The effect of resource aggregation at different scales: optimal foraging behavior of Cotesia rubecula

Resources can be aggregated both within and between patches. In this article, we examine how aggregation at these different scales influences the behavior and performance of foragers. We developed an optimal foraging model of the foraging behavior of the parasitoid wasp Cotesia rubecula parasitizing the larvae of the cabbage butterfly Pieris rapae. The optimal behavior was found using stochastic dynamic programming. The most interesting and novel result is that the effect of resource aggregation within and between patches depends on the degree of aggregation both within and between patches as well as on the local host density in the occupied patch, but lifetime reproductive success depends only on aggregation within patches. Our findings have profound implications for the way in which we measure heterogeneity at different scales and model the response of organisms to spatial heterogeneity.     

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.     

Does variation in patch use among butterfly species contribute to nestedness at fine spatial scales?

A nested pattern occurs whenever the species observed in depauperate habitat patches are a subset of those found in more species‐rich patches. Ecologists have documented many instances of nestedness caused by population‐level processes such as colonization and extinction at biogeographic scales. However, few researchers have examined whether nestedness may exist at fine scales due to the ways in which individual organisms discriminate among potential habitat patches. In 1999, we experimentally fragmented an old‐field habitat into patches of varying size to test whether nestedness could exist on a fine spatial scale. Five treatments of differing patch size were replicated five times in a Latin square design by selectively mowing 15×15 m² plots within an old‐field (patch areas: 225, 180, 135, 90, and 45 m²). Specifically, we tested whether butterflies foraging within a network of patches differing in area conformed to a nested subset structure. We also classified species according to (1) their flight height while foraging (high or low), and (2) their adult habitat breadth (ubiquitous, general, or restricted) to determine whether nestedness could be explained by difference in species’ tendency to discriminate among patches differing in area.
We found significant evidence that a community of foraging Lepidoptera conformed to a nested subset structure based on the difference between the observed nestedness within the butterfly community and the nestedness obtained from randomly generated species presence/absence matrices. Poisson regression analyses demonstrated that high‐flying, habitat‐restricted species avoided the smallest patches (90 and 45 m²) in favor of larger remnants, whereas low‐flying, habitat generalists used all patch sizes. Thus, our study is one of the first to demonstrate that nestedness among species subsets can be observed at fine spatial scales (within a single 1.5 hectare field) and may be maintained by species behavioral differences: discriminating species (i.e. high‐flying, habitat restricted) avoided the smallest patches, and less discriminating species (i.e. low‐flying, ubiquitous) were distributed throughout the field without regard to patch size. Our results also suggest that nestedness should be viewed as yet another scalar pattern in ecology, generated by variation in patch use by individuals at fine‐scales as well as the more traditionally invoked processes of extinction and colonization of species at broad‐scales.     

Top-down effects of foraging decisions on local,landscape and regional biodiversity of resources (DivGUD)

Foraging by consumers acts as a biotic filtering mechanism for biodiversity at the trophic level of resources. Variation in foraging behaviour has cascading effects on abundance, diversity, and functional trait composition of the community of resource species. Here we propose diversity at giving-up density (DivGUD), i.e. when foragers quit exploiting a patch, as a novel concept and simple measure quantifying cascading effects at multiple spatial scales. In experimental landscapes with an assemblage of plant seeds, patch residency of wild rodents decreased local α-DivGUD (via elevated mortality of species with large seeds) and regional γ-DivGUD, while dissimilarity among patches in a landscape (ß-DivGUD) increased. By linking theories of adaptive foraging behaviour with community ecology, DivGUD allows to investigate cascading indirect predation effects, e.g. the ecology-of-fear framework, feedbacks between functional trait composition of resource species and consumer communities, and effects of inter-individual differences among foragers on the biodiversity of resource communities.     

Resource use by the dryad butterfly is scale-dependent

The factors shaping the ways in which animals use resources are a key element of conservation biology, but ecological studies on resource use typically neglect to consider how the study’s spatial scale may have affected the outcomes. We used the dryad butterfly, inhabiting xerothermic grassland and wet meadow, to test for differences in its resource use at two scales–habitat patch and landscape. Based on records of plant species composition from random points within four habitat patches and from points in 53 patches along surveyed transects, we compared the microhabitat preferences of the butterfly on the patch scale, and species occurrence and abundance patterns on the landscape scale. We distinguished four main groups of factors related to vegetation structure which affected the butterfly’s resource use—factors having similar effects on both spatial scales, factors operating primarily on one of the scales considered, factors relevant only on a single spatial scale, and factors operating on both scales but with effects differing between the two habitat types. We suggest that invertebrates may respond on two spatial levels or on only one, and conclude that larger-scale studies can meet the challenges of a sophisticated metapopulation approach and can give insight into the habitat characteristics affecting the persistence of species in landscapes. We stress the value of large-scale studies on species’ habitat preferences when planning conservation strategies, while pointing out that small-scale studies provide useful information about species ecology and behavior, especially if conducted in multiple habitats.     

Energy benefits and emergent space use patterns of an empirically parameterized model of memory‐based patch selection

Many species frequently return to previously visited foraging sites. This bias towards familiar areas suggests that remembering information from past experience is beneficial. Such a memory‐based foraging strategy has also been hypothesized to give rise to restricted space use (i.e. a home range). Nonetheless, the benefits of empirically derived memory‐based foraging tactics and the extent to which they give rise to restricted space use patterns are still relatively unknown. Using a combination of stochastic agent‐based simulations and deterministic integro‐difference equations, we developed an adaptive link (based on energy gains as a foraging currency) between memory‐based patch selection and its resulting spatial distribution. We used a memory‐based foraging model developed and parameterized with patch selection data of free‐ranging bison Bison bison in Prince Albert National Park, Canada. Relative to random use of food patches, simulated foragers using both spatial and attribute memory are more efficient, particularly in landscapes with clumped resources. However, a certain amount of random patch use is necessary to avoid frequent returns to relatively poor‐quality patches, or avoid being caught in a relatively poor quality area of the landscape. Notably, in landscapes with clumped resources, simulated foragers that kept a reference point of the quality of recently visited patches, and returned to previously visited patches when local patch quality was poorer than the reference point, experienced higher energy gains compared to random patch use. Furthermore, the model of memory‐based foraging resulted in restricted space use in simulated landscapes and replicated the restricted space use observed in free‐ranging bison reasonably well. Our work demonstrates the adaptive value of spatial and attribute memory in heterogeneous landscapes, and how home ranges can be a byproduct of non‐omniscient foragers using past experience to minimize temporal variation in energy gains.     

Scale-dependent foraging and patch choice in fractal environments

Many spatially complex environments are fractal, and consumers in these environments face scale-dependent trade-offs between encountering high densities of small resource patches versus low densities of large resource patches. I address the effects of these trade-offs on foraging by incorporating scale-dependent encounter of resources in fractal landscapes into classical optimal foraging theory. This model is then used to predict optimal scales of perception (foraging scale) and patch choice in response to spatial features of landscapes. The model predicts that, for a given density of resources, landscapes with greater extent and fractal dimension and that contain patchy (low fractal dimension) resources favour large foraging scales and specialization on a small proportion of resource patches. Fragmented (low fractal dimension) landscapes of small extent with dispersed (high fractal dimension) resources favour smaller foraging scales and generalists that use a large proportion of available resource patches. These predictions synthesize the results of other spatially explicit consumer–resource models into a simple framework and agree reasonably well with results of several empirical studies. This study thus places optimal foraging theory in a spatial context and suggests evolutionary mechanisms of consumers' responses to important spatial phenomena (e.g. habitat fragmentation, resource aggregation). This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Testing assumptions of central place foraging theory: a study of Adélie penguins Pygoscelis adeliae in the Ross Sea

We investigated central place foraging (CPF) in the context of optimal foraging theory in Adélie penguins Pygoscelis adeliae of the southern Ross Sea by using satellite tracking and time‐depth recorders to explore foraging at two spatio‐temporal scales: within the day‐to‐day (sub‐mesoscale: single foraging trip, 10s of km²) and the entire breeding season (mesoscale: trips by multiple individuals across the collective foraging area, 100s of km²). Specifically, we examine whether three basic assumptions of the Orians–Pearson CPF model, shown to occur in other CPF species, are met: 1) within a patch, the rate of prey acquisition declines with time spent in that patch; 2) food is distributed in discrete patches and is not available between those patches; and 3) CPF species have knowledge of the potential (or average, at least) feeding rate within their universe of patches, and use this knowledge to determine their foraging strategy when planning or engaging in a foraging trip. We found that prey consumption rates did not decline with time spent in patches, and penguins foraged to some degree most of the time when at sea. Food availability, as measured by foraging dive rate, appeared to be predictable within the same day at the same location, but predictability broke down after 2 d at distances > 10 km away. We conclude that the assumptions of the Orians–Pearson CPF model are not a good fit to the circumstances of Ross Sea penguins, which clearly are central place foragers.     

Preference in patchy landscapes: the influence of scale-specific intake rates and variance in reward

Understanding the responses of foragers to patchy distributionsof resources has formed a fundamental challenge in behavioralecology. Two currencies have been used to assess the patch preferencesof herbivores—intake rate maximization and risk sensitivity.We wished to understand if small mammalian foragers, collaredlemmings (Dichrostonyx groenlandicus), choose patches to maximizefood intake rate or to reduce risk of starvation in "variable"environments. Moreover, we examined the possibility that maximizingintake rate depends on the spatial scale of patchiness. We designedan experiment offering two alternative patches of food, varyingthe predictability of food rewards and the "potential intakerate" at different spatial scales. Collared lemmings did notconsistently select patches that maximized their intake rateat either scale studied. Instead, they chose patches offeringthe least variation in food reward over the course of the experiment.Collared lemmings used prior knowledge gained from previousforaging bouts to assess food variability. We interpret theseresults as evidence for risk-averse foraging strategies, whichare predicted for continuous foragers aiming to minimize riskof starvation.     

Local variation in plant quality influences large‐scale population dynamics

Spatial variation in ecological systems can arise both as a consequence of variation in the quality and availability of resources and as an emergent property of spatially structured interactions. We used a spatially explicit model to simulate populations of herbivore hosts and their parasitoids in landscapes with different levels of variance in plant patch quality and different spatial arrangements of high‐ and low‐quality plant patches. We found that even small variation in patch quality at a fine spatial scale decreased overall herbivore populations, as parasitoid populations on low‐quality plant patches were subsidized by those from high‐quality neighbors. On landscapes with large, homogeneous regions of high‐ and low‐quality plant patches, herbivore populations increased with variation in patch quality. Overall, our results demonstrate that local variation in resource quality profoundly influences global population dynamics. In particular, fine‐scale variation in plant patch quality enhanced biological control of herbivores by parasitoids, suggesting that adding back plant genetic variation into perennial production systems may enhance the biological control of herbivores by their natural enemies.     

Resource characteristics and competition affect colony and individual foraging strategies of the wood ant Formica integroides

Abstract.  1. Resource characteristics and competitive pressure can affect an ant colony's foraging strategy. This study examined the ability of the wood ant Formica integroides to respond, at both the colony and individual levels, to changes in competitive pressure for access to terrestrial and arboreal resources.
2. Because foraging behaviours depend on resource characteristics, foraging for different resource types (e.g. terrestrial and arboreal habitats) produces different spatial or territorial arrangements. In this study, terrestrial contests for resources followed an interference-exploitation tradeoff, while arboreal foragers defended entire trees as absolute territories.
3. Competitive pressure for access to arboreal resources was shown to increase with distance from F. integroides nests.
4. In this study, the ability of F. integroides to defend a resource varied with body size. Large foragers were better defenders than small foragers. For groups of foragers, the ability to defend a resource increased with the ratio of large to small foragers.
5. In response to competitive pressure, F. integroides colonies altered the size distribution of arboreal, but not terrestrial, foragers. An increase in competitive pressure was matched by an increase in the number of large foragers allocated to trees. This response to competition affected the relationship between body size and distance from the nest for arboreal foragers.
6. Foraging behaviours for individual arboreal foragers also varied with competitive pressure. As competition increased, large arboreal foragers spent more time in direct contact with the resource rather than standing between resource patches.     

Seed harvesting by a generalist consumer is context‐dependent: Interactive effects across multiple spatial scales

Granivore foraging decisions affect consumer success and determine the quantity and spatial pattern of seed survival. These decisions are influenced by environmental variation at spatial scales ranging from landscapes to local foraging patches. In a field experiment, the effects of seed patch variation across three spatial scales on seed removal by western harvester ants Pogonomyrmex occidentalis were evaluated. At the largest scale we assessed harvesting in different plant communities, at the intermediate scale we assessed harvesting at different distances from ant mounds, and at the smallest scale we assessed the effects of interactions among seed species in local seed neighborhoods on seed harvesting (i.e. resource–consumer interface). Selected seed species were presented alone (monospecific treatment) and in mixture with Bromus tectorum (cheatgrass; mixture treatment) at four distances from P. occidentalis mounds in adjacent intact sagebrush and non‐native cheatgrass‐dominated communities in the Great Basin, Utah, USA. Seed species differed in harvest, with B. tectorum being least preferred. Large and intermediate scale variation influenced harvest. More seeds were harvested in sagebrush than in cheatgrass‐dominated communities (largest scale), and the quantity of seed harvested varied with distance from mounds (intermediate‐scale), although the form of the distance effect differed between plant communities. At the smallest scale, seed neighborhood affected harvest, but the patterns differed among seed species considered. Ants harvested fewer seeds from mixed‐seed neighborhoods than from monospecific neighborhoods, suggesting context dependence and potential associational resistance. Further, the effects of plant community and distance from mound on seed harvest in mixtures differed from their effects in monospecific treatments. Beyond the local seed neighborhood, selection of seed resources is better understood by simultaneously evaluating removal at multiple scales. Associational effects provide a useful theoretical basis for better understanding harvester ant foraging decisions. These results demonstrate the importance of ecological context for seed removal, which has implications for seed pools, plant populations and communities.     

Spatial and temporal scaling in habitat utilization by klipspringers (Oreotragus oreotragus) determined using giving‐up densities

An animal's pattern of habitat use can reveal how different parts of its environment vary in quality based on the costs (such as predation risk) and benefits (such as food intake) of using each habitat. We studied klipspringer habitat use in Augrabies Falls National Park, South Africa using giving‐up densities (GUDs; the amount of food remaining in a resource patch following exploitation) in experimental food patches. We tested hypotheses related to how salient habitat variables might influence klipspringers' perceptions of foraging costs. At small spatial scales (3–4 m), klipspringer GUDs did not vary with cover and open microhabitats, or with the four cardinal aspects (shading) around shrubs. Adding water adjacent to food patches did not influence GUDs, showing that water is not a limiting complementary resource to food. Generally, klipspringers do not appear to be physiologically constrained. There was no difference in GUDs between four daily time periods, or between summer and winter; however, a significant interaction effect of time‐of‐day with season resulted from GUDs during the midday time period in winter being significantly higher (perceived value lower) than during the same time period in summer. At moderate spatial scales (10–60 m), klipspringer GUDs increased with distance from rocks because of increased predation risk. Based on GUDs collected at the largest scale (two 4.41‐ha grids), klipspringers preferred foraging at greater distances from drainage lines and on pebble and cobble substrates. Overall, this study has shown the efficacy of measuring GUDs to determine klipspringers' habitat utilization while foraging.     

Detecting predators and locating competitors while foraging: an experimental study of a medium-sized herbivore in an African savanna

Vigilance allows individuals to escape from predators, but it also reduces time for other activities which determine fitness, in particular resource acquisition. The principles determining how prey trade time between the detection of predators and food acquisition are not fully understood, particularly in herbivores because of many potential confounding factors (such as group size), and the ability of these animals to be vigilant while handling food. We designed a fertilization experiment to manipulate the quality of resources, and compared awareness (distinguishing apprehensive foraging and vigilance) of wild impalas (Aepyceros melampus) foraging on patches of different grass height and quality in a wilderness area with a full community of predators. While handling food, these animals can allocate time to other functions. The impalas were aware of their environment less often when on good food patches and when the grass was short. The animals spent more time in apprehensive foraging when grass was tall, and no other variable affected apprehensive behavior. The probability of exhibiting a vigilance posture decreased with group size. The interaction between grass height and patch enrichment also affected the time spent in vigilance, suggesting that resource quality was the main driver when visibility is good, and the risk of predation the main driver when the risk is high. We discuss various possible mechanisms underlying the perception of predation risk: foraging strategy, opportunities for scrounging, and inter-individual interference. Overall, this experiment shows that improving patch quality modifies the trade-off between vigilance and foraging in favor of feeding, but vigilance remains ultimately driven by the visibility of predators by foragers within their feeding patches.     

Exploration and exploitation of foraging patches by desert sparrows: environmental indicators and local evaluation of spatially correlated costs and benefits

Conventional evolutionary and behavioral reasoning expects foragers to show strong spatial preferences in environments with heterogeneous resource distribution. Moreover, consumers should benefit from exploiting the information embedded in environmental features that indicate resource abundance. In desert soils seed abundance associates strong and reliably with vegetation and litter cover at small spatial scales. However, other spatially correlated factors (substrate complexity, temperature, predation risk) may affect foraging costs, benefits and decisions by ground‐feeding granivores. We used a sequence of three semi‐controlled field experiments of binary spatial choice within a portable aviary to identify the main cause of foraging microhabitat selection by the most abundant postdispersal granivorous bird in the central Monte desert (Argentina). In the first experiment we placed the aviary at field to offer pairs of adjacent microhabitats of unmodified, naturally‐contrasting substrates and environmental conditions to single, untrained rufous‐collared sparrows Zonotrichia capensis. Birds selected covered microhabitats in winter and summer, ruling out substrate complexity or thermoregulation as main single causes of patch selection. The other two experiments dissociated seed abundance, tree cover and litter to reveal their effects on patch selection. The results indicate that 1) sparrows do not restrict microhabitat exploration relying on environmental indicators, 2) distance to tree cover influences the order of patch exploration, probably in association with apprehension or risk‐assessment behavior, and 3) patch exploitation is determined by short‐term local estimation of seed abundance. The integration of these with previous results obtained under variable degrees of realism and experimental control allows for a better explanation of the spatial component of postdispersal granivory and its consequences on plants. The unconstrained selective foraging strategy of these sparrows would allow them to detect sporadic or ephemeral rich patches with structural characteristics indicating ‘low‐quality’, should promote the spatial homogenization of the palatable seed bank, and would favor indirect interactions between plants.     

Density‐Dependent Foraging and Interference Competition by Common Gartersnakes are Temperature Dependent

The ideal free distribution (IFD) predicts that optimal foragers will select foraging patches to maximize food rewards and that groups of foragers should thus be distributed between food patches in proportion to the availability of food in those patches. Because many of the underlying mechanisms of foraging are temperature dependent in ectotherms, the distribution of ectothermic foragers between food patches may similarly depend on temperature because the difference in fitness rewards between these patches may change with temperature. We tested the hypothesis that the distribution of Common Gartersnakes (Thamnophis sirtalis) between food patches can be explained by an IFD, but that conformance to an IFD weakens as temperature departs from the optimal temperature because fitness rewards, interference competition and the number of individuals foraging are highest at the optimal temperature. First, we determined the optimal temperature for foraging. Second, we examined group foraging at three temperatures and three density treatments. Search time was optimized at 27°C, handling time at 29°C and digestion time at 32°C. Gartersnakes did not match an IFD at any temperature, but their distribution did change with temperature: snakes at 20°C and at 30°C selected both food patches equally, while snakes at 25°C selected the low food patch more at low density and the high food patch more at high density. Food consumption and competition increased with temperature, and handling time decreased with temperature. Temperature therefore had a strong impact on foraging, but did not affect the IFD. Future work should examine temperature‐dependent foraging in ectotherms that are known to match an IFD.     

Response of butterflies to structural and resource boundaries

1. Two aspects of landscape composition shape the behavioural response of animals to habitat heterogeneity: physical habitat structure and abundance of key resources. In general, within-habitat movement behaviour has been investigated in relation to resources, and preference at boundaries has been quantified in response to physical structure. 2. Habitat preference studies suggest that responses to resources vs. structure should differ, e.g. between male and female animals, and effects of responses to structure and resources may also interact. However, most studies of animal movement combine various aspects of behavioural responses to 'habitat', implicitly assuming that resources and structure are broadly equivalent. 3. We conducted a large-scale experiment of the movement of Fender's blue (Icaricia icarioides fenderi), an endangered butterfly, to investigate butterfly response to physical structure of the landscape (prairie, open woods and dense woods) and to resources [presence or absence of Kincaid's lupine, Lupinus oreganus (larval hostplant patches)]. The experiment included 606 butterfly flight paths across four habitat types and nine ecotones. 4. Responses to physical structure and resource patches were not congruent. Butterflies were attracted to resource patches within both prairies and open woods and moved more slowly when in resource patches. Butterflies tended to prefer prairie at prairie-forest edges but tended to move faster in prairies than in open woods. Physical structure and resources also interacted; butterflies did not respond to physical habitat structure when resource patches spanned prairie - open woods ecotones. 5. Even dense woods were not perfect barriers, in contrast to a large body of literature that assumes insects from open habitats will not enter dense forests. 6. Movement of both males and females responded to resources and structure. However, female butterflies had stronger responses to both resources and structure in most cases. Females had strongest response to resource (hostplant) patches at patch edges, whereas the strongest preference of males was to return to prairie from open forest. 7. If other species behave like Fender's blue, then combining different definitions of 'habitat' (physical structure vs. resources), different aspects of movement (edge preference vs. within-habitat movement) and/or males and females within species could all lead to misleading conclusions. Our results highlight the importance of investigating these responses, and our study provides a framework for separating them in other systems.     

Population and community consequences of spatial subsidies derived from central-place foraging

Central-place foragers, such as ants, beavers, and colonial seabirds, can act as biological conduits, subsidizing local communities with allochthonous resources. To explore the consequences of such biologically vectored resource redistribution, we draw on an example from cave ecology and develop a population-level model of central-place foraging based on the dispersal kernel framework. We explore how the size of the patch in which central-place foraging occurs and the spatial distribution of foragers within that patch feed back to influence the population dynamics of the central-place forager and the species richness of the associated recipient community. We demonstrate that the particular way in which a population of central-place foragers uses space has two important effects. First, space use determines the stability of the forager population and establishes patch size thresholds for persistence, stable equilibria, and limit cycles. Second, alternative foraging kernels lead to qualitatively different scaling relationships between the size of the foraging patch and species richness back at the central place. These analyses provide a new link among elements of ecology related to animal behavior, population dynamics, and species diversity while also providing a novel perspective on the utility of integrodifference equations for problems in spatial ecology.     

Eavesdropping foragers use level of collective commotion as public information to target high quality patches

Public information offers a valuable means for social foragers to determine the relative quality of foraging patches. Despite much evidence that foragers use public information based on others’ feeding behavior, no experiments have examined whether foragers might use public information based on others’ competitive behavior, particularly the collective commotion that can be generated by aggregations. Such commotion could potentially provide a rich source of public information: as foragers compete in a patch with an especially high value resource, their heightened competition intensity could enable eavesdropping foragers to target this superior patch, based simply on its higher level of collective commotion. To test the hypothesis that the level of collective commotion is used as public information by eavesdropping foragers I conducted field experiments on terrestrial hermit crabs Coenobita compressus. These animals engage in collective competitive interactions in foraging patches for food and shells, generating variable levels of commotion across different quality patches. By experimentally manipulating the level of collective commotion in sham aggregations in the wild I show that a higher level of commotion is exploited by eavesdropping foragers to differentially target more valuable patches. Broadly, these results highlight an underappreciated significance of competitive by‐products and higher‐ order collective pheno mena as forms of public information for foragers.