Characteristics of foraging in the soft-bottom benthic starfish Luidia clathrata (echinodermata: Asteroidea): prey selectivity,switching behavior,functional responses and movement patterns

Summary Luidia clathrata show a strong preference for the infaunal bivalve Mulinia lateralis in Tampa Bay, Florida. Quantitative and qualitative changes in diet occurred over a 7-month period. Individuals may shift from intraoral macrofaunal feeding to intra- and extraoral detrital feeding during periods of low macrofaunal availability. In the laboratory L. clathrata showed switching behavior, feeding disproportionately on the most abundant of two simulataneously presented food models. This switching mechanism may be related to either contact-chemoreceptive rejection of lowdensity food or enhanced distance-chemoreception of high density food. The use of standardized food models eliminated the possibility that handling time was important in switching behavior. Both fed and starved individuals showed functional responses to changes in prey density. However starved individuals ingested greater numbers of prey and spent more time foraging than did fed individuals. Switching and functional response behaviors may be important in promoting nutritional uptake and in causing density-dependent mortality of prey populations. Movement patterns of L. clathrata are directional in the absence of bivalve prey, but become non-directional once patches of prey are encountered. This allows individuals to remain in areas of high prey density. Luidia clathrata has characteristics of an optimal forager, where energy is maximized per unit feeding time.     

Ant foraging strategies vary along a natural resource gradient

Food selection by foragers is sensitive to the availability of resources, which may vary along geographical gradients. Hence, selectivity of food types by foragers is expected to track these resource gradients. Here we addressed this hypothesis and asked if foraging decisions of seed-eating ants differ along a geographic gradient of habitat productivity. The study was carried out for two years at five sites along a natural climatic gradient, ranging from arid to Mediterranean, where plant productivity varies six-fold across a short geographic distance of 250 km. We found that in ant colonies of the genus Messor, collective foraging decisions differed along the gradient. Specifically, at the high-productivity sites, a stronger association was found between plant seed availability and selectivity, suggesting that colonies respond more accurately to within-patch variation in food amounts. In contrast, colonies in low-productivity sites foraged in patches with higher concentration of seeds, suggesting that they respond more accurately to among-patch variation in food amounts. Moreover, at the high-productivity sites, colonies were more discriminating in their choice of food and preferred bigger seeds, while in the low-productivity sites, where smaller seeds were relatively more abundant, food collection depended mostly on seed availability. An experiment with artificial seed patches performed along the same climatic gradient, revealed no difference in food selectivity across sites when food type and availability were similar, and a general preference for bigger over medium-sized seeds. Overall, our findings suggest that resource availability is an important factor explaining food choice along a climatic gradient and imply that in low-productivity regions small-seeded species incur high predation pressure, whereas in high-productivity regions, large-seeded species suffer higher predation. This could have important consequences for plant species composition, particularly at the face of climate change, which could dramatically alter the foraging decisions of granivores.     

The effects of carotenoid and food intake on caudal fin regeneration in male guppies

The trade‐offs involved in allocating carotenoid pigments and food to healing and regrowing damaged caudal fin tissue v . other functions were examined in guppies Poecilia reticulata , a species in which females prefer males that display larger amounts of carotenoids in their skin. The guppies were derived from four natural populations in Trinidad that differed in resource availability but not predation intensity. Carotenoids, food and site of origin did not affect either absolute or relative fin regrowth, which suggested that fin regeneration in guppies was not constrained by carotenoid availability. It is possible that carotenoid intake influences fin regeneration in the presence of natural stressors such as predators. There was a significant negative interaction between food level in the laboratory and resource availability in the field: males from low‐resource‐availability sites regrew more fin tissue when raised on the high food level, and males from high‐resource‐availability sites regrew more fin tissue when raised on the low food level. The direction of this interaction runs counter to theoretical expectations.     

Can spatial and temporal food variability explain the winter foraging movements of a threatened saltmarsh insectivore?

The white‐fronted chat (Epthianura albifrons) is a small, insectivorous passerine that is threatened with extinction in the north‐eastern part of its range, partially due to loss and degradation of its saltmarsh habitat. Food availability is a potential limiting factor for the disjunct populations that survive in saltmarsh refugia, surrounded by urbanized land, because the anthropogenic matrix reduces the capacity of birds to commute to alternative grassland habitat to exploit temporary insect outbreaks. This limitation is likely to be exacerbated during the winter months when local arthropod abundance in saltmarsh is reduced. This study measured temporal and spatial variation in the abundance of saltmarsh arthropods to determine whether patch switching by foraging flocks can be explained by variation in food availability. Arthropods in the size range known to be important in the diet of white‐fronted chats were vacuum‐sampled from six patches within a continuous area of Sarcocornia‐dominated saltmarsh over a four‐month period. The location of foraging birds was recorded during the same period. Despite superficial similarity in vegetation composition and structure, there was significant variation in arthropod biomass among sites through time, such that the patches with the highest food abundance changed from month to month. There was little evidence, however, to suggest that white‐fronted chats foraged in saltmarsh patches with the highest overall food abundance. During the course of the study, birds were discovered flying 2 km from the saltmarsh to a development site where they foraged in weedy grassland. Arthropod samples collected from this site contained an extremely high abundance of Hemiptera and Neuroptera larvae, supporting previous research indicating that white‐fronted chats forage on irruptions of particular arthropod taxa. These findings indicate that food abundance is unlikely to be the main determinant of foraging site selection within saltmarsh, but highlights the potential importance of alternative foraging habitat types for this species.     

Foraging by <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> Larvae in a Patchy Environment

The food resources of Drosophila comprise decaying vegetable matter distributed in patches, yet foraging behavior has not been examined in larvae reared continuously in a patchy environment. Here, the extent and rate of inter-patch movement was studied in larvae of four wild strains of D. melanogaster inhabiting an experimental arena from the egg stage to the third larval instar. The hypotheses were that larvae would forage primarily in the third instar, that larvae would move from low-protein patches at higher rates than from high-protein patches, and that foraging rates would be higher on an agar substrate than on sand. Larvae hatching on a nutrient-poor food patch switched to a nutrient-rich patch during the first instar. The rate of interpatch switching increased with larval age, as did the number of larvae roving on the substrate between food patches. Inter-patch distance affected switching speed---the closer the patches, the faster the switching. High protein patches were preferred over low-protein patches, but there was a bias towards staying on the natal patch. Significant variation among strains in latency to forage, in proportion of larvae that switched patches, and in the rate of roving between patches suggests that there is natural genetic variation for these traits. Larvae switched food patches on a substrate of moist sand as quickly as on an agar substrate.     

The Payoffs to Producing and Scrounging: What Happens when Patches are Divisible?

Although many group-foraging models assume that all individuals search for and share their food equally, most documented instances of group foraging exhibit specialized use of producer and scrounger strategies. In addition, many of the studies have focused on groups with strong individual asymmetries exploiting food that is not easily divisible. In the present study we describe individual foraging behavior of relatively nonaggressive flock foragers exploiting divisible clumps of food. Two experiments, one with flocks of spice finches and another with flocks of zebra finches, suggest that divisibility of food patches may have important consequences for social foraging behavior. Neither dominance nor the distribution and quality of food patches affect the relative advantage that producing individuals enjoy over those that scrounge. Specialized producers and scroungers are absent from flocks of both species. Systems where patches are shared may differ fundamentally from those where patches are monopolized by scroungers.     

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.     

Foraging Ecology of Fall-Migrating Shorebirds in the Illinois River Valley

Populations of many shorebird species appear to be declining in North America, and food resources at stopover habitats may limit migratory bird populations. We investigated body condition of, and foraging habitat and diet selection by 4 species of shorebirds in the central Illinois River valley during fall migrations 2007 and 2008 (Killdeer [Charadrius vociferus], Least Sandpiper [Calidris minutilla], Pectoral Sandpiper [Calidris melanotos], and Lesser Yellowlegs [Tringa flavipes]). All species except Killdeer were in good to excellent condition, based on size-corrected body mass and fat scores. Shorebird diets were dominated by invertebrate taxa from Orders Diptera and Coleoptera. Additionally, Isopoda, Hemiptera, Hirudinea, Nematoda, and Cyprinodontiformes contribution to diets varied by shorebird species and year. We evaluated diet and foraging habitat selection by comparing aggregate percent dry mass of food items in shorebird diets and core samples from foraging substrates. Invertebrate abundances at shorebird collection sites and random sites were generally similar, indicating that birds did not select foraging patches within wetlands based on invertebrate abundance. Conversely, we found considerable evidence for selection of some diet items within particular foraging sites, and consistent avoidance of Oligochaeta. We suspect the diet selectivity we observed was a function of overall invertebrate biomass (51.2±4.4 [SE] kg/ha; dry mass) at our study sites, which was greater than estimates reported in most other food selection studies. Diet selectivity in shorebirds may follow tenants of optimal foraging theory; that is, at low food abundances shorebirds forage opportunistically, with the likelihood of selectivity increasing as food availability increases. Nonetheless, relationships between the abundance, availability, and consumption of Oligochaetes for and by waterbirds should be the focus of future research, because estimates of foraging carrying capacity would need to be revised downward if Oligochaetes are truly avoided or unavailable for consumption.     

Behavioural interactions between native smokey dace and introduced yellowfin shiner: implications from habitat selection theory for an ongoing invasion

The occupation of adjacent, non‐overlapping positions along environmental gradients by closely related and ecologically similar species has drawn considerable attention from ecologists over the past decades. Condition‐specific competition, wherein competitive superiority varies with the abiotic environmental gradient, has been proposed as the major structuring force behind such distributions. These concepts, however, are generally applied to explain the contemporary distribution of organisms that share an evolutionary history. Our aim was to apply these concepts to the naive interactions between native and introduced fishes. In 1990 yellowfin shiner ( Notropis lutipinnis ) were introduced into the headwaters of the Little Tennessee River of western North Carolina, U.S.A. where it exhibits microhabitat preferences that overlap significantly with those of a threatened native minnow, the smokey dace ( Clinostomus funduloides raneyi ). Previous research has established that these drift‐feeding minnows: (1) differ in their average ability to intercept drifting prey as a function of water velocity; (2) generally occupy focal‐point velocities that maximize the rate of prey capture; and, (3) occasionally defend the forward positions in foraging aggregations that form in high quality patches. We present the results of a series of experiments designed to: (1) evaluate the role of aggression in the establishment and maintenance of preferred foraging positions in drift‐feeding minnows; (2) test the effects of prey availability, group size, and velocity on dominance rank, spatial position in groups, and feeding rates of individuals; and, (3) evaluate the potential for condition‐specific competition to establish competitive refugia for the native within the natural heterogeneity of mountain streams.     

BODY SIZE,NATURAL SELECTION,AND SPECIATION IN STICKLEBACKS

There is little evidence from nature that divergent natural selection is crucial to speciation. However, divergent selection is implicated if traits conferring adaptation to alternative environments also form the basis of reproductive isolation. We tested the importance of body size differences to premating isolation between two sympatric sticklebacks. The species differ greatly in size, and several lines of evidence indicate that this difference is an adaptation to alternative foraging habitats. Strong assortative mating was evident in laboratory trials, but a few hybridization events occurred. Probability of interspecific mating was strongly correlated with body size: interspecific spawning occurred only between the largest individuals of the smaller species and the smallest individuals of the larger species. Probability of spawning between similar-sized individuals from different species was comparable to spawning rates within species. Disruption of mating between individuals from different species can be traced to increased levels of male aggression and decreased levels of male courtship as size differences increased between paired individuals. Interspecific mate preferences in sympatric sticklebacks appears to be dominated by body size, implicating natural selection in the origin of species.     

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.     

Long‐Distance Calling by the Willow Tit,Poecile montanus,Facilitates Formation of Mixed‐Species Foraging Flocks

The occurrence of mixed‐species foraging flocks is a worldwide phenomenon in terrestrial bird communities. Previous studies suggest that individuals participating in flocks might derive benefits in terms of improved feeding efficiency and/or reduced risk of predation. However, very little is known about how individuals establish mixed‐species flocks. Here, I provide the first experimental evidence that long‐distance calling by the willow tit, Poecile montanus, facilitates the establishment of mixed‐species flocks at a foraging patch. Observations at experimental foraging patches showed that willow tits that find a food source produce long‐distance calls, particularly when they are isolated from conspecific flockmates. The probability of long‐distance calling was negatively correlated with the number of heterospecific foraging individuals near the food source. A playback experiment confirmed that calls attract both conspecific and heterospecific members of foraging flocks. This study demonstrates that willow tits use long‐distance calls to attract conspecific flockmates to foraging patches, and these calls can also facilitate the formation of mixed‐species flocks on patches.     

Effects of food quality, diet preference and water on patch use by Nubian ibex

Measuring patch use of a forager can reveal not only its cost and benefits from foraging, but also the importance of environmental factors and the significance of energy, nutrients and predation risk to its fitness. In order to assess the effects of various variables that may affect the foraging behavior of free-ranging Nubian ibex in the Negev Desert, Israel, giving-up densities (GUD) in artificial food patches were measured following Kotler et al. In particular, we tested the effects of food quality and water availability on Nubian ibex foraging behavior. To do so, we (1) tested whether the tannic acid content of food affected diet preferences, (2) assayed their diet selection strategy, (3) tested if the foraging decisions of the Nubian ibex were affected by the availability of water and (4) determined the nutritional relationship between food resources and water. Nubian ibex had lower GUDs and used resources patches more intensively where water was available, the food quality was higher and the location was closer to the escape terrain. Nubian ibex showed an expanding specialist diet selection when exploiting resource patches with a mix of items that differ in quality. Overall, food and water were complementary resources for Nubian ibex, and tannins reduced food quality. These factors help to determine patch foraging behavior decisions in Nubian ibex and contribute to habitat quality.     

Prey‐driven behavioral habitat use in a low‐energy ambush predator

Food acquisition is an important modulator of animal behavior and habitat selection that can affect fitness. Optimal foraging theory predicts that predators should select habitat patches to maximize their foraging success and net energy gain, likely achieved by targeting areas with high prey availability. However, it is debated whether prey availability drives fine‐scale habitat selection for predators. We assessed whether an ambush predator, the timber rattlesnake (Crotalus horridus), exhibits optimal foraging site selection based on the spatial distribution and availability of prey. We used passive infrared camera trap detections of potential small mammal prey (Peromyscus spp., Tamias striatus, and Sciurus spp.) to generate variables of prey availability across the study area and used whether a snake was observed in a foraging location or not to model optimal foraging in timber rattlesnakes. Our models of small mammal spatial distributions broadly predicted that prey availability was greatest in mature deciduous forests, but T. striatus and Sciurus spp. exhibited greater spatial heterogeneity compared with Peromyscus spp. We found the spatial distribution of cumulative small mammal encounters (i.e., overall prey availability), rather than the distribution of any one species, to be highly predictive of snake foraging. Timber rattlesnakes appear to forage where the probability of encountering prey is greatest. Our study provides evidence for fine‐scale optimal foraging in a low‐energy, ambush predator and offers new insights into drivers of snake foraging and habitat selection.     

Group-Living Herbivores Weigh Up Food Availability and Dominance Status when Making Patch-Joining Decisions

Two key factors that influence the foraging behaviour of group-living herbivores are food availability and individual dominance status. Yet, how the combination of these factors influences the patch-joining decisions of individuals foraging within groups has scarcely been explored. To address this, we focused on the patch-joining decisions of group-living domestic goats (Capra hircus). When individuals were tested against the top four ranked goats of the herd, we found that at patches with low food availability they avoided these dominant patch-holders and only joined subordinates (i.e. costs outweighed benefits). However, as the amount of food increased, the avoidance of the top ranked individuals declined. Specifically, goats shifted and joined the patch of an individual one dominance rank higher than the previous dominant patch holder when the initial quantity of food in the new patch was twice that of the lower ranking individual’s patch (i.e. benefits outweighed costs). In contrast, when individuals chose between patches held by dominant goats, other than the top four ranked goats, and subordinate individuals, we found that they equally joined the dominant and subordinate patch-holders. This joining was irrespective of the dominance gap, absolute rank of the dominant patch-holder, sex or food availability (i.e. benefits outweighed costs). Ultimately, our results highlight that herbivores weigh up the costs and benefits of both food availability and patch-holder dominance status when making patch-joining decisions. Furthermore, as the initial quantity of food increases, food availability becomes more important than dominance with regard to influencing patch-joining decisions.     

Fitness consequences of foraging success in water striders (Gerris remigis; Heteroptera: Gerridae)

Foraging theory's central premise assumes that behavioral actionsthat affect the acquisition of food also ultimately affect fitness.However, very few investigations in behavioral ecology actuallydemonstrate ultimate fitness consequences of any particularbehavior. Many studies focus on short-term estimates of fitnessin animals with considerable life spans. I investigated whetherdifferences in foraging performance, as related to patch choiceand behavioral dominance, show consistent patterns over extendedperiods of an animal's life such that they translate into differencesin reproductive success. In one experiment, I focused on theability of single female water strider (Gerris remigis) to discriminatebetween foraging patches of differing prey abundances in laboratorystreams simulating natural conditions. In another experiment,I focused on competitive interactions within groups of threefemale water striders foraging in laboratory streams where resourceavailability varied with position in a patch. The first experimentshowed that, overall, the individuals detected and preferredto forage in the richer patch, which directly increased theirforaging success and their lifetime fecundity. However, therewas marked variability among individuals in their ability torespond to the differences in food availability, ranging fromno tracking to fast tracking when the patch qualities were switched.In the second experiment, both the foraging position of individualsin the stream and their dominance rank were reasonably consistentover their entire reproductive life. Foraging position and dominancerank were significant predictors of lifetime fecundity, theformer being the better predictor due to an imperfect correlationbetween the two variables. In both experiments, the increasein fecundity was achieved by higher oviposition rates ratherthan by extending the oviposition period or by inducing firstreproduction at an earlier age. [Behav Ecol 1991; 2: 46-55)     

Individual differences in foraging site fidelity are not related to time-activity budgets in Herring Gulls

Many populations consist of individuals that differ consistently in their foraging behaviour through resource or foraging site selection. Foraging site fidelity has been reported in several seabird species as a common phenomenon. It is considered especially beneficial in spatially and/or temporally predictable environments in which fidelity is thought to increase energy intake, thereby affecting time-energy budgets. However, the consequences for activity and energy budget have not been adequately tested. In this paper, we studied the consequences of fine-scale foraging site fidelity in adult Herring Gulls Larus argentatus in a highly predictable foraging environment with distinct foraging patches. We measured their time-activity budgets using GPS tracking and tri-axial acceleration measurements, which also made it possible to estimate energy expenditure. Individual variation in foraging site fidelity was high, some individuals spending most of their time on a single foraging patch and others spending the same amount of time in up to 21 patches. While time and activity budgets differed between individuals, we found no clear relationship with foraging site fidelity. We did find a relationship between the size of the birds and the level of site fidelity; faithful birds tend to have a larger body size. Although differences in foraging time and habitat use between individuals could play a role in the results of the current study, short-term consequences of variation in foraging site fidelity within a population remain elusive, even when focusing on individuals with a similar foraging specialization (Blue Mussels Mytilus edulis). Studying individuals over multiple years and under varying environmental conditions may provide better insight into the consequences and plasticity of foraging site fidelity.     

Diet of the helmeted guineafowl (Numida meleagris galeata Pallas) in the Waza region of North Cameroon

Through laboratory and field experiments, we investigated the effect of food availability and food nutritive value on food selection by helmeted guineafowl ( Numida meleagris galeata Pallas) during the dry season in the Waza region of North Cameroon. Field study and crop analysis shows that a wide variety of food types are eaten by guineafowl during the dry season. Analysis of 101 crops from wild birds reveals a statistically significant positive correlation between the sodium and water content of food items and the quantity found in the crops. Rhizomes of Stylochiton lancifolius and termites form the bulk of the diet of this species during the dry season. It is concluded that the selection of water‐rich food may be an adaptation to dry environment.     

Transport Infrastructure Shapes Foraging Habitat in a Raptor Community

Transport infrastructure elements are widespread and increasing in size and length in many countries, with the subsequent alteration of landscapes and wildlife communities. Nonetheless, their effects on habitat selection by raptors are still poorly understood. In this paper, we analyzed raptors’ foraging habitat selection in response to conventional roads and high capacity motorways at the landscape scale, and compared their effects with those of other variables, such as habitat structure, food availability, and presence of potential interspecific competitors. We also analyzed whether the raptors’ response towards infrastructure depends on the spatial scale of observation, comparing the attraction or avoidance behavior of the species at the landscape scale with the response of individuals observed in the proximity of the infrastructure. Based on ecological hypotheses for foraging habitat selection, we built generalized linear mixed models, selected the best models according to Akaike Information Criterion and assessed variable importance by Akaike weights. At the community level, the traffic volume was the most relevant variable in the landscape for foraging habitat selection. Abundance, richness, and diversity values reached their maximum at medium traffic volumes and decreased at highest traffic volumes. Individual species showed different degrees of tolerance toward traffic, from higher abundance in areas with high traffic values to avoidance of it. Medium-sized opportunistic raptors increased their abundance near the traffic infrastructures, large scavenger raptors avoided areas with higher traffic values, and other species showed no direct response to traffic but to the presence of prey. Finally, our cross-scale analysis revealed that the effect of transport infrastructures on the behavior of some species might be detectable only at a broad scale. Also, food availability may attract raptor species to risky areas such as motorways.     

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.