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

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

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

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.     

Optimal foraging and fitness in Columbian ground squirrels

Summary Optimal diets were determined for each of 109 individual Columbian ground squirrels (Spermophilus columbianus) at two sites in northwestern Montana. Body mass, daily activity time, and vegetation consumption rates for individuals were measured in the field, along with the average water content of vegetation at each ground squirrel colony. I also measured stomach and caecal capacity and turnover rate of plant food through the digestive tract for individuals in the laboratory to construct regressions of digestive capacity as a function of individual body mass. Finally, I obtained literature estimates of average daily energy requirements as a function of body mass and digestible energy content of vegetation. These data were used to construct a linear programming diet model for each individual. The model for each individual was used to predict the proportion of two food types (monocots and dicots) that maximized daily energy intake, given time and digestive constraints on foraging. Individuals were classified as optimal or deviating, depending on whether their observed diet was significantly different from their predicted optimal diet. I determined the consequences of selecting an optimal diet for energy intake and fitness. As expected, daily energy intake calculated for deviators (based on their observed diet proportion) was less than that for optimal foragers. Deviating foragers do not appear to compensate for their lower calculated energy intake through other factors such as body size or physiological efficiency of processing food. Growth rate, yearly survivorship, and litter size increase with calculated energy intake, and optimal foragers have six times the reproductive success of deviators by age three. Optimal foraging behavior, therefore, appears to confer a considerable fitness advantage.     

Does group foraging promote efficient exploitation of resources?

Increased avoidance of food patches previously exploited by other companions has been proposed as one adaptive benefit of group foraging. However, does group foraging really represent the most efficient way to exploit non- or slowly-renewing resources? Here, I used simulations to explore the costs and benefits of exploiting non-renewing resources by foragers searching for food patches independently or in groups in habitats with different types of resource distribution. Group foragers exploited resources in a patch more quickly and therefore spent proportionately more time locating new patches. Reduced avoidance of areas already exploited by others failed to overcome the increased time cost of searching for new food patches and group foragers thus obtained food at a lower rate than solitary foragers. Group foraging provided one advantage in terms of a reduction in the variance of food intake rate. On its own, reduced avoidance of exploitation competition through group foraging appears unlikely to increase mean food intake rate when exploiting non-renewing patches but may provide a way to reduce the risk of an energy shortfall.     

The hidden cost of information in collective foraging

Many animals nest or roost colonially. At the start of a potential foraging period, they may set out independently or await information from returning foragers. When should such individuals act independently and when should they wait for information? In a social insect colony, for example, information transfer may greatly increase a recruit's probability of finding food, and it is commonly assumed that this will always increase the colony's net energy gain. We test this assumption with a mathematical model. Energy gain by a colony is a function both of the probability of finding food sources and of the duration of their availability. A key factor is the ratio of pro-active foragers to re-active foragers. When leaving the nest, pro-active foragers search for food independently, whereas re-active foragers rely on information from successful foragers to find food. Under certain conditions, the optimum strategy is totally independent (pro-active) foraging because potentially valuable information that re-active foragers may gain from successful foragers is not worth waiting for. This counter-intuitive outcome is remarkably robust over a wide range of parameters. It occurs because food sources are only available for a limited period. Our study emphasizes the importance of time constraints and the analysis of dynamics, not just steady states, to understand social insect foraging.     

Beyond the information centre hypothesis: communal roosting for information on food,predators, travel companions and mates?

Communal roosting – the grouping of more than two individuals resting together – is common among animals, notably birds. The main functions of this complicated social behaviour are thought to be reduced costs of predation and thermoregulation, and increased foraging efficiency. One specific hypothesis is the information centre hypothesis (ICH) which states that roosts act as information centres where individuals actively advertise and share foraging information such as the location of patchily distributed foods. Empirical studies in corvids have demonstrated behaviours consistent with the predictions of the ICH, but some of the assumptions in its original formulation have made its wide acceptance problematic. Here we propose to generalise the ICH in two ways: (1) dropping the assumption that information transfer must be active, and (2) adding the possibilities of information exchange on, for example, predation risk, travel companions and potential mates. A conceptual model, inspired by shorebirds arriving at roosts after foraging on cryptic prey, is proposed to illustrate how testable predictions can be generated. The conceptual model illustrates how roost arrival timing may convey inadvertent information on intake rate, prey density, forager state (i.e. digestive processing capacity) and food quality. Such information could be used by naïve or unsuccessful foragers to select with whom to leave the roost at the subsequent foraging opportunity and thus increase foraging success. We suggest that inadvertent information transfer, rather than active information exchange, predominates in communal roosts.     

Altitudinal Variation in Digestive Tract Lengh in Feirana quadranus

Selective pressures favor variation in organ size in response to environmental changes and evolutionary process. In particular, changes in environmental temperature and rainfall at different altitudes often affect food resources, thereby mediating energy intake and allocation. The digestive tract provided a functional relationship between energy intake and allocation, of which gut morphology was associated with diet changes and food quality under different environments. Here we studied altitudinal variation in the digestive tract across four Feirana quadranus populations and tested the hypothesis that relative size of digestive tract should increase with increasing altitude. The results showed that although significant variation in length of the digestive tract was observed in females among populations, altitudinal variation in relative length of digestive tract or gut was non-significant. In addition, the digestive tract length was not correlated with temperature and precipitation across the four populations. Our findings suggest that individuals living in low-temperature and-precipitation populations at high altitudes did not display longer digestive tract than high temperature and precipitation populations at low altitudes, possibly because of small populations or sample sizes.     

Distinguishing Energy Maximizers from Time Minimizers: A Comparative Study of Two Hummingbird Species

SYNOPSIS. The potential reproductive success of a food energymaximizer increases with foraging time, while that of a foragingtime minimizer increases with time spent in nonforaging activitiesgiven a set energy requirement has been met. How can these foraging"goals" be distinguished for nonbreeding animals in the field?If individuals of two species occupying the same habitat consumethe same foods, face similar foraging constraints, and havesimilar meal sizes (food intake per foraging bout), then relativeto a time minimizer, an energy maximizer should: (1) spend moretime foraging, with greater foragingbout frequency, but no differencein foraging-bout duration; (2) spend less time sitting, withlower sitting-bout duration yet greater sitting-bout frequency;(3) gain mass more rapidly, if net energy intake results inmass accumulation; and (4) exhibit no other differences in timebudgeting. These assumptions and predictions were verified bypopulation- and individual-level comparisons of immature malesof two species of nectar-feeding hummingbirds studied over threefield seasons. The results suggest that, relative to each other,migrant Rufous Hummingbirds are energy maximizers and nonmigrantCosta Hummingbirds are time minimizers. Despite significantdifferences in time budgeting, by far the most striking differencebetween the species was that the Rufous gained mass four toeight times as rapidly as the Costa. This was due to the Rufousentering torpor at night, resulting in relatively little overnightloss in body mass. These patterns underscore the importanceof measuring net energy intake as directly as possible (in thiscase by fat accumulation) in testing foraging theory. Indirectmeasures (such as time budgets) may not always provide the resolutionnecessary to detect important energetic differences betweendifferent foragers.     

Time and energy constraints and the relationships between currencies in foraging theory

Measured foraging strategies often cluster around values thatmaximize the ratio of energy gained over energy spent whileforaging (efficiency), rather than values that would maximizethe long-term net rate of energy gain (rate). The reasons forthis are not understood. This paper focuses on time and energyconstraints while foraging to illustrate the relationship betweenefficiency and rate-maximizing strategies and develops modelsthat provide a simple framework to analyze foraging strategiesin two distinct foraging contexts. We assume that while capturingand ingesting food for their own use (which we term feeding),foragers behave so as to maximize the total net daily energeticgain. When gathering food for others or for storage (which weterm provisioning), we assume that foragers behave so as tomaximize the total daily delivery, subject to meeting theirown energetic requirements. In feeding contexts, the behaviormaximizing total net daily gain also maximizes efficiency whendaily intake is limited by the assimilation capacity. In contrast,when time available to forage sets the limit to gross intake,the behavior maximizing total net daily gain also maximizesrate. In provisioning contexts, when daily delivery is constrainedby the energy needed to power self-feeding, maximizing efficiencyensures the highest total daily delivery. When time needed torecoup energetic expenditure limits total delivery, a low self-feedingrate relative to the rate of energy expenditure favors efficientstrategies. However, as the rate of self-feeding increases,foraging behavior deviates from efficiency maximization in thedirection predicted by rate maximization. Experimental manipulationsof the rate of self-feeding in provisioning contexts could bea powerful tool to explore the relationship between rate andefficiency-maximizing behavior.     

Optimal foraging and gut constraints: reconciling two schools of thought

To ecologists, factors such as a forager's encounter rate with prey and its own susceptibility to predation are dominant determinants of foraging. In contrast, digestive physiologists consider foraging to be determined by factors like rates of digestion and absorption of ingested food. We reconcile these views in a model combining encounter rate, external handling, and internal handling of food in the gut. With internal food handling, two food properties become important; energy: external handling time (e/h) and energy: bulk (e/b). We show that internal handling is only one of a suite of rate limiting factors. The gut never reaches full capacity, indicating that spare capacity may be intrinsic to gut structure. Regardless of gut fullness, a food of sufficiently high e/b will always be harvested. Two isolegs in the state space of resource abundances determine diet selectivity. These isolegs, which we call the Mitchell and Pulliam isolegs, divide the state space into regions in which 1) the forager's optimal strategy is opportunism; 2) the forager is always selective on the food with the greater e/h and partially selective on the second food; 3) the forager is always selective on the food with the greater e/h and ignores the second food. The development and analysis of the isolegs thus reconcile the heretofore disparate perspectives of the ecological and the physiological frameworks of foraging.     

Short-term adaptation of digestive processes in the cockle Cerastoderma edule exposed to different food quantity and quality

Feeding and digestive parameters were analysed in cockles Cerastoderma edule fed for 3 days on two foods of different qualities, both foods given in two different concentrations. With low quality food, gut content was found to increase with ingestion rate. Such increased capacity of the gut to allocate food precludes negative effects upon throughput time, and so absorption efficiency remained nearly constant at the two food concentrations. With high quality food, gut content remained at high constant values and consequently enhancement of food ingestion rate with a high food ration leads to a significant reduction in throughput time, resulting in lower absorption efficiencies. Significantly higher levels of amylases and cellulases have been found within the digestive gland of cockles fed high quality diets. Coincidentally, absorption of carbohydrates is increased and absorption of lipids decreased in such diets as compared to low quality diets. Implications of the positive correlation between digestive enzyme activity and food quality are discussed in relation to the role that both digestive investments and endogenous faecal losses play in digestive processes. Results obtained in this study indicate that investments in the form of digestive enzymes are a key factor in the functional response of cockles to short-term variations in the food regime. Accepted: 13 September 1997     

Evaluating optimal diet models for an African browsing ruminant,the kudu: How constraining are the assumed constraints?

Summary The linear programming model (LPM) of Belovsky (1978, 1986) and modifications of the classical or contingency model incorporating a digestive constraint (CM) were tested using foraging data recorded for kudus (Tragelaphus strepsiceros) browsing savanna vegetation over the late wet season. Food choice was between the herbaceous and woody plant components for LPM and among plant species or categories for CM. The constraints considered were consumption (cropping) rate, foraging time and digestive capacity. Woody communities dominated byBurkea andAcacia represented alternative habitat types. Following a minor adjustment, LPM represented the overall average diet and predicted the dietary differences between habitat types. However, the kudus failed to respond dietarily to variations among days and foraging sessions (meals) in the parameters constraining intake. The kudus accepted a wider dietary range than predicted to be optimal by CM. Evidence suggested that neither foraging time, nor digestive capacity, formed an effective constraint under the study conditions. Thermal tolerance and gut space may become limiting only towards the extremes of environmental variability that animals experience. LPM is vulnerable to circularity if average parameter values are used to estimate constraint settings. The energy maximizer—time minimizer dichotomy fails to take into account the fitness consequences of alternative foraging responses. CM is less cryptic in its application than LPM and so has greater heuristic value, despite its predictive failures. However, there may be no consistent ranking of food types where multiple constraints that are variable in their effectiveness apply. Dynamic programming models offer a solution, but pose a formidable challenge in complex natural environments.     

A pilot study on the ontogeny of digestive physiology in Japanese macaques (Macaca fuscata)

An assumption based on the Jarman–Bell principle suggests a positive relationship between body size and the digestive efficiency in animals, where smaller animals are less effective at digesting fibrous food due to shorter digesta passage. To examine the effect of body size within a species and explore a potential physiological background of ontogenetic diet shifts, we measured food intake, digestibility, digesta passage and gut fill in nine Japanese macaques, including three juveniles/subadult animals. Although these three showed a comparable digestive efficiency as the older animals on a low-fiber diet, they did not achieve the long retention times of adults in spite of similar levels of indigestible food intake and gut capacity. While the limited sample size would not allow generalized conclusions on ontogenetic digestive development in primates, this study suggests additional, yet unexplored effects other than food intake, digestion and gut capacity on digesta retention during ontogeny.     

Intake rate at differently scaled heterogeneous food distributions explained by the ability of tactile-foraging mallard to concentrate foraging effort within profitable areas

The ability to respond to spatial heterogeneity in food abundance depends on the scale of the food distribution and the foraging scale of the forager. The aim of this study is to illustrate that a foraging scale exists, and that at larger scaled food distributions foragers benefit from the ability to subdivide a continuous (non-discrete) heterogeneous environment into profitable and non-profitable areas. We recorded search patterns of mallards Anas plathyrhynchos foraging in shallow water on cryptic prey items (millet seeds), distributed at different scales. A small magnet attached to the lower mandible allowed us to record in great detail the position and movements of the bill tip within a feeding tray underlain by magnet sensors. Instantaneous intake rate was determined in a subsequent experiment. We successfully determined the foraging scale (about 2×2 cm), defined as the scale above which foragers do respond (coarse scaled distribution) and below which foragers do not respond (fine scaled distribution) to spatial heterogeneity, by concentrating foraging effort within areas of high food density. A response resulted in a significantly higher intake rate, compared to a homogeneous distribution with an equal overall density. Unlike systematic search cell revisitation was common in trials, and at coarse scaled food distributions even slightly (but significantly) more frequently observed than predicted for random search. Mallards respond to food capture by restricting displacement (area restricted search) at food distributions that are considered to be clumped for the forager (large scaled coarse distributions). We argue that partitioning the environment at the foraging scale in itself could be a mechanism to concentrate foraging efforts within profitable areas, because mallard were able to respond to heterogeneity at coarse scaled food distributions even when non-clumped (i.e. without conducting area restricted search).     

The Regulation of Ant Colony Foraging Activity without Spatial Information

Many dynamical networks, such as the ones that produce the collective behavior of social insects, operate without any central control, instead arising from local interactions among individuals. A well-studied example is the formation of recruitment trails in ant colonies, but many ant species do not use pheromone trails. We present a model of the regulation of foraging by harvester ant (Pogonomyrmex barbatus) colonies. This species forages for scattered seeds that one ant can retrieve on its own, so there is no need for spatial information such as pheromone trails that lead ants to specific locations. Previous work shows that colony foraging activity, the rate at which ants go out to search individually for seeds, is regulated in response to current food availability throughout the colony's foraging area. Ants use the rate of brief antennal contacts inside the nest between foragers returning with food and outgoing foragers available to leave the nest on the next foraging trip. Here we present a feedback-based algorithm that captures the main features of data from field experiments in which the rate of returning foragers was manipulated. The algorithm draws on our finding that the distribution of intervals between successive ants returning to the nest is a Poisson process. We fitted the parameter that estimates the effect of each returning forager on the rate at which outgoing foragers leave the nest. We found that correlations between observed rates of returning foragers and simulated rates of outgoing foragers, using our model, were similar to those in the data. Our simple stochastic model shows how the regulation of ant colony foraging can operate without spatial information, describing a process at the level of individual ants that predicts the overall foraging activity of the colony.     

Assessing the Jarman–Bell Principle: Scaling of intake,digestibility, retention time and gut fill with body mass in mammalian herbivores

Differences in allometric scaling of physiological characters have the appeal to explain species diversification and niche differentiation along a body mass (BM) gradient — because they lead to different combinations of physiological properties, and thus may facilitate different adaptive strategies. An important argument in physiological ecology is built on the allometries of gut fill (assumed to scale to BM^1.0) and energy requirements/intake (assumed to scale to BM^0.75) in mammalian herbivores. From the difference in exponents, it has been postulated that the mean retention time (MRT) of digesta should scale to BM^1.0–0.75 = BM^0.25. This has been used to argue that larger animals have an advantage in digestive efficiency and hence can tolerate lower-quality diets. However, empirical data does not support the BM^0.25 scaling of MRT, and the deduction of MRT scaling implies, according to physical principles, no scaling of digestibility; basing assumptions on digestive efficiency on the thus-derived MRT scaling amounts to circular reasoning. An alternative explanation considers a higher scaling exponent for food intake than for metabolism, allowing larger animals to eat more of a lower quality food without having to increase digestive efficiency; to date, this concept has only been explored in ruminants. Here, using data for 77 species in which intake, digestibility and MRT were measured (allowing the calculation of the dry matter gut contents (DMC)), we show that the unexpected shallow scaling of MRT is common in herbivores and may result from deviations of other scaling exponents from expectations. Notably, DMC have a lower scaling exponent than 1.0, and the 95% confidence intervals of the scaling exponents for intake and DMC generally overlap. Differences in the scaling of wet gut contents and dry matter gut contents confirm a previous finding that the dry matter concentration of gut contents decreases with body mass, possibly compensating for the less favorable volume–surface ratio in the guts of larger organisms. These findings suggest that traditional explanations for herbivore niche differentiation along a BM gradient should not be based on allometries of digestive physiology. In contrast, they support the recent interpretation that larger species can tolerate lower-quality diets because their intake has a higher allometric scaling than their basal metabolism, allowing them to eat relatively more of a lower quality food without having to increase digestive efficiency.     

Phenotypic flexibility in digestive system structure and function in migratory birds and its ecological significance

Birds during migration must satisfy the high energy and nutrient demands associated with repeated, intensive flight while often experiencing unpredictable variation in food supply and food quality. Solutions to such different challenges may often be physiologically incompatible. For example, increased food intake and gut size are primarily responsible for satisfying the high energy and nutrient demands associated with migration in birds. However, short-term fasting or food restriction during flight may cause partial atrophy of the gut that may limit utilization of ingested food energy and nutrients. We review the evidence available on the effects of long- and short-term changes in food quality and quantity on digestive performance in migratory birds, and the importance of digestive constraints in limiting the tempo of migration in birds. Another important physiological consequence of feeding in birds is the effect of diet on body composition dynamics during migration. Recent evidence suggests that birds utilize and replenish both protein and fat reserves during migration, and diet quality influences the rate of replenishment of both these reserves. We conclude that diet and phenotypic flexibility in both body composition and the digestive system of migratory birds are important in allowing birds to successfully overcome the often-conflicting physiological challenges of migration.     

Multiple pathways from three types of sugar receptor sites to metabotropic transduction pathways of the blowfly: study by the whole cell-clamp experiments

Differences in the allometric scaling between gut capacity (with body mass, BM^1.00) and food intake (with BM^0.75) should theoretically result in a scaling of digesta retention time with BM^0.25 and therefore a higher digestive efficiency in larger herbivores. This concept is an important part of the so-called ‘Jarman–Bell principle’ (JBP) that explains niche differentiation along a body size gradient in terms of digestive physiology. Empirical data in herbivorous mammals, however, do not confirm the scaling of retention time, or of digestive efficiency, with body mass. Here, we test these concepts in herbivorous reptiles, adding data of an experiment that measured food intake, digesta retention, digestibility and gut capacity in 23 tortoises (Testudo graeca, T. hermanni , Geochelone nigra, G. sulcata, Dipsochelys dussumieri) across a large BM range (0.5–180 kg) to a literature data collection. While dry matter gut fill scaled to BM^1.07 and dry matter intake to BM^0.76, digesta mean retention time (MRT) scaled to BM^0.17; the scaling exponent was not significantly different from zero for species > 1 kg. Food intake level was a major determinant of MRT across reptiles and mammals. In contrast to dietary fibre level, BM was not a significant contributor to dry matter digestibility in a General Linear Model. Digestibility coefficients in reptiles depended on diet nutrient composition in a similar way as described in mammals. Although food intake is generally lower and digesta retention longer in reptiles than in mammals, digestive functions scale in a similar way in both clades, indicating universal principles in herbivore digestive physiology. The reasons why the theoretically derived JBP has little empirical support remain to be investigated. Until then, the JBP should not be evoked to explain niche differentiation along a body size axis in terms of digestive physiology.     

Directional fidelity as a foraging constraint in the western harvester ant,Pogonomyrmex occidentalis

Summary Understanding the foraging behavior of an animal is critically dependent upon knowledge of the constraints on that animal. In this study, I tested whether fidelity to foraging direction acts as a behavioral constraint to foraging western harvester ants, Pogonomyrmex occidentalis. Individual P. occidentalis foragers showed strong fidelity to foraging route and direction. Directional fidelity in this population was not related to trunk trail use, food specialization, colony activity levels, or mortality risks. Directional fidelity constrained individual foraging decisions; when colonies were offered seeds of different quality in 2 directions, individuals did not switch directions to obtain the energetically more rewarding seeds. Colony-level recruitment was increased for energetically more profitable seeds, indicating that colonial responses may compensate for the constraints of directional fidelity on individual foragers.     

Foraging on spatially distributed resources with sub‐optimal movement,imperfect information,and travelling costs: departures from the ideal free distribution

Ideal free distribution (IFD) theory offers an important baseline for predicting the distribution of foragers across resource patches. Yet it is well known that IFD theory relies on several over‐simplifying assumptions that are unlikely to be met in reality. Here we relax three of the most critical assumptions: (1) optimal foraging moves among patches, (2) omniscience about the utility of resource patches, and (3) cost‐free travelling between patches. Based on these generalizations, we investigate the distributions of a constant number of foragers in models with explicit resource dynamics of logistic type. We find that, first, when foragers do not always move to the patch offering maximum intake rate (optimal foraging), but instead move probabilistically according to differences in resource intake rates between patches (sub‐optimal foraging), the distribution of foragers becomes less skewed than the IFD, so that high‐quality patches attract fewer foragers. Second, this homogenization is strengthened when foragers have less than perfect knowledge about the utility of resource patches. Third, and perhaps most surprisingly, the introduction of travelling costs causes departures in the opposite direction: the distribution of sub‐optimal foragers approaches the IFD as travelling costs increase. We demonstrate that these three findings are robust when considering patches that differ in the resource's carrying capacity or intrinsic growth rate, and when considering simple two‐patch and more complex multiple‐patch models. By overcoming three major over‐simplifications of IFD theory, our analyses contribute to the systematic investigation of ecological factors influencing the spatial distribution of foragers, and thus help in deriving new hypotheses that are testable in empirical systems. A confluence of theoretical and empirical studies that go beyond classical IFD theory is essential for improving insights into how animal distributions across resource patches are determined in nature.