Harvester ant response to spatial and temporal heterogeneity in seed availability: pattern in the process of granivory

The influence of temporal and spatial heterogeneity in seed availability on the foraging behaviour of the harvester ant Messor arenarius was studied in an arid shrubland in the Negev Desert, Israel. The study investigated the implications of behavioural responses to heterogeneity in seed availability for the seed predation process and the potential for feedback effects on vegetation. Vegetation and seed rain were monitored across two landscape patch types (shrub patches and inter-shrub patches) in 1997. Shrub patches were shown to have higher plant and seed-rain density than inter-shrub patches. Patch use and seed selection by M. arenarius foragers were monitored through the spring, summer and autumn of 1997. After a pulse of seed production in the spring, the ants exhibited very narrow diet breadth, specialising on a single annual grass species, Stipa capensis. At this time, ants were foraging and collecting seeds mainly from inter-shrub patches. In the summer, diet breadth broadened and use of shrub patches increased, although the rate of seed collection per unit area was approximately equal in the two patch types. The increase in the use of shrub patches was due to colony-level selection of foraging areas with relatively high shrub cover and an increase in the use of shrub patches by individual foragers. In the autumn, a pulse of seed production by the shrub species Atractylis serratuloides and Noaea mucronata led to a reduction in diet breadth as foragers specialised on these species. During this period, foragers exhibited a large increase in the proportion of time spent in shrub patches and in the proportion of food items collected from shrub patches. The seasonal patterns in foraging behaviour showed linked changes in seed selection and patch use resulting in important differences in the seed predation process between the two landscape patch types. For much of the study period, there was higher seed predation pressure on the inter-shrub patches, which were of relatively low productivity compared with the shrub patches. This suggests that the seed predation process may help maintain the spatial heterogeneity in the density of ephemeral plants in the landscape.     

A field assessment of optimal foraging in ants: trail patterns and seed retrieval by the European harvester ant Messor barbarus

Summary: The ant Messor barbarus is a major seed predator on annual grasslands of the Mediterranean area. This paper is an attempt to relate the foraging ecology of this species to resource availability and to address several predictions of optimal foraging theory under natural conditions of seed harvesting.¶Spatial patterns of foraging trails tended to maximise acquisition of food resources, as trails led the ants to areas where seeds were more abundant locally. Moreover, harvesting activity concentrated on highly frequented trails, on which seeds were brought into the nest in larger numbers and more efficiently, at a higher mean rate per worker.¶The predictions of optimal foraging theory that ants should be more selective in both more resource-rich and more distant patches were tested in the native seed background. We confirm that selectivity of ants is positively related to trail length and thus to distance from the nest of foraged seeds. Conversely, we fail to find a consistent relationship between selectivity and density or species diversity of seed patches. We discuss how selectivity assessed at the colony level may depend on factors other than hitherto reported behavioural changes in seed choice by individual foragers.     

Opportunity costs influence food selection and giving‐up density of dabbling ducks

The interaction of animals with their food can yield insights into habitat characteristics, such as perceived predation risk and relative quality. We deployed experimental foraging patches in wetlands used by migrating dabbling ducks Anas spp. in the central Illinois River Valley to estimate variation in seed removal and giving‐up density (GUD; i.e. density of food remaining in patches following abandonment) with respect to seed density, seed size, seed depth in the substrate, substrate firmness, perceived predation risk, and an energetic profitability threshold (i.e. critical food density). Seed depth and the density of naturally‐occurring seeds outside of experimental plots affected seed removal and GUD in experimental patches more than perceived predation risk, seed density, seed size or substrate firmness. The greatest seed removal and lowest GUDs in experimental patches occurred when food resources in alternative foraging locations outside of plots (i.e. opportunity costs) appeared to be near or below a critical food density (i.e. 119–181 kg ha^–1). Giving‐up densities varied substantially from a critical food density across a range of food densities in alternative foraging locations suggesting that fixed GUDs should not be used as surrogates for critical food densities in energetic carrying capacity models. Foraging and resting rates in and near experimental foraging patches did not reflect patterns of seed removal and were poor predictors of GUD and foraging habitat quality. Our results demonstrated the usefulness of GUDs as indicators of habitat quality for subsurface, benthic foragers relative to other available foraging patches and suggested that food may be limited for dabbling ducks during spring migration in some years in the midwestern USA.     

Modification of Diet and Foraging Range by Harvester Ants in Response to Altered Seed Availability

Food collection is a critical component of an individual’s life, and for eusocial insects, the colony that individual foragers support and maintain. Changes to the distribution and composition of food types in the environment are expected influence diet selection if the economics of foraging are altered. For seed-harvesting ants, the abundance and composition of seed types available on the ground typically shows a high degree of spatial and temporal variability, and not all types of seed are equally valued by foragers. We evaluated the response of Owyhee harvester ants (Pogonomyrmex salinus) to reductions in the availability of Sandberg bluegrass (Poa secunda) seeds, a preferred food type, while leaving the availability of cheatgrass (Bromus tectorum) seeds, a less favored food type, unmanipulated. At control colonies (N?=?8), cheatgrass seeds comprised 3.9?±?1.6% of total seed intake, while Sandberg bluegrass seeds accounted for the remainder of the diet. At colonies where bluegrass was trimmed to prevent new seeds from dropping within 12 m of the nest (N?=?8), cheatgrass seed intake increased significantly to 8.2?±?1.4% of the diet. Despite the uptick in collection of cheatgrass seeds, bluegrass seed collection remained high and very similar between treatment and control colonies. Treatment colonies were significantly more likely than control colonies to have at least one trunk trail that extended beyond the 12 m foraging range of the colony, and ants returning along these trails carried bluegrass seeds but not cheatgrass seeds. These results suggest that when preferred seeds dropped in abundance near nests, the economics of foraging by harvester ants favored a small increase in acceptance of less preferred seeds as well as more distant forays to locate and collect preferred seeds.     

Effect of predation risk on selectivity in heteromyid rodents

Variations in predation risk affect the costs of foraging and may therefore warrant different foraging decisions. One class of models ("higher requisite profit") predicts that foragers should become more selective when predation risk increases, as low-profitability items that do not cover the increased costs are dropped from the diet. An alternative class of models ("reduced finickiness") predicts that foragers should become less selective when predation risk increases, because selectivity requires more extensive assessment and/or search behaviour, prolonging exposure to risk. We assessed the selectivity of foraging heteromyid rodents (Merriam's kangaroo rats, Dipodomys merriami, and pocket mice, Chaetodipus spp.) by comparing differences in "giving up densities" (GUD: the quantity of cryptic food left in a patch by animals for whom the diminishing marginal gains from foraging have dropped below the threshold for continued search) for foods of different value as a measure of selectivity in patches varying in predation risk. Data collected over two field seasons revealed that heteromyids were more selective when predation risk was highest; away from the protective cover of shrubs during the full moon. These findings support the predictions of higher requisite profit models.     

Interactions with Combined Chemical Cues Inform Harvester Ant Foragers' Decisions to Leave the Nest in Search of Food

Social insect colonies operate without central control or any global assessment of what needs to be done by workers. Colony organization arises from the responses of individuals to local cues. Red harvester ants (Pogonomyrmex barbatus) regulate foraging using interactions between returning and outgoing foragers. The rate at which foragers return with seeds, a measure of food availability, sets the rate at which outgoing foragers leave the nest on foraging trips. We used mimics to test whether outgoing foragers inside the nest respond to the odor of food, oleic acid, the odor of the forager itself, cuticular hydrocarbons, or a combination of both with increased foraging activity. We compared foraging activity, the rate at which foragers passed a line on a trail, before and after the addition of mimics. The combination of both odors, those of food and of foragers, is required to stimulate foraging. The addition of blank mimics, mimics coated with food odor alone, or mimics coated with forager odor alone did not increase foraging activity. We compared the rates at which foragers inside the nest interacted with other ants, blank mimics, and mimics coated with a combination of food and forager odor. Foragers inside the nest interacted more with mimics coated with combined forager/seed odors than with blank mimics, and these interactions had the same effect as those with other foragers. Outgoing foragers inside the nest entrance are stimulated to leave the nest in search of food by interacting with foragers returning with seeds. By using the combined odors of forager cuticular hydrocarbons and of seeds, the colony captures precise information, on the timescale of seconds, about the current availability of food.     

Linking traits of foraging animals to spatial patterns of plants: social and solitary ants generate opposing patterns of surviving seeds

Foraging traits of seed predators are expected to impact the spatial structure of plant populations, community dynamics and diversity. Yet, many of the key mechanisms governing distance- or density-dependent seed predation are poorly understood. We designed an extensive set of field experiments to test how seed predation by two harvester ant species interact with seed dispersal in shaping the spatial patterns of surviving seeds. We show that the Janzen–Connell establishment pattern can be generated by central-place foragers even if their focal point is located away from the seed source. Furthermore, we found that differences in the social behaviour of seed predators influence their sensitivity to seed density gradients and yield opposing spatial patterns of surviving seeds. Our results support the predictions of a recent theoretical framework that unifies apparently opposing plant establishment patterns, and suggest that differences in foraging traits among seed predators can drive divergent pathways of plant community dynamics.     

Patch Use in Free‐Ranging Goats: Does a Large Mammalian Herbivore Forage like Other Central Place Foragers?

Classic central place foraging theory does not focus on the foraging of central place herbivores. This is especially true with regard to large mammalian herbivores. To understand the foraging dynamics of these neglected foragers, we measured giving‐up densities (GUDs) in artificial food patches. We did this at different distances away from the central point (i.e. corral) for a herd of free‐ranging domestic goats. To determine temporal changes, we conducted the study over a 3‐mo period during an extended dry season. Throughout our study, goats foraged across a gradient of food availability where forage was more available farther away from the central point. In contrast to the prediction that predation risk and/or increased travel costs were the main drivers of foraging decisions, we found that the goats increased their feeding effort (i.e. achieved lower GUDs) the farther away they moved from the central point. This suggests that either metabolic or missed opportunity costs were the main factors that influenced foraging decisions. In addition, we suggest that social foraging may have also played a role. With increases in foraging opportunities away from the central point, a herd will likely move slowly while foraging. As a result, individuals can feed intensively from patches but remain part of the group. Ironically, owing to the sustained close proximity of other group members, individuals may perceive patches farther from the central point as being safer. Temporally, the goats increased their feeding effort throughout the dry season. This suggests there was a decline in food quality and/or availability across the environment as the study progressed. Despite this increase in feeding effort, the negative relationship with distance did not change. Ultimately, our results provide key insight into how metabolic, missed opportunity and perceived predation costs influence the feeding decisions of large central place herbivores.     

Consequences of climate and body size on the foraging performance of seed‐eating ants

1. Changes in climatic factors could have major effects on the foraging performance of animals. To date, however, no study has attempted to examine the concurrent effect of different climatic factors on foraging performance of individual organisms. 2. In the present study, this issue was addressed by studying changes in foraging performance of seed‐eating ant colonies of the genus Messor in response to variation in precipitation and ambient temperature along a macroecological gradient. In addition, we examined the way three colony‐level attributes, foraging distance, forager number, and variance in worker‐size, could affect foraging performance in those ants. Foraging performance was measured as size matching, i.e. the correlation between forager size and load size. The study was carried out for 2 years in six sites along a south‐north productivity gradient in a semi‐arid region of the Eastern‐Mediterranean. 3. Size matching increased with increased precipitation as well as with an increase in worker‐size variability, but slightly decreased with increasing temperatures, as predicted by foraging‐decision models. In contrast, foraging distance had no effect on size matching. Interestingly, size matching showed a unimodal relationship with forager number. 4. These results indicate that interplay between climate and body size affects foraging performance either directly via physiological constraints, or indirectly through their effect on food availability. Moreover, this is one of the first evidences to support the assumption that ant colonies can differ in their ability to optimally allocate their workforce in natural environments. This emphasises the importance of studying the way foraging strategies vary across environmental gradients at macroecological scales.     

Leaf-cutting ant nests support less dense and impoverished seed assemblages in a human-modified Caatinga dry forest

Regenerating forests make up an increasingly large portion of tropical landscapes worldwide and regeneration dynamics may be influenced by leaf-cutting ants (LCA), which proliferate in disturbed areas and collect seeds for fungus culturing. Here, we investigate how LCA influences seed fate in human-modified areas of Caatinga dry forest. We evaluate the seed deposition and predation on Atta opaciceps nests, foraging habitat surrounding nest and control habitat away of nest influence of 15 colonies located along a forest cover gradient during the rainy and dry seasons. For each habitat, four 50-cm² plots were established and all seeds on the soil surface were collected along 1 year. We recorded 13,628 seeds distributed among 47 species and 36.57% of the total seeds did not show any sign of predation. Nest mound habitats supported low-density and species-poor seed assemblages, which were taxonomically distinct from the control habitats. These effects only occurred in the rainy season. The proportion of undamaged seeds were similar across the habitats. While forest cover did not influence seed assemblage in terms of species richness or seed predation, it did interact with habitat type via increments in seed abundance as forest cover increased across the nests. Forest cover also affected seed composition, but only in the rainy season. These results indicate that LCA decrease seed deposition in areas under their influence, particularly on the nest mounds. As LCA profit from human disturbance in the Caatinga, their role as seed ‘sinks’ should be enhanced in disturbed Caatinga patches, particularly during the rainy season, when most of the plant recruitment occurs. Our findings reinforce the importance of LCA as drivers of forest dynamics and resilience in human-modified landscapes.     

Linking optimal foraging behavior to bird community structure in an urban-desert landscape: field experiments with artificial food patches

Urban bird communities exhibit high population densities and low species diversity, yet mechanisms behind these patterns remain largely untested. We present results from experimental studies of behavioral mechanisms underlying these patterns and provide a test of foraging theory applied to urban bird communities. We measured foraging decisions at artificial food patches to assess how urban habitats differ from wildlands in predation risk, missed-opportunity cost, competition, and metabolic cost. By manipulating seed trays, we compared leftover seed (giving-up density) in urban and desert habitats in Arizona. Deserts exhibited higher predation risk than urban habitats. Only desert birds quit patches earlier when increasing the missed-opportunity cost. House finches and house sparrows coexist by trading off travel cost against foraging efficiency. In exclusion experiments, urban doves were more efficient foragers than passerines. Providing water decreased digestive costs only in the desert. At the population level, reduced predation and higher resource abundance drive the increased densities in cities. At the community level, the decline in diversity may involve exclusion of native species by highly efficient urban specialists. Competitive interactions play significant roles in structuring urban bird communities. Our results indicate the importance and potential of mechanistic approaches for future urban bird community studies.     

Scale-dependent neighborhood effects: shared doom and associational refuge

A resource’s susceptibility to predation may be influenced by its own palatability and the palatability of its neighbors. We tested for effects of plant chemical defenses on seed survival by manipulating the frequency of palatable and less palatable sunflower seeds in food patches subject to harvest by fox squirrels (Sciurus niger) and gray squirrels (Sciurus carolinensis). We varied resource distributions at three scales: among stations (aggregates of patches ca. 50 m apart), among patches immediately adjacent to each other, and within patches. When food patches were segregated into high-palatability and low-palatability stations (Experiment 1), seeds suffered greater mortality at stations with high levels of palatable seeds. In the same experiment, within patches, squirrels selected strongly for palatable seeds over less palatable seeds. When high- and low-palatability food patches were placed together at the same stations (Experiment 2), increasing densities of co-occurring palatable seeds amplified the mortality of less palatable seeds, indicating “shared doom.” When palatable and less palatable seeds were partitioned into micropatches (Experiment 3), associational effects disappeared, as predicted. Furthermore, selectivity in less palatable patches increased as the initial densities of palatable seeds increased, and selectivity in palatable patches decreased as the initial densities of less palatable seeds increased. Foraging theory predicts associational effects among prey that vary in palatability. Our results show how the type and magnitude of associational effects emerge from the interplay among the spatial scale of prey heterogeneity, the diet selection strategy, and the scale-dependent foraging responses of the consumer.     

Quantifying the effect of colony size and food distribution on harvester ant foraging

Desert seed-harvester ants, genus Pogonomyrmex, are central place foragers that search for resources collectively. We quantify how seed harvesters exploit the spatial distribution of seeds to improve their rate of seed collection. We find that foraging rates are significantly influenced by the clumpiness of experimental seed baits. Colonies collected seeds from larger piles faster than randomly distributed seeds. We developed a method to compare foraging rates on clumped versus random seeds across three Pogonomyrmex species that differ substantially in forager population size. The increase in foraging rate when food was clumped in larger piles was indistinguishable across the three species, suggesting that species with larger colonies are no better than species with smaller colonies at collecting clumped seeds. These findings contradict the theoretical expectation that larger groups are more efficient at exploiting clumped resources, thus contributing to our understanding of the importance of the spatial distribution of food sources and colony size for communication and organization in social insects.     

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.     

Impact of habitat structure and fruit abundance on avian seed dispersal and fruit predation

So far, it is poorly understood how differential responses of avian seed dispersers and fruit predators to changes in habitat structure and fruit abundance along land-use gradients may translate into consequences for the seed dispersal of associated plants. We selected a gradient of habitat modification (forest, semi-natural, and rural habitat) characterized by decreasing tree cover and a high variation in local fruit availability. Along this gradient we quantified fruit removal by avian seed dispersers and fruit predators from 18 Sorbus aucuparia trees. We analyzed the relative importance of tree cover and fruit abundance in explaining species richness, abundance and fruit removal rates of both guilds from S. aucuparia trees. Species richness and abundance of seed dispersers decreased with decreasing tree cover, whereas fruit removal by seed dispersers decreased with decreasing fruit abundance independent of tree cover. Both variables had no effect on species richness, abundance and fruit removal by fruit predators. Consequently, seed dispersers dominated relative fruit removal in fruit-rich sites but the dispersal/predation ratio shifted in favor of predation in fruit-poor habitat patches. Our study demonstrates that variation in local habitat structure and fruit abundance can cause guild-specific responses. Such responses may result in a shift in fruit removal regimes and might affect the dispersal ability of dependent fruiting plants. Future studies should aim at possible consequences for plant recruitment and guild-specific responses of frugivores to disturbance gradients on the level of entire plant–frugivore associations.     

The spatial scale of seed collection by harvester ants

Colonies of the seed-eating ant, Pogonomyrmex barbatus, compete with neighboring colonies for foraging areas. In a conflict over foraging area, what is at stake? This depends on how resources are distributed in time and space: if certain regions consistently provide particularly nutritious seed species, or especially abundant seeds, such regions will be of greater value to a colony. During the summer, seeds were taken from returning foragers in colonies located in 4 different vegetation types. There was no relation between the vegetation currently growing in the foraging area, and the species of seeds collected by ants. During the summer, ants collect mostly seeds produced in previous seasons and dispersed by wind and flooding. In 1991, colonies in all vegetation types collected mostly Bouteloua aristidoides; in 1992, Eriastrum diffusum and Plantago patagonica. There was no relation between colony density and numbers of seeds collected. Seed species collected by ants were compared in different colonies, and on different foraging trails within a colony. The results show that seed patches are distributed on the scale of distances between nests, not the smaller scale of different foraging trails of one colony. It appears that colonies are competing for any space in which to search for seeds, not competing for certain regions of consistently high value.     

Overdispersion of ant colonies: a test of hypotheses

Summary The nest locations of two ant species in the Colorado Desert are intraspecifically overdispersed. Intraspecific overdispersion has been thought to represent strong intraspecific competition. Here we consider this hypothesis along with three competing hypotheses: microhabitat selection by foundress queens, predation on foundress queens, and predation on established colonies. To test these hypotheses five types of data were collected: (1) the forager population sizes of Veromessor pergandei and Pogonomyrmex californicus, (2) the response of the territory use of V. pergandei to varying levels of food, (3) the encounter rates of conspecifics and other ant species to foundress queens artificially placed near and far from conspecific colonies, (4) predation on colonies as a function of colony spacing, and (5) the relationship between the plant microhabitat at the nest and colony spacing. The results show that established colonies have no apparent selectivity for a particular type of plant microhabitat nor do foundress queens show avoidance or attraction toward conspecifics. V. pergandei workers show only a slight ability to find V. pergandei queens that are artificially placed near their entrances. Certain spiders are the most common ant predators on our study area. Direct observations on spiders indicate that colonies with closer neighbors are not prone to a higher risk of predation. In addition, the estimates of the death rate of workers from a mark-recapture technique indicate that colonies with closer neighbors lose similar numbers of workers as compared to colonies with further neighbors. In favor of the competition hypothesis, the summed size of intraspecific nearest neighbor pairs are larger for colonies that are spaced further apart than those colonies that are spaced closer together. We also develop an index of foraging directionality for the column foraging species V. pergandei. Using this measure, we find that nearest neighbors tend to avoid foraging toward each other. The response of territory use to food levels was tested with experiments involving patches of cracked wheat. These experiments showed that patches away from nearest neighbors were found significantly sooner than patches toward nearest neighbors. The above five sets of data together suggest that resource competition and perhaps queen predation by established colonies account for the intraspecific spatial patterns of these species.     

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.     

Seed limitation of woody plants in Neotropical savannas

The failure of seeds to arrive at all suitable sites (seed limitation) greatly affects plant distribution and abundance. In contrast to tropical forests, the degree of seed limitation in Neotropical savannas is unclear because empirical studies at the community level are scarce. We estimated seed limitation of 23 woody species from annual seed rain measurements along a tree density gradient in the savannas of Central Brazil. These savannas differ in tree density and canopy cover, from closed to open savannas, and are located along shallow topographic gradients. We also studied post-dispersal seed predation and removal of 17 representative woody species, and seed viability loss over time of 12 common woody species under dry-storage conditions. Annual seed rain was lower in open (410 seeds/m²) than in closed savannas (773 seeds/m²). Average seed limitation across woody species was higher than 80% along the tree density gradient. More than 60% of seeds of the studied woody species were predated or removed within 30–45 days in all savannah types. Seeds of most common woody species (66%) lost their viability in less than 12 months of dry storage. This study shows that Neotropical savannah woody plants are strongly seed-limited because of low and poor distribution of seeds among sites, post-dispersal seed removal, and short seed longevity. The high seed limitation of tree species in Neotropical savannas, particularly in open savannas, also may contribute to maintain their relatively low tree densities and help to explain the spatial variation of tree abundance along topographic gradients.     

The dilemma of foraging herbivores: dealing with food and fear

For foraging herbivores, both food quality and predation risk vary across the landscape. Animals should avoid low-quality food patches in favour of high-quality ones, and seek safe patches while avoiding risky ones. Herbivores often face the foraging dilemma, however, of choosing between high-quality food in risky places or low-quality food in safe places. Here, we explore how and why the interaction between food quality and predation risk affects foraging decisions of mammalian herbivores, focusing on browsers confronting plant toxins in a landscape of fear. We draw together themes of plant–herbivore and predator–prey interactions, and the roles of animal ecophysiology, behaviour and personality. The response of herbivores to the dual costs of food and fear depends on the interplay of physiology and behaviour. We discuss detoxification physiology in dealing with plant toxins, and stress physiology associated with perceived predation risk. We argue that behaviour is the interface enabling herbivores to stay or quit food patches in response to their physiological tolerance to these risks. We hypothesise that generalist and specialist herbivores perceive the relative costs of plant defence and predation risk differently and intra-specifically, individuals with different personalities and physiologies should do so too, creating individualised landscapes of food and fear. We explore the ecological significance and emergent impacts of these individual-based foraging outcomes on populations and communities, and offer predictions that can be clearly tested. In doing so, we provide an integrated platform advancing herbivore foraging theory with food quality and predation risk at its core.