When carnivores are “full and lazy”

Are animals usually hungry and busily looking for food, or do they often meet their energetic and other needs in the 24 h of a day? Focusing on carnivores, I provide evidence for the latter scenario. I develop a model that predicts the minimum food abundance at which a carnivore reaches satiation and is released from time constraints. Literature data from five invertebrate and vertebrate species suggest that food abundances experienced in the field often exceed this threshold. A comparison of energetic demands to kill rates also suggests that carnivores often reach satiation: for the 16 bird and mammal species analyzed, this frequency is 88% (average across species). Because pressure of time would likely lead to trade-offs in time allocation and thus to a nonsatiating food consumption, these results suggest that carnivores are often released from time constraints.     

Experimental duration and predator satiation levels systematically affect functional response parameters

Empirical feeding studies where density‐dependent consumption rates are fitted to functional response models are often used to parameterize the interaction strengths in models of population or food‐web dynamics. However, the relationship between functional response parameter estimates from short‐term feeding studies and real‐world, long‐term, trophic interaction strengths remains largely unexamined. In a critical first step to address this void, we tested for systematic effects of experimental duration and predator satiation on the estimate of functional response parameters, namely attack rate and handling time. Analyzing a large data set covering a wide range of predator taxa and body masses, we show that attack rates decrease with increasing experimental duration, and that handling times of starved predators are consistently shorter than those of satiated predators. Therefore, both the experimental duration and the predator satiation level have a strong and systematic impact on the predictions of population dynamics and food‐web stability. Our study highlights potential pitfalls at the intersection of empirical and theoretical applications of functional responses. We conclude our study with some practical suggestions for how these implications should be addressed in the future to improve predictive abilities and realism in models of predator–prey interactions.     

Effects of satiation on feeding and swimming behaviour of planktivores

Hunger affects the feeding and swimming behaviour in fish. After 36 h of food deprivation, the feeding and swimming behaviour of Pseudorasbora parva (Cyprinidae) was studied under different prey densities (0.5, 1, 2, 5, 10 and 25 of Daphnia pulex per liter). The initial feeding rates showed marked variations in relation to prey availability. Under high prey densities, the initial feeding rate of fish was higher and subsequently decreased faster, when compared to those feeding under low prey densities. At higher prey densities, two factors were involved: that of higher prey encounter rates and also the attainment of food satiation at a faster rate. Across all prey densities, the feeding rates of fish reached a plateau after satiation. The swimming speed of fish was found to be negatively related to the prey density and a significant change in swimming speed was noted as being directly related to the level of satiation. It was found that the increasing satiation level greatly influenced the handling time and reactive volume of predator, which finally caused reduced feeding rates.     

Optimal foraging and community structure: implications for a guild of generalist grassland herbivores

Summary A particular linear programming model is constructed to predict the diets of each of 14 species of generalist herbivores at the National Bison Range, Montana. The herbivores have body masses ranging over seven orders of magnitude and belonging to two major taxa: insects and mammals. The linear programming model has three feeding constraints: digestive capacity, feeding time and energy requirements. A foraging strategy that maximizes daily energy intake agrees very well with the observed diets. Body size appears to be an underlying determinant of the foraging parameters leading to diet selection. Species that possess digestive capacity and feeding time constraints which approach each other in magnitude have the most generalized diets. The degree that the linear programming models change their diet predictions with a given percent change in parameter values (sensitivity) may reflect the observed ability of the species to vary their diets. In particular, the species which show the most diet variability are those whose diets tend to be balanced between monocots and dicots. The community-ecological parameters of herbivore body-size ranges and species number can possibly be related to foraging behavior.     

Orangutan activity budgets: Monthly variations and the effects of body size,parturition, and sociality

The activity budgets of individual orangutans were investigated at the Kutai Reserve, Indonesia. Activity profiles within and between individuals were compared to examine monthly variations in feeding patterns, potential energetic constraints imposed by large body size and parturition, and the costs of sociality. Animals showed monthly changes in travelling, feeding, and resting patterns. Monthly increases in travelling and feeding were associated with marked reductions in the time spent resting. Inter-individual variations in activity budgets did not exist among animals of the same age-sex class. Activity patterns differed, however, as a function of age and sex. Adult females and subadult males travelled and fed significantly longer than an adult male. Parturition had predictable effects on activity; one female reduced her feeding and travelling immediately following parturition. Adult male orangutan sociality appears to be limited by travel costs. Associations with females forced a male orangutan to travel significantly more compared with periods in which he was solitary. The male did not lose an appreciable amount of time feeding when accompanying a female.     

A review of feeding and nutrition of herbivorous land crabs: adaptations to low quality plant diets

This paper reviews the nutritional ecology, the digestive physiology, and biochemistry of herbivorous land crabs and the adaptations that they possess towards a diet of plant material. Land crab species that breathe air and forage out of water can be divided into three feeding specialisations: primarily carnivorous, deposit feeders feeding on micro-organisms and organic matter in the sediment, and herbivores consuming mainly plant material and its detritus. The last forms the focus of this review. The diets of the herbivores are low in nitrogen and high in carbon, are difficult to digest since they contain cellulose and hemicellulose, and may disrupt digestion due to the presence of tannins. Herbivorous crustaceans are able to efficiently utilise plant material as their primary nutrient source and are indeed able to meet their nitrogen requirements from it. Herbivorous land crabs display a range of adaptations towards a low nitrogen intake and these are discussed in this review. They also appear to endogenously produce cellulase and hemicellulase enzymes for the digestion of cellulose and hemicellulose. Generalised and specific adaptations allow them to inhibit the potentially negative digestive effects of tannins. To digest plant material, they possess a plastic digestive strategy of high food intake, short retention time, high assimilation of cell contents, and substantial digestion of cellulose and hemicellulose.     

内蒙古达赉湖地区蒙原羚繁殖期及其前后昼间行为时间分配及能量平衡策略

2007年11月、12月和2008年3月,在内蒙古达赉湖地区,采用扫描取样法对雌雄蒙原羚繁殖期及其前后昼间行为时间分配进行了研究。 研究表明：（1）繁殖期前、繁殖期和繁殖期后,雌性蒙原羚采食时间,占昼间活动时间的比例分别为（44.9±3.8）%、（43.5±4.0）% 和 (46.2±3.1)%;卧息时间,占昼间活动时间的比例分别 为（32.3±4.8）%、（29.2±2.9）% 和 (28.0±4.8)%;雌性蒙原羚在繁殖期及其前后采食、移动和卧息的行为时间分配差异不显著（P>0.05）,站立、繁殖、“其他”行为时间分配差异性显著（P<0.05）。（2）繁殖期前、繁殖期和繁殖期后, 雄性蒙原羚采食时间,占昼间活动时间的比例分别为 (52.6±3.8)%、(17.5±2.8)% 和 (29.8±4.8)%;卧息时间,占昼间活动时间的比例分别为 (13.4±6.4)%、(24.2±4.1)% 和 (44.2±4.7)%。雄性蒙原羚在繁殖期及其前后采食、卧息、站立、移动、繁殖、“其他”时间分配均有显著差异（P<0.05）。动物采食卧息的行为时间分配反映动物的能量平衡策略。雌性蒙原羚的时间分配表明,雌性蒙原羚的能量平衡策略在繁殖期前、繁殖期和繁殖期后没有发生显著变化,均为能量摄入最优化策略,尽可能多的时间分配在采食上;雄性蒙原羚的时间分配表明,在繁殖期前,其能量平衡策略为能量摄入最优化策略,尽可能多的时间分配在采食上;雄性蒙原羚繁殖期及繁殖期后其能量平衡策略转变为能量支出优化策略,尽可能少的支出能量,尽可能多的时间分配在卧息上。     

Facilitation of tiger moths by outbreaking tussock moths that share the same host plants

1.?Ecologists have argued about the commonness and strength of interspecific competition between insect herbivores, but facilitation between herbivores has received much less consideration. We previously found that when two species of folivorous caterpillars co-occurred on a shared host plant, feeding by early season tiger moth caterpillars reduced the growth and reproduction of later season tussock caterpillars. However, densities of tussock caterpillars in summer were positively correlated with densities of tiger moth caterpillars the following spring. 2.?In this study, we experimentally manipulated numbers of feeding tussock caterpillars and found that they facilitated tiger moth caterpillars. 3.?The depth of the litter layer beneath host lupine bushes was positively correlated with the number of tussock caterpillars feeding on each bush. Experimental additions of litter beneath lupine canopies during summer resulted in increased numbers of tiger moth caterpillars in the following spring, indicating a causal role of litter. Litter potentially provides food, habitat and protection from desiccation and predation. We failed to find evidence that tussock caterpillars facilitated tiger moth caterpillars by mechanisms independent of litter. 4.?Our study demonstrates that facilitation may operate between insect herbivores, across life-stages through indirect interactions that are non-trophic. Facilitation operated by a novel mechanism, the accumulation of litter which was a by-product of feeding by one species was valuable to a second species. Facilitation persisted in time and space far beyond the creation of litter by tussock caterpillars which should be considered important ecosystem engineers from the point of view of tiger moths. Facilitations that involve habitat modification may generally connect species that do not interact directly or trophically, and have not previously been considered to affect one another.     

Wolf spider feeding strategies: optimality of prey consumption in Pardosa hortensis

Feeding behaviour of the wolf spider Pardosa hortensis Thorell (Araneae, Lycosidae) was studied in the laboratory. Characteristics of feeding were measured while prey availability was increased and the results were compared with the predictions of three models: the marginal value theorem (MVT), gut limitation theory (GLT) and the digestion rate limitation model (DRL). As a result of more frequent encounters with prey, the wolf spiders were able to modify their feeding behaviour so that their net energy intake rate increased substantially. Handling time decreased by 30%, and consumption rate increased by 40%. Partial consumption of prey did not occur until the spiders became nearly satiated. This indicated that spiders did not reach the optimum predicted by MVT. The most plausible mechanism for the increased efficiency was prey-stimulated digestive enzyme production as suggested in DRL. The predictions of GLT were not applicable for most of the feeding session, though gut satiation had an influence on the final stages of feeding. P. hortensis seemed to apply a responsive but cautious strategy: (i) spiders improved feeding efficiency on entering the higher quality habitat, but (ii) feeding times appeared to be sub-optimal and (iii) spiders were also willing to continue feeding when, as they approached satiation, the previously high efficiency could not be maintained. Such feeding behaviour optimizes long-term energy intake when food is scarce and unpredictable, which corresponds well with the known degree of natural food limitation of these animals.     

Experimental evidence of density dependent activity pattern of a large herbivore in an alpine ecosystem

Density dependent processes affecting foraging strategies may in turn influence vital rates and population regulation in large herbivores. Increased competition may lower both forage availability and quality, but whether the main activity constraint at high density is increased searching time or increased digestion time is poorly investigated. In a fully replicated landscape‐scale experiment, we used long‐term data (2003–2009) from domestic sheep grazing at high and low density (80 and 25 sheep km^–2, respectively) on alpine summer ranges to test density dependence in allocation of time to feeding (moving) vs digestion (resting) activities and how this in turn affected body growth. Sheep at high density spent more time actively feeding than sheep at low density, but sheep moved shorter distances while foraging at high density. Increased activity levels at high density suggest that the main activity constraint at high density was availability of high‐quality food increasing searching time and possibly reducing intake rates. Increased movement distances at low density is consistent with a higher selection for more productive vegetation types since high‐quality patches are dispersed in the landscape. The alternative hypothesis, that food processing time increased at high density was not supported as it would have reduced overall activity levels. Individual activity levels increased body growth, but this was not sufficient to fully compensate for lower habitat quality leading to an overall reduced body growth at high density. Our experiment clearly documents changes in activity budgets and movement distances of a large herbivore at high population density, providing one potential behavioural mechanism of density dependent responses observed in vital rates.     

The feeding of darwin's finches on Tribulus cistoides (L.) seeds

Food-handling skills of finches vary as a function of bill size. Geospiza magnirostris crush and shatter the woody mericarps of caltrop (Tribulus cistoides) to reach the seeds, whereas G. fortis (a smaller species) bite and tear at them. G. magnirostris accept and crack most of the mericarps picked up; fortis reject most mericarps but often feed on fragments. Energy rewards are greater for magnirostris than for fortis. Intraspecific variation in handling skills parallels interspecific variation. G. fortis individuals with large bills spend more time on mericarps and extract more seeds than do those with small bills, and they reject mericarps with a lower frequency. Those observed feeding on seeds from Tribulus mericarps were larger, particularly in bill size, than those not observed feeding on them.     

Consumer-food systems: why type I functional responses are exclusive to filter feeders

The functional response of a consumer is the relationship between its consumption rate and the abundance of its food. A functional response is said to be of type I if consumption rate increases linearly with food abundance up to a threshold level at which it remains constant. According to conventional wisdom, such type I responses are more frequent among filter feeders than among other consumers. However, the validity of this claim has never been tested. We review 814 functional responses from 235 studies, thereby showing that type I responses are not only exceptionally frequent among filter feeders but that they have only been reported from these consumers. These findings can be understood by considering the conditions that a consumer must fulfil in order to show a type I response. First, the handling condition: the consumer must have a negligibly small handling time (i.e. the time needed for capturing and eating a food item), or it must be able to search for and to capture food while handling other food. Second, the satiation condition: unless its gut is completely filled and gut passage time is minimal, the consumer must search for food at a maximal rate with maximal effort. It thus has to spend much time on foraging (i.e. searching for food and handling it). Our functional response review suggests that only filter feeders sometimes meet both of these conditions. This suggestion is reasonable because filter feeders typically fulfil the handling condition and can meet the satiation condition without losing time, for they are, by contrast to non-filter feeders, able simultaneously to perform foraging and non-foraging activities, such as migration or reproduction.     

Thermal and digestive constraints to foraging behaviour in marine mammals

While foraging models of terrestrial mammals are concerned primarily with optimizing time/energy budgets, models of foraging behaviour in marine mammals have been primarily concerned with physiological constraints. This has historically centred on calculations of aerobic dive limits. However, other physiological limits are key to forming foraging behaviour, including digestive limitations to food intake and thermoregulation. The ability of an animal to consume sufficient prey to meet its energy requirements is partly determined by its ability to acquire prey (limited by available foraging time, diving capabilities and thermoregulatory costs) and process that prey (limited by maximum digestion capacity and the time devoted to digestion). Failure to consume sufficient prey will have feedback effects on foraging, thermoregulation and digestive capacity through several interacting avenues. Energy deficits will be met through catabolism of tissues, principally the hypodermal lipid layer. Depletion of this blubber layer can affect both buoyancy and gait, increasing the costs and decreasing the efficiency of subsequent foraging attempts. Depletion of the insulative blubber layer may also increase thermoregulatory costs, which will decrease the foraging abilities through higher metabolic overheads. Thus, an energy deficit may lead to a downward spiral of increased tissue catabolism to pay for increased energy costs. Conversely, the heat generated through digestion and foraging activity may help to offset thermoregulatory costs. Finally, the circulatory demands of diving, thermoregulation and digestion may be mutually incompatible. This may force animals to alter time budgets to balance these exclusive demands. Analysis of these interacting processes will lead to a greater understanding of the physiological constraints within which the foraging behaviour must operate.     

A critical period for nutritional control of early gametogenesis in female winter flounder, Pleuronectes americanus (Pisces: Teleostei)

When female winter flounder ( Pleuronectes americanus ) were subjected to periods of satiation feeding alternating with starvation it was found that the first part of their normal six-month feeding period could be associated with subsequent gametogenesis, whereas feeding in the later part of the normal feeding period was not necessary. Conversely if females were not fed during the first part of the normal feeding season they were likely to become non-reproductive, although high condition fish or a non-spawner could become gametogenic in spite of starvation at this time. Feeding restricted to the later part of the normal feeding season was therefore not generally associated with successful gametogenesis for the following year's spawn. When the first part of the feeding period was further subdivided with satiation feeding limited to one or more months within it, most fish became non-reproductive. The exceptions which became reproductive were females which had high post-spawn condition maintained in the month following the immediate spawning period for the individual fish. A nutritionally sensitive period for early gametogenesis in female winter flounder therefore appears to occur in the early part of the normal feeding season, close to the normal spawning period. The experimentally produced non-reproductive females were generally halted in a previtellogenic stage of development for the most advanced oocytes which is consistent with a nutritionally related inhibition of gametogenesis close to the previous spawning period.     

Changing handling times during feeding and consequences for prey size selection of 0+ zooplanktivorous fish

The interrelationship of fish size, prey size and handling time within a 15-min feeding period was studied in three size groups of 0 + roach, Rutilus rutilus, and bleak, Alburnus alburnus. Four size classes of cladoceran prey were used to measure changes in feeding rate and handling time from initial rapid feeding to sustained feeding. Observed differences in increase of handling time between prey size classes led to a change in the prey profitability ranking of those size classes within the first 2 min of the experiments. A 1-min feeding period is interpreted as reflecting an intermediate motivational status between extreme hunger and satiation. The use of average handling times for this period revealed a substantial change in prey profitability estimates compared to previous studies which used handling times based on short-term (a few seconds up to 1 min) feeding. It is not the largest prey items a fish can handle and swallow that are most profitable, but prey of intermediate size. By this approach a closer fit between expectations derived from optimal foraging theory and empirical data on prey size selection of 0 + zooplanktivorous fish is qualitatively achieved. Optimal prey size was found to be close the mouth gape width in small fish of 15 mm standard length, decreasing to 50% of mouth gape width in fish of 40 mm standard length.     

How feeding performance and energy intake change with a small increase in the body size of the three-spined stickleback

Changes in the foraging behaviour due to variation in the body size of the three-spined stickleback Gasterosteus aculeatus were investigated. All sizes of fish had a high probability of attacking prey whenever encountered. The probability of eating the prey increased with the size of the fish, as the larger fish had larger jaws and a greater stomach capacity. Therefore, as fish increased in size there was an increase in the probability of successful prey capture. The level of satiation did not have an effect on the prey handling time, which is contrary to other studies and is probably a result of the large prey sizes. The physical size of the prey meant that the handling times were long regardless of the motivational level of the fish. The larger fish took in more energy and at a faster rate, although the time to reach satiation was similar for all fish sizes. The advantage that large fish appear to have in successfully gaining large prey is negated by their greater metabolic requirement. The changes in feeding performance induced by small increases in body size could have important consequences for intraspecific competition, habitat Use and risk of predation.     

A new method of monitoring ventilatory activity in mussels and its use in a study of the ventilatory patterns of Mytilus edulis L.

An apparatus for measuring pumping rates in mussels, based on the delivery of exhaled sea water into a constant flow of fresh water, is described. When food is available, pumping is continuous for several days although there are signs of satiation after ≈ 1 wk. When food is withdrawn pumping does not cease for several hours especially in animals which have been food-deprived for some time before feeding. Food-deprived mussels often fail to pump for periods of > 24 h and ventilatory bursts are carried out at flow rates well below maximum. Shell valve movements and diffusion of oxygen through the gape between open valves can supplement ciliary ventilation.     

Temperature constraints on foraging behaviour of male Alpine ibex (Capra ibex) in summer

In arctic and alpine environments, warm summer temperatures may force a reduction in foraging time of large herbivores, whose tolerance for heat is lower than for species adapted to warmer weather. We constructed time budgets for marked ibex (Capra ibex) males over two summers to test whether warm temperatures constrained foraging behaviour and forced altitudinal migrations. As daily temperature and solar radiation increased, feeding activity was reduced at midday and evening, but increased in the early morning, probably to anticipate for an expected reduction in foraging later in the day. With increasing temperature and solar radiation, ibex moved to higher elevations where they spent very little time feeding. Changes in forage quality and availability could not explain altitudinal migration. Temperatures above 15–20°C apparently result in heat discomfort in male Alpine ibex. As temperature and solar radiation increased, older and larger ibex spent less time feeding during daylight and showed a steeper decrease in feeding time than younger and smaller ibex. Larger males may be more sensitive to temperature and solar radiation, or may have more flexibility in allocating time to different activities, given their lower relative energetic requirements. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Chemically-mediated host-plant location and selection by root-feeding insects

Abstract.  Recent studies have shown that root-feeding insects can be of considerable importance in terms of agricultural damage, their indirect impacts on above-ground herbivores and their efficacy as biocontrol agents of weeds. To date, isolated studies have made it difficult to identify the mechanisms by which soil-dwelling insects locate and select host-plant roots. This review synthesizes 78 studies describing root location and selection. Soil insect herbivores do not rely on encountering roots at random, but orientate towards them using semiochemicals that enable specialist insects to distinguish host-plants from unsuitable plants. Secondary plant metabolites released into the rhizosphere (alcohols, esters and aldehydes representing 37% of reported examples) underpin host-plant location and recognition, with 80% having 'attractant' properties. Insects feeding on a limited range of plants tend to exploit host-specific secondary metabolites, whereas nonspecialist feeders appear to use more general semiochemicals. When insects reach the roots, contact chemosensory cues act as either 'phagostimulants' (48% of the compounds being sugars) or feeding 'deterrents' (notably phenolic compounds). Twenty studies conclude that CO₂ is the major primary plant metabolite that allows insects to locate to roots. However, several features of CO₂ emissions from roots mitigate against it as a precise location cue. In addition to its lack of specificity, gradients of root emitted CO₂ do not persist for long periods and vertical gradients of CO₂ in the soil tend to be stronger than horizontal gradients. A conceptual model is presented, emphasizing the importance of soil properties (e.g. porosity, moisture) on chemical diffusion and insect motility.