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The relationship between aquatic and avian predators and prey is a fundamental process that influences the ecological dynamics of freshwater communities; a landscape of fear underpins spatial and temporal habitat use of prey, i.e., non‐consumptive predation effects. For example, complex marginal vegetation and other natural in‐river refuges are known to be important for prey to manage predation risk and predators must alter their behaviour in response to habitat patches prey occupy. However, it is unclear how prey respond to predators, and vice versa, in heavily modified degraded lowland rivers with a high degree of river maintenance measures; a component critical for flood risk management globally. Such modifications could lead to prey seeking refuge at hazardous anthropogenic infrastructure, but a robust quantification of predator–prey interactions in this context is required to develop this understanding.Using multi‐beam sonar (Dual‐Frequency Identification Sonar), we non‐invasively and simultaneously quantified the temporal rate of predator–prey interactions, the attack behaviour of predators, and the refuge seeking behaviour of prey at a pumping station intake during winter in a heavily modified lowland river.Prey fish experienced temporally dynamic, density‐dependant, and species‐specific predation risks from two dissimilar predators (i.e., aquatic vs. avian); pike (Esox lucius) and cormorant (Phalacrocorax carbo). Generalised linear modelling revealed that prey refuge use was positively associated with predator attack rate. Non‐consumptive effects were evidenced by quantified changes to shoal structure (density, area), shoaling (group aggregation), and schooling (coordinated directional movement), including diurnal migrations to and from the pumping station intake for refuge.Our results show that in the absence of natural refuge habitats the natural landscape of fear shifted and speculate that prey fish were paradoxically dependant on hazardous anthropogenic infrastructure, i.e., a pumping station intake, for refuge from predators in a degraded lowland river.These findings strongly enhance our understanding of the impact of anthropogenic infrastructure on predator–prey interactions by demonstrating how flood risk management, including river maintenance measures, and associated anthropogenic infrastructure can impact the behavioural game played between aquatic and avian predators and their prey. [ABSTRACT FROM AUTHOR]

Because littoral cladocerans are common prey for odonate larvae, they are ideal organisms to examine prey and predator interactions in aquatic habitats. Although death‐feigning behaviour observed in littoral cladocerans is viewed as a trait to reduce predation risk, no study has examined the effectiveness of death‐feigning at reducing mortality. We studied the effectiveness of death‐feigning behaviour by two littoral cladocerans, Chydorus sphaericus and Oxyurella tenuicaudis, against the odonate larvae of Sympetrum frequens.We first examined how the odonate larvae detected the prey and found that the larvae consumed active cladocerans, even under dark conditions, but they did not consume anaesthetised cladocerans, indicating that the larvae detect the prey using mechanical cues such as vibrational currents created by the prey individuals.We then observed behavioural events of odonate larvae and prey cladocerans using a video‐recording system to count the number of cladocerans that showed death‐feigning behaviours when odonate larvae attacked and those that were not consumed when they showed death‐feigning behaviours.We observed a total of 1,099 behavioural events in prey–predator interactions. On average, the odonate larvae pursued 63% of the cladocerans encountered, attacked 89% of the cladocerans pursued, and successfully captured only 29% of the cladocerans with the first attack. Among the cladocerans that were not captured, 38% of the individuals continually swam, but 62% ceased to move and exhibited death‐feigning behaviours. The odonate larvae's capture rate for cladocerans exhibiting the death‐feigning behaviours fell significantly short of that for cladocerans that were continually swimming.The experiments clearly showed that the littoral cladocerans' death‐feigning behaviour effectively decreased predation rate by odonate larvae. The results suggest that the death feigning serves as an adaptive behaviour to reduce mortality risk in littoral cladocerans under predation by such predators that can detect prey using mechanical cues such as those of vibrational currents. [ABSTRACT FROM AUTHOR]

To understand the effects of environmental changes on ecosystems, it is important to determine the factors and mechanisms influencing the strength of species interactions in food webs. However, joint effects of predation risk and additional environmental factors on species interaction strengths in multitrophic systems remain largely unexplored, leaving a substantial gap in our understanding of the links between local environmental characteristics and food web properties.To fill this gap, we investigated the effects of habitat complexity and predation risk by top predatory dragonfly larvae (Aeshna cyanea) on feeding rates and energetic efficiency (i.e. the ratio of acquired and expended energy) of the larvae of three intermediate predatory odonate species (Libellula quadrimaculata, Sympetrum sanguineum, and Ischnura elegans) preying on cladocerans.We hypothesised that predation risk would decrease the feeding rate, especially in the structurally simple habitat, and increase the metabolic rate of all intermediate predators. We also expected higher feeding rates of intermediate predators using aquatic vegetation as a perching site (i.e. Sympetrum and Ischnura) in the structurally complex habitat. Finally, we expected to observe habitat‐ and predation risk‐dependent energetic efficiencies of the intermediate predators driven by changes in feeding and metabolic rates.The effect of predation risk on feeding rates was species specific and differed between the structurally simple and complex habitat. Habitat complexity increased feeding rates but only in the absence of predation risk. Moreover, predation risk signalled by chemical cues significantly increased Sympetrum vulgatum feeding rates but did not influence the feeding rates of the two other intermediate predators.Metabolic rates varied among the three intermediate predators but were not affected by predation risk. Estimated energetic efficiency decreased with intermediate predator body mass and depended, to a lesser extent, on the interactive effect of habitat complexity and predation risk.Our results imply that the effects of habitat complexity and predation risk on trophic interactions are likely to be determined by traits related to foraging and defence of the intermediate predators and their habitat domains, and that energetic efficiency is mainly determined by predator mass. Given that habitat complexity and predation risk can vary substantially across habitats, we conclude that it is important to consider habitat complexity and predation risk to better understand and predict the effects of environmentally driven variations on trophic interaction strength and metabolic rates that underlie the energetic efficiency of individual consumers. This has important implications for population and community dynamics as well as ecosystem functioning. [ABSTRACT FROM AUTHOR]

The role of inducible defences in trophic cascades is poorly understood. The shrimp shredder Xiphocaris elongata has a short rostrum in the absence of predatory fishes and a long rostrum in their presence. The long rostrum in X. elongata is a morphological defence that is inducible by the predatory fish Agonostomus monticola (mountain mullet)., Our objective was to measure the effect of fish presence and absence and shrimp phenotype (long rostrum versus short rostrum) on the foraging behaviour of X. elongata and on the decomposition of leaves of the riparian tree Cecropia schreberiana, including their potential for direct or trait-mediated top-down trophic cascades effects., Experiments were carried out in wading pools in which leaf discs of C. schreberiana were exposed for 24 days to processing by either microbes or short-rostrum or long-rostrum X. elongata in either the presence or absence of the predatory fish A. monticola. Shrimp foraging activities, shrimp survival and leaf decomposition were quantified., Shrimp density was not affected by fish presence. However, fish presence decreased foraging activity of long-rostrum X. elongata presumably by increasing their use of refugia throughout the experiments. The foraging of short-rostrum shrimps did not respond to fish presence., The fraction of leaf mass remaining was significantly higher when shrimps were in the presence of fish than when fish were absent, particularly when short-rostrum shrimps were shredding leaves. Shrimps decreased the fraction of mass remaining of C. schreberiana more than the effect of microbial colonisation alone., These results demonstrate that the presence of the predatory fish A. monticola can create trait-mediated top-down trophic cascades in the presence of short-rostrum X. elongata. This study provides evidence that predators have different effects on prey with morphological inducible defences than prey without defences and that these interactions may have critical consequences for other trophic levels. [ABSTRACT FROM AUTHOR]

We conducted a paired large-scale predation experiment over 32 months in two streams being seasonally shaded by deciduous riparian trees, using the benthivorous fish species gudgeon ( Gobio gobio) and stone loach ( Barbatula barbatula) as top predators. The biomass of benthic grazers and periphyton in the presence/absence of fish was measured and the periphyton production was compared with the consumption rates using a model-based approach., A three-level trophic cascade from benthivorous fish via benthic grazers to periphyton was evident from the field experiment. Integrated over the whole study period, fish reduced the biomass of benthic grazers and indirectly increased the periphyton biomass., Scenario analyses, using a simple dynamic model, indicated top-down control of periphyton to be strongest during autumn, when periphyton growth was light-limited, and weaker in the spring, when periphyton growth was not light-limited. The seasonal light supply variation was caused by shading due to deciduous riparian trees during the vegetation period., This asymmetry in temporal processes weakened the top-down control in a natural benthic community. Even though grazer biomass is naturally reduced in summer, due to the emergence of the most abundant species (mayflies), a grazer biomasses high enough to reduce the spring periphyton peak could not be sustained by the low summer periphyton growth., We suppose that the temporal decoupling of grazer biomass from periphyton biomass might be caused by the very short generation time of the primary producers (days) compared with the long generation time of the primary consumers (mostly 1 year). [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

1. Aquatic predators may influence drift periodicity either directly or indirectly (by non-consumptive effects involving chemical cues). We took drift samples (eight successive 3-h sampling intervals over a 24-h period) on five dates (September 2007, March, April, June and August 2008). Samples were taken at three sites (one site with trout throughout the year, two sites without trout but with fire salamander larvae as top predators from April to August, but without vertebrate predators during the rest of the year) in a stream near Vienna, Austria, to examine the effects of predators on drift periodicity. 2. Of 45 331 specimens caught, the most abundant taxa were Ephemeroptera (32.3%; mainly Baetidae), Diptera (21.5%; mainly Chironomidae), Amphipoda (17.4%; all Gammarus fossarum), Plecoptera (5.4%), Coleoptera (3.5%) and Trichoptera (1.2%). For more detailed analyses, we chose Ephemeroptera (Baetidae; n = 13 457) and Amphipoda ( G. fossarum; n = 7888), which were numerous on all sampling dates. 3. The number of drifting baetids and amphipods, as well as total drift density, was generally higher at night than by day, although without predators these differences were significant for Gammaridae but not for Baetidae. 4. When broken down to size classes, night-day drift ratios generally were not significantly different from equality in all size classes of baetids when larval fire salamanders and trout were absent. When predators were present, however, baetid drift density was usually higher at night, except in the smallest and largest size classes. In all size classes of G. fossarum, drift density was usually higher at night, whether with or without the top predators. 5. Although we could study predator effects on drift periodicity at three sites on only a single stream, it seems that non-consumptive effects may affect Baetidae. Salamander larvae, most probably via kairomones, induced a shift towards mainly nocturnal drift, which could be interpreted as predator avoidance. [ABSTRACT FROM AUTHOR]

1. Invasive predators negatively affect native prey to varying degrees across landscapes, and spatial configuration of invader-free refugia may affect prey distributions across invaded river networks. In New Zealand, introduced trout ( Salmo trutta and Oncorhynchus mykiss) create source-sink dynamics in native Galaxias vulgaris populations, and their co-occurrence with trout may be enhanced by immigration from trout-free reaches. 2. We investigated how network configuration of trout-free demographic sources affected the distribution of G. vulgaris across trout-invaded riverscapes. Using quantitative biomass surveys and spatially extensive presence-absence surveys, the interaction between habitat variability and location relative to sources in limiting distributions of G. vulgaris in trout-invaded reaches was assessed. 3. Galaxias vulgaris biomass at invaded sink sites decreased with increasing network distance to the nearest trout barrier. The maximum distance to barriers at which G. vulgaris occurred in the riverscape was limited, so that galaxiids were excluded from small and stable streams far from sources. 4. Large predatory trout (i.e. >150 mm fork length) occurred in high densities at stable sites all year round and were seasonally excluded from sites disturbed by flooding. Large streams probably provide increased refugia for galaxiids to avoid predation from trout, but narrowness and habitat stability may act synergistically to extirpate G. vulgaris from sites that are too far from sources to receive regular immigrants. 5. The interaction between immigration and habitat configuration in mediating effects of trout on G. vulgaris distributions indicates the spatial dependency of predator-prey interactions in river networks. 6. These results indicate creating new invader-free source habitat should enhance co-occurrence in nearby invader-occupied reaches. Moreover, adding source habitat in sink streams far from existing sources, and ensuring barriers prevent future invasion, will also allow native fish dispersal between sources and sinks and will maximise the conservation gains from management across invaded riverscapes. [ABSTRACT FROM AUTHOR]

1. To examine spatial heterogeneity of trophic pathways on a small scale (<5 m diameter), we conducted dual stable isotope (δ13C and δ15N) analyses of invertebrate communities and their potential food sources in three patchy habitats [sphagnum lawn (SL), vascular-plant carpet (VC) and sphagnum carpet] within a temperate bog (Mizorogaike Pond, Kyoto, Japan). 2. In total, 19 invertebrate taxa were collected from the three habitats, most of which were stenotopic, i.e. collected from a single habitat. Amongst the habitats, significant variation was observed in the isotopic signatures of dominant plant tissues and their detrital matter [benthic particulate organic matter (BPOM)], both of which were potential organic food sources for invertebrates. Site-specific isotopic variation amongst detritivores was found in δ13C but not in δ15N, reflecting site-specificity in the isotopic signatures of basal foods. The eurytopic hydrophilid beetle Helochares striatus was found in all habitats, but showed clear site variation in its isotopic signatures, suggesting that it strongly relies on foods within its own habitat. 3. The most promising potential foods for detritivores were the dead leaf stalks of a dominant plant in the VC and BPOM in the SL and carpet. An isotopic mixing model (IsoSource version 1.3.1) estimated that aquatic predators rely on unknown trophic sources with higher δ13C than detritus, whereas terrestrial predators forage on allochthonous as well as autochthonous prey, suggesting that the latter predators might play key roles in coupling between habitats. 4. Our stable isotope approach revealed that immobile detritivores are confined to their small patchy habitats but that heterogeneous trophic pathways can be coupled by mobile predators, stressing the importance of habitat heterogeneity and predator coupling in characterising food webs in bog ecosystems. [ABSTRACT FROM AUTHOR]

1. Spatial subsidies, defined as the flow of energy, nutrients, organisms or pollutants from one habitat to another, have been shown to affect the food–web dynamics in a wide range of ecosystems. An important subsidy to riparian communities is the contribution of adult stream insects to terrestrial predators such as birds, bats and lizards, but also invertebrates including ground and web-building spiders. 2. We surveyed 37 first- and second-order forest streams across differing environmental gradients in the Central South Island, New Zealand, to investigate the relationship between potential aquatic prey subsidies and predatory riparian arachnids. We anticipated that stream-insect biomass would be positively associated with riparian arachnids, as a result of emergent adult aquatic insect subsidies to the adjacent habitat. 3. We confirmed positive associations between stream-insect biomass as a predictor variable and riparian arachnid biomass ( R2 = 0.42, F1,34 = 25.2, P < 0.001) and web densities ( R2 = 0.45, F1,14 = 11.5, P < 0.01) respectively as dependent variables after adjusting for the confounding effects of environmental variables. Hierarchical partitioning confirmed the importance of stream insect biomass as a statistically significant contributor to the total explained variance in analyses calculated for arachnid biomass, abundance and web density. 4. A concurrent survey of spider-web density along 20-m transects from the stream edge into the forest indicated a strong decline in web-building spider density moving away from the stream ( R2 = 0.41, F1,158 = 109, P < 0.001), with stream-insect biomass as a significant covariate ( F1,149 = 17.7, P < 0.001). 5. Our results suggest that productivity gradients present in the donor system affect the magnitude of the interaction between adjacent habitats. Productivity gradients may lead to increased reciprocal subsidies through a positive feedback loop involving the predation of spiders and other predatory terrestrial invertebrates by aquatic predators. However, terrestrial insectivores such as birds, bats and lizards that are not readily used as prey by aquatic predators may circumvent the feedback cycle by consuming a large proportion of emergent aquatic-insect biomass. This may lead to asymmetry in the strength of food–web linkages between aquatic and terrestrial habitats. [ABSTRACT FROM AUTHOR]

1. Ecologists have struggled to describe general patterns in the impacts of predators on stream prey, particularly at large, realistic spatial and temporal scales. Among the confounding variables in many systems is the presence of multiple predators whose interactions can be complex and unpredictable. 2. We studied the interactions between brook trout ( Salvelinus fontinalis) and larval two-lined salamanders ( Eurycea bislineata), two dominant vertebrate predators in New England stream systems, by examining patterns of two-lined salamander abundance in stream reaches above and below waterfalls that are barriers to fish dispersal, by measuring the effects of trout on salamander density and activity using a large-scale manipulation of brook trout presence, and by conducting a small-scale laboratory experiment to study how brook trout and larval two-lined salamanders affect each other's prey consumption. 3. We captured more salamanders above waterfalls, in the absence of trout, than below waterfalls where trout were present. Salamander density and daytime activity decreased following trout addition to streams, and salamander activity shifted from aperiodic to more nocturnal with fish. Analysis of stomach contents from our laboratory experiment revealed that salamanders eat fewer prey with trout, but trout eat more prey in the presence of salamanders. 4. We suggest that as predators in streams, salamanders can influence invertebrate prey communities both directly and through density- and trait-mediated interactions with other predators. [ABSTRACT FROM AUTHOR]

1. Invasions of top predators may have strong cascading effects in ecosystems affecting both prey species abundance and lower trophic levels. A recently discussed factor that may enhance species invasion is climate change and in this context, we studied the effects of an invasion of northern pike into a subarctic lake ecosystem formerly inhabited by the native top predator Arctic char and its prey fish, ninespined stickleback. 2. Our study demonstrated a strong change in fish community composition from a system with Arctic char as top predator and high densities of sticklebacks to a system with northern pike as top predator and very low densities of sticklebacks. A combination of both predation and competition from pike is the likely cause of the extinction of char. 3. The change in top predator species also cascaded down to primary consumers as both zooplankton and predator-sensitive macroinvertebrates increased in abundance. 4. Although the pike invasion coincided with increasing summer temperatures in the study area we have no conclusive evidence that the temperature increase is the causal mechanism behind the pike invasion. But still, our study provides possible effects of future pike invasions in mountain lakes related to climate change. We suggest that future pike invasions will have strong effects in lake ecosystems, both by replacing native top consumers and through cascading effects on lower trophic levels. [ABSTRACT FROM AUTHOR]

1. We experimentally tested if a multiplicative risk model accurately predicted the consumption of a common mayfly at risk of predation from three predator species in New Zealand streams. Deviations between model predictions and experimental observations were interpreted as indicators of ecologically important interactions between predators. 2. The predators included a drift-feeding fish [brown trout (T), Salmo trutta], a benthivorous fish [galaxiid (G), koaro, Galaxias brevipennis] and a benthic predatory stonefly (S; Stenoperla sp.) with Deleatidium sp. mayflies as prey. Eight treatments with all predator species combinations and a predator-free control were used. Experiments were performed in aquaria with cobbles as predator refuges for mayflies and we measured the proportion of prey consumed after 6 h for both day and night trials. 3. Trout consumed a higher proportion of prey than other predators. For the two predator treatments we found less than expected prey consumption in the galaxiid + trout treatment (G + T) for both day and night trials, whereas a higher than expected proportion of prey was consumed during night time in the stonefly + trout (S + T) treatment. 4. The results indicate interference (G + T) and facilitation (S + T) between predators depending on predator identity and time of day. Thus, to make accurate predictions of interspecific interactions, it is necessary to consider the ecology of individual species and how differences influence the direction and magnitude of interactions. [ABSTRACT FROM AUTHOR]