Maximum daily energy intake: it takes time to lift the metabolic ceiling

Conventionally, maximum capacities for energy assimilation are presented as daily averages. However, maximum daily energy intake is determined by the maximum metabolizable energy intake rate and the time available for assimilation of food energy. Thrush nightingales (Luscinia luscinia) in migratory disposition were given limited food rations for 3 d to reduce their energy stores. Subsequently, groups of birds were fed ad lib. during fixed time periods varying between 7 and 23 h per day. Metabolizable energy intake rate, averaged over the available feeding time, was 1.9 W and showed no difference between groups on the first day of refueling. Total daily metabolizable energy intake increased linearly with available feeding time, and for the 23-h group, it was well above suggested maximum levels for animals. We conclude that both intake rate and available feeding time must be taken into account when interpreting potential constraints acting on animals' energy budgets. In the 7-h group, energy intake rates increased from 1.9 W on the first day to 3.1 W on the seventh day. This supports the idea that small birds can adaptively increase their energy intake rates on a short timescale.     

Optimal foraging of a herbivorous lizard,the green iguana in a seasonal environment

Food selection was studied in free living green iguanas (Iguana iguana) throughout the year in a semiarid environment, Curaçao (Netherlands Antilles). Food intake was determined by direct observations and converted into biomass intake. Comparison between intake and biomass availability of the various food items revealed that the lizards were selective, and that changes in seasonal food availability led to periodic switching of food plants. The extent to which nutrient constraints determine iguana feeding ecology was investigated. Potential constraints were the requirements for water, digestible crude protein, and metabolizable energy. By using a linear programming model that incorporates characteristics of the food (chemical composition, energy content, item size) and requirements and constraints of the green iguanas (nutrient and energy requirements digestive tract capacity, feeding rate) it was possible to identify which factors determine food choice over the year. During the dry period, when the iguanas had no access to drinking water they consumed flowers to increase water intake, though the amount of flowers consumed was too low to cover maintenance requirements for either energy or protein. After the young leaf flush, following the early rains in May, the biomass increased, free surface water was available during showers, and the linear programming solutions indicate that food selection conformed to the protein maximization criterion. Reproduction in green iguanas shows an annual cycle, in which oviposition takes place at the end of the dry season, when intake is below maintenance levels. Females show a 8–10 month gap between acquisition of most of the protein required for egg synthesis and the act of laying. Thus, as in avian and mammalian herbivores, food availability during a period prior to the energy and protein demanding reproductive season of iguanas determines reproductive success.     

Insights from the eco‐physiological book of records: Bewick's swans outperform the canonical intake‐maximizing vertebrate

During periods of high energy demand an animal may be constrained by a physiological maximum to its energy intake rate. Predictions by allometric equations describing this maximum for endotherms were significantly surpassed during a few recent laboratory experiments on birds and mammals, being given access to food 24 h day^?1. How relevant this is in the field remains to be assessed. We predicted that Bewick's swans Cygnus columbianus bewickii might surpass this maximum during stopover on their migration. We determined intake rate by measuring initial and final biomass density, and dividing the biomass difference by the feeding time required to reach this difference. This feeding time was given by the functional response. After conversion to daily energy intake rates, these exceeded the previously assumed maximum on two of the three stopover sites studied. The exception was a stopover site where daily foraging time was limited by the tidal cycle. Our study confirms that intake rates may exceed the formerly generally supposed maximum under natural conditions when foraging is possible day and night.     

Prediction of bird-day carrying capacity on a staging site: a test of depletion models

1. The carrying capacity of a site for migratory water birds, expressed in bird-days, can be of particular conservation value. Several attempts have been made to model this carrying capacity using ideal free distribution models such as, for instance, depletion models, in which the distribution is fully determined by exploitative competition. 2. In the tests of depletion models carried out so far, no alternative models were compared; rather, one specific model was tested. We tested whether bird-days were more in accordance with birds depleting the food resource (a1) until a critical food density which just enabled survival or (a2) until a threshold food density which renders the site as profitable as an alternative site; and birds (b1) satisfying their daily requirements or (b2) maximizing daily intake. 3. We studied Bewick's swans feeding on below-ground tubers of fennel pondweed in one part of an autumn staging site. In most years between 1995 and 2005, we measured tuber biomass densities around September, November and March, and counted swans daily during their stopover in October. 4. The best fit between observed and predicted bird-days was obtained by assuming that the swans were maximizing their daily intake and depleting the tubers until a threshold biomass density (which yielded the same energetic return as the alternative food source after accounting for a small part of the initial tuber biomass being out of reach of the swans). Also in line with daily intake maximization, the daily feeding time did not differ from 10 h day(-1), the value predicted for Bewick's swans based on their feeding costs. 5. Our results suggests that the applicable model to calculate carrying capacity may depend strongly on whether birds use a site to stopover or to winter, because it determines whether the birds are more likely to use a threshold or critical food density, and to behave as energy maximizers or satisficers.     

Sex differences in digestive traits in sexually size-dimorphic birds: Insights from an assimilation efficiency experiment on Black-tailed Godwit

Digestive assimilation efficiency is considered a trait with important implications for animal ecology. However, practically all studies have ignored the importance of sex differences in food assimilation efficiency (AE). Here, we investigated sex differences in dietary and physiological parameters in the Black-tailed Godwit Limosa limosa limosa feeding on rice seeds, a species with sexual dimorphism in body size and body mass. Gross daily food intake, gross energy intake, gross energy output and metabolizable energy intake did not vary significantly between sexes, but godwit females showed lower faeces energy density and higher AE than males. Mass-specific AE was similar in males and females, and the difference in AE could be attributed to the females' greater body mass. We suggest that a differential AE could play a role in explaining sex differences in habitat or micro-habitat selection during the non-breeding season in bird species with sexual dimorphism in size. Finally, we addressed the question about assimilation efficiency accuracy in models that estimate prey acquisitions by declining shorebirds as the Black-tailed Godwit.     

Quantitative characterization of the nutrition of the free-living horse (Equus caballus) on Vodnyi Island (Manych-Gudilo Lake)

The nutritional value of plant fodder, daily consumption, and digestibility of forage were assessed in an isolated group of free-living (wild) horses inhabiting the pastures of Vodnyi Island during different seasons of 2010–2011. The digestibility was determined by the proportion between inert food components (silicon, lignin) in the diet and the feces. The daily intake of food was calculated according to the weight of the daily feces and digestibility of food. Daily food consumption of the free-living horses during the snowless period is from 8 to 14 kg/ind. and 16 kg/ind. (dry weight) during the winter period. Food digestibility changes from 49 to 54% per year; the mean digestibility is 52%. The daily metabolic energy intake during the snowy period of the year (130.7 MJ/ind.) is almost twofold higher than in spring (67.4 MJ/ind.). In all the seasons, it exceeds the requirements for energy. The free-living horses of Vodnyi Island have parameters of digestibility and consumption of forage similar to other horses.     

An energy-based model of optimal feeding-territory size

An energy-based model of feeding territoriality is described. The model predicts an optimal territory size where the territory holder's net energy intake is maximized, on a daily or seasonal time scale. Simulated effects on optimal territory size of animal size, food availability, and competitor density are in general agreement with observed relationships in a wide variety of animals. When salmonid data are used to estimate the model parameter values, predicted territory sizes are similar to those actually observed. When emigration is allowed, the model predicts that territoriality, through individual selection alone, can regulate population size, but that this regulation breaks down when initial densities exceed some threshold value. Sensitivity analysis shows optimal territory size to be most affected by those parameters influencing food intake and energy expenditure. Some alternative criteria for optimization are also discussed. An animal maximizing net foraging efficiency has a smaller territory than one maximizing net energy, but the effects of animal size, food availability, and competitor density on territory size are the same in either case.     

Living near the limits: Effects of interannual variation in food availability on diet and reproduction in a temperate primate,the Taihangshan macaque (Macaca mulatta tcheliensis)

Nutrient intake of animals is influenced by an interplay of external and internal factors, such as food availability and reproductive state, respectively. We used the nutritional geometry framework to analyze individual-based data on energy and nutrient intake in relation to reproductive state in a population of rhesus macaques (Macaca mulatta tcheliensis), which live in a harsh high-latitude habitat, the Taihangshan mountains of China, and exhibit strong reproductive seasonality. We combined data over a 3-year period on food availability, diets, reproductive output, and components of maternal investment to understand how Taihangshan macaques respond to variation in food availability and nutrition in reproduction. Our results show there was high interannual variation in availability of an important staple source of fat and carbohydrates (nonprotein energy), seeds of oak (Quercus spp). Despite this variability in seed availability skewing the dietary macronutrient ratios considerably (from 12.96% to 30.12% dietary energy from protein), total metabolizable energy intake was maintained across years during pregnancy. Lactating females had higher mean daily energy intakes than pregnant females. As in pregnant females, energy intake was maintained constant across years, but only when seed availability enabled the contribution of available protein to energy intake to be maintained between 15.32% (2013) and 17.97% (2015). In 2014, when seeds were scarce, lactating females had a shortfall in energy intake compared with 2013 and 2015. This corresponded with a reduction in the number of females giving birth (11 out of 23), but there was no interannual difference in survival rates. Compared to 2013 and 2015, in 2014 females had greater weight loss (drew on body reserves), moved less, and spent more time nursing their offspring. We discuss implications of these results for range limitation in Taihangshan macaques.     

Nutritional and behavioral effects of gorge and fast feeding in captive lions

Nonhuman animals in captivity manifest behaviors and physiological conditions that are not common in the wild. Lions in captivity face problems of obesity, inactivity, and stereotypy. To mediate common problems of captive lions, this study implemented a gorge and fast feeding schedule that better models naturalistic patterns: African lions (Panthera leo) gradually adapted from a conventional feeding program to a random gorge and fast feeding schedule. Digestibility increased significantly and food intake and metabolizable energy intake correspondingly decreased. Lions also showed an increase in appetitive active behaviors, no increase in agonistic behavior, and paced half as frequently on fast days as on feeding days. Thus, switching captive lions to a gorge and fast feeding schedule resulted in improved nutritional status and increased activity.     

The relationship of food intake and ingesta passage predicts feeding ecology in two different megaherbivore groups

Digestion, especially of plant material, is a time-dependent process. In herbivores, an increase in food intake is usually correlated to an acceleration of ingesta passage through the gut, and could hence depress digestive efficiency. Therefore, the nature of the relationship between food intake and ingesta passage (i.e. whether the increase in ingesta passage due to the increase in food intake is mild or drastic) should determine the flexibility of the feeding strategy of herbivore and omnivore species. Using two megaherbivore groups, the elephants and the hippopotamuses, as examples from opposing ends of the range of potential adaptations to this problem, we demonstrate that the species-specific relationship of food intake and ingesta passage can precisely predict feeding ecology and activity budgets. In hippos, the distinct acceleration in ingesta passage due to increased intake limits the additional energy gained from eating more forage, and explains the comparatively low food intake and short feeding times generally observed in these animals. In elephants, increased food intake only leads to a very moderate increase of ingesta passage, thus theoretically allowing to optimize energy gain by eating more, which is in accord with the high food intake and long feeding times observed in these animals. We suggest that the characterization of the intake-passage relationship in herbi- and omnivorous species is of much higher ecological relevance than the determination of a supposedly species-specific "passage time/mean retention time".     

An experiment on the relation between the feeding speed and the caloric intake through leaf eating in Japanese monkeys

In order to know the bioenergetic effect of leaf eating in Japanese monkeys experiments were conducted on caged animals. Two monkeys from the Koshima troop were fed with leaves in a cage shortly after their capture. The monkeys were tested to determine in what duration they could fulfill their daily energy requirements by solely leaf eating or by solely wheat eating. Twelve hours of feeding solely on leaves did not fulfill the monkeys' maximum daily intake, whereas 4 hr of feeding solely on wheat satisfied their daily energy requirements. The ratio of the daily intake to the daily energy consumption was 90% for leaf eating and 120% for wheat eating. It is difficult for Japanese monkeys to fulfill their daily energy requirements by leaf eating only. Thus, the combination of fruits (nuts) and leaves must be necessary for their energy intake. These facts are to be considered in the studies of feeding activity, food abundance, or the home range size.     

Induction of low-nutritious food intake by subsequent nutrient supplementation in sheep (Ovis aries)

Acceptance of and preference for a particular food depends not only on its intrinsic (e.g. nutritional) properties but also on expected or recent food experiences. An instance of this type of phenomenon has been called induction effect, which consists of an increased intake of a type of food when it precedes a hedonically preferred food in a sequence familiar to the animal, relative to controls that have access only to the less-preferred food. The purpose of our study was to assess intake induction of a low-nutritious food when followed by different high-nutritious supplements in sheep (Ovis aries). In this experiment, we ran a supplemented phase where animals fed oat hay (a low-nutritious food) in the first part of the daily feeding sessions followed by a supplement with either a high (soya bean meal; group GS) or a low (ground corn; group GC) protein–energy ratio in the second part ate more oat hay than controls that were fed oat hay in both parts of sessions (group GH). In addition, supplemented animals presented a stronger preference for oat hay over alfalfa hay than controls in a subsequent choice. When all animals received no food in the second part of the sessions (Non-supplemented phase), intake of oat hay converged to the control's intake level in all the groups, suggesting that the presence of supplements after access to oat hay was responsible for intake induction. Lastly, we repeated the supplemented phase with a different control group where animals received oat hay in the first part of the sessions and no food in the second part (group NF), thus equalizing groups in terms of the time of access to oat hay in a session. Groups GS and GC still developed higher intake of oat hay than group NF. In both supplemented phases of the experiment, we estimated animals’ daily metabolizable energy (ME) and crude protein (CP) intake. CP intake was higher in group GS than in groups GC, GH and NF, but there was no difference between group GC and the controls. In turn, groups did not differ in ME intake in the First supplemented phase, and only group GS presented higher ME intake than the rest of the groups in the Second supplemented phase. Therefore, a nutritional account of the present induction effect seems insufficient. We propose that a learned association between oat hay and the post-ingestive feedback from the subsequent high-nutritious supplements underlay sheep's intake induction and increased preference for oat hay.     

Individual variation in the ability of Columbian ground squirrels to select an optimal diet

Summary Columbian ground squirrels (Spermophilus columbianus) were examined for ability to select a diet that maximizes daily energy intake (optimal diet) under free-living field conditions. The optimal diet for each squirrel was determined given constraints (e.g. body size, feeding time) on individual foraging behavior. Most squirrels (63%) consumed a diet not significantly different from one that would maximize their daily energy intake. The remainder (37%) approached an energy maximized diet but appeared to make some incorrect foraging decisions. Both males and females appeared to approach energy maximized diets. An individual's deviation from its optimal diet is relatively constant within a season and not significantly affected by immediate environmental influences such as food abundance, thermal conditions and social environment. The energy cost of deviating from an optimal diet may be large enough to affect fitness. These results suggest that the ability to select an optimal diet can be viewed as a behavioral trait that might be subject to natural selection.     

Nutritional estimate of populations of some wild free-ranging African ungulates in grassland (Nechisar national park, Ethiopia) in dry season

The amount and nutritive value of forage plants, diet composition, digestibility of dry matter and nutrients were recorded for zebra. Grant's gazelle, Swayne's hartebeest and hippopotamus in November-December 1991 Besides, daily egest of feces, the level of food and nutrient consumption, energy and protein requirements were recorded for zebra and Grant's gazelle The digestibility of pasture forage was determined as a ratio of lignin concentration in food to the concentration m feces (lignin tracer technique), a daily intake was calculated on the basis of the daily feces egest Protein percentage m the diet of zebra and hartebeest consuming dry parts of grasses did not exceed 5% Gazelle diet consists of green parts of plants and included 18% of protein The digestibility of dry matter in nonruminants (zebra, hippopotamus) was 40-45%, in hartebeest - 50%, in gazelle - 60% Due to the abundance of dry grasses (3 7 ton ha^-1) the daily food consumption of zebra was high - 7 2 kg ind^-1 (dry weight), the metabolizable energy intake (ME) being 51 MJ Adult gazelles consumed 15-25 kg ind^-1 of food and 14-24 MJ of ME The energy requirements of adult males and non-lactating females of zebras and gazelles (48 and 13 MJ respectively) were met, the energy balance berig negative for lactating animals The daily protein requirement was not met in zebra (392-704 g md^-1 vs 134 g ind^-1 of intake) and in lactating gazelles (250 g ind^-1 vs 197 g md^-1) Non-lactating gazelles consume sufficient amount of both energy and protein due to the high feeding selectivity of the species and thanks to the abundance of burnt areas with young green after-grass m the dry period     

Anthropogenic food provisioning and immune phenotype: Association among supplemental food,body condition,and immunological parameters in urban environments

Direct or indirect supplemental feeding of free‐ranging animals occurs worldwide, resulting in significant impacts on population density or altered demographic processes. Another potential impact of increased energy intake from supplemental feeding is altered immunocompetence. As immune system maintenance is energetically costly, there may be trade‐offs between immune responses and other energy‐demanding physiological processes in individual animals. Although increased availability of food sources through supplemental feeding is expected to increase the overall immunocompetence of animals, empirical data verifying the association between supplemental feeding and different immune parameters are lacking. Understanding the potential influence of supplemental feeding on immune phenotypes is critical, as it may also impact host–pathogen dynamics in free‐ranging animals. Using urban stray cats as a study model, we tested for associations between the intensity of supplemental feeding due to cat caretaker activity (CCA); body condition; and immune phenotype (bacterial killing assay (BKA), immunoglobulin G (IgG) concentration, and leukocyte counts). Significantly higher bacterial killing ability was observed in cats from high CCA districts, whereas higher IgG concentration and eosinophil counts were observed in cats from low CCA districts. Other leukocyte counts and body condition indices showed no significant association with CCA. We observed varying patterns of different immune components in relation to supplemental feeding. Out data suggest that supplemental feeding influences immune phenotype, not only by means of energy provisioning, but also by potentially reducing exposure rates to parasite infections through stray cat behavioral changes.     

Nutritional Ecology of <Emphasis Type="Italic">Ateles chamek</Emphasis> in lowland Bolivia: How Macronutrient Balancing Influences Food Choices

All free-living animals must make choices regarding which foods to eat, with the choices influencing their health and fitness. An important goal in nutritional ecology is therefore to understand what governs animals’ diet selection. Despite large variation in the availability of different food items, Peruvian spider monkeys (Ateles chamek) maintain a relatively stable daily protein intake, but allow total energy intake to vary as a function of the composition of available food items. This is referred to as protein-dominated macronutrient balancing. Here we assess the influence of this nutritional strategy on daily and seasonal nutritional intakes, estimate the nutritional value of different foods, and interpret unusual food choices. We conducted continuous all-day observations of focal spider monkeys inhabiting a semideciduous forest in Bolivia. We recorded feeding events, collected foods, and analyzed their nutrient content. By using the Geometric Framework for nutrition, we show that individuals reached their daily end-point in nutrient space —balance between protein and nonprotein energy intake— by consuming nutritionally balanced foods or by alternating between nutritionally complementary foods. The macronutritionally balanced figs of Ficus boliviana were their primary staple food and therefore dominated their overall nutritional intake. Our results also demonstrate that spider monkeys consumed a diverse array of ripe fruits to overcome periods of fig scarcity rather than vice versa; they could obtain sufficient protein on a diet of pure fruit; and unripe figs constituted a nutritionally rewarding and reliable food resource. We hope that the approaches taken and the conclusions reached in this study will catalyze further inquiries into the nutritional ecology of frugivorous primates.     

黑龙江省完达山东部林区马鹿冬季环境容纳量估算

2005 年和2006 年冬季,在黑龙江省完达山东部林区采用分层抽样技术,测定马鹿生境中主要食物的生物量供给量。通过食物营养成分分析,确定野外生境食物营养供给量。经饲喂实验,测定圈养马鹿冬季的日营养需求。结合研究地区马鹿生境食物资源类型,以干物质、代谢能和氮为基础估算了完达山东部林区野生马鹿的营养容纳量。研究结果表明:以干物质为估算基础,完达山东部林区冬季马鹿容纳量为11 115 ± 1 419头,以代谢能为基础估算值为5 845 ± 1 077头,而基于氮的计算结果为16 958 ± 2 983头;显示该地区马鹿主要食物含氮量超出马鹿日平均需求量,而代谢能供给量则略显不足,成为种群增长的主要限制因子,所以本文以代谢能为基础估算的容纳量作为该地区冬季马鹿种群环境容纳量。此外,由于受雪被厚度、食物生物量、光照等环境因子的影响,两年估算的容纳量数值存在一定差异。      

饥饿和食物单宁酸对东方田鼠(Microtus fortis)食物摄入量和觅食行为的影响

实验室条件下,测定饥饿和食物单宁酸对东方田鼠食物摄入量和觅食行为的影响。结果表明,饥饿使实验个体的食物总摄入量增加,食物摄入率及口量大小随饥饿强度的增大而增加,而觅食频次则无显著改变,实验个体每取食回合的觅食时间呈缓慢增加的趋势,与对照组比较,觅食时间差异不显著。东方田鼠优先选择0%单宁酸食物,次为3%单宁酸食物,而对6%单宁酸食物的摄入量最少。在饥饿条件下,东方田鼠食物摄入率的增加主要源于其口量大小,觅食频次和觅摄食时间对食物摄入量增加的贡献不显著。在饥饿条件下,植食性小哺乳动物并未通过延长觅食时间,降低用于防卫、繁殖活动时间来增加食物摄入量,而是通过增加口量大小,提高其食物摄入率来满足其营养需要。验证了饥饿与植物次生化合物共同作用引起田鼠类动物生理的改变,能影响其食物摄入量及觅食行为的假设。     

Comparison of different approaches for the calculation of energy expenditure using doubly labeled water in a small mammal

The doubly labeled water (DLW) method is an isotope-based technique for the estimation of the CO(2) production, and hence energy expenditure, of free-living animals and humans. Several methods are available for the calculation of CO(2) production from the isotope fluxes, depending on different assumptions about the behavior of isotopes during the elimination process. We used the DLW method to estimate the daily energy expenditures (DEE) of 55 field voles (Microtus agrestis) held in a captive facility at 8 degrees C. We calculated DEE using both plateau and intercept approaches for estimating the sizes of the isotope dilution spaces, three different assumptions about fractionation processes, and two ways of treating the different dilution spaces of the oxygen and hydrogen isotopes. We compared the resultant DEE estimates with metabolizable energy intake (MEI) measured during a 3-d feeding trial immediately before the DLW measurements, during which the animals were in energy balance. By making different assumptions about the apparent energy absorption efficiency, we generated a range of direct estimates of MEI. When we compared DEE and MEI, we found that the two-pool model formulations consistently underestimated energy demands by up to 29.8%, depending on the assumptions made in the reference calculation. However, while our data suggest that some correction for fractionation is necessary, with the present data we were unable to separate the two most common treatments of fractionation. These data strongly support the previous suggestion that for small mammals single-pool models provide more accurate estimates of energy demands than two-pool formulation of the DLW method.     

Energetic cost of a meal in a frequent feeding lizard

Specific dynamic action (SDA) describes the rise in metabolism following feeding in animals and represents the energetic cost of digesting and assimilating a meal. The overall energetic cost of feeding may depend on whether or not an animal is post-absorptive at the time of feeding. The aim of this study was to compare the energetic cost of SDA due to feeding frequently compared with infrequently in the eastern water skink, Eulamprus quoyii. For similar quantities of food, repeated feeding incurred an energetic cost equal to 8.8% of the metabolizable energy of the meal (25,220 J), while single feeding incurred an energetic cost of 9.4% of the metabolizable energy of the meal (26,072 J). Experimental lizards maintained a rise in (VO2) that was on average 1.8 times greater than the (VO2) of the unfed controls over a 50-h interval as a result of feeding frequently. This prolonged rise in metabolism resulting from frequent feeding does not result in a higher energetic cost of SDA compared with that resulting from infrequent single feeding.