Indirect effects of prey swamping: differential seed predation during a bamboo masting event

Resource pulses often involve extraordinary increases in prey availability that "swamp" consumers and reverberate through indirect interactions affecting other community members. We developed a model that predicts predator-mediated indirect effects induced by an epidemic prey on co-occurring prey types differing in relative profitability/preference and validated our model by examining current-season and delayed effects of a bamboo mass seeding event on seed survival of canopy tree species in mixed Patagonian forests. The model shows that predator foraging behavior, prey profitability, and the scale of prey swamping influence the character and strength of short-term indirect effects on various alternative prey. When in large prey-swamped patches, nonselective predators decrease predation on all prey types. Selective predators, instead, only benefit prey of similar quality to the swamping species, while very low or high preference prey remain unaffected. Negative indirect effects (apparent competition) may override such positive effects (apparent mutualism), especially for highly preferred prey, when prey-swamped patches are small enough to allow predator aggregation and/or predators show a reproductive numerical response to elevated food supply. Seed predation patterns during bamboo (Chusquea culeou) masting were consistent with predicted short-term indirect effects mediated by a selective predator foraging in large prey-swamped patches. Bamboo seeds and similarly-sized Austrocedrus chilensis (ciprés) and Nothofagus obliqua (roble) seeds suffered lower predation in bamboo flowered than nonflowered patches. Predation rates on the small-seeded Nothofagus dombeyi (coihue) and the large-seeded Nothofagus alpina (rauli) were independent of bamboo flowering. Indirect positive effects were transient; three months after bamboo seeding, granivores preyed heavily upon all seed types, irrespective of patch flowering condition. Moreover, one year after bamboo seeding, predation rates on the most preferred seed (rauli) was higher in flowered than in nonflowered patches. Despite rapid predator numerical responses, short-term positive effects can still influence community recruitment dynamics because surviving seeds may find refuge beneath the litter produced by bamboo dieback. Together, our theoretical analysis and experiments indicate that indirect effects experienced by alternative prey during and after prey-swamping episodes need not be universal but can change across a prey quality spectrum, and they critically depend on predator-foraging rules and the spatial scale of swamping.     

Landscape of fear influences the relative importance of consumptive and nonconsumptive predator effects

Predators can initiate trophic cascades by consuming and/or scaring their prey. Although both forms of predator effect can increase the overall abundance of prey's resources, nonconsumptive effects may be more important to the spatial and temporal distribution of resources because predation risk often determines where and when prey choose to forage. Our experiment characterized temporal and spatial variation in the strength of consumptive and nonconsumptive predator effects in a rocky intertidal food chain consisting of the predatory green crab (Carcinus maenas), an intermediate consumer (the dogwhelk, Nucella lapillus), and barnacles (Semibalanus balanoides) as a resource. We tracked the survival of individual barnacles through time to map the strength of predator effects in experimental communities. These maps revealed striking spatiotemporal patterns in Nucella foraging behavior in response to each predator effect. However, only the nonconsumptive effect of green crabs produced strong spatial patterns in barnacle survivorship. Predation risk may play a pivotal role in determining the small-scale distribution patterns of this important rocky intertidal foundation species. We suggest that the effects of predation risk on individual foraging behavior may scale up to shape community structure and dynamics at a landscape level.     

Hierarchical patch choice by an insectivorous bat through prey availability components

Food availability does not only refer to the abundance of edible items; accessibility and detectability of food are also essential components of the availability concept. Constraints imposed by a habitat’s physical structure on the accessibility and detectability of food have been seldom treated simultaneously to the abundance of prey at the foraging patch level in observational studies. We designed a research that allowed decoupling the effects of microhabitat structure and prey abundance on foraging patch selection of the trawling insectivorous long-fingered bat (Myotis capaccinii). The use of different patches of river was surveyed by radiotelemetry during three periods of the bat’s annual cycle, and prey abundance was accordingly measured in and out of the hunting grounds of the tracked bats by insect traps emulating the species’ foraging. Bats preferentially used river stretches characterised by an open course and smooth water surfaces, i.e. they used the most suitable patches in terms of prey accessibility and detectability, respectively. In addition, prey abundance in the selected river stretches was higher than in others where bat activity was not recorded, although the latter also offered good access and prey detection possibilities. Bats also shifted foraging stretches seasonally, likely following the spatiotemporal dynamics of prey production over the watershed. We suggest that the decisions of bats during the patch choice process fitted a hierarchical sequence driven first by the species’ morphological specialisations and ability to hunt in unobstructed spaces, then by the detectability of prey on water surfaces and, finally, by the relative abundance of prey.     

Food webs and intraguild predation: community interactions of a native mesocarnivore

Trophic level interactions between predators create complex relationships such as intraguild predation. Theoretical research has predicted two possible paths to stability in intraguild systems: intermediate predators either outcompete higher-order predators for shared resources or select habitat based on security. The effects of intraguild predation on intermediate mammalian predators such as swift foxes (Vulpes velox) are not well understood. We examined the relationships between swift foxes and both their predators and prey, as well the effect of vegetation structure on swift fox-coyote (Canis latrans) interactions, between August 2001 and August 2004. In a natural experiment created by the Pinon Canyon Maneuver Site in southeastern Colorado, USA, we documented swift fox survival and density in a variety of landscapes and compared these parameters in relation to prey availability, coyote abundance, and vegetation structure. Swift fox density varied significantly between study sites, while survival did not. Coyote abundance was positively related to the basal prey species and vegetation structure, while swift fox density was negatively related to coyote abundance, basal prey species, and vegetation structure. Our results support the prediction that, under intraguild predation in terrestrial systems, top predator distribution matches resource availability (resource match), while intermediate predator distribution inversely matches predation risk (safety match). While predation by coyotes may be the specific cause of swift fox mortality in this system, the more general mechanism appears to be exposure to predation moderated by shrub density.     

Foraging in a tidally structured environment by Red Knots (Calidris canutus): ideal, but not free

Besides the "normal" challenge of obtaining adequate intake rates in a patchy and dangerous world, shorebirds foraging in intertidal habitats face additional environmental hurdles. The tide forces them to commute between a roosting site and feeding grounds, twice a day. Moreover, because intertidal food patches are not all available at the same time, shorebirds should follow itineraries along the best patches available at a given time. Finally, shorebirds need additional energy stores in order to survive unpredictable periods of bad weather, during which food patches are covered by extreme tides. In order to model such tide-specific decisions, we applied stochastic dynamic programming in a spatially explicit context. Two assumptions were varied, leading to four models. First, birds had either perfect (ideal) or no (non-ideal) information about the intake rate at each site. Second, traveling between sites was either for free or incurred time and energy costs (non-free). Predictions were generated for three aspects of foraging: area use, foraging routines, and energy stores. In general, non-ideal foragers should feed most intensely and should maintain low energy stores. If traveling for such birds is free, they should feed at a random site; otherwise, they should feed close to their roost. Ideal foragers should concentrate their feeding around low tide (especially when free) and should maintain larger energy stores (especially when non-free). If traveling for such birds is free, they should feed at the site offering the highest intake rate; otherwise, they should trade off travel costs and intake rate. Models were parameterized for Red Knots (Calidris canutus) living in the Dutch Wadden Sea in late summer, an area for which detailed, spatially explicit data on prey densities and tidal heights are available. Observations of radio-marked knots (area use) and unmarked knots (foraging routines, energy stores) showed the closest match with the ideal/non-free model. We conclude that knots make state-dependent decisions by trading off starvation against foraging-associated risks, including predation. Presumably, knots share public information about resource quality that enables them to behave in a more or less ideal manner. We suggest that our modeling approach may be applicable in other systems where resources fluctuate in space and time.     

Predation risk and foraging behavior of the hoary marmot in Alaska

Summary I observed hoary marmots for three field seasons to determine how the distribution of food and the risk of predation influenced marmots' foraging behavior. I quantified the amount of time Marmota caligata foraged in different patches of alpine meadows and assessed the distribution and abundance of vegetation eaten by marmots in these meadows. Because marmots dig burrows and run to them when attacked by predators, marmot-toburrow distance provided an index of predation risk that could be specified for different meadow patches.Patch use correlated positively with food abundance and negatively with predation risk. However, these significant relationships disappeared when partial correlations were calculated because food abundance and risk were intercorrelated. Using multiple regression, 77.0% of the variance in patch use was explained by a combination of food abundance, refuge burrow density, and a patch's distance from the talus where sleeping burrows were located. Variations in vigilance behavior (look-ups to search for predators while feeding) according to marmots' ages, the presence of other conspecifics, and animals' proximity to their sleeping burrows all indicated that predation risk influenced foraging.In a forage-manipulation experiment, the use of forage-enhanced patches increased six-fold, verifying directly the role of food availability on patch used. Concomitant with increased feeding, however, was the intense construction of refuge burrows in experimental patches that presumably reduced the risk of feeding. Thus, I suggest that food and predation risk jointly influence patch use by hoary marmots and that both factors must be considered when modeling the foraging behavior of species that can be predator and prey simultaneously.     

Behavioral response races, predator-prey shell games, ecology of fear, and patch use of pumas and their ungulate prey

The predator-prey shell game predicts random movement of prey across the landscape, whereas the behavioral response race and landscape of fear models predict that there should be a negative relationship between the spatial distribution of a predator and its behaviorally active prey. Additionally, prey have imperfect information on the whereabouts of their predator, which the predator should incorporate in its patch use strategy. I used a one-predator-one-prey system, puma (Puma concolor)-mule deer (Odocoileus hemionus) to test the following predictions regarding predator-prey distribution and patch use by the predator. (1) Pumas will spend more time in high prey risk/low prey use habitat types, while deer will spend their time in low-risk habitats. Pumas should (2) select large forage patches more often, (3) remain in large patches longer, and (4) revisit individual large patches more often than individual smaller ones. I tested these predictions with an extensive telemetry data set collected over 16 years in a study area of patchy forested habitat. When active, pumas spent significantly less time in open areas of low intrinsic predation risk than did deer. Pumas used large patches more than expected, revisited individual large patches significantly more often than smaller ones, and stayed significantly longer in larger patches than in smaller ones. The results supported the prediction of a negative relationship in the spatial distribution of a predator and its prey and indicated that the predator is incorporating the prey's imperfect information about its presence. These results indicate a behavioral complexity on the landscape scale that can have far-reaching impacts on predator-prey interactions.     

Behavioural responses to indirect and direct predator cues by a mammalian herbivore, the common brushtail possum

Cues for detecting and responding to perceived predation risk may be indirect, i.e., correlated with the probability of encountering a predator, or direct, i.e., produced by or related to the actual presence of a predator. Research shows, independently, both types of cues can influence anti-predator and foraging behaviours in prey species. However, since animals naturally encounter indirect and direct cues simultaneously, we were interested in quantifying their cumulative effect. Our aim was to evaluate food intake and behaviours (patch use, feeding (rate and time), vigilance) of a nocturnal mammalian herbivore to indirect (open vs. covered microhabitats; illumination) and direct (fox/owl odours) predator cues. We ran a preference trial with four paired treatments using a covered Safe food patch and an open Risk food patch, with one of four combinations of indirect and direct predator cues. Predation risk had a significant effect on both intake and behaviour (including feeding time, rate, and vigilance), but these effects differed depending on cues. No two combinations of cues produced exactly the same effects, illustrating the complexity of interactions that occur between cues. Covered patches were always perceived as less risky than open patches, but unexpectedly, open patches were perceived as riskier when dark rather than light. The strongest suite of (negative) responses to risk was associated with combined indirect and direct cues. These results highlight the importance of considering jointly, intake from a patch, intake rate, and behaviours, such as the proportion of time spent vigilant, when quantifying predation risk, rather than intake alone.     

Predators choosing between patches with standing crop: the influence of switching rules and input types

Where prey arriving in a patch are not consumed immediately, they will accumulate. Predators are then presented with a prey density or standing crop that increases through further input, and decreases through the consumption by predators. Firstly, I show that the switching rule of predators has a significant influence on the expected predator equilibrium distribution in such a dynamic system. Three rules are compared; for all rules, analytical solutions are calculated (where possible). To test their plausibility for natural situations, predator distributions are simulated given the assumption that each predator obtains individual patch profitability estimates by using a common learning rule. As long as prey arrive in the patches in constant numbers per time unit, the first rule leads to input matching because predators stop switching when consumption in the two patches is equal. The other two rules, where predators continue to sample both patches even in the equilibrium state, lead to predator distributions where the more profitable patch is underused. The final equilibrium depends on the exact assumptions of the switching rule; however, it is independent of interference. But if the input delivered into a patch is a function of the current prey standing crop (for example in a reproducing prey population), predator and prey distributions will not reach an equilibrium in most cases: either standing crops increase indefinitely, or they approach zero, with all predators concentrating on the better patch. Only a small number of parameter sets show intermediate crops that are reasonably stable. With this input type, only up to 54% of the simulations reach the expected distribution. In a system with competition for dynamic standing crop, it is therefore essential to know the type of input and the switching-rule used by predators to be able to predict equilibrium predator distributions. Received: 17 March 1995/Accepted after revision: 5 November 1995     

Resource distributions affect social learning on multiple timescales

We study how learning is shaped by foraging opportunities and self-organizing processes and how this impacts on the effects of “copying what neighbors eat” on multiple timescales. We use an individual-based model with a rich environment, where group foragers learn what to eat. We vary foraging opportunities by changing local variation in resources, studying copying in environments with pure patches, varied patches, and uniform distributed resources. We find that copying can help individuals explore the environment by sharing information, but this depends on how foraging opportunities shape the learning process. Copying has the greatest impact in varied patches, where local resource variation makes learning difficult, but local resource abundance makes copying easy. In contrast, copying is redundant or excessive in pure patches where learning is easy, and mostly ineffective in uniform environments where learning is difficult. Our results reveal that the mediation of copying behavior by individual experience is crucial for the impact of copying. Moreover, we find that the dynamics of social learning at short timescales shapes cultural phenomena. In fact, the integration of learning on short and long timescales generates cumulative cultural improvement in diet. Our results therefore provide insight into how and when such processes can arise. These insights need to be taken into account when considering behavioral patterns in nature.

What limits predator detection in blue tits (<Emphasis Type="Italic">Parus caeruleus</Emphasis>): posture,task or orientation?

To detect threats and reduce predation risk prey animals need to be alert. Early predator detection and rapid anti-predatory action increase the likelihood of survival. We investigated how foraging affects predator detection and time to take-off in blue tits (Parus caeruleus) by subjecting them to a simulated raptor attack. To investigate the impact of body posture we compared birds feeding head-down with birds feeding head-up, but could not find any effect of posture on either time to detection or time to take-off. To investigate the impact of orientation we compared birds having their side towards the attacking predator with birds having their back towards it. Predator detection, but not time to take-off, was delayed when the back was oriented towards the predator. We also investigated the impact of foraging task by comparing birds that were either not foraging, foraging on chopped mealworms, or foraging on whole ones. Foraging on chopped mealworms did not delay detection compared to nonforaging showing that foraging does not always restrict vigilance. However, detection was delayed more than 150% when the birds were foraging on whole, live mealworms, which apparently demanded much attention and handling skill. Time to take-off was affected by foraging task in the same way as detection was. We show that when studying foraging and vigilance one must include the difficulty of the foraging task and prey orientation.Communicated by P.A. Bednekoff     

Costs and benefits of pocket gopher foraging: linking behavior and physiology

Animals can attain fitness benefits by maintaining a positive net energy balance, including costs of movement during resource acquisition and the profits from foraging. Subterranean rodent burrowing provides an excellent system in which to examine the effects of movement costs on foraging behavior because it is energetically expensive to excavate burrows. We used an individual-based modeling approach to study pocket gopher foraging and its relationship to digging cost, food abundance, and food distribution. We used a unique combination of an individual-based foraging-behavior model and an energetic model to assess survival, body mass dynamics, and burrow configurations. Our model revealed that even the extreme cost of digging is not as costly as it appears when compared to metabolic costs. Concentrating digging in the area where food was found, or area-restricted search (ARS), was the most energetically efficient digging strategy compared to a random strategy. Field data show that natural burrow configurations were more closely approximated by the animals we modeled using ARS compared to random diggers. By using behavior and simple physiological principles in our model, we were able to observe realistic body mass dynamics and recreate natural movement patterns.     

Prey dynamics affect foraging by a pelagic predator (Stenella longirostris) over a range of spatial and temporal scales

Studies have shown that pelagic predators do not overlap with their prey at small scales. However, we hypothesized that spinner dolphin foraging would be affected by the spatio-temporal dynamics of their prey at both small and large scales. A modified echosounder was used to simultaneously measure the abundance of dolphins and their prey as a function of space and time off three Hawaiian islands. Spinner dolphin abundance closely matched the abundance patterns in the boundary community both horizontally and vertically. As hypothesized, spinner dolphins followed the diel horizontal migration of their prey, rather than feeding offshore the entire night. Spinner dolphins also followed the vertical migrations of their prey and exploited the vertical areas within the boundary layer that had the highest prey density. Cooperative foraging by pairs of dolphins within large groups was evident. The geometric and density characteristics of prey patches containing dolphins indicate that dolphins may alter the characteristics of prey patches through this cooperative foraging. The overlap of Hawaiian spinner dolphins and their prey at many temporal and spatial scales, ranging from several minutes to an entire night and 20 m to several kilometers, indicates that the availability of truly synoptic data may fundamentally alter our conclusions about pelagic predator-prey interactions.     

Behavioral resource depression and decaying perceived risk of predation in two species of coexisting gerbils

Summary Behavioral resource depression occurs when the behavior of prey individuals changes in response to the presence of a predator, resulting in a reduction of the encounter rate of the predator with its prey. Here I present experimental evidence on the response of two species of gerbils (Gerbillus allenbyi and G. pyramidum) to the presence of barn owls. I conducted the experiments in a large aviary. Both gerbils responded to the presence of barn owl predators by foraging in fewer resource patches (seed trays) and by quitting foraged resource patches at a higher resource harvest rate (giving-up density of resource; GUD). This reduced the amount of time gerbils were exposed to owl predation, and hence the encounter rate of owls with gerbils, i.e., behavioral resource depression. Thus, the presence of owls imposes a foraging cost on gerbils due to risk of predation, and also on the owls themselves due to resource depression. I then examined how resource depression relaxed over time following exposure to owls. In the days following an encounter with the predator, the reduction in foraging activity for both gerbil species eased. Increasing numbers of trays were foraged each day, and GUDs in seed trays declined. The two gerbils differed in their rate of recovery, with G. pyramidum returning to prepredator levels of foraging after 1 or 2 nights and G. allenbyi taking 5 nights or longer. Interspecific differences in recovery rates may be based on differences between the species in vulnerability to predation and/or ability to detect the presence of predators. The differences in recovery rates may be due to optimal memory windows or decay rates, where differences between species are based on risk of predation or on how perceived risk changes with time since a predator was last encountered. Finally, differences between or among competitors in recovery from resource depression may provide foraging opportunities in time for the species which recover most quickly and may have implications for species coexistence.     

Locating food in a spatially heterogeneous environment: Implications for fitness of the macrodecomposer Armadillidium vulgare (Isopoda: Oniscidea)

To assess the fitness consequences of foraging on patchy resources, consumption rates, growth rates and survivorship of Armadillidium vulgare were monitored while feeding in arenas in which the spatial distribution of patches of high quality food (powdered dicotyledonous leaf litter) was varied within a matrix of low quality food (powdered grass leaf litter). Predictions from behavioural experiments that these fitness correlates would be lower when high quality food is more heterogeneously distributed in space were tested but not supported either by laboratory or field experiments. To investigate whether A. vulgare can develop the ability to relocate high quality food patches, changes in foraging behaviour, over a comparable time period to that used in the fitness experiments, were monitored in arenas in which there was a high quality food patch in a low quality matrix. A. vulgare increased its ability to relocate the position of high quality food over time. It reduced time spent in low quality food matrices and increased time spent in high quality food patches with time after the start of the experiment. When the position of a high quality food patch was moved, the time spent in the low quality food matrix increased and less time was spent in high quality food patches, compared to arenas in which the food was not moved. The fitness benefits for saprophages of developing the ability to relocate high quality patches while foraging in spatially heterogeneous environments are discussed.     

Diet of young Atlantic bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis>) in eastern and western Atlantic foraging grounds

Atlantic bluefin tuna (Thunnus thynnus) are highly migratory predators whose abundance, distribution, and somatic condition have changed over the past decades. Prey community composition and abundance have also varied in several foraging grounds. To better understand underlying food webs and regional energy sources, we performed stomach content and stable isotope analyses on mainly juvenile (60–150 cm curved fork length) bluefin tuna captured in foraging grounds in the western (Mid-Atlantic Bight) and eastern (Bay of Biscay) Atlantic Ocean. In the Mid-Atlantic Bight, bluefin tuna diet was mainly sand lance (Ammodytes spp., 29% prey weight), consistent with historic findings. In the Bay of Biscay, krill (Meganyctiphanes norvegica) and anchovy (Engraulis encrasicolus) made up 39% prey weight, with relative consumption of each reflecting annual changes in prey abundance. Consumption of anchovies apparently declined after the local collapse of this prey resource. In both regions, stable isotope analysis results showed that juvenile bluefin tuna fed at a lower trophic position than indicated by stomach content analysis. In the Mid-Atlantic Bight, stable isotope analyses suggested that >30% of the diet was prey from lower trophic levels that composed <10% of the prey weights based upon traditional stomach content analyses. Trophic position was similar to juvenile fish sampled in the NW Atlantic but lower than juveniles sampled in the Mediterranean Sea in previous studies. Our findings indicate that juvenile bluefin tuna targeted a relatively small range of prey species and regional foraging patterns remained consistent over time in the Mid-Atlantic Bight but changed in relation to local prey availability in the Bay of Biscay.     

Sampling behavior of starlings foraging in simple patchy environments

Summary Starlings were allowed to forage in patchy laboratory environments where patches contained either zero or a fixed number of prey. The condition of a given patch (prey or no prey) could only be determined from information gained while exploiting the patch. A starling's task was to determine to what extent to sample an apparently prey-less patch before giving it up as such, in a way which maximizes long-term energy intake rate. The simple model presented to predict the optimal sampling solutions was qualitatively but not quantitatively supported by the data. The main discrepancy was in the fact that an apparently prey-less patch should have been sampled to a fixed extent before leaving, whereas a distribution of sampling behavior was actually observed. The qualitative agreement was very good, however, as the modes of the observed sampling distributions often corresponded to the predicted optimal sampling solutions. Starlings seem to possess a patch-sampling ability which, at least for those simple situations analyzed, can lead to an efficient foraging strategy.     

Abundance,population structure and claw morphology of the semi-terrestrial crab <Emphasis Type="Italic">Pachygrapsus marmoratus</Emphasis> (Fabricius, 1787) on shores of differing wave exposure

Wave action is known to influence the abundance and distribution of intertidal organisms. Wave action will also determine the duration and suitability of various foraging windows (high-tide and low-tide, day and night) for predation and can also affect predator behaviour, both directly by impeding prey handling and indirectly by influencing prey abundance. It remains uncertain whether semi-terrestrial mobile predators such as crabs which can access intertidal prey during emersion when the effects of wave action are minimal, are influenced by exposure. Here, we assessed the effect of wave action on the abundance and population structure (size and gender) of the semi-terrestrial intertidal crab Pachygrapsus marmoratus on rocky shores in Portugal. The activity of P. marmoratus with the tidal cycle on sheltered and exposed shores was established using baited pots at high-tide to examine whether there was activity during intertidal immersion and by low-tide searches. Because prey abundance varies along a wave exposure gradient on most Portuguese shores and because morphology of crab chelipeds are known to be related to diet composition, we further tested the hypothesis that predator stomach contents reflected differences in prey abundance along the horizontal gradient in wave exposure and that this would be correlated with the crab cheliped morphology. Thus, we examined phenotypic variation in P. marmoratus chelipeds across shores of differing exposure to wave action. P. marmoratus was only active during low-tide. Patterns of abundance and population structure of crabs did not vary with exposure to wave action. Stomach contents, however, varied significantly between shores of differing exposure with a higher consumption of hard-shelled prey (mussels) on exposed locations, where this type of prey is more abundant, and a higher consumption of barnacles on sheltered shores. Multivariate geometric analysis of crab claws showed that claws were significantly larger on exposed shores. There was a significant correlation between animals with larger claws and the abundance of mussels in their stomach. Variation in cheliped size may have resulted from differing food availability on sheltered and exposed shores.     

Effects of small-scale habitat fragmentation on predator–prey interactions in a temperate sea grass system

During the last decades, fragmentation has become an important issue in ecological research. Habitat fragmentation operates on spatial scales ranging over several magnitudes from patches to landscapes. We focus on small-scale fragmentation effects relevant to animal foraging decision making that could ultimately generate distribution patterns. In a controlled experimental environment, we tested small-scale fragmentation effects in artificial sea grass on the feeding behaviour of juvenile cod (Gadus morhua). Moreover, we examined the influence of fragmentation on the distribution of one of the juvenile cod’s main prey resources, the grass shrimp (Palaemon elegans), in association with three levels of risk provided by cod (no cod, cod chemical cues and actively foraging cod). Time spent by cod within sea grass was lower in fragmented landscapes, but total shrimp consumption was not affected. Shrimp utilised vegetation to a greater extent in fragmented treatments in combination with active predation. We suggest that shrimp choose between sand and vegetation habitats to minimize risk of predation according to cod habitat-specific foraging capacities, while cod aim to maximize prey-dependent foraging rates, generating a habitat-choice game between predator and prey. Moreover, aggregating behaviour in grass shrimp was only found in treatments with active predation. Hence, we argue that both aggregation and vegetation use are anti-predator defence strategies applied by shrimp. We therefore stress the importance of considering small-scale behavioural mechanisms when evaluating consequences from habitat fragmentation on trophic processes in coastal environments.     

Learning during competitive positioning in the nest: do nestlings use ideal free ‘foraging’ tactics?

Begging behaviour of nestling birds may involve more than a simple, honest source of information for parents to use in provisioning. Many aspects of begging behaviour relate instead to sibling competition for food items within the nest, and we might expect evidence of adaptive learning and behavioural adjustment in response to experience of the competitive environment. In this study, we consider begging in different locations within the nest as analogous to foraging in different patches, varying in food availability. Using hand-feeding trials, we created zones of differing profitability within an artificial nest by adjusting either the prey size or number of items delivered, and allowed only indirect competition between pairs of southern grey shrike (Lanius meridionalis) nestlings. Nestlings demonstrated the ability to detect differences in zone profitability and position themselves accordingly. By the end of both the prey size and delivery rate trials nestlings had increased the amount of time spent in the high quality zone. Such movement in response to differences in load quality, as well as frequency, demonstrates the ability of nestlings to learn about their environment and to facultatively adjust their begging in order to maximise energetic rewards.