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The extent to which prey traits combine to influence the abundance of predators is still poorly understood, particularly for mixed predators in sympatry and in aquatic ecosystems. In this study, we characterise prey use and distribution in iconic bird (grey wagtails and Eurasian dippers) and fish species (brown trout and Atlantic salmon) to assess whether prey traits could predict populations of these four riverine predators. Specifically, we hypothesised that: 1) prey key traits would predict predator populations more effectively than 2) diversity of prey traits, 3) the taxonomic abundance or richness of prey (known as traditional or mass-effect types of biodiversity) or 4) the prevailing environmental conditions. Combined predator population sizes were predicted better by a few key traits – specifically those revealing prey habitat use, size and drifting behaviour – than by prey diversity or prey trait diversity or environmental conditions. Our findings demonstrate that the complex relationships between prey assemblages and multiple predator species can be represented mechanistically when the key prey traits that govern encounter and consumption rates are identified. Given their apparent potential to reveal trophic relationships, and to complement more traditional measures of prey abundance, we advocate further development of trait-based approaches in predator–prey research.

Roads have impacts on the fauna arising from habitat fragmentation, roadkill and the barrier effect. Furthermore, roads lead species to change their activity with repercussions on predator–prey interactions and trigger indirect effects that are currently unknown. This study analyzes the effect of a motorway on the trophic behavior of the terrestrial carnivore community of its surroundings. Monthly scat sampling was conducted over a year at three distances from a motorway (0–50 m, 500–550 m and 1000–1050 m). We collected 498 scats, these originating from red fox (39.16%), cat (24.50%), stone marten (24.09%) and badger (12.25%). The relative abundance of the trophic resources in them was estimated together with the trophic diversity and niche overlap of the carnivore species. The results showed a distinct effect of distance from the road on trophic behavior of carnivores, as well as differences between species and seasons. The scats nearest the road had 10–20% more biomass of small mammals, equivalent in relative terms to a 21–48% increase in small mammals’ biomass when compared with scats collected further from the road. This finding indicates changes in predator–prey interactions near the road and shows that the human-generated structural and functional changes to ecosystems spread throughout trophic networks.

Simple Summary Growing human populations are challenging scientists to find effective ways to control and mitigate human–wildlife conflict while preserving biodiversity. It has been reported that predator odor and calls can drive away rodents, but little is known about species-specific responses of prey. For these reasons, we compared the behavioral changes of common rodent species inhabiting the Chilean temperate forest (Abrothrix spp., the long-tailed pygmy rice rat Oligoryzomys longicaudatus and the black rat Rattus rattus) when exposed to two different native predator calls (the austral pygmy owl Glaucidium nana and the rufous-legged owl Strix rufipes) and a control (no predator calls). Our results showed that all rodent species modified their behavior in the presence of predator calls, but the effects were species dependent. These findings point to the need to carefully study target rodent species instead of applying a general control plan for all rodent species. Abstract Ecologically based rodent management strategies are arising as a sustainable approach to rodent control, allowing us to preserve biodiversity while safeguarding human economic activities. Despite predator signals being known to generally repel rodents, few field-based studies have compared the behavioral effects of several predators on different prey species, especially in Neotropical ecosystems. Here, we used camera traps to study the behavior of rodent species native to the Chilean temperate forest (Abrothrix spp., long-tailed pygmy rice rat Oligoryzomys longicaudatus) and an introduced rodent (black rat Rattus rattus). Using playbacks of raptor calls, we experimentally exposed rodents to three predation risk treatments: austral pygmy owl calls (Glaucidium nana), rufous-legged owl calls (Strix rufipes) and a control treatment (absence of owl calls). We evaluated the effects of the treatments on the time allocated to three behaviors: feeding time, locomotor activity and vigilance. Moonlight and vegetation cover were also considered in the analyses, as they can modify perceived predation risk. Results showed that predator calls and environmental factors modified prey behavior depending not only on the predator species, but also on the rodent species. Consequently, owl playbacks could be regarded as a promising rodent control tool, knowing that future studies would be critical to deeply understand differences between species in order to select the most effective predator cues.

Aim: We tested whether there is a strong effect of species interactions on assembly of local lake fish communities, in addition to environmental filters and dispersal. Location: Seven hundred and seventy-two European lakes and reservoirs. Time period: 1993–2012. Major taxa studied: Nineteen species of freshwater fishes. Methods: We applied a latent variable approach using Bayesian Markov chain Monte Carlo algorithms (R package “BORAL”). We compared the contributions of six environmental predictors and the spatial organization of 772 European lakes in 209 river basins on the presence/absence of the 19 most frequent fish species and on the biomass and mean mass of the six dominant species. We inspected the residual correlation matrix for positive and negative correlations between species. Results: Environmental (50%) and spatial (10%) predictors contributed to the presence/absence assembly of lake fish communities, whereas lake size and productivity contributed strongly to the biomass and mean mass structures. We found highly significant negative correlations between predator and prey fish species pairs in the presence/absence, biomass and mean mass datasets. There were more significantly positive than negative correlations between species pairs in all three datasets. In addition, unmeasured abiotic predictors might explain some of the correlations between species. Main conclusions: Strong effects of species interactions on assembly of lake fish communities are very likely. We admit that our approach is of a correlational nature and does not generate mechanistic evidence that interactions strongly shape fish community structures; however, the results fit with present knowledge about the interactions between the most frequent fish species in European lakes and they support the assumption that, in particular, the mean masses of fish species in lakes are modified by species interactions. Türkiye Bilimsel ve Teknolojik Araştirma Kurumu, Grant/Award Number: 118C250; Spanish Ministry of Science, Innovation and Universities, Grant/ Award Number: RTI2018-095363-B-I00; European Commission; Environmental Investment Centre KIK, Grant/Award Number: 8603/2014; Deutsche Forschungsgemeinschaft, Grant/Award Number: Me 1686/7-1 Türkiye Bilimsel ve Teknolojik Araştirma Kurumu, Grant/Award Number: 118C250; Spanish Ministry of Science, Innovation and Universities, Grant/ Award Number: RTI2018-095363-B-I00; European Commission; Environmental Investment Centre KIK, Grant/Award Number: 8603/2014; Deutsche Forschungsgemeinschaft, Grant/Award Number: Me 1686/7-1

Fisheries in the Adriatic Sea and Chesapeake Bay are heavily exploited, with some overfished. Adriatic landings fluctuated around 140,000 metric tons (t) year-1 from 1992 to 2002, increasing to ~185,000 t year-1 in 2016. Over the same period, Chesapeake landings decreased from ~350,000 to ~200,000 t year-1 , so that 2016 landings were roughly equivalent between systems. While Chesapeake landings per unit of the bay's surface area were three times higher than for the Adriatic, landings per unit phytoplankton production were one and a half times higher in the Adriatic. Although fish migrations from adjacent water bodies can affect harvests, landings per unit area may reflect the Chesapeake's higher phytoplankton production, while landings per unit phytoplankton produc- tion may reflect differences in the fraction of phytoplankton production deposited in the benthos. Adriatic fish- eries exploit several small pelagic species, whereas only one Chesapeake fishery targets a pelagic species. Both regions harvest a variety of demersal species. Adriatic invertebrate fisheries involve a variety of crustaceans and mollusks but Chesapeake invertebrate fisheries target just one crustacean and three mollusk species. Coupled benthic-pelagic food webs are important ecologically in both systems, but food webs have become decoupled in the seasonally hypoxic mid-Chesapeake. Dams, coastal structures, sediment, altered river flows, and diminished water quality and habitat affect fishery species negatively. Management in both regions involves interagency col- laboration and cooperative agreements.

The foraging behaviour of species determines their diet and, therefore, also emergent food-web structure. Optimal foraging theory (OFT) has previously been applied to understand the emergence of food-web structure through a consumer-centric consideration of diet choice. However, the resource-centric viewpoint, where species adjust their behaviour to reduce the risk of predation, has not been considered. We develop a mechanistic model that merges metabolic theory with OFT to incorporate the effect of predation risk on diet choice to assemble food webs. This 'predation-risk-compromise' (PR) model better captures the nestedness and modularity of empirical food webs relative to the classical optimal foraging model. Specifically, compared with optimal foraging alone, risk-mitigated foraging leads to more-nested but less-modular webs by broadening the diet of consumers at intermediate trophic levels. Thus, predation risk significantly affects food-web structure by constraining species' ability to forage optimally, and needs to be considered in future work.

The review highlights the main results of two decades of research on climacostol (5-[(2Z)-non-2-en-1-yl]benzene-1,3-diol), the resorcinolic lipid produced and used by the ciliated protozoan Climacostomum virens for chemical defense against a wide range of predators, and to assist its carnivorous feeding. After the first studies on the physiological function of climacostol, the compound and some analogues were chemically synthesized, thus allowing us to explore both its effect on different prokaryotic and eukaryotic biological systems, and the role of its relevant structural traits. In particular, the results obtained in the last 10 years indicate climacostol is an effective antimicrobial and anticancer agent, bringing new clues to the attempt to design and synthesize additional novel analogues that can increase or optimize its pharmacological properties.

In this study, we assessed the impact of synergistic/antagonistic interactions between grazing by crustacean predator (Daphnia magna) and infection by cyanophage (Vb-AphaS-CL131) on the population dynamics of the harmful bloom-forming filamentous cyanobacterium Aphanizomenon flos-aquae. We observed synergistic effect of cyanophage infection on D. magna survival and grazing trough the lysis-induced shift in cyanobacteria population structure toward the shorter filaments. However, lysis-mediated- and grazing-enhanced removal of short A. flos-aquae filaments resulted in the dominance of grazing- and infection-resistant A. flos-aquae population. In addition, the presence of D. magna generated a trait-mediated response in the A. flos-aquae population by promoting the aggregation of filaments into colony-like structures. Experiments using temperate A. flos-aquae colony isolates from natural environment demonstrated that colony-embedded A. flos-aquae filaments are insensitive to the addition of both D. magna and cyanophages. Therefore, we propose that interactions between crustacean grazers and cyanophages may promote the emergence of defensive A. flos-aquae genotypes and population traits that eventually lead to bloom formation in aquatic environments.

The costs and benefits of group living often depend on the spatial position of individuals within groups and the ability of individuals to occupy preferred positions. For example, models of predation events for moving prey groups predict higher mortality risk for individuals at the periphery and front of groups. We investigated these predictions in sardine (Sardinella aurita) schools under attack from group hunting sailfish (Istiophorus platypterus) in the open ocean. Sailfish approached sardine schools about equally often from the front and rear, but prior to attack there was a chasing period in which sardines attempted to swim away from the predator. Consequently, all sailfish attacks were directed at the rear and peripheral positions of the school, resulting in higher predation risk for individuals at these positions. During attacks, sailfish slash at sardines with their bill causing prey injury including scale removal and tissue damage. Sardines injured in previous attacks were more often found in the rear half of the school than in the front half. Moreover, injured fish had lower tail-beat frequencies and lagged behind uninjured fish. Injuries inflicted by sailfish bills may, therefore, hinder prey swimming speed and drive spatial sorting in prey schools through passive self-assortment. We found only partial support for the theoretical predictions from current predator–prey models, highlighting the importance of incorporating more realistic predator–prey dynamics into these models.This article is part of the themed issue ‘Physiological determinants of social behaviour in animals’.

The fieldwork was supported by Fondation Segré-Whitley Fund for Nature, Conservation Leadership Programme and National Geographic Young Explorer fund. These grants supported K.R.S., Y.V.B. and C.M. Laboratory analysis was supported by the Department of Science and Technology, Government of India. This grant supported U.R., V.C., Y.V.B., K.R.S. and C.M. Data Dryad Repository. (http://dx.doi.org/10.5061/dryad.8p689) An increasing proportion of the world’s poor is rearing livestock today, and the global livestock population is growing. Livestock predation by large carnivores and their retaliatory killing is becoming an economic and conservation concern. A common recommendation for carnivore conservation and for reducing predation on livestock is to increase wild prey populations based on the assumption that the carnivores will consume this alternative food. Livestock predation, however, could either reduce or intensify with increases in wild prey depending on prey choice and trends in carnivore abundance. We show that the extent of livestock predation by the endangered snow leopard Panthera uncia intensifies with increases in the density of wild ungulate prey, and subsequently stabilizes. We found that snow leopard density, estimated at seven sites, was a positive linear function of the density of wild ungulates—the preferred prey—and showed no discernible relationship with livestock density. We also found that modelled livestock predation increased with livestock density. Our results suggest that snow leopard conservation would benefit from an increase in wild ungulates, but that would intensify the problem of livestock predation for pastoralists. The potential benefits of increased wild prey abundance in reducing livestock predation can be overwhelmed by a resultant increase in snow leopard populations. Snow leopard conservation efforts aimed at facilitating increases in wild prey must be accompanied by greater assistance for better livestock protection and offsetting the economic damage caused by carnivores. Publisher PDF