Effects of Reproductive Status on Energy Intake,Ingestion Rates,and Dietary Composition of Female <Emphasis Type="BoldItalic">Cebus capucinus</Emphasis> at Santa Rosa,Costa Rica

The limiting factor for fitness in female primates is the acquisition of high-quality food, i.e., food that is high in energy and nutrients, such as protein, fat, and carbohydrates. Reproductive status can influence female feeding patterns, e.g., lactating females in some primate species consume greater quantities of food and specific nutrients than do nonlactating females. We examined the energy intake, ingestion rate, and composition of the diet in female white-faced capuchins in 3 reproductive states: lactating, gestating, and cycling. We observed 12 reproductively active females for 7 mo and compared their energy intake, ingestion rates, and intake rates of nutrients: protein, fat, sugar, and fiber. Lactating females took in significantly more energy per hour while feeding than pregnant and cycling females did. Lactating females also ingested significantly more food items per hour, but they did not spend more time eating than other females did, and they did not differ in the composition of their diet as measured by insect consumption and proportion of protein. Pregnant and cycling females did not differ from each other in any of the measures. We predicted that as the infants aged and began to move independently to forage and play, their mothers’ energy intake rates would decrease in concert with decreased energy demands by the infant. We found a statistically significant relationship between these 2 factors, with infant age explaining 75.4% of variation in mothers’ energy intake, supporting previous studies that found lactation to be the most energetically expensive reproductive state.     

An experimental analysis of ingestion rates in an omnivorous species

Food intake is difficult to estimate under natural conditions. We investigated ingestion rates of 14 different food types in 26 captive capuchin monkeys (Cebus apella). The procedure consisted in weighing a piece of food and using a two alternative choice tests to present food to the subject, alone in its cage. We recorded the food chosen and the time it took the subject to consume the food entirely. Consumption time was converted into ingestion rates (g/s) for each food type. Ingestion rates of food types significantly differed, and the difference was significantly higher among foods than among subjects. In particular, ingestion rates of the fruits were higher than those of human-processed food. Interestingly, food preferences were significantly related to energy intake rate, i.e., to the amount of energy ingested per unit of time, but not with ingestion rates or energy content alone. The energy acquired by eating different types of food cannot be calculated on the basis of the time spent eating unless a correction factor for each given food (or similar ones) is applied. Future controlled studies should provide field researchers with such corrections factors, possibly using foods collected in the wild.     

Food competition in captive female sooty mangabeys (Cercocebus torquatus atys)

We studied the social and foraging behavior of two captive groups of sooty mangabeys under two different spatial food situations. These food conditions were clumped (food was placed in a box) and dispersed (food was dispersed over the entire enclosure). In each group five adult females and two adult males were observed. As a criterion for food competition, individual differences in the relative food intake were used. Adult female mangabeys had a linear, stable, and unidirectional dominance hierarchy. Access to food was rank dependent among females only under clumped food distribution, as current models of the evolution of primate social systems predict. However, feeding success appeared to be mediated not by female but by male agonistic behavior toward females. High-ranking females received relatively less aggression from males and could, therefore, stay and feed longer in the feeding area. Male tolerance of higher-ranking females seems to mediate female feeding success under restricted food resources. The establishment of a special relationship with a high-ranking male might, therefore, be a strategy to get better access to food. This study demonstrates that female competition for access to food should not be analyzed separately from male influences on females and suggests that a more integral role of males in socioecological models of the evolution of primate social systems should be considered.     

Social organization of a stable natal group of captive Guyanese squirrel monkeys (<Emphasis Type="Italic">Saimiri sciureus sciureus</Emphasis>)

Socioecological models suggest competition for food, foraging efficiency, predation, infanticide risk, and the costs of dispersal regulate primate social structure and organization. Wild populations of squirrel monkeys (Saimiri spp.) appear to conform to the predictions of the predation/competition socioecological model (Sterck et al. in Behav Ecol Sociobiol 41:291–309, 1997) and the dispersal/foraging efficiency model (Isbell in Kinship and behavior in primates. Oxford University, New York, pp 71–108, 2004). However, squirrel monkeys in captivity are reported to maintain patterns of social behavior observed in their wild conspecifics despite different food distribution, predation risk, and dispersal options. This behavioral similarity suggests squirrel monkeys’ social behavior has limited flexibility to respond to environmental changes. In this study, we experimentally evaluated the flexibility of social behavior within a captive group of S. sciureus. First, we determined whether dominance and affiliative relationships observed under normal laboratory conditions (with abundant, widely distributed, food; no dispersal option; and no predators) better matched published reports of relationships among wild conspecifics or the predictions of the predation/competition model. Second, we made preferred food items defensible to determine whether dominance interactions would become more frequent and linear, as predicted by the model. The model correctly predicted rates of dominance behavior in both conditions and a linear hierarchy in the defensible food condition but did not predict the consistent affiliative relationships and linear dominance hierarchy observed in normal lab conditions. Although hierarchies were linear and male dominant, manipulating food distribution changed the dominant individual within each sex. Our findings suggest interaction rates adapt more rapidly than social structure to environmental changes in Saimiri and recommend caution in interpreting tests of socioecological models.     

Variation in langur social organization in relation to the socioecological model, human habitat alteration, and phylogenetic constraints

The socioecological model is to date the best evolutionary model to explain variation in primate behaviour. Some species or populations, however, deviate from the predictions. These deviations may be due to a disequilibrium between evolutionary causes and behavioural adaptations, caused by recent human changes of the environment. The relationship between human habitat alteration and primate social behaviour is reviewed and investigated for langurs. Provisioning affects the spatial distribution of food. In these areas, but also in areas with natural monopolizable food sources, female dominance relationships are linear, but not nepotistic. This does not fit into the evolutionary model. Provisioning also affects the temporal distribution of food. This reduces the seasonality of mating, increases female monopolizability and gives rise to more one-male groups than in undisturbed areas. A human reduction of the number of predators leads to fewer males per group. It also results in female philopatry. Infanticide risk was higher in disturbed than in undisturbed areas. This was not caused by the lower proportion of one-male groups in disturbed areas, but by the lack of female dispersal. Thus, female behaviour was affected by human habitat disturbance in a way that does not fit the socioecological model. However, the extension of habitat disturbance does not explain all results. We could say that the model is refuted. Phylogenetic constraints, however, do explain the behaviour of despotic Hanuman langurs. Such phylogenetic constraints complement the socioecological model. To understand the evolutionary history of a current set of features, these two approaches should be studied simultaneously.     

Ingestion patterns and daily energy intake on a sugary diet: the Red Lory Eos bornea and the Malachite Sunbird Nectarinia famosa

This study examines whether nectarivorous birds regulate daily energy intake as proposed by Lloyd in 1991. Two Old World nectarivorous species, a large non-passerine, the Red Lory Eos bornea, and a small passerine, the Malachite Sunbird Nectarinia famosa, were fed 0.25 mol/1 sucrose (9%), 0.73 mol/1 sucrose [24%] or 0.73 mol/1 glucose in separate laboratory trials to determine hourly and overall daily rate of sugar intake and consumption. Overall daily energy intake rates of the Malachite Sunbird and the Red Lory support the hypothesis of regulated energy intake for nectarivorous Old World birds. However, the species differ in their ingestion patterns through the day. The Red Lory ingests large volumes initially, regardless of sugar type. This is possibly a consequence of their large size and having a crop in which food can be stored. The Malachite Sunbird showed more regular hourly consumption through the day, and no change in mass during the day. Intake rates of both species were greater on lower sugar concentrations.     

Feeding rate as valuable information in primate feeding ecology

In this review I outline studies on wild non-human primates using information on feeding rate, which is defined as the food intake per minute on a dry-weight basis; further, I summarize the significance of feeding rate in primate feeding ecology. The optimal foraging theory has addressed three aspects of animal feeding: (1) optimal food patch choice, (2) optimal time allocation to different patches, and (3) optimal food choice. In order to gain a better understanding of these three aspects, the feeding rate itself or its relevance indices (e.g., rates of calorie and protein intake) could be appropriate measures to assess the quality of food and food patches. Moreover, the feeding rate plays an essential role in estimation of total food intake, because it varies greatly for different food items and the feeding time is not a precise measure. The feeding rate could also vary across individuals who simultaneously feed on the same food items in the same food patch. Body size-dependent and rank-dependent differences in the feeding rate sometimes cause individuals to take strategic behavioral options. In the closing remarks, I discuss the usefulness of even limited data on feeding rate obtained under adverse observational conditions in understanding primate feeding ecology.     

A nutritional analysis of foraging in the Malabar giant squirrel (Ratufa indica)

The effect of nutrients and their availability on the diet of the herbivorous Malabar giant squirrel Ratufa indica (Sciuridae) was investigated at Magod and Bhimashankar in western India. The daily consumption of food items (percent wet diet) and the intake rates of these items and the contained nutrients (wet g s^-1) were determined by continuous observation of focal animals. Water content was a significant positive predictor of relative food item consumption while mineral contents in general had the opposite effect. The intake rates of water and more digestible nutrients such as nonstructural carbohydrates, as well as the intake rate of minerals such as zinc (at Magod), were significant positive predictors of the relative contribution of an item to the daily diet, thus indicating considerations of feeding costs versus benefits. Tannins, some alkaloids, and other secondary metabolites may negatively influence food choice. Protein content, relative to digestibility reducers, influenced food item consumption only at Bhimashankar. There was seasonal variation in daily biomass consumption. At Bhimashankar, daily biomass consumption increased with the proportion of fruit in the diet while this did not occur at Magod. This is perhaps a result of the higher water content and the lower content of some soluble nutrients within fruit at Bhimashankar relative to Magod. There was also intra-month variation between individual squirrels in daily biomass of food consumed. Squirrels consumed ephemeral food items opportunistically and non-ephemeral items such as mature leaves and bark on a regular daily basis. Squirrels probably obtained minerals and nitrogen from both fruit (especially seeds) and non-fruit sources (mature leaves and bark in the case of minerals, young and mature leaves in the case of nitrogen). However, they obtained lipid and non-structural carbohydrates mostly from fruit. Squirrels were selective in their utilization of tree species on a monthly basis, but this selectivity was not evident over a longer time period because individuals were constrained to use different phenological stages of tree species present within their territories. Large body size in this squirrel permits dietary flexibility and enables an overall generalist feeding strategy.     

捕食风险对高原鼠兔食物大小选择的影响

文章报道了捕食风险条件下高原鼠兔对食物大小选择的格局。在实验箱中放置艾虎以改变捕食风险水平, 食物按体积大小分为4种食物项目, 并测定各项目摄入率和取食单个食物项目的进食时间, 结果表明, 摄入率与进食时间依食物项目体积的增大而增加。将大食物与小食物项目配对并供高原鼠兔选择时, 食物项目的利用率视环境状况而不同。捕食风险处理中, 小食物利用率依其进食时间的减少而增加, 其程度与所配对的食物项目的摄入率和进食时间有关。在捕食风险的作用下, 高原鼠兔的食物选择格局反映了能量摄取与风险避免间的权衡。     

Foraging behavior adjustments related to changes in nectar sugar concentration in phyllostomid bats

Nectar-feeding bats regulate their food ingestion in response to changes in sugar concentration as a way to achieve a constant energy intake. However, their digestive capability to assimilate sugars can limit their total energy intake, particularly when sugar concentration in nectar is low. Our experimental study evaluated the effect that changes in sugar concentration of nectar have on the foraging behavior of the nectar-feeding bats Glossophaga soricina and Leptonycteris yerbabuenae in captivity. We measured foraging behavior and food intake when bats fed at different concentrations of sucrose (5, 15, 25 and 35%wt/vol.). To compensate for low-energy intake, both bat species reduced their flight time, and increased feeding time when sugar concentration decreased. Our results suggest that nectar-feeding bats in nature confront two scenarios with complementary ecological effects: 1) bats feeding on dilute nectars (i.e. ≤15%wt/vol.) should increase the number of flowers visited per night enhancing pollination, and 2) bats feeding on concentrated nectars could spend more time flying, including long- and short-distance-flights increasing food patch exploration for use during subsequent nights, and thus enhancing plant gene flow. Further studies on foraging behavior of nectarivorous bats under natural conditions are necessary to corroborate these hypotheses.     

Downy woodpecker foraging behavior: foraging by expectation and energy intake rate

Summary I describe an artificial patch system that was used to study the foraging behavior of free-roaming downy woodpeckers (Picoides pubescens) in a woodlot in southeastern Michigan. The artificial patches used were thin logs into which were drilled small holes to hold food items (bits of sunflower seed kernels). Downy woodpeckers would systematically search the holes of a patch for food items and thus by manipulating the food distribution within the patches, the birds could be made to experience differing rates of energy intake while foraging.Simple deterministic theories of optimal foraging in patchy environments indicate that an optimal forager, who experiences a decreasing rate of energy intake while foraging in a patch, should leave a patch when its rate of energy intake falls below the average intake rate for the overall environment. In other words, an optimal forager is continually assessing the quality of a patch and makes decisions as to when to leave a patch via its energy intake rate. When the downy woodpeckers studied could encounter any one of several types of patches each with differing, decreasing rates of energy intake, they followed a patch quality assessment strategy similar to that suggested by theory. Upon encountering a single type of patch for a number of consecutive days, however, the birds appeared to forage according to prior expectations of patch quality and not according to a quality assessment strategy based on energy intake rates. The observed expectations were not related to the number of food items per patch but they appeared to be based on expectations of when or where to leave a patch.     

Added Sugar,Macro- and Micronutrient Intakes and Anthropometry of Children in a Developing World Context

Objective

The objective of this study was to determine the relationship between added sugar and dietary diversity, micronutrient intakes and anthropometric status in a nationally representative study of children, 1–8.9 years of age in South Africa.

Methods

Secondary analysis of a national survey of children (weighted n = 2,200; non weighted n = 2818) was undertaken. Validated 24-hour recalls of children were collected from mothers/caregivers and stratified into quartiles of percentage energy from added sugar (% EAS). A dietary diversity score (DDS) using 9 food groups, a food variety score (FVS) of individual food items, and a mean adequacy ratio (MAR) based on 11 micronutrients were calculated. The prevalence of stunting and overweight/obesity was also determined.

Results

Added sugar intake varied from 7.5–10.3% of energy intake for rural and urban areas, respectively. Mean added sugar intake ranged from 1.0% of energy intake in Quartile 1 (1–3 years) (Q1) to 19.3% in Q4 (4–8 years). Main sources of added sugar were white sugar (60.1%), cool drinks (squash type) (10.4%) and carbonated cool drinks (6.0%). Added sugar intake, correlated positively with most micronutrient intakes, DDS, FVS, and MAR. Significant negative partial correlations, adjusted for energy intake, were found between added sugar intake and intakes of protein, fibre, thiamin, pantothenic acid, biotin, vitamin E, calcium (1–3 years), phosphorus, iron (4–8 years), magnesium and zinc. The prevalence of overweight/obesity was higher in children aged 4–8 years in Q4 of %EAS than in other quartiles [mean (95%CI) % prevalence overweight 23.0 (16.2–29.8)% in Q4 compared to 13.0 (8.7–17.3)% in Q1, p = 0.0063].

Conclusion

Although DDS, FVS, MAR and micronutrient intakes were positively correlated with added sugar intakes, overall negative associations between micronutrients and added sugar intakes, adjusted for dietary energy, indicate micronutrient dilution. Overweight/obesity was increased with higher added sugar intakes in the 4–8 year old children.     

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.     

Unpacking chimpanzee (Pan troglodytes) patch use: Do individuals respond to food patches as predicted by the marginal value theorem?

The marginal value theorem is an optimal foraging model that predicts how efficient foragers should respond to both their ecological and social environments when foraging in food patches, and it has strongly influenced hypotheses for primate behavior. Nevertheless, experimental tests of the marginal value theorem have been rare in primates and observational studies have provided conflicting support. As a step towards filling this gap, we test whether the foraging decisions of captive chimpanzees (Pan troglodytes) adhere to the assumptions and qualitative predictions of the marginal value theorem. We presented 12 adult chimpanzees with a two-patch foraging environment consisting of both low-quality (i.e., low-food density) and high-quality (i.e., high-food density) patches and examined the effect of patch quality on their search behavior, foraging duration, marginal capture rate, and its proxy measures: giving-up density and giving-up time. Chimpanzees foraged longer in high-quality patches, as predicted. In contrast to predictions, they did not depress high-quality patches as thoroughly as low-quality patches. Furthermore, since chimpanzees searched in a manner that fell between systematic and random, their intake rates did not decline at a steady rate over time, especially in high-quality patches, violating an assumption of the marginal value theorem. Our study provides evidence that chimpanzees are sensitive to their rate of energy intake and that their foraging durations correlate with patch quality, supporting many assumptions underlying primate foraging and social behavior. However, our results question whether the marginal value theorem is a constructive model of chimpanzee foraging behavior, and we suggest a Bayesian foraging framework (i.e., combining past foraging experiences with current patch sampling information) as a potential alternative. More work is needed to build an understanding of the proximate mechanisms underlying primate foraging decisions, especially in more complex socioecological environments.     

Difference in food selection between patas monkeys (Erythrocebus patas) and tantalus monkeys (<Emphasis Type="Italic">Cercopithecus aethiops tantalus</Emphasis>) in Kala Maloue National Park,Cameroon, in relation to nutrient content

Phytochemical or nutrient analyses of primate diets have revealed clues to their food selection in a single species. On the other hand, few interspecific comparisons of phytochemical or nutrient composition of primate diets have been made, although diets are considered to differ in phytochemical or nutrient content from primate species to species, since different species have different body weights and different morphological and physiological characteristics. I compared the nutrient content of diet between patas monkeys (Erythrocebus patas) and tantalus monkeys (Cercopithecus aethiops tantalus) living sympatrically in Cameroon. Patas subsisted on a smaller number of food items, most of which were also tantalus food items. Then, I compared the protein–fiber ratio and the available energy content of the food items eaten by patas (patas foods) with those items eaten only by tantalus (tantalus foods). Both variables were higher in patas than tantalus foods, although there was no significant difference in available energy of plant foods. Next, when I performed discriminant analysis for patas foods and tantalus foods, employing the above two variables, a discriminant function with positive coefficients for both variables was obtained. The mean discriminant-function score of patas foods was higher than that of tantalus foods. Despite being somewhat larger in weight, patas selectively fed on a smaller number of foods of higher quality than did tantalus. I discuss why the results are inconsistent with a well known body weight–diet relationship (Jarman–Bell principle). Energy-efficient locomotion enables patas to exploit not only small dispersed food items of high quality but also areas where high-quality foods are distributed in clumps. Electronic Publication     

松嫩平原旱地生境芦苇种群不同龄级根茎的干物质贮藏及水溶糖含量

通过对松嫩平原旱地生境单优种群落芦苇种群不同龄级根茎的调查测定,分析了一个生长季内3个生育期芦苇种群各龄级根茎干物质贮量和水溶糖含量的季节变化.结果表明:各生育期低龄级芦苇种群根茎中干物质贮量和水溶糖含量均较少,且与高龄级的差异较大;随着生长季的进程,低龄级根茎中干物质贮量和水溶糖含量迅速增加,且与高龄级的差异逐步缩小.在整个生长季,芦苇种群各龄级根茎均具有养分消耗和再贮藏乃至超补偿性贮藏的活性,其中,幼龄级根茎的活性更大.高龄级根茎的干物质贮量和水溶糖含量有一个逐年累积的增加过程.根茎干物质贮量在龄级间和龄级内的差异均达到了极显著水平(P<0.01),并且龄级间的差异大于龄级内.水溶糖含量仅在龄级间差异达到显著水平(P<0.05).随着龄级的增加,芦苇种群根茎的干物质贮量和水溶糖含量均呈二次曲线变化.     

Fluid intake rates in ants correlate with their feeding habits

This study investigates the techniques of nectar feeding in 11 different ant species, and quantitatively compares fluid intake rates over a wide range of nectar concentrations in four species that largely differ in their feeding habits. Ants were observed to employ two different techniques for liquid food intake, in which the glossa works either as a passive duct-like structure (sucking), or as an up- and downwards moving shovel (licking). The technique employed for collecting fluids at ad libitum food sources was observed to be species-specific and to correlate with the presence or absence of a well-developed crop in the species under scrutiny. Workers of ponerine ants licked fluid food during foraging and transported it as a droplet between their mandibles, whereas workers of species belonging to phylogenetically more advanced subfamilies, with a crop capable of storing liquids, sucked the fluid food, such as formicine ants of the genus Camponotus. In order to evaluate the performance of fluid collection during foraging, intake rates for sucrose solutions of different concentrations were measured in four ant species that differ in their foraging ecology. Scaling functions between fluid intake rates and ant size were first established for the polymorphic species, so as to compare ants of different size across species. Results showed that fluid intake rate depended, as expected and previously reported in the literature, on sugar concentration and the associated fluid viscosity. It also depended on both the species-specific feeding technique and the extent of specialization on foraging on liquid food. For similarly-sized ants, workers of two nectar-feeding ant species, Camponotus rufipes (Formicinae) and Pachycondyla villosa (Ponerinae), collected fluids with the highest intake rates, while workers of the leaf-cutting ant Atta sexdens (Myrmicinae) and a predatory ant from the Rhytidoponera impressa-complex (Ponerinae) did so with the lowest rate. Calculating the energy intake rates in mg sucrose per unit time, licking was shown to be a more advantageous technique at higher sugar concentrations than sucking, whereas sucking provided a higher energy intake rate at lower sugar concentrations.     

The Relationship of Sugar to Population-Level Diabetes Prevalence: An Econometric Analysis of Repeated Cross-Sectional Data

While experimental and observational studies suggest that sugar intake is associated with the development of type 2 diabetes, independent of its role in obesity, it is unclear whether alterations in sugar intake can account for differences in diabetes prevalence among overall populations. Using econometric models of repeated cross-sectional data on diabetes and nutritional components of food from 175 countries, we found that every 150 kcal/person/day increase in sugar availability (about one can of soda/day) was associated with increased diabetes prevalence by 1.1% (p <0.001) after testing for potential selection biases and controlling for other food types (including fibers, meats, fruits, oils, cereals), total calories, overweight and obesity, period-effects, and several socioeconomic variables such as aging, urbanization and income. No other food types yielded significant individual associations with diabetes prevalence after controlling for obesity and other confounders. The impact of sugar on diabetes was independent of sedentary behavior and alcohol use, and the effect was modified but not confounded by obesity or overweight. Duration and degree of sugar exposure correlated significantly with diabetes prevalence in a dose-dependent manner, while declines in sugar exposure correlated with significant subsequent declines in diabetes rates independently of other socioeconomic, dietary and obesity prevalence changes. Differences in sugar availability statistically explain variations in diabetes prevalence rates at a population level that are not explained by physical activity, overweight or obesity.     

Does gut function limit hummingbird food intake?

Many nectar-feeding bird species decrease food intake when sugar concentration in food is increased. This feeding response can be explained by two alternative hypotheses: compensatory feeding and physiological constraint. The compensatory feeding hypothesis predicts that if birds vary intake to maintain a constant energy intake to match energy expenditures, then they should increase intake when expenditures are increased. Broad-tailed hummingbirds were presented with sucrose solutions at four concentrations (292, 584, 876, and 1,168 mmol L(-1)) and exposed to two environmental temperatures (10 degrees and 22 degrees C). Birds decreased volumetric food intake in response to sugar concentration. However, when they were exposed to a relatively sudden drop in environmental temperature and, hence, to an acute increase in thermoregulatory energy expenditures, they did not increase their rate of energy consumption and lost mass. These results support the existence of a physiological constraint on feeding intake. A simple chemical reactor model based on intestinal morphology and in vitro measurements of sucrose hydrolysis predicted observed intake rates closely. This model suggests that intestinal sucrose hydrolysis rates were near maximal and, thus, may have imposed limits to sugar assimilation. Although sugar assimilation was high (95%), the proportions of excreted sucrose, glucose, and fructose found in excreta differed significantly. The monosaccharides glucose and fructose were about eight and three times more abundant than sucrose, respectively. Broad-tailed hummingbirds are small high-altitude endotherms that face unpredictable weather and the energetic expense of premigratory fattening. Digestive processes have the potential to impose severe challenges to their energy budgets.     

Nutritional Differences between Two Orangutan Habitats: Implications for Population Density

Bottom-up regulatory factors have been proposed to exert a strong influence on mammalian population density. Studies relating habitat quality to population density have typically made comparisons among distant species or communities without considering variation in food quality among localities. We compared dietary nutritional quality of two Bornean orangutan populations with differing population densities in peatland habitats, Tuanan and Sabangau, separated by 63 km. We hypothesized that because Tuanan is alluvial, the plant species included in the orangutan diet would be of higher nutritional quality compared to Sabangau, resulting in higher daily caloric intake in Tuanan. We also predicted that forest productivity would be greater in Tuanan compared to Sabangau. In support of these hypotheses, the overall quality of the diet and the quality of matched dietary items were higher in Tuanan, resulting in higher daily caloric intake compared to Sabangau. These differences in dietary nutritional quality may provide insights into why orangutan population density is almost two times greater in Tuanan compared to Sabangau, in agreement with a potentially important influence of diet quality on primate population density.