Small ruminants: Digestive capacity differences among four species weighing less than 20 kg

Small ruminants are generally classified as either browsers or frugivores. We compared intake and digestion in one browsing species, the pudu (Pudu pudu), body weight 9 kg, and three frugivorous species, the red brocket (Mazama americana), 20 kg, the bay duiker (Cephalophus dorsalis), 12 kg, and Maxwell's duiker (C. maxwellii), 9 kg. Rations comprised: a commercial grain and alfalfa pellet, a small amount of vegetables, and mixed hay. Across species, neutral-detergent fiber (insoluble fiber) consumed averaged 34.2 ± 2.6% of dry matter (DM) while the crude protein consumed averaged 16.1 ± 0.5% DM. Apparent DM digestion was similar in pudu (75.2 ± 4.7%), brocket (73.2 ± 1.1%), and Maxwell's duikers (73.0 ± 2.8%), and significantly lower (P = 0.0167) in bay duikers (67.1 ± 4.3%). There were significant differences among species in digestibilities of neutral-detergent fiber, hemicellulose, and cellulose, but they did not follow body size differences, since larger species were expected to show higher digestion coefficients for fiber compared to smaller species. The type of fiber fed may have influenced these results. Frugivores may be adapted to a diet of soluble fibers, as might be found in wild fruits, instead of the insoluble fibers in the diet fed. Passage trials were conducted on the two smallest species. The mean transit time for pudu was 29.9 ± 0.8 hr, and for the Maxwell's duiker was 42.2 ± 6.4 hr. © 1996 Wiley-Liss, Inc.     

Dietary Response of Chimpanzees and Cercopithecines to Seasonal Variation in Fruit Abundance. II. Macronutrients

In a continuation of our study of dietary differentiation among frugivorous primates with simple stomachs, we present the first comparison of differences in dietary macronutrient content between chimpanzees and cercopithecine monkeys. Previously we have shown that chimpanzee and monkey diets differ markedly in plant part and species content. We now examine whether this diet diversity is reflected in markedly different dietary macronutrient levels or the different feeding strategies yield the same macronutrient levels in their diets. For each primate group we calculated the total weighted mean dietary content of 4 macronutrients: crude lipid (lipid), crude protein (CP), water-soluble carbohydrates (WSC), and total nonstructural carbohydrates (TNC). We also calculated 4 fiber fractions: neutral-detergent fiber (NDF), which includes the subfractions hemicellulose (HC), cellulose (Cs), and sulfuric acid lignin (Ls). The HC and Cs are potentially fermentable fibers and would contribute to the energy provided by plant food, depending on the hind gut fermenting capacity of the individual primate species. The chimpanzee diet contained higher levels of WSC and TNC because during times of fruit abundance the chimpanzees took special advantage of ripe fruit, while the monkeys did not. The monkey diets contained higher levels of CP because the monkeys consumed a constant amount of leaf throughout the year. All four primate species consumed diets with similar NDF levels. However, the chimpanzees also took advantage of periods of ripe fruit abundance to decrease their Ls levels and to increase their HC levels. Conversely, the monkey diets maintained constant levels of the different fiber fractions thoughout the year. Nevertheless, despite these differences, the diets of the 4 frugivores were surprisingly similar, considering the substantial differences in body size. We conclude that the chimpanzee diet is of higher quality, particularly of lower fiber content, than expected on the basis of their body size.     

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.     

Male and female western gorilla diet: Preferred foods,use of fallback resources,and implications for ape versus old world monkey foraging strategies

Most of what is currently known about western gorilla (Gorilla gorilla) diet is based on indirect studies using fecal samples and trail signs rather than measures based on direct observations. Here we report results on adult male and female western gorilla foraging behavior, based on systematic focal observations and nutritional analyses of foods. We found that western gorillas, like other apes, are highly selective ripe fruit specialists, seeking fruit high in energy, low in antifeedants, and rare in the environment. During seasonal fruiting peaks, fruit accounted for up to 70% of feeding time. When ripe fruit was scarce, gorillas increased time spent feeding on leaves and nonpreferred fruits and herbs. Leaves were the major fallback food, accounting for up to 70% of feeding time in males and 50% in females during periods of fruit scarcity. In spite of large differences in body size, the sexes were remarkably similar in their overall diet, not differing in time spent feeding on fruit or preferred herbs. However, the male consistently fed more often and on a greater variety of leaves than did females, whereas females fed more often on fallback herbs and termites. Our findings, when considered in light of previous findings on sympatric mangabeys, indicate that the foraging strategy of western gorillas is broadly similar to that of chimpanzees and orangutans, and distinct from that of old world monkeys. Am J Phys Anthropol 140:727–738, 2009. © 2009 Wiley-Liss, Inc.     

Hardness of cercopithecine foods: implications for the critical function of enamel thickness in exploiting fallback foods

We evaluate the hardness of foods consumed by sympatric Cercopithecus ascanius (redtail guenons) and Lophocebus albigena (grey-cheeked mangabeys), and consider how selection might operate to influence foraging adaptations. Since L. albigena has among the thickest dental enamel in extant primates and is commonly referred to as a hard-object consumer, we predicted that their diet would be harder than that of the guenon. Data on diet and food hardness (as measured by resistance to puncture and crushing) were collected between June-October of 1997 at Kibale National Park, Uganda, and were compared to similar data collected in Kibale between 1991-1994. Contrary to what we predicted, there was no difference in dietary hardness when the puncture resistance of all fruit consumed by the two species was compared (31 tree species in both study periods). However, in June-October 1997, L. albigena exploited a diet more resistant to puncture and crushing than C. ascanius. This difference is largely explained by the higher percentage of bark and seeds consumed by the L. albigena during this period. We suggest that it is the difference in the mechanical properties of fallback foods during critical periods that may have served as the selective pressure for thick enamel in L. albigena.     

'Cooking as a biological trait'

No human foragers have been recorded as living without cooking, and people who choose a 'raw-foodist' life-style experience low energy and impaired reproductive function. This suggests that cooking may be obligatory for humans. The possibility that cooking is obligatory is supported by calculations suggesting that a diet of raw food could not supply sufficient calories for a normal hunter-gatherer lifestyle. In particular, many plant foods are too fiber-rich when raw, while most raw meat appears too tough to allow easy chewing. If cooking is indeed obligatory for humans but not for other apes, this means that human biology must have adapted to the ingestion of cooked food (i.e. food that is tender and low in fiber) in ways that no longer allow efficient processing of raw foods. Cooking has been practiced for ample time to allow the evolution of such adaptations. Digestive adaptations have not been investigated in detail but may include small teeth, small hind-guts, large small intestines, a fast gut passage rate, and possibly reduced ability to detoxify. The adoption of cooking can also be expected to have had far-reaching effects on such aspects of human biology as life-history, social behavior, and evolutionary psychology. Since dietary adaptations are central to understanding species evolution, cooking appears to have been a key feature of the environment of human evolutionary adaptedness. Further investigation is therefore needed of the ways in which human digestive physiology is constrained by the need for food of relatively high caloric density compared to other great apes.     

Variation on Frugivory: The Diet of Venezuelan White-Faced Sakis

White-faced sakis (Pithecia pithecia) are Neotropical seed predators that ingest a mixed diet of fruit, leaves, and insects. We report timed feeding data for a 12-mo period on a group of 8 white-faced sakis occupying an island—a portion of their original home range—in Lago Guri, Venezuela. We collected fruit and leaf samples, dried them in the field, and analyzed them to measure nutrient content—free simple sugars (FSS), crude protein (CP), lipids, and total nonstructural carbohydrates (TNC)—and the presence of antifeedants: total tannins, condensed tannins and dietary fiber. We weighted nutrients and antifeedants by timed feeding samples to estimate actual intake. Then we compared intake among months and seasons. Compared with other frugivores, the average monthly intake of lipids was extremely high (16.1% by dry matter estimate(DM)), attributed to ingestion of young seeds and other plant parts that were relatively high in lipids, e.g., seed arils. Intake of FSS and CP were relatively low: 3.4% DM and 6.5% DM, respectively. The average intake of total cell wall or neutral detergent fiber (NDF = 38.4% DM) was only slightly lower than the range reported for colobines. Average intake of tannins was within the range reported for cercopithecines: condensed tannins of 3.3% Quebracho units standard (QU). We suggest that white-faced sakis accept a trade-off for food items that are fibrous or astringent if they are also rich in lipids. White-faced sakis expand the typical definition of primate fruit-eater in their high lipid-relatively high NDF-low FSS diet.