Intake Rate (intake + rate)

Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Intake Rate

  • energy intake rate
  • food intake rate


  • Selected Abstracts


    How a mega-grazer copes with the dry season: food and nutrient intake rates by white rhinoceros in the wild

    FUNCTIONAL ECOLOGY, Issue 2 2006
    A. M. SHRADER
    Summary 1Few studies have investigated how free-ranging wild herbivores adjust their food intake rate and nutrient gains during the dry season. Our study focused on the largest extant grazer, the white rhinoceros (Ceratotherium simum Burchell 1817). Field measurements were made on changes in bite mass, bite rate and nutrient concentrations of food eaten during the dry season. 2As the dry season progressed, the quality and availability of food resources declined. During this time white rhinos foraged mainly in high-quality short and woodland grasslands. Late in the dry season they also used flushes of green grass in previously burnt Themeda grasslands. 3Bite mass increased linearly with increasing sward height, while bite rate declined. Intake rate was determined primarily by bite mass and thus tended to increase linearly with sward height. Maximum bite mass and intake rate was obtained in swards >20 cm. 4White rhinos did not compensate for seasonal declines in food quality by adjusting their food intake rate or diet breadth. We suggest that white rhinos mobilize fat reserves to help meet their nutritional needs during the dry season. [source]


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

    IBIS, Issue 3 2000
    COLLEEN T. DOWNS
    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. [source]


    Browsing in a heterogeneons savanna

    ECOGRAPHY, Issue 5 2000
    C. Skarpe
    Large herbivores generally depend on and interact with a food resource that is heterogeneous at different spatial scales. Plants allocate resources to rapid growth or to defence mechanisms depending on the availability of resources relative to loss of resources from herbivory. Herbivores select food and feeding habitats in order to maximize intake rate of nutrients and digestible energy, while avoiding chemical and structural deterrents. To optimize foraging, herbivores select habitats and food items in a hierarchical way, and different attracting and deterring factors may govern selection at different scales. We studied the impact of twig biting by a guild of indigenous browsers in three vegetation types in a semi-arid savanna in Botswana. The heaviest browsing pressure was in the vegetation type richest in preferred plant species, although that type was also richest in defended species. There were large differences in relative utilization between plant species, and ranking of species was roughly similar in the different vegetation types. Browsing pressure varied between species from almost 0-30%. Overall, spinescent trees were less browsed than non-spinescent ones, and evergreen species were less browsed than deciduous ones. In two of the three vegetation types there was a negative correlation between browsing pressure on a species and its frequency. There was a high incidence of rebrowsing, and once a tree had been browsed, the probability that it would be browsed again increased. The results largely agree with predictions based on the resource availability hypothesis, the scarcity accessibility hypothesis and recent theories on the significance of plant defences and on plant's response to browsing and the subsequent response by herbivores on the plant's responses. [source]


    Effects of predator-induced visual and olfactory cues on 0+ perch (Perca fluviatilis L.) foraging behaviour

    ECOLOGY OF FRESHWATER FISH, Issue 2 2006
    V. N. Mikheev
    Abstract,,, Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis, were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius, as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch. [source]


    Bioenergetic and pharmacokinetic model for exposure of common loon (Gavia Immer) chicks to methylmercury

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2007
    William H. Karasov
    Abstract A bioenergetics model was used to predict food intake of common loon (Gavia immer) chicks as a function of body mass during development, and a pharmacokinetics model, based on first-order kinetics in a single compartment, was used to predict blood Hg level as a function of food intake rate, food Hg content, body mass, and Hg absorption and elimination. Predictions were tested in captive growing chicks fed trout (Salmo gairdneri) with average MeHg concentrations of 0.02 (control), 0.4, and 1.2 ,g/g wet mass (delivered as CH3HgCl). Predicted food intake matched observed intake through 50 d of age but then exceeded observed intake by an amount that grew progressively larger with age, reaching a significant overestimate of 28% by the end of the trial. Respiration in older, nongrowing birds probably was overestimated by using rates measured in younger, growing birds. Close agreement was found between simulations and measured blood Hg, which varied significantly with dietary Hg and age. Although chicks may hatch with different blood Hg levels, their blood level is determined mainly by dietary Hg level beyond approximately two weeks of age. The model also may be useful for predicting Hg levels in adults and in the eggs that they lay, but its accuracy in both chicks and adults needs to be tested in free-living birds. [source]


    How a mega-grazer copes with the dry season: food and nutrient intake rates by white rhinoceros in the wild

    FUNCTIONAL ECOLOGY, Issue 2 2006
    A. M. SHRADER
    Summary 1Few studies have investigated how free-ranging wild herbivores adjust their food intake rate and nutrient gains during the dry season. Our study focused on the largest extant grazer, the white rhinoceros (Ceratotherium simum Burchell 1817). Field measurements were made on changes in bite mass, bite rate and nutrient concentrations of food eaten during the dry season. 2As the dry season progressed, the quality and availability of food resources declined. During this time white rhinos foraged mainly in high-quality short and woodland grasslands. Late in the dry season they also used flushes of green grass in previously burnt Themeda grasslands. 3Bite mass increased linearly with increasing sward height, while bite rate declined. Intake rate was determined primarily by bite mass and thus tended to increase linearly with sward height. Maximum bite mass and intake rate was obtained in swards >20 cm. 4White rhinos did not compensate for seasonal declines in food quality by adjusting their food intake rate or diet breadth. We suggest that white rhinos mobilize fat reserves to help meet their nutritional needs during the dry season. [source]


    Release of cell contents and comminution of particles of perennial ryegrass herbage during ingestion by dairy cows fed indoors or grazing

    GRASS & FORAGE SCIENCE, Issue 3 2006
    A. Boudon
    Abstract The effect of feeding indoors fresh perennial ryegrass vs. grazing on ingestive behaviour, release of cell contents and comminution of particles during ingestion, as well as on gas production of ingested boli fermented in vitro, was studied. Indoor feeding and grazing were compared using four dairy cows according to a triple reversal design with six periods. Chemical and morphological composition of the ingested herbage was similar for both indoor feeding and grazing treatments. The intake rate was markedly higher indoors compared with grazing [52·1 vs. 22·9 g dry matter (DM) min,1] with heavier boli and less saliva added per gram of DM intake. The proportions of intracellular nitrogen and chlorophyll released during mastication after ingestion of herbage fed indoors were lower, and the median size of the particles in the boli was larger (5·97 vs. 4·44 mm) compared with grazing. As a result, the rate of gas production in vitro was also lower for herbage fed indoors compared with grazing (0·423 vs. 0·469 mL min,1 g,1 incubated DM). Indoor feeding or grazing may have limited consequences in vivo on the kinetics of availability of nutrients for micro-organisms in the rumen, because the consequences of the more extensive physical damage suffered by herbage ingested at grazing could be compensated by a lower intake rate. [source]


    The effect of sward structure as influenced by ryegrass genotype on bite dimensions and short-term intake rate by dairy cows

    GRASS & FORAGE SCIENCE, Issue 1 2003
    P. D. Barrett
    Abstract The effects of genotypic variation in ryegrasses on sward structure, bite dimensions and intake rate by dairy cows were investigated. Two experiments were conducted. In Experiment 1, swards were in a vegetative state whereas, in Experiment 2, they were partly reproductive and were taller with higher herbage mass but lower leaf proportion than in Experiment 1. Applicability of relationships between sward structure and bite characteristics, previously established from artificial or hand-constructed swards, to field conditions were tested. Additional short-term intake rates and/or sward structural characteristics were considered as indicators of potential intake for use in protocols for the evaluation of grass varieties. Four cultivars were studied: AberElan, Twins (diploid and tetraploid perennial ryegrasses respectively), Polly, a hybrid ryegrass (perennial × Italian ryegrass) and Multimo (Italian ryegrass), each established in 200-m2 plots in four replicated blocks. Herbage intake rate was determined by short-term liveweight change (taking account of insensible weight loss) using 16 dairy cows allocated to four balanced groups with each plot grazed by one group for a 1-h assessment period. One block was grazed per day, over a 4-d experimental period, with each group grazing each variety in a complete crossover design. Sward characteristics and bite rate were also measured in both experiments. Bite dimensions were subsequently estimated, with bite depth being determined as a function of extended tiller height (ETH) in both experiments. Within both experiments, bite mass and intake rate did not differ significantly between swards of different cultivars despite swards containing Multimo generally having a higher ETH and water-soluble carbohydrate concentration and lower green leaf mass, sward bulk density and neutral-detergent fibre concentration than the other swards. However, bite depth was significantly higher (P < 0·01) in swards containing Multimo swards than in the others and, in Experiment 1, bite depth, as a proportion of ETH, was higher in swards containing Multimo and lower in those containing Twins than in the other two cultivars, whereas there was no difference in Experiment 2. Taking both experiments together, the mean bite depth was 0·5 of ETH with sward bulk density accounting for almost half the variance in the relationship between bite depth and ETH. The bulk density of the bite (bite mass per unit bite volume), measured in Experiment 2, followed a similar pattern to sward bulk density, increasing in the order Multimo, Polly, AberElan and Twins. It is concluded that the relationships between sward characteristics and bite dimensions, derived from artificial swards, are applicable to field swards, although the range in natural ryegrass sward characteristics is usually not as wide as in experiments using artificial swards. Lack of precision in the measurement of short-term intake and in sward-based measurements is likely to preclude their use in the evaluation of grass varieties. [source]


    Longer guts and higher food quality increase energy intake in migratory swans

    JOURNAL OF ANIMAL ECOLOGY, Issue 6 2008
    Jan A. Van Gils
    Summary 1Within the broad field of optimal foraging, it is increasingly acknowledged that animals often face digestive constraints rather than constraints on rates of food collection. This therefore calls for a formalization of how animals could optimize food absorption rates. 2Here we generate predictions from a simple graphical optimal digestion model for foragers that aim to maximize their (true) metabolizable food intake over total time (i.e. including nonforaging bouts) under a digestive constraint. 3,The model predicts that such foragers should maintain a constant food retention time, even if gut length or food quality changes. For phenotypically flexible foragers, which are able to change the size of their digestive machinery, this means that an increase in gut length should go hand in hand with an increase in gross intake rate. It also means that better quality food should be digested more efficiently. 4These latter two predictions are tested in a large avian long-distance migrant, the Bewick's swan (Cygnus columbianus bewickii), feeding on grasslands in its Dutch wintering quarters. 5Throughout winter, free-ranging Bewick's swans, growing a longer gut and experiencing improved food quality, increased their gross intake rate (i.e. bite rate) and showed a higher digestive efficiency. These responses were in accordance with the model and suggest maintenance of a constant food retention time. 6These changes doubled the birds' absorption rate. Had only food quality changed (and not gut length), then absorption rate would have increased by only 67%; absorption rate would have increased by only 17% had only gut length changed (and not food quality). 7The prediction that gross intake rate should go up with gut length parallels the mechanism included in some proximate models of foraging that feeding motivation scales inversely to gut fullness. We plea for a tighter integration between ultimate and proximate foraging models. [source]


    Shorebird predation of horseshoe crab eggs in Delaware Bay: species contrasts and availability constraints

    JOURNAL OF ANIMAL ECOLOGY, Issue 3 2007
    S. GILLINGS
    Summary 1Functional responses , the relationship between resource intake rate and resource abundance , are widely used in explaining predator,prey interactions yet many studies indicate that resource availability is crucial in dictating intake rates. 2For time-stressed migrant birds refuelling at passage sites, correct decisions concerning patch use are crucial as they determine fattening rates and an individual's future survival and reproduction. Measuring availability alongside abundance is essential if spatial and temporal patterns of foraging are to be explained. 3A suite of shorebird species stage in Delaware Bay where they consume horseshoe crab Limulus polyphemus eggs. Several factors including spawning activity and weather give rise to marked spatial and temporal variation in the abundance and availability of eggs. We undertook field experiments to determine and contrast the intake rates of shorebird species pecking for surface and probing for buried eggs. 4Whether eggs were presented on the sand surface or buried, we demonstrate strong aggregative responses and rapid depletion (up to 80%). Depletion was greater at deeper depths when more eggs were present. No consistent give-up densities were found. Type II functional responses were found for surface eggs and buried eggs, with peck success twice as high in the former. Maximum intake rates of surface eggs were up to 83% higher than those of buried eggs. 5Caution is needed when applying functional responses predicted on the basis of morphology. Our expectation of a positive relationship between body size and intake rate was not fully supported. The smallest species, semipalmated sandpiper, had the lowest intake rate but the largest species, red knot, achieved only the same intake rate as the mid-sized dunlin. 6These functional responses indicate that probing is rarely more profitable than pecking. Currently, few beaches provide egg densities sufficient for efficient probing. Areas where eggs are deposited on the sand surface are critical for successful foraging and ongoing migration. This may be especially true for red knot, which have higher energetic demands owing to their larger body size yet appear to have depressed intake rates because they consume smaller prey than their body size should permit. [source]


    Predation of beech seed by mice: effects of numerical and functional responses

    JOURNAL OF ANIMAL ECOLOGY, Issue 6 2005
    WENDY A. RUSCOE
    Summary 1The functional response of post-dispersal seed predators (house mouse, Mus musculus) to absolute densities of southern beech seed (Nothofagus solandri var. cliffortioides) was studied in laboratory and field trials. House mice showed a Type II (hyperbolic) functional response to seed availability and this was not modified by the presence of an alternative food source. 2Maximum daily intake rate of beech seeds during field trials averaged 1042 seeds mouse,1. This is sufficient to provide house mice with both the energy and protein required for growth and reproduction. 3We explicitly incorporated the functional response into the numerical response of house mice to beech seed, measured for field populations monitored in a New Zealand beech forest. House mice showed a strong numerical response to beech seed intake rate that was modified by some density-dependent mechanism(s). 4We developed a model that simulated seedfall, house mouse population growth and seed reserve depletion over one year. We found that the previously reported decline in house-mouse populations in beech forests during spring and summer is likely to be related to spring beech seed germination that renders seed no longer available as a food source for house mice. 5From our simulation model it does not appear that house-mouse populations can completely eat-out beech seed reserves prior to germination in a year of large seedfall. ,Masting' behaviour in New Zealand native beech trees is therefore sufficient to satiate an eruptive population of an exotic mammalian omnivore, despite the lack of a long co-evolutionary interaction. [source]


    Gain functions for large herbivores: tests of alternative models

    JOURNAL OF ANIMAL ECOLOGY, Issue 1 2005
    KATE R. SEARLE
    Summary 1The gain function describes the amount of food consumed in a patch as a function of patch residence time. Gain functions play a central role in foraging theory but alternative functional forms portraying dynamics of gain have not been evaluated. We evaluated the strength of evidence in the data for alternative gain functions of mule deer (Odocoileus hemionus, Rafinesque 1817) and blue duikers (Cephalophus monticola, Blythe 1848) feeding in patches composed of different plant species and plant sizes. 2Gain functions decelerated with patch residence time, but there was considerable variation among individual animals and patch types in the nature of this response. Asymptotic and piecewise-linear models received the greatest support in the data. 3Deceleration in gain was caused by a composite of effects that retarded instantaneous intake rate, including reductions in bite mass and increases in bite interval (time between successive bites). Bite interval increased as a result of increases in processing time of accumulated forage in the mouth, rather than increases in time allocated to cropping. 4We demonstrated that unwarranted assumptions about the shape of gain functions can have profound effects on predictions of patch models. Predictions of the classical patch model using purely asymptotic gain functions contrasted sharply with predictions of model-averaged gain functions that were supported by the data. [source]


    A simulation model of foraging behaviour and the effect of predation risk

    JOURNAL OF ANIMAL ECOLOGY, Issue 1 2000
    Jane F. Ward
    Summary 1.,The effect of predation risk on the distribution of animals foraging in a patchy environment was explored using a simulation model based on the work of Bernstein, Kacelnik & Krebs (1988, 1991), extended to incorporate predation risk. 2.,Modelled foragers consume prey within patches, having different prey densities, at a rate that depends only on prey density and interference from other foragers in the patch. Prey density remains constant (no depletion). A forager leaves a patch if its intake rate drops below its estimate of the average intake rate available in the environment. This estimate is continually updated by taking a weighted average of current intake and the previous estimate, giving a simple learning process. Decisions on whether to leave are made at regular intervals and a forager leaving a patch may arrive at random at any other patch. 3.,Simulation results were sensitive to the computational scheme used to represent estimates of average intake rate in the environment and to the way in which foragers' decisions were distributed over time, illustrating the need for careful formulation of such models. 4.,Predation risk was modelled as a cost that reduced effective intake, and could be distributed uniformly or skewed to patches of high prey density. The effects of different levels and distributions of predation risk on distribution of foragers were examined using model parameters broadly appropriate to hedgehogs (Erinaceous europaeus L.) foraging for earthworms (Lumbricus spp.) and risking opportunistic predation by badgers (Meles meles L.). The distribution of foragers with respect to prey density took an ,ideal free' form for zero or uniform risk, and was domed when cost of predation risk was relatively high and concentrated in the richer patches, as might be the case when predators and foragers share a common food resource. [source]


    Lack of an osmotic constraint on intake rate of the eastern curlew Numenius madagascariensis

    JOURNAL OF AVIAN BIOLOGY, Issue 4 2006
    Rachel Blakey
    Rates of food intake in animals consuming abundant prey can be constrained by the rates of digestion or excretion of ingested substances, such as salt, particularly so in the animals that regularly migrate between freshwater and saltwater environments. We tested this hypothesis in a long-distance migrant shorebird, the eastern curlew Numenius madagascariensis (suborder Charadrii), foraging on intertidal decapods in eastern Australia. We predicted that if food intake rates are constrained osmotically, individuals with access to freshwater and less saline prey (FW group) would have higher rates of food and water intake than individuals with seawater-only access (SW group). Food intake rates did not differ between the FW and SW groups (0.14 g ash-free dry mass min,1), nor did the water influx rates (0.75 g,min,1). Salt intake rates were lower at FW sites (19.3 versus 23.3 mg NaCl min,1) and overall they were similar to those of marine birds. Food intake rate in the eastern curlew appeared limited by digestive rather than by osmoregulatory capacity. [source]


    Time allocation between feeding and incubation in uniparental arctic-breeding shorebirds: energy reserves provide leeway in a tight schedule

    JOURNAL OF AVIAN BIOLOGY, Issue 3 2006
    Ingrid Tulp
    Birds with uniparental incubation may face a time allocation problem between incubation and feeding. Eggs need regular warming to hatch successfully, but the parent must leave the nest to feed and safeguard its own survival. Time allocation during incubation is likely to depend on factors influencing egg cooling rates, parental energy requirements and feeding intake rate. How this allocation problem is resolved was subject of this study on arctic-breeding shorebirds. We compared incubation rhythms between four uniparental shorebird species differing in size and expected to find both species differences and weather effects on the organisation of incubation. Attentive behaviour and responses to variation in weather showed a remarkable consistency across species. All species alternated feeding bouts (recesses) with brooding bouts throughout the day. Recesses were concentrated in the warmer parts of the day, while recess duration showed little diurnal variation. Despite continuous daylight, a pronounced day-night rhythmicity was apparent. The four species in this study spent a similar proportion (13,19%) of the time off their nest. After correction for weather effects, the number of recesses was largest in the smallest species, while recess duration was longest in the largest species. Total recess time per day increased on cold days through an increase of mean recess length, while the number of recesses decreased. Comparing our observations to predictions derived from criteria that birds might use to organise their attentive behaviour, showed that the limits are set by parental requirements, while the energy stores of adults provide some leeway for short-term adjustments to environmental variability. If breeding birds trade off feeding time against incubation time, energy stores are expected to be influenced by weather. We expected uniparental species to be more likely to show weather effects on condition than biparentals, as in the latter ,off duty' time is much larger and independent of weather. This prediction was tested by comparing energy stores in two uniparental species and a biparental congener. While body mass of uniparental incubators decreased after a period with low temperatures, body mass of the biparental species did not. [source]


    Retrodicting patch use by foraging swans in a heterogeneous environment using a set of functional responses

    OIKOS, Issue 3 2009
    Bart A. Nolet
    Effective conservation of important bird areas requires insight in the number of birds an area can support, and how this carrying capacity changes with habitat modifications. When food depletion is the dominant mechanism of competition, it should in principle be possible to calculate the total time foragers can spend per patch from their functional response (intake rate as a function of food density). However, in the field there are likely to be factors modulating the functional response. In this study previously published results of experiments on captive Bewick's swans were used to obtain functional responses of swans digging for tubers of Fennel pondweed on different foraging substrates: sandy and clayey sediment, and in shallow and deep water. In a field study, four 250×250 m sections belonging to different types (sandy,shallow, clayey,shallow, sandy,deep and clayey,deep) were delineated. Here tubers were sampled with sediment corers in three years, both before and after swan exploitation in autumn, and swans were observed and mapped from a hide in two of these years. Giving-up tuber biomass densities varied among sections. Substitution of these giving-up densities in the derived patch-type-specific functional responses yielded the quitting net energy intake rates in the four sections. As expected from the marginal value theorem, the quitting net energy intake rates did not vary among sections. Moreover, the observed foraging pressure (total foraging time per area) per patch type was in quantitative agreement with the integrated functional responses. These results suggest that in spatially heterogeneous environments, patch exploitation by foragers can be predicted from their functional responses after accounting for foraging substrate. [source]


    The influence of bite size on foraging at larger spatial and temporal scales by mammalian herbivores

    OIKOS, Issue 12 2007
    Lisa A. Shipley
    Organisms respond to their heterogeneous environment in complex ways at many temporal and spatial scales. Here, I examine how the smallest scale process in foraging by mammalian herbivores, taking a bite, influences plants and herbivores over larger scales. First, because cropping bites competes with chewing them, bite size influences short-term intake rate of herbivores within plant patches. On the other hand, herbivores can chew bites while searching for new ones, thus influencing the time spent vigilant and intake rate as animals move among food patches. Therefore, bite size affects how much time herbivores must spend foraging each day. Because acquiring energy is necessary for fitness, herbivores recognize the importance of bite size and select bites, patches and diets based on tradeoffs between harvesting rates, digestion, and sheering forces. In turn, induced structural defenses of plants, such as thorns, allow plants to respond immediately to herbivory by reducing bite size and thus tissue loss. Over evolutionary time, herbivores have adapted mouth morphology that allows them to maximize bite size on their primary forage plant, whereas plants faced with large mammalian herbivores have adapted structures such as divarication that minimize bite size and protect themselves from herbivory. Finally, bite size available among plant communities can drive habitat segregation and migration of larger herbivores across landscapes. [source]


    An experimental analysis of ingestion rates in an omnivorous species

    AMERICAN JOURNAL OF PRIMATOLOGY, Issue 5 2008
    M. Stammati
    Abstract 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. Am. J. Primatol. 70:510,513, 2008. © 2008 Wiley-Liss, Inc. [source]


    Radio frequency magnetic field effects on molecular dynamics and iron uptake in cage proteins

    BIOELECTROMAGNETICS, Issue 4 2010
    Oscar Céspedes
    Abstract The protein ferritin has a natural ferrihydrite nanoparticle that is superparamagnetic at room temperature. For native horse spleen ferritin, we measure the low field magnetic susceptibility of the nanoparticle as 2.2,×,10,6,m3,kg,1 and its Néel relaxation time at about 10,10,s. Superparamagnetic nanoparticles increase their internal energy when exposed to radio frequency magnetic fields due to the lag between magnetization and applied field. The energy is dissipated to the surrounding peptidic cage, altering the molecular dynamics and functioning of the protein. This leads to an increased population of low energy vibrational states under a magnetic field of 30,µT at 1,MHz, as measured via Raman spectroscopy. After 2,h of exposure, the proteins have a reduced iron intake rate of about 20%. Our results open a new path for the study of non-thermal bioeffects of radio frequency magnetic fields at the molecular scale. Bioelectromagnetics 31:311,317, 2010. © 2010 Wiley-Liss, Inc. [source]


    Effects of predator-induced visual and olfactory cues on 0+ perch (Perca fluviatilis L.) foraging behaviour

    ECOLOGY OF FRESHWATER FISH, Issue 2 2006
    V. N. Mikheev
    Abstract,,, Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis, were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius, as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch. [source]


    How a mega-grazer copes with the dry season: food and nutrient intake rates by white rhinoceros in the wild

    FUNCTIONAL ECOLOGY, Issue 2 2006
    A. M. SHRADER
    Summary 1Few studies have investigated how free-ranging wild herbivores adjust their food intake rate and nutrient gains during the dry season. Our study focused on the largest extant grazer, the white rhinoceros (Ceratotherium simum Burchell 1817). Field measurements were made on changes in bite mass, bite rate and nutrient concentrations of food eaten during the dry season. 2As the dry season progressed, the quality and availability of food resources declined. During this time white rhinos foraged mainly in high-quality short and woodland grasslands. Late in the dry season they also used flushes of green grass in previously burnt Themeda grasslands. 3Bite mass increased linearly with increasing sward height, while bite rate declined. Intake rate was determined primarily by bite mass and thus tended to increase linearly with sward height. Maximum bite mass and intake rate was obtained in swards >20 cm. 4White rhinos did not compensate for seasonal declines in food quality by adjusting their food intake rate or diet breadth. We suggest that white rhinos mobilize fat reserves to help meet their nutritional needs during the dry season. [source]


    The effect of sward structure as influenced by ryegrass genotype on bite dimensions and short-term intake rate by dairy cows

    GRASS & FORAGE SCIENCE, Issue 1 2003
    P. D. Barrett
    Abstract The effects of genotypic variation in ryegrasses on sward structure, bite dimensions and intake rate by dairy cows were investigated. Two experiments were conducted. In Experiment 1, swards were in a vegetative state whereas, in Experiment 2, they were partly reproductive and were taller with higher herbage mass but lower leaf proportion than in Experiment 1. Applicability of relationships between sward structure and bite characteristics, previously established from artificial or hand-constructed swards, to field conditions were tested. Additional short-term intake rates and/or sward structural characteristics were considered as indicators of potential intake for use in protocols for the evaluation of grass varieties. Four cultivars were studied: AberElan, Twins (diploid and tetraploid perennial ryegrasses respectively), Polly, a hybrid ryegrass (perennial × Italian ryegrass) and Multimo (Italian ryegrass), each established in 200-m2 plots in four replicated blocks. Herbage intake rate was determined by short-term liveweight change (taking account of insensible weight loss) using 16 dairy cows allocated to four balanced groups with each plot grazed by one group for a 1-h assessment period. One block was grazed per day, over a 4-d experimental period, with each group grazing each variety in a complete crossover design. Sward characteristics and bite rate were also measured in both experiments. Bite dimensions were subsequently estimated, with bite depth being determined as a function of extended tiller height (ETH) in both experiments. Within both experiments, bite mass and intake rate did not differ significantly between swards of different cultivars despite swards containing Multimo generally having a higher ETH and water-soluble carbohydrate concentration and lower green leaf mass, sward bulk density and neutral-detergent fibre concentration than the other swards. However, bite depth was significantly higher (P < 0·01) in swards containing Multimo swards than in the others and, in Experiment 1, bite depth, as a proportion of ETH, was higher in swards containing Multimo and lower in those containing Twins than in the other two cultivars, whereas there was no difference in Experiment 2. Taking both experiments together, the mean bite depth was 0·5 of ETH with sward bulk density accounting for almost half the variance in the relationship between bite depth and ETH. The bulk density of the bite (bite mass per unit bite volume), measured in Experiment 2, followed a similar pattern to sward bulk density, increasing in the order Multimo, Polly, AberElan and Twins. It is concluded that the relationships between sward characteristics and bite dimensions, derived from artificial swards, are applicable to field swards, although the range in natural ryegrass sward characteristics is usually not as wide as in experiments using artificial swards. Lack of precision in the measurement of short-term intake and in sward-based measurements is likely to preclude their use in the evaluation of grass varieties. [source]


    Time budgets of Snow Geese Chen caerulescens and Ross's Geese Chen rossii in mixed flocks: implications of body size, ambient temperature and family associations

    IBIS, Issue 1 2009
    JÓN EINAR JÓNSSON
    Body size affects foraging and forage intake rates directly via energetic processes and indirectly through interactions with social status and social behaviour. Ambient temperature has a relatively greater effect on the energetics of smaller species, which also generally are more vulnerable to predator attacks than are larger species. We examined variability in an index of intake rates and an index of alertness in Lesser Snow Geese Chen caerulescens caerulescens and Ross's Geese Chen rossii wintering in southwest Louisiana. Specifically we examined variation in these response variables that could be attributed to species, age, family size and ambient temperature. We hypothesized that the smaller Ross's Geese would spend relatively more time feeding, exhibit relatively higher peck rates, spend more time alert or raise their heads up from feeding more frequently, and would respond to declining temperatures by increasing their proportion of time spent feeding. As predicted, we found that Ross's Geese spent more time feeding than did Snow Geese and had slightly higher peck rates than Snow Geese in one of two winters. Ross's Geese spent more time alert than did Snow Geese in one winter, but alert rates differed by family size, independent of species, in contrast to our prediction. In one winter, time spent foraging and walking was inversely related to average daily temperature, but both varied independently of species. Effects of age and family size on time budgets were generally independent of species and in accordance with previous studies. We conclude that body size is a key variable influencing time spent feeding in Ross's Geese, which may require a high time spent feeding at the expense of other activities. [source]


    How starvation risk in Redshanks Tringa totanus results in predation mortality from Sparrowhawks Accipiter nisus

    IBIS, Issue 2008
    WILL CRESSWELL
    Redshanks Tringa totanus that are preyed upon by Sparrowhawks Accipiter nisus at the Tyninghame Estuary, Firth of Forth, Scotland, provide an example of how the starvation,predation risk trade-off results in mortality. In this trade-off, animals cannot always optimize anti-predation behaviour because anti-predation behaviours, such as avoiding predators, are usually incompatible with foraging behaviours that might maximize intake rates. Therefore, as animals compensate for starvation risk, predation risk increases. Sparrowhawks are the main direct cause of death in Redshanks at Tyninghame. Sparrowhawk attack rate is determined by Redshank vulnerability, and vulnerability decreases as group size and distance to cover increase, and probably as spacing decreases. But reduction of predation vulnerability reduces feeding rate because areas away from cover are less food-profitable and grouping results in increased interference competition. Increased starvation risk in midwinter means Redshanks are forced to feed on highly profitable prey, Orchestia amphipods, the behaviour of which means that Redshanks are forced to feed vulnerably, in widely spaced groups, close to predator-concealing cover. Therefore, it is the constraints that limit the ability of Redshanks to feed in large, dense flocks away from cover that ultimately lead to mortality. We investigate this hypothesis further by testing the prediction that mortality can be predicted directly by cold weather and population density. We demonstrate that the overall number of Redshanks and the proportion of Redshanks killed increase in cold months when controlling for population size. We also demonstrate that the proportion of Redshanks killed increases when there are fewer Redshanks present, because the success rate of hunting Sparrowhawks increases, probably because effective management of predation risk through flocking is constrained by a low population size. Redshanks therefore provide an example of how directly mortality caused by predation arises from starvation risk and other constraints that prevent animals from optimizing anti-predation behaviour. [source]


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

    IBIS, Issue 3 2000
    COLLEEN T. DOWNS
    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. [source]


    Predator size, prey size and threshold food densities of diving ducks: does a common prey base support fewer large animals?

    JOURNAL OF ANIMAL ECOLOGY, Issue 5 2009
    Samantha E. Richman
    Summary 1. Allometry predicts that a given habitat area or common prey biomass supports fewer numbers of larger than smaller predators; however, birds from related taxa or the same feeding guild often deviate from this pattern. In particular, foraging costs of birds may differ among locomotor modes, while intake rates vary with accessibility, handling times and energy content of different-sized prey. Such mechanisms might affect threshold prey densities needed for energy balance, and thus relative numbers of different-sized predators in habitats with varying prey patches. 2. We compared the foraging profitability (energy gain minus cost) of two diving ducks: smaller lesser scaup (Aythya affinis, 450,1090 g) and larger white-winged scoters (Melanitta fusca, 950,1800 g). Calculations were based on past measurements of dive costs with respirometry, and of intake rates of a common bivalve prey ranging in size, energy content and burial depth in sediments. 3. For scaup feeding on small prey <12 mm long, all clams buried deeper than 5 cm were unprofitable at realistic prey densities. For clams buried in the top 5 cm, the profitability threshold decreased from 216 to 34 clams m,2 as energy content increased from 50 to 300 J clam,1. 4. For larger scoters feeding on larger prey 18,24 mm long, foraging was profitable for clams buried deeper than 5 cm, with a threshold density of 147 m,2 for clams containing 380 J clam,1. For clams <5 cm deep, the threshold density decreased from 86 to 36 clams m,2 as energy content increased from 380 to 850 J clam,1. If scoters decreased dive costs by swimming with wings as well as feet (not an option for scaup), threshold prey densities were 11,12% lower. 5. Our results show that threshold densities of total prey numbers for different-sized ducks depend on prey size structure and depth in the sediments. Thus, heterogeneity in disturbance regimes and prey population dynamics can create a mosaic of patches favouring large or small predators. Whether a given area or total prey biomass will support greater numbers of larger or smaller predators will vary with these effects. [source]


    Shorebird predation of horseshoe crab eggs in Delaware Bay: species contrasts and availability constraints

    JOURNAL OF ANIMAL ECOLOGY, Issue 3 2007
    S. GILLINGS
    Summary 1Functional responses , the relationship between resource intake rate and resource abundance , are widely used in explaining predator,prey interactions yet many studies indicate that resource availability is crucial in dictating intake rates. 2For time-stressed migrant birds refuelling at passage sites, correct decisions concerning patch use are crucial as they determine fattening rates and an individual's future survival and reproduction. Measuring availability alongside abundance is essential if spatial and temporal patterns of foraging are to be explained. 3A suite of shorebird species stage in Delaware Bay where they consume horseshoe crab Limulus polyphemus eggs. Several factors including spawning activity and weather give rise to marked spatial and temporal variation in the abundance and availability of eggs. We undertook field experiments to determine and contrast the intake rates of shorebird species pecking for surface and probing for buried eggs. 4Whether eggs were presented on the sand surface or buried, we demonstrate strong aggregative responses and rapid depletion (up to 80%). Depletion was greater at deeper depths when more eggs were present. No consistent give-up densities were found. Type II functional responses were found for surface eggs and buried eggs, with peck success twice as high in the former. Maximum intake rates of surface eggs were up to 83% higher than those of buried eggs. 5Caution is needed when applying functional responses predicted on the basis of morphology. Our expectation of a positive relationship between body size and intake rate was not fully supported. The smallest species, semipalmated sandpiper, had the lowest intake rate but the largest species, red knot, achieved only the same intake rate as the mid-sized dunlin. 6These functional responses indicate that probing is rarely more profitable than pecking. Currently, few beaches provide egg densities sufficient for efficient probing. Areas where eggs are deposited on the sand surface are critical for successful foraging and ongoing migration. This may be especially true for red knot, which have higher energetic demands owing to their larger body size yet appear to have depressed intake rates because they consume smaller prey than their body size should permit. [source]


    Resolving the departures of observed results from the Ideal Free Distribution with simple random movements

    JOURNAL OF ANIMAL ECOLOGY, Issue 4 2004
    A. L. Jackson
    Summary 1The Ideal Free Distribution (IFD) is one of the most widely applied theoretical concepts in ecology. Many experimental tests of the IFD incorporating unequal competitors have revealed three consistent departures of observed results from those predicted by the theory. Specifically these are: (1) the full range of predicted equilibria are rarely realized; (2) under-matching of individuals to resource inputs; and (3) continued movement of individuals after equilibrium is reached. 2It has been suggested previously that a model including simple random movements can explain simultaneously all three of these departures. The acceptance of this theory has been hindered by arguments about model construction relating to the timing of events and whether an analytical or individual-based model is more appropriate. 3Here we present the first internally consistent and biologically realistic model of the IFD incorporating random non-IFD movements (movements made at a rate independent of intake rates). We use this model to confirm that random movements alone can explain all three of the observed departures from the IFD. Furthermore, it is not necessary to have any detailed a priori knowledge about the motivation behind the non-IFD movements, in order to predict their consequences. We expect non-IFD movements to be widespread in animal systems, and so warrant further experimental consideration and investigation. [source]


    Ungulate foraging strategies: energy maximizing or time minimizing?

    JOURNAL OF ANIMAL ECOLOGY, Issue 2 2001
    Carita M. Bergman
    Summary 1,Many classical models of ungulate foraging are premised on energy maximization, yet limited empirical evidence and untested currency assumptions make the choice of currency a non-trivial issue. The primary constraints on forage intake of ungulates are forage quality and availability. Using a model that incorporates these two constraints, we predicted the optimal biomass of forage patches for ungulate grazers using an energy maximizing vs. a time minimizing strategy. 2,We tested these predictions on wood bison (Bison bison athabascae Rhoads) grazing naturally occurring sedge (Carex atherodes Spreng). The digestive constraint was determined by a series of ad libitum feeding trials using sedge at different stages of growth. Sedge digestibility declined with biomass. Ad libitum intake of sedge by bison declined with sedge digestibility and thus decreased with sedge biomass. On the other hand, short-term sedge intake rates of wood bison increased with biomass. 3,Incorporation of these constraints resulted in the prediction that daily energy gain of bison should be maximized by grazing patches with a biomass of 10 g m,2, whereas a bison could minimize daily foraging time needed to fulfil its energy requirement by cropping patches with a biomass of 279 g m,2. 4,To test these quantitative predictions, we used a staggered mowing regime to convert even-aged stands of sedge to a mosaic of patches varying in quality and quantity. Observations of bison grazing these mosaics indicated that patches of biomass below 120 g m,2 were avoided, while patches of biomass 156 and 219 g m,2 were highly preferred, with the greatest preference for the latter. 5,These results indicate that bison were behaving as time minimizers rather than energy maximizers. Daily cropping times of free-ranging bison from the literature corroborate our results. [source]


    Lack of an osmotic constraint on intake rate of the eastern curlew Numenius madagascariensis

    JOURNAL OF AVIAN BIOLOGY, Issue 4 2006
    Rachel Blakey
    Rates of food intake in animals consuming abundant prey can be constrained by the rates of digestion or excretion of ingested substances, such as salt, particularly so in the animals that regularly migrate between freshwater and saltwater environments. We tested this hypothesis in a long-distance migrant shorebird, the eastern curlew Numenius madagascariensis (suborder Charadrii), foraging on intertidal decapods in eastern Australia. We predicted that if food intake rates are constrained osmotically, individuals with access to freshwater and less saline prey (FW group) would have higher rates of food and water intake than individuals with seawater-only access (SW group). Food intake rates did not differ between the FW and SW groups (0.14 g ash-free dry mass min,1), nor did the water influx rates (0.75 g,min,1). Salt intake rates were lower at FW sites (19.3 versus 23.3 mg NaCl min,1) and overall they were similar to those of marine birds. Food intake rate in the eastern curlew appeared limited by digestive rather than by osmoregulatory capacity. [source]