebus atys than in the other two taxa, with the greatest difference in the outer enamel. All taxa had decussated enamel, but that of Cercocebus atys uniquely exhibited a bundle of transversely oriented prisms cervical to the radial enamel. Quantitative comparison of in-plane and out-of-plane prism angles suggests that decussation in trigon basin enamel is more complex in Cercocebus atys than it is in either Lophocebus albigena or Cercopithecus cephus. These findings suggest that Cercocebus atys molars are more fracture and wear resistant than those of Lophocebus albigena and Cercopithecus. Recognition of these differences between Cercocebus atys and Lophocebus albigena molars sharpens our understanding of associations between hard-object feeding and dental anatomy under conditions of routine vs. fallback hard-object feeding and provides a basis for dietary inference in fossil primates, including hominins.

Fallback foods and foraging demographics in early Thule diets: Paleoethnobotanical and zooarchaeological results of a column sample from Ganigak (49-NOB-001), Norton Sound, Alaska

Bulk sediment samples can contribute high-resolution subsistence and paleoenvironmental data from archaeological sites excavated before the adoption of modern zooarchaeological and paleoethnobotanical recovery methods in the 1990s. We present faunal and botanical analyses of sediment samples collected from Ganigak (49-NOB-001; 1185–1465 cal CE), Norton Sound, from a “fish layer” identified by J. Louis Giddings in his excavation trench in 1948. Findings reveal that saffron cod and salmonberries were a crucial resource. Although these food items have low caloric yields, we argue that both provide essential nutrients to supplement marine-mammal dominant diets. Drawing on ethnographic accounts, we argue that saffron cod were crucial fallback resources, likely harvested by women and were relied on in times of resource scarcity. These data shed novel insight into Thule coastal subsistence strategies, which may otherwise be overlooked when the focus is on analysis of tool technologies or on unscreened faunal samples. Future research requires additional processing of sediment samples to fully understand the role of small-bodied fauna and plant foods to Thule subsistence strategies.

Basal Primatomorpha colonized Ellesmere Island (Arctic Canada) during the hyperthermal conditions of the early Eocene climatic optimum.

Anthropogenically induced warming is transforming Arctic ecosystems across a geologically short timescale, but earlier episodes of Earth history provide insights on the nature and limitations of biotic change in a rapidly warming Arctic. Late early Eocene strata (~52 Ma) of the Margaret Formation on Ellesmere Island, Nunavut, Canada sample a warm temperate ecosystem with a polar light regime situated at ~77°N paleolatitude. This extinct boreal ecosystem hosted a diversity of early Cenozoic vertebrates, including thermophilic taxa such as crocodilians and tapiroid perissodactyls. Here we describe two new species of the early primatomorphan Ignacius from Ellesmere, which are by far the northernmost known records for Paleogene Primatomorpha. Ellesmere species of Ignacius are sister taxa, indicating a single colonization of Ellesmere from farther south in North America coincident with the onset of the hyperthermal Early Eocene Climatic Optimum (EECO). The Ellesmere Ignacius clade differs from closely related taxa inhabiting mid-latitudes in being larger (thereby conforming to Bergmann's rule) and having modified dentition and muscles of mastication for a dietary regime emphasizing hard objects, possibly reflecting an increased reliance on fallback foods during long polar winters. The late early Eocene mammalian fauna of Ellesmere indicates that its unique paleoenvironment rendered it uninhabitable to some clades, including euprimates, while selected taxa were able to adapt to its challenging conditions and diversify.

Fine-scaled climate variation in equatorial Africa revealed by modern and fossil primate teeth

Variability in resource availability is hypothesized to be a significant driver of primate adaptation and evolution, but most paleoclimate proxies cannot recover environmental seasonality on the scale of an individual lifespan. Oxygen isotopecompositions (δ18O values) sampled at high spatial resolution in the dentitions of modern African primates (n = 2,352 near weekly measurements from 26 teeth) track concurrent seasonal precipitation, regional climatic patterns, discrete meteorological events, and niche partitioning. We leverage these data to contextualize the first δ18O values of two 17 Ma Afropithecus turkanensis individuals from Kalodirr, Kenya, from which we infer variably bimodal wet seasons, supported by rainfall reconstructions in a global Earth system model. Afropithecus' δ18O fluctuations are intermediate in magnitude between those measured at high resolution in baboons (Papio spp.) living across a gradient of aridity and modern forest-dwelling chimpanzees (Pan troglodytes verus). This large-bodied Miocene ape consumed seasonally variable food and water sources enriched in 18O compared to contemporaneous terrestrial fauna (n = 66 fossil specimens). Reliance on fallback foods during documented dry seasons potentially contributed to novel dental features long considered adaptations to hard-object feeding. Developmentally informed microsampling recovers greater ecological complexity than conventional isotope sampling; the two Miocene apes (n = 248 near weekly measurements) evince as great a range of seasonal δ18O variation as more time-averaged bulk measurements from 101 eastern African Plio-Pleistocene hominins and 42 papionins spanning 4 million y. These results reveal unprecedented environmental histories in primate teeth and suggest a framework for evaluating climate change and primate paleoecology throughout the Cenozoic.

Diet and feeding behavior of a group of high-altitude rhesus macaques: high adaptation to food shortages and seasonal fluctuations.

Diet and feeding behavior data are crucial to a deep understanding of the behavioral response and adaptation of primates to a high-altitude environment. From August 2019 to June 2021, we collected data on the feeding behavior of a high-altitude rhesus macaque Macaca mulatta group from Yajiang County, Western Sichuan Plateau, which has an altitude of over 3,500 m. The results showed that feeding (33.0 ± 1.8%) and moving (28.3 ± 2.6%) were the dominant behavior of rhesus macaques. Macaques ate 193 food items, comprising 11 food categories from 90 species. Our study found that plant roots (30.9 ± 30.1%) and young leaves (28.0 ± 33.1%) were the main foods eaten by macaques. The preferred foods of rhesus macaques were young leaves, fruits, and seeds, and the consumption of these items was positively correlated with its food availability. When the availability of preferred foods was low, macaques took plant roots, barks, and fallen leaves as fallback foods. In particular, roots were a dominant food item in winter, and this way of feeding became a key survival strategy. Our results suggest that, facing the relative scarcity and strong seasonal fluctuations of food resources in high-altitude habitat, macaques adopt active foraging strategies, relying on a variety of food species and adjusting flexibly their food choices based on food availability, which may help to maximize the energy efficiency of high-altitude macaques.

Effects of food availability and its seasonal changes on the dietary habits of wild silvery lutungs (Trachypithecus cristatus) in a coastal forest in west Sumatra, Indonesia

Abstract The dietary composition of primates is often affected by the availability of food, as well as seasonal variations within their habitat. This study presents quantitative data on the feeding behavior of wild silvery lutungs (Trachypithecus cristatus) inhabiting a coastal forest in West Sumatra, Indonesia. This research emphasizes the relationship between food availability and the way this changes by season. Feeding strategies of these primates was also examined. Feeding behavior of a group of wild silvery lutungs was observed for 12 months from August 2018 to July 2019, with a total observation time of 482 hours. We recorded 74 items from 37 different plant species that were included in the lutungs’ diet. Nineteen out of 37 plant species comprised > 1% of the lutung’s annual diet. They can therefore be considered the main plant food sources for the lutungs. The lutungs mainly fed on young leaves (68.3%). However, during certain months, both ripe and unripe fruit formed a major part of their diet. Plant part-based analyses showed a negative correlation between the availability of young leaves and ripe fruit feeding. Plant species-based analyses revealed few significant positive relationships between the feeding percentages of the main dietary items (mainly young leaves) and their availability. This implies that young leaves and ripe fruit were both the preferred and the fallback foods. This also indicates that lutung activity, ranging patterns, and activity at the study site are affected mainly by food distribution and availability. Further research is needed to increase the understanding of Asian colobine feeding strategies, feeding patterns, and food resource characteristics.

Early Pleistocene faunivorous hominins were not kleptoparasitic, and this impacted the evolution of human anatomy and socio-ecology

Humans are unique in their diet, physiology and socio-reproductive behavior compared to other primates. They are also unique in the ubiquitous adaptation to all biomes and habitats. From an evolutionary perspective, these trends seem to have started about two million years ago, coinciding with the emergence of encephalization, the reduction of the dental apparatus, the adoption of a fully terrestrial lifestyle, resulting in the emergence of the modern anatomical bauplan, the focalization of certain activities in the landscape, the use of stone tools, and the exit from Africa. It is in this period that clear taphonomic evidence of a switch in diet with respect to Pliocene hominins occurred, with the adoption of carnivory. Until now, the degree of carnivorism in early humans remained controversial. A persistent hypothesis is that hominins acquired meat irregularly (potentially as fallback food) and opportunistically through klepto-foraging. Here, we test this hypothesis and show, in contrast, that the butchery practices of early Pleistocene hominins (unveiled through systematic study of the patterning and intensity of cut marks on their prey) could not have resulted from having frequent secondary access to carcasses. We provide evidence of hominin primary access to animal resources and emphasize the role that meat played in their diets, their ecology and their anatomical evolution, ultimately resulting in the ecologically unrestricted terrestrial adaptation of our species. This has major implications to the evolution of human physiology and potentially for the evolution of the human brain.

Importance of subterranean fungi in the diet of bonobos in Kokolopori

Nonstaple food is a food resource which sole consumption does not allow the maintenance of regular physiological functions, thus constituting a minor portion of an individual's diet. Many primates consume nonstaple food such as meat, insects, and fungi. Hypotheses on the dietary importance of nonstaple food include its role as fallback food and as source of specific nutrients. We tested these two hypotheses by investigating mycophagy (i.e., the consumption of fungi) in a population of wild bonobos in the Kokolopori Bonobo Reserve, DRC. Specifically, we examined the relationship between fungus consumption and various factors relevant to bonobo feeding ecology (i.e., fruit abundance and the consumption of other food types). Additionally, we measured the deviation from linear travel when bonobos searched for fungi to evaluate the nature of fungus consumption (e.g., opportunistic or targeted). Lastly, we examined the nutritional content of the major fungus species consumed (Hysterangium bonobo) to test whether this food item was potentially consumed as source of specific nutrients. We found that bonobos spent a higher proportion of their time feeding on fungi when fruit abundance was higher, indicating that fungi were not consumed as a fallback food. Moreover, bonobos deviated from linear travel when visiting fungus patches more than observed when visiting fruit patches, suggesting that they actively sought out fungi. Lastly, initial analyses suggest that H. bonobo samples contained high concentration of sodium. Collectively, these results suggest that subterranean fungi appear to be attractive food source to Kokolopori bonobos, and that mycophagy may serve to supplement nutrients, like sodium, in bonobo diet.

Feeding ecology and diet of the southern geladas (Theropithecus gelada obscurus) in human-modified landscape, Wollo, Ethiopia.

Studying the dietary flexibility of primates that live in human‐modified environments is crucial for understanding their ecological adaptations as well as developing management and conservation plans. Southern gelada (Theropithecus gelada obscurus) is an endemic little‐known subspecies of gelada that inhabits human‐modified landscapes in the northern central highlands of Ethiopia. During an 18‐month period, we conducted this intensive study in an unprotected area of a human‐modified landscape at Kosheme in Wollo to investigate the feeding ecology of southern geladas and their dietary responses to seasonal variations. We quantified the monthly and seasonal diet data from a band of southern geladas using instantaneous scan sampling method at 15‐min intervals, and green grass phenology and availability using visual inspection from the randomly selected permanent plots. The overall average diet of southern geladas at Kosheme constituted grass blades 55.4%, grass undergrounds 13.2%, grass bulbs 5.6%, grass seeds 5.4%, herb leaves 4.0, fruits 7.3%, and cereal crops 5.6%. Grass blade consumption increased with increasing green grass availability, while underground food consumption increased with decreasing green grass availability, and vice versa. Southern geladas spent significantly more time feeding on the grass blades and herb leaves and significantly less time on bulbs during the wet season than the dry season. Underground grass items (rhizomes and corms) were not consumed during the wet season, but made up 22.3% of the dry season diet. Thus, although grass blades are staple diet items for geladas, underground diet items are important “fallback foods” at Kosheme. Our result shows insights into the dietary flexibility southern geladas adopt to cope with human‐modified landscapes of the north‐central Ethiopian Highlands. Thus, the study contributes to a better understanding of how changing environments shape primate ecology and evolution.

Dental microwear textures differ in pigs with overall similar diets but fed with different seeds

The thick-enameled, bunodont dentition shared by most early hominins has traditionally been interpreted as reflecting durophagy, especially in the robust genus Paranthropus. However, subsequent works on dental microwear textures (DMT) and biogeochemical compositions have challenged this hypothesis. Some authors argued that their robust morphology might have been driven by the consumption of mechanically challenging resources during periods of food scarcity. An experimental baseline using a model taxon with bunodont, thick-enameled cheek teeth, could help better interpret DMT and test hypotheses regarding the consumption of mechanically challenging foods that could be fallback foods. Besides, earlier studies have shown that DMT can track subtle dietary variations in extant taxa. This study aims at testing the hypothesis that the consumption of various seeds has an impact on DMT of bunodont mammals despite similar overall diets. Trials were conducted on four groups of domestic pigs (Sus scrofa) all fed on mixed cereal and soy flours: the control group received only flours (n = 12), and the three others were supplemented with either 20% corn kernels (n = 6), 30% barley seeds (n = 5), or 10 hazelnuts in shell per day (n = 6). We studied phases I and II facets on first molars and on fourth deciduous premolars, and applied a subsampling surface strategy to identify discriminative parameters among dietary groups. Principal Component Analyses show that DMT differ between pigs fed on different types of seeds. Our results also demonstrate that combining both crushing and shearing facets into analyses improves dietary discriminations. This study shows that variables that contribute most to dietary discriminations as selected from the subsampling strategy are mainly height parameters. These results thus support the idea that the consumption of seeds has an impact on the relief of surface textures.

Insights into short- and long-term crop-foraging strategies in a chacma baboon (Papio ursinus) from GPS and accelerometer data.

Crop‐foraging by animals is a leading cause of human–wildlife “conflict” globally, affecting farmers and resulting in the death of many animals in retaliation, including primates. Despite significant research into crop‐foraging by primates, relatively little is understood about the behavior and movements of primates in and around crop fields, largely due to the limitations of traditional observational methods. Crop‐foraging by primates in large‐scale agriculture has also received little attention. We used GPS and accelerometer bio‐loggers, along with environmental data, to gain an understanding of the spatial and temporal patterns of activity for a female in a crop‐foraging baboon group in and around commercial farms in South Africa over one year. Crop fields were avoided for most of the year, suggesting that fields are perceived as a high‐risk habitat. When field visits did occur, this was generally when plant primary productivity was low, suggesting that crops were a “fallback food”. All recorded field visits were at or before 15:00. Activity was significantly higher in crop fields than in the landscape in general, evidence that crop‐foraging is an energetically costly strategy and that fields are perceived as a risky habitat. In contrast, activity was significantly lower within 100 m of the field edge than in the rest of the landscape, suggesting that baboons wait near the field edge to assess risks before crop‐foraging. Together, this understanding of the spatiotemporal dynamics of crop‐foraging can help to inform crop protection strategies and reduce conflict between humans and baboons in South Africa.

Diet and Activity Budget in Colobus angolensis ruwenzorii at Nabugabo, Uganda: Are They Energy Maximizers?

Introduction: Colobine monkeys are specialized folivores that use foregut fermentation to digest leaves. The slow process of fermentation forces them to spend a lot of time resting and to minimize their energy expenditure to subsist on a lower-quality diet. Methods: We recorded the diet and activity budget of Colobus angolensis ruwenzorii, which form a three-tiered multi-level society, at Lake Nabugabo, Uganda, over 12 months using scan sampling on adults and subadults, to determine whether they utilize the energy minimization strategy typical of colobines. Results: We found that the annual diet was primarily comprised of high-quality food resources (young leaves 65% and fruit 31%), and fruits were the only plant part the monkeysselected when available. Both the fruits and young leaves of some species were preferred food items in some months, and mature leaf consumption correlated negatively with preferred food availability. Mature leaves appear to be a fallback food for this population but are rarely relied upon (3%). The C. a. ruwenzoriiat Nabugabo spent less time resting (40%) and more time moving (25%) than is typical for other species of black-and-white colobus. Discussion/Conclusion: The high-quality diet of this population appears to allow them to utilize an energy maximization strategy. Their reliance on food items that tend to be clumped in space and time likely explains the frequent fission-fusion behaviour that we observe between core units. Our findings demonstrate that the foraging strategies of colobines may be more flexible than was previously thought and illustrate how food availability and distribution can impact primate social organization.

Stable isotopic reconstruction of dietary changes across Late Antiquity and the Middle Ages in Tuscany

The transition from Late Antiquity to the Medieval period is considered one of the greatest periods of social, political, and economic upheaval in Europe, and has left its mark on the historical consciousness of people in this part of the world. Nevertheless, there remains considerable debate as to the degree to which the diets and economic status of different sections of society were impacted by this transition, with these so-called ‘Dark Ages’ often being uniformly considered as static and impoverished, particularly for populations along the Mediterranean rim. Such questions are especially important in central Italy, with its position at the former core of the Roman Empire leaving it most vulnerable to the major social and political shifts of the first millennium AD. However, direct insights into the diets of individuals in this region, across this key period, have been scarce, particularly in diachronic perspective. Here, we apply stable carbon (δ13C) and nitrogen (δ15N) analysis to bone collagen (n = 76), and stable carbon (δ13C) and oxygen (δ18O) isotope analysis to tooth enamel (n = 34), to human, and associated faunal, individuals dated to Late Antiquity (3rd–5th centuries AD) and the Medieval period (mid 6th–mid 13th centuries AD) in Tuscany. δ13C measurements of both tooth enamel bioapatite and bone collagen suggest that a predominantly C3 diet during Late Antiquity was gradually supplemented by increased C4 consumption during the Medieval period. We interpret this as a shift from an agricultural focus on wheat following the Roman agrarian tradition towards the inclusion of millet as a reliable fallback food. We argue that this was part of a growing local and regional resilience amongst communities in the Medieval period, with more diverse agricultural systems and cultural preferences following a transition from the Roman classical civilization toward a Germanic tradition whose economy was based on the diverse cultivation of “minor crops” and close integration of pastoral husbandry livestock.

Sustainable Peeling of Kapok Tree (Ceiba pentandra) Bark by the Chimpanzees (Pan troglodytes verus) of Como\xe9 National Park, Ivory Coast

Primates often consume either bark or cambium (inner bark) as a fallback food to complete their diet during periods of food scarcity. Wild chimpanzees exhibit great behavioral diversity across Africa, as studies of new populations frequently reveal. Since 2014, we have been using a combination of camera traps and indirect signs to study the ecology and behavior of wild chimpanzees (Pan troglodytes verus) in Comoé National Park, Ivory Coast, to document and understand the behavioral adaptations that help them to survive in a savanna–forest mosaic landscape. We found that Comoé chimpanzees peel the bark of the buttresses of kapok tree (Ceiba pentandra) trees to eat the cambium underneath. Individuals of all sex/age classes across at least six neighboring communities peeled the bark, but only during the late rainy season and beginning of the dry season, when cambium may represent an important fallback food. Baboons (Papio anubis) also target the same trees but mainly eat the bark itself. Most of the bark-peeling wounds on Ceiba trees healed completely within 2 years, seemingly without any permanent damage. We recorded chimpanzees visiting trees in early stages of wound recovery but leaving them unpeeled. Only 6% of peeled trees (N = 53) were reexploited after a year, suggesting that chimpanzees waited for the rest of the trees to regrow the bark fully before peeling them again, thus using them sustainably. Many human groups of hunter-gatherers and herders exploited cambium sustainably in the past. The observation that similar sustainable bark-peeling behavior evolved in both chimpanzees and humans suggests that it has an important adaptive value in harsh environments when other food sources become seasonally scarce, by avoiding the depletion of the resource and keeping it available for periods of scarcity.

Caching in or Falling Back at the Sevilleta: The Effects of Body Size and Seasonal Uncertainty on Desert Rodent Foraging.

Foraging in uncertain environments requires balancing the risks associated with finding alternative resources against potential gains. In arid-land environments characterized by extreme variation in the amount and seasonal timing of primary production, consumers must weigh the risks associated with foraging for preferred seeds that can be cached against fallback foods of low nutritional quality (e.g., leaves) that must be consumed immediately. Here, we explore the influence of resource scarcity, body size, and seasonal uncertainty on the expected foraging behaviors of caching rodents in the northern Chihuahaun Desert by integrating these elements with a stochastic dynamic program to determine fitness-maximizing foraging strategies. We demonstrate that resource-limited environments promote dependence on fallback foods, reducing the likelihood of starvation while increasing future risk exposure. Our results point to a qualitative difference in the use of fallback foods and the fitness benefits of caching at the threshold body size of 50 g. Above this 50-g body size threshold, we observe large fitness gains associated with the maintenance of even a modest-sized cache, whereas similar gains for smaller consumers require maintenance of unrealistically large caches. This suggests that larger-bodied consumers that cache may be less sensitive to the future uncertainties in monsoonal onset predicted by global climate scenarios, whereas smaller consumers, regardless of caching behavior, may be at greater risk.

Oral Processing Behavior of Diana Monkeys (Cercopithecus diana) in Taï National Park, Côte d’Ivoire

Primates are hypothesized to “fall back” on challenging-to-process foods when preferred foods are less available. Such dietary shifts may be accompanied by changes in oral processing behavior argued to be selectively important. Here, we examine the oral processing behavior of Diana monkeys (Cercopithecus diana) in the Taï Forest across their dietary breadth, testing relationships among food intake, fruit availability, preference, and oral processing behaviors including those involved in food ingestion and breakdown. We conducted 1,066 focal follows from April 2016 to September 2017 documenting frequencies of incisor, canine, and cheek tooth mastications (i.e., chews) per ingestive action (n = 11,906 feeding events). We used phenological survey and scan sample data collected between 2004 and 2009 to examine dietary preference and food availability. Our analyses show that Diana monkeys processed foods in significantly different ways (H₂ = 360.8, p < 0.001), with invertebrates requiring the least oral processing, fruit requiring intermediate amounts, and leaves requiring the most oral processing. There was no relationship between fruit availability and consumption of preferred or nonpreferred fruits (p > 0.05); however, preferred fruits were processed with significantly fewer mastications (i.e., less chewing) than nonpreferred fruits (U = 6,557, p < 0.001). We thus demonstrate that, when preferred foods are scarce, Diana monkeys do not fall back on difficult-to-process foods. Changes in processing profiles occurred throughout the year and not solely when preferred foods were in short supply. Though preferred fruits required less processing than nonpreferred fruits, we found no relationship between fruit preference and fruit availability. Diana monkeys’ lack of readily identifiable fallback foods may be attributable to the relatively high tree diversity and productivity of the Taï Forest. We conclude that Diana monkeys engage in resource switching, consuming a relatively easy-to-process diet year-round.

Diet and Use of Fallback Foods by Rwenzori Black-and-White Colobus (Colobus angolensis ruwenzorii) in Rwanda: Implications for Supergroup Formation

When preferred foods are scarce, one strategy employed by primates is to switch to an alternative food item of lower quality or preferability, i.e., a fallback food. In the montane rainforest of Nyungwe National Park in southwestern Rwanda, Rwenzori black-and-white colobus (Colobus angolensis ruwenzorii) (hereafter Rwenzori colobus) form a supergroup comprising hundreds of individuals. Over 13 mo we investigated how this supergroup uses resources in periods of resource abundance vs. periods of resource scarcity. Based on 5603 feeding records we first identified preferred foods and then identified fallback foods as those food categories or species whose consumption increases when preferred foods, or preferred food categories, are less available. When the availability of 19 preferred food items was low, fruticose lichens (Usnea sp.) contributed >50% of the monthly diet for the Rwenzori colobus. Moreover, consumption of lichens was significantly negatively related to the availability of preferred foods. Fruticose lichens can therefore be considered a fallback food for Rwenzori colobus that sustains the supergroup during periods of reduced food availability. This result, in combination with previous findings that mature foliage in Nyungwe is of high quality and does not elicit feeding competition, points to the importance of resources in facilitating supergroup formation. However, several other montane forests in Eastern Africa also harbor fruticose lichens and yet support only small groups of Angolan colobus, suggesting that additional factors such as sufficient forest size and limited fragmentation and hunting pressure by humans are required for supergroups to form.

Seasonal variation in energy balance of wild Japanese macaques (Macaca fucata yakui) in a warm-temperate forest: a preliminary assessment in the coastal forest of Yakushima.

Food scarcity is a major challenge for primates living in temperate forests, where food availability varies markedly among seasons. In Japanese macaques, which are exclusively distributed in temperate zones, the fat accumulation ability has been highlighted as an adaptation for survival during the lean season and for reproductive success. However, the knowledge of energetic strategies of Japanese macaques has been mainly derived from data on cool-temperate forests, where fallback foods comprise winter buds and bark. Data on Japanese macaques in warm-temperate forests where fallback foods comprise mature leaves are still lacking. We aimed to identify seasonal variations in energy balance and the relative importance of ingestion rates (dry matter intake per feeding time), energy content of the food, and feeding time in energy intake of Japanese macaques in the coastal forest of Yakushima. We estimated energy balance of 6-12 adult females from October 2012 to October 2013. We estimated energy intake based on the data on feeding behavior and energy content of the diet and calculated energy expenditure based on the previously established relationship between body mass and total energy expenditure. We also quantified urinary C-peptide, which is a non-invasive biomarker of energetic conditions. We demonstrated that energy balance was more positive in the fruit/seed-feeding period than in the mature-leaf-feeding and fruit/fungi-feeding periods and that ingestion rates were the most important component of energy intake. The present study suggests that the fat accumulation ability is an essential adaptation in Japanese macaques even in warm-temperate forests.