Search

Many predators ambush prey rather than pursue them or shift between foraging modes. Active predators typically encounter prey more frequently than ambush predators. I designed a simulation model to examine whether this always holds and how active and ambush predators fare in capturing mobile prey. Prey foraged for clumped resources using area‐restricted search, shifting from directional movement before resource encounter to less directional movement afterward. While active predators succeeded more than ambush predators, the advantage of active predators diminished when ambush predators were positioned inside resource patches rather than outside. I investigated the impact of eight treatments and their interactions. For example, regeneration of prey resources increased the difference between ambush predators inside and outside patches, and uncertain prey capture by predators decreased this difference. Several interactions resulted in outcomes different from each factor in isolation. For instance, reducing the directionality level of active predators impacted moderately when applied alone, but when combined with resource regeneration it led to the worst success of active predators against ambush predators inside patches. Ambush predators may not always be inferior to active predators, and one should consider the key traits of the studied system to predict the relative success of these two foraging modes. [ABSTRACT FROM AUTHOR]

Desert ant foragers are well known for their visual navigation abilities, relying on visual cues in the environment to find their way along routes back to the nest. If the inconspicuous nest entrance is missed, ants engage in a highly structured systematic search until it is discovered. Searching ants continue to be guided by visual cues surrounding the nest, from which they derive a location estimate. The precision level of this estimate depends on the information content of the nest panorama. This study examines whether search precision is also affected by the directional distribution of visual information. The systematic searching behavior of ants is examined under laboratory settings. Two different visual scenarios are compared – a balanced one where visual information is evenly distributed, and an unbalanced one where all visual information is located on one side of an experimental arena. The identity and number of visual objects is similar over both conditions. The ants search with comparable precision in both conditions. Even in the visually unbalanced condition, searches are characterized by balanced precision on both sides of the arena. This finding lends support to the idea that ants memorize the visual scenery at the nest as panoramic views from different locations. A searching ant is thus able to estimate its location with equal precision in all directions, leading to symmetrical search paths. [ABSTRACT FROM AUTHOR]

Abstract Background Studying animal movement in the context of the optimal foraging theory has led to the development of simple movement metrics for inferring feeding activity. Yet, the predictive capacity of these metrics in natural environments has been given little attention, raising serious questions of the validity of these metrics. The aim of this study is to test whether simple continuous movement metrics predict feeding intensity in a marine predator, the southern elephant seal (SES; Mirounga leonine), and investigate potential factors influencing the predictive capacity of these metrics. Methods We equipped 21 female SES from the Kerguelen Archipelago with loggers and recorded their movements during post-breeding foraging trips at sea. From accelerometry, we estimated the number of prey encounter events (nPEE) and used it as a reference for feeding intensity. We also extracted several track- and dive-based movement metrics and evaluated how well they explain and predict the variance in nPEE. We conducted our analysis at two temporal scales (dive and day), with two dive profile resolutions (high at 1 Hz and low with five dive segments), and two types of models (linear models and regression trees). Results We found that none of the movement metrics predict nPEE with satisfactory power. The vertical transit rates (primarily the ascent rate) during dives had the best predictive performance among all metrics. Dive metrics performed better than track metrics and all metrics performed on average better at the scale of days than the scale of dives. However, the performance of the models at the scale of days showed higher variability among individuals suggesting distinct foraging tactics. Dive-based metrics performed better when computed from high-resolution dive profiles than low-resolution dive profiles. Finally, regression trees produced more accurate predictions than linear models. Conclusions Our study reveals that simple movement metrics do not predict feeding activity in free-ranging marine predators. This could emerge from differences between individuals, temporal scales, and the data resolution used, among many other factors. We conclude that these simple metrics should be avoided or carefully tested a priori with the studied species and the ecological context to account for significant influencing factors.

This paper deals with the global boundedness and asymptotic stability of the solution of the two-predator and one-prey systems with density-dependent motion in a n-dimensional bounded domain with Neumann boundary conditions. In a previous paper, Qiu et al. (J Dyn Differ Equ, 1–25, 2021) proved the global existence and uniform boundedness of classical solution by limiting the conditions on motility functions and the coefficients of logistic source. By contrast, we relax the limitation conditions in Qiu et al. (2021) by constructing the weight function. Moreover, under diverse competition circumstances, the global stabilities of nonnegative spatially homogeneous equilibria for the special model are established. [ABSTRACT FROM AUTHOR]

We develop a method of analysis for testing the marginal value theorem (MVT) in natural settings that does not require an independent definition or mapping of patches. We draw on recent theoretical work on area-restricted search (ARS) that links turning-angle and step-size changes to geographically localized encounter-rates. These models allow us to estimate "giving-up times" using encounter-annotated GPS tracking data. Applied to a case study of Nahua mushroom foragers, these models identify distinct forms of intrapatch and interpatch search behavior, with intrapatch search transitioning to interpatch search after a predictable interval of time since the last encounter with a harvested mushroom. Our empirical estimate of giving-up time coincides with the theoretically optimal giving-up time derived under the MVT in the same environment. The MVT is currently underused in studies of human foraging and settlement patterns, due in large part to the difficulty of identifying discrete resource patches and quantifying their characteristics. Our methods mitigate the need to make such discrete maps of patches and thus have the potential to broaden the scope for empirical evaluations of the MVT and related theory in humans. Beyond studies of naturalistic foraging in humans and other animals, our approach has implications for optimization of search behavior in a range of applied fields where search dynamics must be adapted to shifting patterns of environmental heterogeneity affecting prey density and patchiness.

Background: Studying animal movement in the context of the optimal foraging theory has led to the development of simple movement metrics for inferring feeding activity. Yet, the predictive capacity of these metrics in natural environments has been given little attention, raising serious questions of the validity of these metrics. The aim of this study is to test whether simple continuous movement metrics predict feeding intensity in a marine predator, the southern elephant seal (SES; Mirounga leonine), and investigate potential factors influencing the predictive capacity of these metrics. Methods: We equipped 21 female SES from the Kerguelen Archipelago with loggers and recorded their movements during post-breeding foraging trips at sea. From accelerometry, we estimated the number of prey encounter events (nPEE) and used it as a reference for feeding intensity. We also extracted several track- and dive-based movement metrics and evaluated how well they explain and predict the variance in nPEE. We conducted our analysis at two temporal scales (dive and day), with two dive profile resolutions (high at 1 Hz and low with five dive segments), and two types of models (linear models and regression trees). Results: We found that none of the movement metrics predict nPEE with satisfactory power. The vertical transit rates (primarily the ascent rate) during dives had the best predictive performance among all metrics. Dive metrics performed better than track metrics and all metrics performed on average better at the scale of days than the scale of dives. However, the performance of the models at the scale of days showed higher variability among individuals suggesting distinct foraging tactics. Dive-based metrics performed better when computed from high-resolution dive profiles than low-resolution dive profiles. Finally, regression trees produced more accurate predictions than linear models. Conclusions: Our study reveals that simple movement metrics do not predict feeding activity in free-ranging marine predators. This could emerge from differences between individuals, temporal scales, and the data resolution used, among many other factors. We conclude that these simple metrics should be avoided or carefully tested a priori with the studied species and the ecological context to account for significant influencing factors. [ABSTRACT FROM AUTHOR]

A theoretical and applied literature has suggested that foragers search using Lévy flights, since Lévy flights can maximize the efficiency of search in the absence of information on the location of randomly distributed prey. Foragers, however, often have available to them at least some information about the distribution of prey, gained either through evolved mechanisms, experience and memory, or social transmission of information. As such, we might expect selection for heuristics that make use of such information to further improve the efficiency of random search. Here we present a general model of random search behavior that includes as special cases: area-restricted search, correlated random walks, Brownian search, and Lévy flights. This generative model allows foragers to adjust search parameters based on encounter-conditional and other heuristics. Using a simulation model, we demonstrate the efficiency gains of these search heuristics, and illustrate the resulting differences in the distributions of step-size and heading angle change they imply, relative to Lévy flights. We conclude by presenting a statistical model that can be fit to empirical data and a set of testable, quantitative predictions that contrast our model of adaptive search with the Lévy flight foraging hypothesis.

Active search for prey is energetically costly, so understanding how foragers optimize search has been central to foraging theory. Some theoretical work has suggested that foragers of randomly distributed prey should search using Lévy flights, while work on area-restricted and intermittent search strategies has demonstrated that foragers can use the information provided by prey encounters to more effectively adapt search direction and velocity. Previous empirical comparisons of these search modes have tended to rely on distribution-level analyses, due to the difficulty of collecting event-level data on encounters linked to the GPS tracks of foragers. Here we use a preliminary event-level data-set (18.7 hours of encounter-annotated focal follows over 6 trips) to show that two Colombian blowgun hunters use adaptive encounter-conditional heuristics, not non-conditional Lévy flights, when searching for prey. Using a theoretically derived Bayesian model, we estimate changes in turning-angle and search velocity as a function of encounters with prey at lagged time-steps, and find that: 1) hunters increase average turning-angle in response to encounters, producing a more tortuous search of patches of higher prey density, but adopt more efficient uni-directional, inter-patch movement after failing to encounter prey over a sufficient period of time; and, 2) hunters reduce search velocity in response to encounters, causing them to spend more of their search time in patches with demonstrably higher prey density. These results illustrate the importance of using event-level data to contrast encounter-conditional, area-restricted search and Lévy flights in explaining the search behavior of humans and other organisms.

Movement of foraging animals can be used as an indirect index of habitat quality because movement patterns are expected to shift in association with resources resulting in increased time spent in high‐quality habitat. Here, we observed movement of bumblebee (Bombus impatiens) queens as an indirect metric of nesting habitat quality.At a farm in Massachusetts, we recorded flight paths by visual observation of nest‐searching B. impatiens queens in three land cover types (hay fields, meadows and forests). According to previous research at this field site, these land cover types represent both high‐quality (meadows, forests) and low‐quality habitat (hay fields) for nesting bumblebees. Using flight path data, we estimated diffusion coefficients of nest‐searching queens (i.e., the rate at which queens explore habitat during nest‐searching), as an integrative measure of movement.We found that nest‐searching queens explored meadows and forests more slowly than hay fields; we calculated diffusion coefficients of 0.198, 0.272, and 0.762 m2 s−1 for bees searching for nests in meadows, forests, and hay fields, respectively. In hay fields, nest‐searching queens had smaller step lengths and straighter flightpaths than in other land cover types.Nesting ecology of bumblebees is a key knowledge gap. We showed that nest‐searching queens search more thoroughly in areas associated with previously reported high nest densities. Therefore, our research suggests that behaviour of nest‐searching queens can also be a proxy for nesting habitat quality. Extending these methods to other Bombus species in other landscapes would be a valuable direction for future research. [ABSTRACT FROM AUTHOR]

Abstract Background Diving marine predators forage in a three-dimensional environment, adjusting their horizontal and vertical movement behaviour in response to environmental conditions and the spatial distribution of prey. Expectations regarding horizontal-vertical movements are derived from optimal foraging theories, however, inconsistent empirical findings across a range of taxa suggests these behavioural assumptions are not universally applicable. Methods Here, we examined how changes in horizontal movement trajectories corresponded with diving behaviour and marine environmental conditions for a ubiquitous Southern Ocean predator, the Adélie penguin. Integrating extensive telemetry-based movement and environmental datasets for chick-rearing Adélie penguins at Béchervaise Island, we tested the relationships between horizontal move persistence (continuous scale indicating low [‘resident’] to high [‘directed’] movement autocorrelation), vertical dive effort and environmental variables. Results Penguins dived continuously over the course of their foraging trips and lower horizontal move persistence corresponded with less intense foraging activity, likely indicative of resting behaviour. This challenges the traditional interpretation of horizontal-vertical movement relationships based on optimal foraging models, which assumes increased residency within an area translates to increased foraging activity. Movement was also influenced by different environmental conditions during the two stages of chick-rearing: guard and crèche. These differences highlight the strong seasonality of foraging habitat for chick-rearing Adélie penguins at Béchervaise Island. Conclusions Our findings advance our understanding of the foraging behaviour for this marine predator and demonstrates the importance of integrating spatial location and behavioural data before inferring habitat use.

Given the patchiness and long-term predictability of marine resources, memory of high-quality foraging grounds is expected to provide fitness advantages for central place foragers. However, it remains challenging to characterize how marine predators integrate memory with recent prey encounters to adjust fine-scale movement and use of foraging patches. Here, we used two months of movement data from harbour seals (Phoca vitulina) to quantify the repeatability in foraging patches as a proxy for memory. We then integrated these data into analyses of fine-scale movement and underwater behaviour to test how both spatial memory and prey encounter rates influenced the seals' area-restricted search (ARS) behaviour. Specifically, we used one month's GPS data from 29 individuals to build spatial memory maps of searched areas and archived accelerometery data from a subset of five individuals to detect prey catch attempts, a proxy for prey encounters. Individuals were highly consistent in the areas they visited over two consecutive months. Hidden Markov models showed that both spatial memory and prey encounters increased the probability of seals initiating ARS. These results provide evidence that predators use memory to adjust their fine-scale movement, and this ability should be accounted for in movement models. [ABSTRACT FROM AUTHOR]

Animals may use long-distance foraging trips to capitalize on spatiotemporal variation in food availability, allowing individuals to maximize resource gain from foraging effort. This is particularly important for dimorphic species with polygynous mating where males face strong selection pressures to attain large size and access to reproductive females. We tracked 17 male Antarctic fur seals, Arctocephalus gazella , during their prolonged postbreeding trips and assessed links between their movements and environmental predictors of profitable feeding areas. Males made one of two types of trips: a long trip to the Antarctic ice edge or shorter trips to areas where the southern Antarctic Circumpolar Current fronts generate high biological activity. The trip type was not determined by body size but was related to departure date from the breeding area, suggesting that males must trade off opportunities at the breeding area (reproductive, social interactions) and foraging opportunities between breeding seasons. Regardless of trip structure, males focused search effort far from foraging areas of central-place foraging seabirds and seals including female Antarctic fur seals provisioning offspring. Males showed clear spatiotemporal patterns in dive behaviour, with deep dives in shelf waters during the day and predominantly shallower dives in pelagic waters at night. Diel dive patterns showed monthly changes in photoperiod and lunar phase, consistent with feeding on vertically migrating prey. However, males did not use area-restricted search to focus dive effort, instead performing a mix of foraging and nonforaging behaviour within and between restricted search areas. We discuss the scale and type of inference that can be made from movement models, given the behavioural constraints that govern long-distance trips in vast, heterogeneous environments like the Southern Ocean. • Males made two types of long-distance trip, related to departure date not body size. • Foraging and nonforaging behaviour occurred throughout these trips. • Males foraged mostly away from breeding seals, in areas of high biological activity. • Diel dive behaviour aligned with changes in solar and lunar light. [ABSTRACT FROM AUTHOR]

Background: Diving marine predators forage in a three-dimensional environment, adjusting their horizontal and vertical movement behaviour in response to environmental conditions and the spatial distribution of prey. Expectations regarding horizontal-vertical movements are derived from optimal foraging theories, however, inconsistent empirical findings across a range of taxa suggests these behavioural assumptions are not universally applicable. Methods: Here, we examined how changes in horizontal movement trajectories corresponded with diving behaviour and marine environmental conditions for a ubiquitous Southern Ocean predator, the Adélie penguin. Integrating extensive telemetry-based movement and environmental datasets for chick-rearing Adélie penguins at Béchervaise Island, we tested the relationships between horizontal move persistence (continuous scale indicating low ['resident'] to high ['directed'] movement autocorrelation), vertical dive effort and environmental variables. Results: Penguins dived continuously over the course of their foraging trips and lower horizontal move persistence corresponded with less intense foraging activity, likely indicative of resting behaviour. This challenges the traditional interpretation of horizontal-vertical movement relationships based on optimal foraging models, which assumes increased residency within an area translates to increased foraging activity. Movement was also influenced by different environmental conditions during the two stages of chick-rearing: guard and crèche. These differences highlight the strong seasonality of foraging habitat for chick-rearing Adélie penguins at Béchervaise Island. Conclusions: Our findings advance our understanding of the foraging behaviour for this marine predator and demonstrates the importance of integrating spatial location and behavioural data before inferring habitat use. [ABSTRACT FROM AUTHOR]

Free-recall tasks suggest human memory foraging may follow a heavy-tailed distribution, such as a Lévy flight, patch foraging, or area-restricted search – walk procedures that are common in other activities of cognitive agents, such as food foraging in both animals and humans. To date, research merely equates memory foraging with hunting in the physical world based on similarities in statistical structure. The current work supports that memory foraging follows a heavy-tailed distribution by using categories with quantitative distances between each item: countries, which have physical distances, and animals, from which cognitive distances can be derived using a multidimensional scaling (MDS) procedure. Likewise, inter-item lag times follow a heavy-tailed distribution. The current work also demonstrates that inter-item distances and times are positively correlated, suggesting the organization of items in memory may be akin to the organization of a physical landscape. Finally, both studies show that participants' original, heavy-tailed lists of countries and animal names produce shorter overall distances traveled than random selection. Human memory foraging follows the same pattern as foraging in the natural world – perhaps because exposure to ecological settings informs our inner cognitive experience – leading to a processing and retrieval time benefit. [ABSTRACT FROM AUTHOR]

• C. elegans shows ARS behavior, changing its velocity and turn frequency over time. • Pre-exposure to dopamine inhibits changes in searching behavior. • A dopamine-synthesis defect inhibits changes in searching behavior. • Inverse reinforcement learning reveals a change in the value function for velocity. • A change in value function is absent in dopamine exposed and deficient animals. Food exploration is an essential survival behavior in organisms. To find food efficiently, many organisms use a foraging strategy called area-restricted search (ARS) wherein individuals first turn more frequently, restricting their search to one area, then turn less frequently, moving along a straight path to widen the search area. Previous research suggests that the nematode Caenorhabditis elegans shows ARS behavior by changing turn frequency, and that dopamine is a crucial determinant. However, the effects of dopamine on multiple behavioral parameters have remained unknown. Here, we evaluated turn (pirouette) frequency, moving velocity, and specific area occupancy (cell occupancy) over time by using a multiple-worms tracking system. In the control (mock) experiments, all parameters changed over time, but no changes were observed in experiments with dopamine pre-exposed and dopamine-deficient animals. In inverse reinforcement learning analysis, the value function for specific velocity was found to modulate over time in mock animals only. These results demonstrate that dopamine regulates ARS via changes not only to pirouette frequency change but also to velocity. [ABSTRACT FROM AUTHOR]

1. Individuals do not have complete information about the environment and therefore they face a trade-off between gathering information (exploration) and gathering resources (exploitation). Studies have shown individual differences in components of this trade-off but how stable these strategies are in a population and the intrinsic drivers of these differences is not well understood. 2. Top marine predators are expected to experience a particularly strong trade-off as many species have large foraging ranges and their prey often have a patchy distribution. This environment leads these species to exhibit pronounced exploration and exploitation phases but differences between individuals are poorly resolved. Personality differences are known to be important in foraging behaviour but also in the trade-off between exploration and exploitation. Here we test whether personality predicts an individual exploration-exploitation strategy using wide ranging wandering albatrosses (Diomedea exulans) as a model system. 3. Using GPS tracking data from 276 wandering albatrosses, we extract foraging parameters indicative of exploration (searching) and exploitation (foraging) and show that foraging effort, time in patch and size of patch are strongly correlated, demonstrating these are indicative of an exploration-exploitation (EE) strategy. Furthermore, we show these are consistent within individuals and appear stable in the population, with no reproductive advantage. 4. The searching and foraging behaviour of bolder birds placed them towards the exploration end of the trade-off, whereas shy birds showed greater exploitation. This result provides a mechanism through which individual foraging strategies may emerge. Age and sex affected components of the trade-off, but not the trade-off itself, suggesting these factors may drive behavioural compensation to maintain resource acquisition and this was supported by the evidence that there were no fitness consequence of any EE trait nor the trade-off itself. 5. These results demonstrate a clear trade-off between information gathering and exploitation of prey patches and reveals for the first time that boldness may drive these differences. This provides a mechanism through which widely reported links between personality and foraging may emerge. [ABSTRACT FROM AUTHOR]

Foraging theory predicts that predators adjust their movements according to the spatial distribution of prey. Since prey is often patchily distributed, area-restricted search ( ARS) behaviour, characterized by sinuous search paths of predators with increased turning frequency, should be effective in foraging., However, it remains unclear whether ARS behaviour actually enhances foraging success in free-ranging animals, especially in marine animals that forage in a three-dimensional (3D) environment., Here, we reconstructed 3D dive paths of a highly pelagic marine predator, the northern elephant seal ( n = 3), with multisensor data loggers that recorded depth, tri-axis acceleration, tri-axis magnetism and swim speed. We identified spatial scales of volume-restricted search ( VRS, termed for 3D ARS) behaviour using spherical first-passage time analysis on 3D dive paths, accompanied with quantifying feeding rates in VRS by using mandible accelerometers that recorded feeding events., Seals exhibited VRS behaviour at two spatial scales (radius of spheres): small- VRS (8-10 m) and large- VRS (17-19 m). Most feeding events occurred in VRS zones (78 and 86% for small and large- VRS, respectively), although VRS accounted for a small proportion of bottom phase of dives in distance travelled. This suggests a strong link between VRS behaviour and foraging success., There was a hierarchical structure to the VRS; most small- VRS (95%) were nested within large- VRS (i.e. nested VRS). Importantly, nested VRS had significantly higher feeding rates than non-nested VRS, because nested VRS contained small- and large- VRS with higher and lower feeding rates, respectively. These results suggest that seals forage on mesopelagic prey in a hierarchical patch system where high-density patches at small scales are nested within low-density patches at larger scales., We demonstrated that seals employed scale-dependent, hierarchical 3D movements and that underwater fine-scale sinuous movements (i.e. VRS) were strongly linked to higher foraging success, particularly within nested VRS zones. We suggest that seals enhanced foraging success by employing hierarchical movements that possibly reflect the hierarchical property of prey distribution. Although recent studies advocate that optimal searching behaviour would be scale-independent (e.g. Lévy walk), our study suggests that scale-dependent processes are important components of successful foraging behaviour. [ABSTRACT FROM AUTHOR]

Background: The use of multi-sensor tags is increasingly providing insights into the behavior of whales. However, due to limitations in tag attachment duration and the transmission bandwidth of the Argos system, little is known about fine-scale diving behavior over time or the reliability of assigning behavioral states based on horizontal movement data for whale species. How whales use the water column while migrating has not been closely examined, yet the strategy used is likely to influence the vulnerability of whales to ship strike. Here we present information from a rare week long multi-sensor tag deployment on a pygmy blue whale (Balaenoptera musculus brevicauda) that provided a great opportunity to examine the fine-scale diving behavior of a migrating whale and to compare the occurrence of feeding lunges with assigned behavioral states. Results: The depth of migratory dives was highly consistent over time and unrelated to local bathymetry. The mean depth of migratory dives (~13 m when corrected for the tag position on the whale) was just below the threshold depth (12 m) that blue whales are predicted to travel below to remove the influence of wave drag at the surface. The whale spent 94 % of observed time and completed 99 % of observed migratory dives within the range of large container ship drafts (<24 m). Areas of high residence identified using the horizontal movement data (FastLoc GPS) did not reflect where lunge feeding occurred. Conclusions: The lack of correspondence between areas of high residence inferred from horizontal movement data and the locations where the whale performed feeding lunges highlights the need for further research to determine whether movement models can accurately detect whale feeding areas or only areas of prey searching. While migrating, the whale made dives to a depth that is likely to allow it to avoid wave drag and maximize horizontal movement. Although this strategy may reduce energy expenditure during migration, it also placed the whale at greater risk of ship strike for a much longer period than currently thought. If other whales have similar diving behavior to this animal during migration, many whale species may spend much longer periods than currently estimated within the parts of the water column where the risk of ship strike is high. [ABSTRACT FROM AUTHOR]

Foraging and foraging-like processes are found in spatial navigation, memory, visual search, and many other search functions in human cognition and behavior. Foraging is commonly theorized using either random or correlated movements based on Lévy walks, or a series of decisions to remain or leave proximal areas known as "patches". Neither class of model makes use of spatial memory, but search performance may be enhanced when information about searched and unsearched locations is encoded. A video game was developed to test the role of human spatial memory in a canonical foraging task. Analyses of search trajectories from over 2000 human players yielded evidence that foraging movements were inherently clustered, and that clustering was facilitated by spatial memory cues and influenced by memory for spatial locations of targets found. A simple foraging model is presented in which spatial memory is used to integrate aspects of Lévy-based and patch-based foraging theories to perform a kind of area-restricted search, and thereby enhance performance as search unfolds. Using only two free parameters, the model accounts for a variety of findings that individually support competing theories, but together they argue for the integration of spatial memory into theories of foraging. [ABSTRACT FROM AUTHOR]

Understanding how to find targets with very limited information is a topic of interest in many disciplines. In ecology, such research has often focused on the development of two movement models: (i) the Lévy walk and (ii) the composite correlated random walk and its associated area-restricted search behaviour. Although the processes underlying these models differ, they can produce similar movement patterns. Due to this similarity and because of their disparate formulation, current methods cannot reliably differentiate between these two models., Here, we present a method that differentiates between the two models. It consists of likelihood functions, including one for a hidden Markov model, and associated statistical measures that assess the relative support for and absolute fit of each model., Using a simulation study, we show that our method can differentiate between the two search models over a range of parameter values. Using the movement data of two polar bears ( Ursus maritimus), we show that the method can be applied to complex, real-world movement paths., By providing the means to differentiate between the two most prominent search models in the literature, and a framework that could be extended to include other models, we facilitate further research into the strategies animals use to find resources. [ABSTRACT FROM AUTHOR]

Many foraging animals find food using composite random search strategies, which consist of intensive and extensive search modes. Models of composite search can generate predictions about how optimal foragers should behave in each search mode, and how they should determine when to switch between search modes. Most of these models assume that foragers use resource encounters to decide when to switch between search modes. Empirical observations indicate that a variety of organisms use non-directional sensory cues to identify areas that warrant intensive search. These cues are not precise enough to allow a forager to directly orient itself to a resource, but can be used as a criterion to determine the appropriate search mode. As a potential example, a forager might use olfactory information as a non-directional cue. Even if scent is too imprecise for the forager to immediately locate a specific food item, it might inform the forager that the area is worth searching carefully. We developed a model of composite search based on non-directional sensory cues. With simulations, we compared the search efficiencies of composite foragers that use resource encounters as their mode-switching criterion with those that use non-directional sensory cues. We identified optimal search patterns and mode-switching criteria on a variety of resource distributions, characterized by different levels of resource aggregation and density. On all resource distributions, foraging strategies based on the non-directional sensory criterion were more efficient than those based on the resource encounter criterion. Strategies based on the non-directional sensory criterion were also more robust to changes in resource distribution. Our results suggest that current assumptions about the role of resource encounters in models of optimal composite search should be re-examined. The search strategies predicted by our model can help bridge the gap between random search theory and traditional patch-use foraging theory. [ABSTRACT FROM AUTHOR]

Mobile organisms frequently forage for patchy resources; e.g. herbivorous insects searching for host plants. The resource diffusion hypothesis predicts that insect herbivores, such as Pieris rapae butterflies, are disproportionally attracted to more isolated, or 'diffused', host plants. Surprisingly little is known about how this response to variation in resource density manifests itself at different spatial scales. We measured the outcome of oviposition by P. rapae butterflies foraging among groups of host plants, with plant density experimentally varied to achieve comparability between three nested scales: fine (1 × 1 m), medium (6 × 6 m), and coarse (36 × 36 m). Hierarchical linear models were used to measure density-dependent responses in the number of eggs laid per plant, with plant density measured at nested spatial scales. At a fine scale, isolated plants received significantly more eggs, while at medium and coarse scales the differences were less pronounced, and tended towards a neutral distribution of eggs across plants. Larger plants also tended to receive more eggs. Since multiple processes, acting at multiple scales, are likely to be the rule rather than the exception in ecology, methods for detecting and characterising multi-scale responses are important to ensure a robust transfer of ecological models from one situation to another. [ABSTRACT FROM AUTHOR]

Organisms can increase their foraging efficiency by modifying their behaviour according to information about the quality of currently exploited resource patches. Here we examine the effect of food concentration on the foraging strategies of two previously unstudied species of slime mould: Didymium iridis and Didymium bahiense . We studied two main foraging decisions: how long to wait before commencing exploration of the surrounding environment (exploitation strategy) and how intensely to search the environment for new opportunities (exploration strategy). Food concentration did not affect exploitation behaviour in either D. iridis or D. bahiense . Food concentration did affect exploration behaviour in D. iridis , but not in D. bahiense . Encounters with food resources, irrespective of concentration, resulted in increased exploitation and decreased exploration in D. iridis but did not influence foraging behaviour in D. bahiense . We suggest that the varying foraging strategies of slime moulds may have evolved to exploit different resource distributions in their natural environments. We also discuss the potential impact of microbial contamination and differences in handling regimes. [ABSTRACT FROM AUTHOR]

Oceanic structures such as mesoscale fronts may become hotspots of biological activity through concentration and enrichment processes. These fronts generally attract fish and may therefore be targeted by marine top-predators. In the southern Benguela upwelling system, such fronts might be used as environmental cues by foraging seabirds. In this study we analyzed high-frequency foraging tracks (GPS, 1 s sampling) of Cape gannets Morus capensis from two colonies located on the west and east coast of South Africa in relation to mesoscale fronts detected on daily high-resolution chlorophyll- a maps (MODIS, 1 km). We tested the association of (i) searching behavior and (ii) diving activity of foraging birds with mesoscale fronts. We found that Cape gannets shift from transiting to area-restricted search mode (ARS) at a distance from fronts ranging between 2 and 11 km (median is 6.7 km). This suggests that Cape gannets may be able to sense fronts (smell or vision) or other predators, and that such detection triggers an intensified investigation of their surroundings (i.e. ARS). Also we found that diving probability increases near fronts in 11 out of 20 tracks investigated (55%), suggesting that Cape gannets substantially use fronts for feeding; in the remaining cases (45%), birds may have used other cues for feeding including fishing vessels, particularly for gannets breeding on the west coast. We demonstrated in this study that oceanographic structures such as mesoscale fronts are important environmental cues used by a foraging seabird within the rich waters of an upwelling system. There is now need for further investigations on how Cape gannets actually detect these fronts. [ABSTRACT FROM AUTHOR]

The benefits of spatial memory for foraging animals can be assessed on two distinct spatial scales: small-scale space (travel within patches) and large-scale space (travel between patches). While the patches themselves may be distributed at low density, within patches resources are likely densely distributed. We propose, therefore, that spatial memory for recalling the particular locations of previously visited feeding sites will be more advantageous during between-patch movement, where it may reduce the distances traveled by animals that possess this ability compared to those that must rely on random search. We address this hypothesis by employing descriptive statistics and spectral analyses to characterize the daily foraging routes of a band of wild hamadryas baboons in Filoha, Ethiopia. The baboons slept on two main cliffs-the Filoha cliff and the Wasaro cliff-and daily travel began and ended on a cliff; thus four daily travel routes exist: Filoha-Filoha, Filoha-Wasaro, Wasaro-Wasaro, Wasaro-Filoha. We use newly developed partial sum methods and distribution-fitting analyses to distinguish periods of area-restricted search from more extensive movements. The results indicate a single peak in travel activity in the Filoha-Filoha and Wasaro-Filoha routes, three peaks of travel activity in the Filoha-Wasaro routes, and two peaks in the Wasaro-Wasaro routes; and are consistent with on-the-ground observations of foraging and ranging behavior of the baboons. In each of the four daily travel routes the 'tipping points' identified by the partial sum analyses indicate transitions between travel in small- versus large-scale space. The correspondence between the quantitative analyses and the field observations suggest great utility for using these types of analyses to examine primate travel patterns and especially in distinguishing between movement in small versus large-scale space. Only the distribution-fitting analyses are inconsistent with the field observations, which may be due to the scale at which these analyses were conducted. Am. J. Primatol. 76:421-435, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Searching individuals need to take decisions on where and how long to search. When food is spatially aggregated, detection of a food item signals a probability for the presence of further prey items in its surrounding. Organisms can thus intensify search effort upon detecting a prey item, but after unsuccessfully searching for a while, return to the previous, extensive search, this strategy is known as ‘area-concentrated-search’ (ACS). Here we present results of simulations where individuals perform ACS employing a correlated random walk with variable directional persistence. Switching between intensive and extensive search (with respectively low and high directional persistence) is a function of searcher''s internal state represented as ‘satiety’ level depending on preceding consumption of prey items. We explore the effect of this function’s control parameters (‘switching level’ i.e., the satiety at which the switching occurs, and the switchover shape parameter) on searching efficiency in dependence of (1) prey items’ spatial distribution ranging from randomly uniform to highly contagious, (2) the overall prey density, and (3) prey ‘caloric’ value. Our main conclusions: (1) the form of the adopted switchover exerts an effect on searching efficiency, and this effect is most pronounced in landscapes with highly aggregated resources. Except for the most homogeneous prey distributions, there was a clear optimum area within the movement parameter space, yielding highest efficiency. (2) The optimal switching level is larger in heterogeneous landscapes, but optimum switchover shape is little affected by any of the landscape attributes. In most landscapes, it is most profitable to switch gradually rather than abruptly. (3) The success and optimal switching level depend not only on the prey''s spatial distribution but also on average prey density while the value of prey items has little effect on the optimal movement parameters. [Copyright &y& Elsevier]

Optimal decisions in classical foraging models depend on the encounter rate with food items that are often distributed heterogeneously at one or multiple spatial scales. Only a few studies, however, provide a detailed assessment of the determinants of foraging efficiency by free-ranging animals across spatial scales. We evaluated multilevel search efficiency of free-ranging plains bison, Bison bison bison, and whether it varies with social factors, sex and season. We assessed search efficiency by contrasting encounters with the most profitable plant species, Carex atherodes, from random expectations within meadows or along foraging paths. We found that bison selectively occupied areas of meadows rich in C. atherodes. Once in these areas, females took shorter steps in locations of high C. atherodes biomass in summer and winter, as expected from an area-restricted search tactic. In winter, the presence of conspecifics further increased the chances of finding locations of high C. atherodes biomass, presumably due to social information. Unlike females, once males were in areas generally rich in C. atherodes during summer, they moved towards locations with lower C. atherodes biomass more than expected by chance alone. The fine-scale movement strategy of males does not appear to maximize instantaneous energy intake rate, but might reflect a tactic for efficient guarding of females during the rut. Overall, our study shows that the efficiency with which free-ranging herbivores find high-quality food during social foraging strongly differs between sexes, and depends on conspecific distribution and season. [ABSTRACT FROM AUTHOR]

An understanding of how animals alter their behaviour in relation to environmental conditions is a key element in the study of animal movement, foraging ecology and habitat use, and can provide valuable information for practical conservation and management applications. To exploit resources in heterogeneous landscapes optimally, foragers should intensively search in profitable patches while minimizing foraging activities in low-quality areas. We used first-passage time (FPT) analysis to identify and characterize area-restricted search (ARS) behaviour along the nightly movement paths of racoons. While FPT analysis has been successfully applied to a variety of pelagic species, our goal was to determine the ability of FPT to detect habitat characteristics associated with changes in searching behaviour for a terrestrial predator. Racoons, Procyon lotor, were tracked via radiotelemetry during their nightly movements. We found evidence of ARS behaviour in 55 of 58 paths, with racoons concentrating intensive searching bouts in areas with an average radius of 42.6m (range 20–100m). To test whether our detection of ARS represented an actual change in behaviour, we tracked five racoons in relation to an artificial food patch. We detected ARS behaviour during 9 of 10 occasions in which a tracked animal encountered the food patch. Racoons showed ARS behaviour in areas with abundant shallow water, and they moved quickly through openings and dry areas with sparse ground-level vegetation. Application of this method should prove useful for studies of habitat use and foraging ecology of terrestrial predators by providing links between animal movements and the environment. [ABSTRACT FROM AUTHOR]

We experimentally determined that the lizard Pedioplanis namaquensis engages in area-restricted searching (=ARS, localized searching after encounters with food) while foraging and that prey characteristics influence ARS. Single prey items were introduced to free-ranging lizards, and their subsequent search effort was characterized using first passage times (=FPT, time required for an animal to cross a circle of a given radius). Three prey types were used: termites, flies, and rice (control). FPTs were longer following termite encounters than following fly or control encounters. Control treatments produced no change in FPT, while lizards searching for termites showed the greatest change. The use by Pedioplanis namaquensis of ARS was most pronounced for the typically aggregated prey type. [ABSTRACT FROM AUTHOR]

Individual variation in behavioral strategies is ubiquitous in nature. Yet, explaining how this variation is being maintained remains a challenging task. We use a spatially-explicit individual-based simulation model to evaluate the extent to which the efficiency of an alternative spacing tactic of prey and an alternative search tactic of predators are influenced by the spatial pattern of prey, social interactions among predators (i.e., interference and information sharing) and predator density. In response to predation risk, prey individuals can either spread out or aggregate. We demonstrate that if prey is extremely clumped, spreading out may help when predators share information regarding prey locations and when predators shift to area-restricted search following an encounter with prey. However, dispersion is counter-selected when predators interact by interference, especially under high predator density. When predators search for more randomly distributed prey, interference and information sharing similarly affect the relative advantage of spreading out. Under a clumped prey spatial pattern, predators benefit from shifting their search tactic to an area-restricted search following an encounter with prey. This advantage is moderated as predator density increases and when predators interact either by interference or information sharing. Under a more random prey pattern, information sharing may deteriorate the inferior search tactic even more, compared to interference or no interaction among predators. Our simulation clarifies how interactions among searching predators may affect aggregation behavior of prey, the relative success of alternative search tactics and their potential to invade established populations using some other search or spacing tactics. [ABSTRACT FROM AUTHOR]

The article presents a study on diet and foraging behaviour of masked and red-footed boobies at Tromelin Island in western Indian Ocean to determine the resource partitioning of these species. The study used Argos transmitters and Global Positioning System (GPS) loggers to plot foraging movements, while time-depth recorders were employed to detect dive depths. Results showed that the tropical boobies have greater dietary partitioning differences than those in a less oligotrophic area.

The functional response is a fundamental model of the relationship between consumer intake rate and resource abundance. The random walk is a fundamental model of animal movement and is well approximated by simple diffusion. Both models are central to our understanding of numerous ecological processes but are rarely linked in ecological theory. To derive a synthetic model, we draw on the common logical premise underlying these models and show how the diffusion and consumption rates of consumers depend on elementary attributes of naturally occurring consumer-resource interactions: the abundance, spatial aggregation, and traveling speed of resources as well as consumer handling time and directional persistence. We show that resource aggregation may lead to increased consumer diffusion and, in the case of mobile resources, reduced consumption rate. Resource-dependent movement patterns have traditionally been attributed to area-restricted search, reflecting adaptive decision making by the consumer. Our synthesis provides a simple alternative hypothesis that such patterns could also arise as a byproduct of statistical movement mechanics. [ABSTRACT FROM AUTHOR]

Identifying the primary foraging grounds of abundant top predators is of importance in marine management to identify areas of high biological significance, and to assess the extent of competition with fisheries. We studied the search effort and habitat selection of the highly abundant short-tailed shearwater Puffinus tenuirostris to assess the search strategies employed by this wide-ranging seabird. During the chick-rearing period 52 individuals were tracked performing 39 short foraging trips (1-2 days), and 13 long trips (11-32 days). First-passage time analysis revealed that 46% of birds performing short trips employed area-restricted searches, concentrating search effort at an average scale of 14 ± 5 km. Foraging searches were more continuous for the other 54%, who travelled faster to cover greater distances, with little evidence of area-restricted searches. The prey returned indicated that continuous searchers consumed similar prey mass, but greater prey diversity than area-restricted search birds. On long trips 23% of birds travelled 500-1000 km to neritic (continental shelf) habitats, showing weak evidence of preference for areas of higher chlorophyll a concentration, and foraged at a similar spatial scale to short trips. The other 76% performed rapid outbound flights of 1000-3600 km across oceanic habitats commuting to regions with higher chlorophyll a. The spatial scale of search effort in oceanic habitat varied widely with some performing broad-scale searches (260-560 km) followed by finer-scale nested searches (16-170 km). This study demonstrates that a range of search strategies are employed when exploiting prey across ocean basins. The trade-offs between different search strategies are discussed to identify the value of these contrasting behaviours to wide-ranging seabirds. [ABSTRACT FROM AUTHOR]

Predators are thought to reduce travel speed and increase turning rate in areas where resources are relatively more abundant, a behavior termed "area-restricted search." However, evidence for this is rare, and few empirical data exist for large predators. Animals exhibiting foraging site fidelity could also be spatially aware of suitable feeding areas based on prior experience; changes in movement patterns might therefore arise from the anticipation of higher prey density. We tested the hypothesis that regions of area-restricted search were associated with a higher number of daily speed spikes (a proxy for potential prey encounter rate) and foraging success in southern elephant seals (Mirounga leonina), a species exhibiting both area-restricted searches and high interannual foraging site fidelity. We used onshore morphological measurements and diving data from archival tags deployed during winter foraging trips. Foraging success was inferred from in situ changes in relative lipid content derived from measured changes in buoyancy, and first-passage time analysis was used to identify area-restricted search behavior. Seals exhibited relatively direct southerly movement on average, with intensive search behavior predominantly located at the distal end of tracks. The probability of being in search mode was positively related to changes in relative lipid content; thus, intensively searched areas were associated with the highest foraging success. However, there was high foraging success during the outward transit even though seals moved through quickly without slowing down and increasing turning rate to exploit these areas. In addition, the probability of being in search mode was negatively related to the number of daily speed spikes. These results suggest that movement patterns represent a response to prior expectation of the location of predictable and profitable resources. Shelf habitat was 4-9 times more profitable than the other habitats, emphasizing the importance of the East Antarctic shelf for this and other predators in the region. We have provided rare empirical data with which to investigate the relationship between predator foraging strategy and prey encounter/foraging success, underlining the importance of inferring the timing and spatial arrangement of successful food acquisition for interpreting foraging strategies correctly. [ABSTRACT FROM AUTHOR]

Within a landscape where prey has an aggregated distribution, predators can take advantage of the spatial autocorrelation of prey density and intensify their search effort in areas of high prey density by using area-restricted search behaviour. In African arid and semi-arid savannas, large herbivores tend to aggregate around scarce water sources. We tested the hypothesis that water sources are a key determinant of habitat selection and movement patterns of large free-ranging predators in such savannas, using the example of the African lion. We used data from 19 GPS radio-collared lions in Hwange National Park, Zimbabwe. Maps of lions' trajectories showed that waterholes are key loci on the lions' route-maps. Compositional analyses revealed that lions significantly selected for areas locatedwithin 2 kmof awaterhole. In addition, analysis of lions' night paths showed that when lions are close to a waterhole (<2 km), they move at lower speed, cover shorter distances per night (both path length and net displacement) and follow a more tortuous path (higher turning angle, lower straightness index and higher fractal dimension) than when they are further from a waterhole.Hence, our results strongly suggest that lions adopt area-restricted searching in the vicinity of waterholes, and reduce their search effort to minimize the time spent far from a waterhole. They provide an illustration of how key habitat features that determine the dispersion of prey (e.g. waterholes in this study) have an influence on the spatial ecology and movement patterns of terrestrial predators. [ABSTRACT FROM AUTHOR]

When searching for resources, organisms can increase the efficiency of search and exploitation behavior by using information about the quality of a current resource patch in their decision making. The search strategy used by an organism can in turn affect its performance in different landscapes. Here we examine the effect of resource quality on 2 foraging decisions: how much time to allocate to explore the environment for new resources and what search strategy to use during exploration. We used the slime mould Physarum polycephalum as our model system. Physarum polycephalum is an amoeboid organism that forages as a flowing mass of pseudopods. We quantified the search pattern of plasmodia after engulfment of food of 6 different qualities. Food quality had a significant, positive effect on how long plasmodia waited before resuming search behavior and on how long it took to abandon food disks. Food quality had a positive effect on fractal dimension, indicating that the amount of localized search performed by plasmodia increased with food quality. Our results suggest that increasing food quality results in a shift from extensive to intensive search. Next, we examined foraging performance in landscapes with different patch structures. Plasmodia in correlated landscapes (half the patches contained only high-quality food, half contained only low-quality food) gained more weight than plasmodia foraging in noncorrelated landscapes (patches contained both high- and low-quality food disks). Our results show that food quality affects exploitation and search behavior and that both behaviors influence foraging performance in different landscapes. [ABSTRACT FROM PUBLISHER]

The article presents the study conducted regarding the species-specific and sex-specific differences in the foraging behaviour and zones of the two sympatric seabirds in the Gulf of California, Mexico. The study will examine the diving behavior, movement and activity of brown boobies and blue-footed boobies rearing young chicks using the highly accurate data loggers. The scheme also aims to disentangle the respective impact of species and sex on the observed foraging behaviour of the boobies. The result shows that the sex-specific differences of the seabirds which totally determined by their body size and mass are affected by the biomechanical constraints.

The article presents the study conducted regarding the spatial interaction of seabirds and its prey. It states that the review and synthesis will determine the spatial interaction between the predator and the prey in consideration with the spatial distribution of resources, breeding areas, interspecific competition and location of spawning. It highlights the result depicting the aggregation and elusiveness of the spatial pattern of seabirds and its prey that cause positive local scales and density dependence.

When foraging in a landscape, predators choose travelling directions according to their immediate knowledge of prey distribution within their perceptual fields and, when appropriate, to their past foraging experience. A substantial part of foraging theory is based on patch use in spatially implicit domains, and rarely has it considered foraging paths involving directional choices driven by memory and perception. Using a model mixing directed and random movements of a predator, we investigated how perception range and duration of spatial memory influence the long-term intake rate of a central place forager depending on prey spatial distribution. We found that intake rate increased and eventually saturated with increasing perception range regardless of prey spatial distribution. In contrast, the effect of spatial memory duration was mediated by the level of prey spatial aggregation. Assuming that an increase in memory or perception abilities has a cost, we found that it was not beneficial to possess simultaneously a wide perception range and a long-term spatial memory when prey distribution was aggregated. Moreover, when looking at the functional response of predators with different ‘cognitive strategies’, we found that those relying mainly on memory were limited by the prey global densities while those relying mainly on perception were limited by the level of prey aggregation. These results suggest that cognitive strategies might have evolved as a response to the prey spatial distribution and that prey spatial aggregation, not only prey global density, should be considered an important component of the functional response. [Copyright &y& Elsevier]

Predators that feed on clustered prey tend to have an ‘area-restricted search’ (ARS), characterized by a combination of a slow and tortuous movement in prey-rich areas, and a fast and straight movement in poorer areas. Waders that forage in intertidal areas usually prey upon buried macroinvertebrates, whose distribution is often clustered. However, wader species differ in the strategy used to find their prey: some rely mainly on visual cues, some rely on tactile cues, and others follow a more generalist method, simply sweeping the sediment surface with the bill. We hypothesized that these strategies influence the adoption of an ARS by waders. We analysed this hypothesis by comparing the fine-scale movement of a ‘tactile’ predator (black-tailed godwit, Limosa limosa), with that of a ‘visual’ predator (redshank, Tringa totanus) and a ‘sweeper’ (avocet, Recurvirostra avosetta). We filmed 190 individuals of the three species and, using GIS facilities, obtained more than 12 000 spatial positions, along with detailed records of feeding activity. We analysed several parameters of fine-scale movement of waders, such as foraging and searching speeds, tortuosity, and the relationship between these parameters and foraging success. Only the tactile predator, the black-tailed godwit, followed an ARS, reducing searching speed and increasing spatial turning rate whenever the prey intake was higher. Furthermore, its foraging strategy involved short-term adjustments of movement that maximized the likelihood of finding subsequent prey, suggesting a prior knowledge or an ability to perceive rapidly the distribution pattern of its prey. [Copyright &y& Elsevier]

Resource distribution can vary greatly in space and time. Consequently, animals should adjust their searching tactics to such spatio-temporal patterns in accordance with their innate capabilities, or alternatively, they should use a genetically fixed searching tactic that has been evolved in response to the specific pattern of the food they experience. Using a simulation model and a genetic algorithm, we show how optimal searching tactics change as a function of food spatial pattern. Searching tactics for hidden prey can be approximated using the following three components: (1) Extensive search mode (ESM), the type of movement before encountering a food item; (2) Intensive search mode (ISM), the type of movement after encountering a food item; and (3) ISM duration. Both ESM and ISM are characterized by movement tortuosity. We show that searching behavior adaptively changes as a function of food pattern. When food is distributed in a regular pattern, ISM is more directional than ESM, but under a clumped food pattern, ISM is much more tortuous than ESM. It may suggest that animals with larger spectra of searching tactics should experience greater variance or seasonal changes in their food pattern than animals with narrow spectra of searching tactics. Increased forager attack radius diminishes the differences between ESM and ISM, and thus the use of these three components to model searching in animals with higher attack radii is not appropriate. Increased handling time, which is a surrogate of reducing habitat profitability results in longer patch residency time as expected by optimal foraging theory. To conclude, we suggest that using such a combined approach of simulation models and genetic algorithms may improve our understanding of how extrinsic and intrinsic factors interact to influence searching behavior. [ABSTRACT FROM AUTHOR]

Although density-edge effects are commonly reported, we have only scratched the surface in understanding the mechanisms underlying how habitat edges mediate species interactions. Here, I use a combination of field surveys and experiments to explore the linkages between the presence of host-plant edges (Scolochloa festucacea), the within-patch distribution of planthopper eggs (Delphacodes scolochloa), and the oviposition behavior of their egg parasitoids (Anagrus spp.). The field surveys revealed that densities of hosts and parasitoids at the edge were >2.5 times lower than densities in the patch interior and that the effect was independent of patch size. As a consequence of its edge-avoidance behavior, host within-patch dispersion was significantly more aggregated in the presence, as compared to the absence, of an edge. Also. as patch size decreased, the proportion of the patch that was core (i.e.. beyond the influence of the edge) decreased, and the degree of host aggregation increased, In a subsequent field experiment, I found that the dispersion of hosts affected Anagrus oviposition behavior only when hosts were present on islands with discrete edges. Under these circumstances, the proportion parasitized and per capita parasitized were 2.3 and 3.4 times higher, respectively, when hosts were clumped as compared to when hosts were uniformly or randomly distributed. Based on a laboratory experiment using small S. festucacea patches, I found that Anagrus had 40% shorter step lengths, spent 52% more time in the patch, and parasitized 84% more hosts when hosts were clumped as compared to uniformly distributed. These results were indicative of area-restricted search by Anagrus, which is an effective foraging strategy when hosts are clumped. This is the first study to demonstrate that predator foraging behavior in response to prey dispersion can be mediated by the presence of a patch edge. Also, because edge-averse behavior is commonly reported in the literature, an underappreciated effect of fragmentation on predator prey interactions and stability could arise from edge-mediated effects on prey within-patch aggregation. [ABSTRACT FROM AUTHOR]

Because of the heterogeneity of natural landscapes, animals have to move through various types of areas that are more or less suitable with respect to their current needs. The locations of the profitable places actually used, which may be only a subset of the whole set of suitable areas available, are usually unknown, but can be inferred from movement analysis by assuming that these places correspond to the limited areas where the animals spend more time than elsewhere. Identifying these intensively used areas makes it possible, through subsequent analyses, to address both how they. are distributed with respect to key habitat features, and the underlying behavioral mechanisms used to find these areas and capitalize on such habitats. We critically reviewed the few previously published methods to detect changes in movement behavior likely to occur when an animal enters a profitable place. As all of them appeared to be too narrowly tuned to specific situations, we designed a new, easy-to-use method based on the time spent in the vicinity of successive path locations. We used computer simulations to show that our method is both quite general and robust to noisy data. [ABSTRACT FROM AUTHOR]

Wandering albatrosses (Diomedea exulans) forage over thousands of square kilometers of open ocean for patchily distributed live prey and carrion. These birds have large olfactory bulbs and respond to fishy-scented odors in at-sea trials, suggesting that olfaction plays a role in natural foraging behavior. With the advent of new, fine-scale tracking technologies, we are beginning to explore how birds track prey in the pelagic environment, and we relate these observations to models of odor transport in natural situations. These models suggest that odors emanating from prey will tend to disperse laterally and downwind of the odor source and acquire an irregular and patchy concentration distribution due to turbulent transport. For a seabird foraging over the ocean, this scenario suggests that olfactory search would be facilitated by crosswind flight to optimize the probability of encountering a plume emanating from a prey item, followed by upwind, zigzag flight to localize the prey. By contrast, birds approaching prey by sight would be expected to fly directly to a prey item, irrespective of wind direction. Using high-precision global positioning system (GPS) loggers in conjunction with stomach temperature recorders to simultaneously monitor feeding events, we confirm these predictions in freely ranging wandering albatrosses. We found that initial olfactory detection was implicated in nearly half (46.8%) of all flown approaches preceding prey-capture events, accounting for 45.5% of total prey mass captured by in-flight foraging. These results offer insights into the sensory basis for area-restricted search at the large spatial scales of the open ocean. [ABSTRACT FROM AUTHOR]

The Texas coastal prairie is composed of habitat patches characterized by monocots, dicots, or a mixture of both plant types. Radiotelemetry revealed that reproductive female hispid cotton rats (Sigmodon hispidus) preferred mixed habitats and avoided dicot habitats, whereas males did not show a preference. Such habitat selection can be attained by shorter distances moved or increased turning (i.e., area-restricted search). Reproductive females, but not males, moved shorter distances in mixed habitats. However, turns relative to straight-ahead movements for females, but not males, were fewer in mixed habitats than in monocot or dicot habitats suggesting directed foraging rather than area-restricted search. To obtain necessary amounts of nutrients, especially carbohydrates, protein, phosphorus, and calcium, reproductive females ingest both monocots and dicots. Directed movement may facilitate foraging for dicots because these food items occur in clumps in mixed habitats. Because their nutritional needs are less than those of females, males do not exhibit the same patterns of habitat selection. Differential patch occupancy was not explained by overhead plant cover, but more bare ground in dicot habitats may explain avoidance of these habitat types because of increased predation risk. [ABSTRACT FROM AUTHOR]

1. How and at what spatial scale(s) animals change their movements in relation to their environment is central to several topics in ecology and conservation, including foraging ecology, habitat selection and dispersal. A method (first-passage time analysis, FPT) has recently been proposed to measure changes in movements through the landscape, as an index of search effort at the pertinent spatial scales. This method seems largely applicable to an increasing number of studies using satellite, radio-tracking or global positioning system (GPS), but its limits have not yet been assessed. 2. Here I used several movement simulations to examine the ability of FPT analysis to detect area-restricted search (ARS) according to different changes in movements, different patch structures and tracking accuracy. 3. FPT analysis was able to detect changes in movements when both speed and sinuosity changed, or when the animal reacted to patch boundaries. It was also able to detect ARS within the same path at several spatial scales in patches (nested or not) of different sizes. 4. Tracking accuracy affected the detection of ARS by FPT analysis. With the widely used Argos system, a minimum of 13 locations in effective ARS was necessary to detect this behaviour; seven when velocity filtering was applied. Similarly, spatial error in location affected the estimation of the ARS scale value, but the application of velocity filtering reduced this effect. 5. Comparisons between a real GPS track and pathways simulating the Argos error showed that the time-sampling rate of locations (due to satellite-pass frequency) decreased the probability of detecting ARS at small scales (<10 km), while the spatial error decreased this probability by >50% across the whole range of scales. A velocity filter enabled significant reductions in this effect. 6. Synthesis and application. Within limits, FPT analysis is highly suitable for animal movement analysis, either to quantify habitat use, or to determine the scale most relevant for describing an ecological system or factors affecting movement decisions. In anticipation of increasing applications of FPT analysis in applied ecology, I provide recommendations for the use of the technique with several tracking methods. [ABSTRACT FROM AUTHOR]

In a patchy environment, predators are expected to increase turning rate and start an area-restricted search (ARS) when prey have been encountered, but few empirical data exist for large predators. By using GPS loggers with devices measuring prey capture, we studied how a marine predator adjusts foraging movements at various scales in relation to prey capture. Wandering albatrosses use two tactics, sit and wait and foraging in flight, the former tactic being three times less efficient than the latter. During flight foraging, birds caught large isolated prey and used ARS at scales varying from 5 to 90 km, with large-scale ARS being used only by young animals. Birds did not show strong responses to prey capture at a large scale, few ARS events occurred after prey capture, and birds did not have high rates of prey capture in ARS. Only at small scales did birds increase sinuosity after prey captures for a limited time period, and this occurred only after they had caught a large prey item within an ARS zone. When this species searches over a large scale, the most effective search rule was to follow a nearly straight path. ARS may be used to restrict search to a particular environment where prey capture is more predictable and profitable. [ABSTRACT FROM AUTHOR]