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Predators can provide a valuable ecosystem service by suppressing crop pests. However, intraguild predation, where predators compete for the same prey resource whilst consuming each other, may destabilize population dynamics and increase the risk of pest outbreaks. Very little is known about intraguild predation in open fields or the strengths of trophic links between predators which may negatively affect pest control., We tested the null hypothesis that predation by the epigeal predator Pterostichus melanarius (Coleoptera: Carabidae) on different spiders is species-independent (proportional to density). A combination of population monitoring in winter wheat, molecular identification of juvenile spiders, molecular analysis of predator gut contents and a Monte Carlo simulation model were used to analyse prey choice., Pterostichus melanarius were pitfall-trapped over three months, and 622 individuals were screened for the remains of four spider species. Predation rates on spiders were 43·6% in June and 33·3% in August and showed clear evidence of prey choice., Predation on the web-dependent Tenuiphantes tenuis (Linyphiidae) was significantly greater than predicted from a random choice model, while predation on Bathyphantes gracilis (Linyphiidae) was significantly lower. The beetles may be selecting the most abundant species disproportionately (switching) or responding in some cases to spatial niche separation ( T. tenuis locate their webs marginally lower than B. gracilis). However, two itinerant hunters, Erigone spp. (Linyphiidae) and Pachygnatha degeeri (Tetragnathidae), were consumed in proportion to their density., Synthesis and applications. High levels of intraguild predation were revealed using molecular diagnostics. The gut analysis approach provided invaluable data that will inform the future design of appropriate pest management and integrated farming strategies that encourage these predators. The data showed strong evidence of prey choice. Managers can, however, probably encourage high densities of all these known aphid predators (spiders and carabids) because disproportionately high rates of predation on the most common spiders at our field sites ( T. tenuis) were not sufficient to prevent strong growth in the density of this species between June and August (adults increased × 1·6 and juveniles × 8·6). Such work is essential if we are to reveal the processes behind functional biodiversity in crops. [ABSTRACT FROM AUTHOR]

1. The large amount of discards produced by commercial fisheries can have major impacts on marine predator populations: this abundant food may increase populations of some scavengers or decrease others via accidental bycatch. Yet, despite the conservation implications of discard practices, the ecology of individual scavengers is poorly understood. 2. Here, we assess the influence of commercial fisheries’ activity on the foraging behaviour of individual breeding northern gannets Morus bassanus. Using recent developments in stable isotope mixing models (Stable Isotope Analysis in R or SIAR) we estimate individual discard consumption. Using GPS tracking and the Vessel Monitoring System (VMS), we investigate behavioural responses to trawlers. 3. Analysis of conventional diet samples, as well as stable isotope ratios of carbon and nitrogen in blood (plasma and cells), highlight marked individual differences in the proportion of fishery discards in the diet. Individual differences in foraging behaviour revealed by stable isotopes show evidence of both short-term consistency and behavioural flexibility. 4. At-sea path tortuosity of 25 gannets (tracked using GPS loggers) revealed scale-dependent adjustments in response to VMS-derived fishing vessel locations, as well as to sea surface temperature, chlorophyll a concentration and copepod abundance. The results also indicate individual variability in behavioural response to trawlers. 5. Individual differences in the amount of discards estimated from SIAR were negatively correlated with differences in foraging trip length and body condition, indicating potential fitness consequences. 6. Synthesis and applications. The management of commercial fisheries and apex predators is a daunting task. Ultimately, reducing bycatch and removing dependency on discards remain key conservation priorities, but managers should also ensure that scavenging species have sufficient alternative food to meet their energetic needs, to ameliorate potential unforeseen knock-on consequences. The results of Stable Isotope Analysis (SIAR) reveal intra-population differences in discard consumption by gannets; differences that have impacts on foraging effort and body condition. The use of GPS tracking and Vessel Monitoring Systems (VMS) reveal that gannet at-sea behaviour is influenced by fishing vessels, although this also varies among individuals. A combination of SIAR, GPS tracking and VMS can be used to study fishery/scavenger interactions in detail at the individual level, to answer fundamental questions about scavenging behaviour. [ABSTRACT FROM AUTHOR]

Summary 1. The hunting of wild animals for consumption by people currently threatens many species with extinction. In the tropics, where the threat is most acute, hunting frequently targets many prey species simultaneously, yet our understanding of the dynamics of hunting in such multi-prey systems is limited. This study addressed this issue by modelling the effects of human hunters on prey population dynamics in a multi-species prey community. Both pursuit hunting (in which offtake depends partly on hunters’ prey preferences) and trap hunting (in which the offtake is determined solely by random processes) were considered as submodels. 2. The pursuit hunting submodel was validated against studies of subsistence hunting in tropical forests, while the trap hunting submodel was validated against data from five studies of offtake rates by snare hunters in subSaharan Africa. In all cases, observed prey removal rates were predicted well by the model. 3. Simulations demonstrated the emergence of distinctive prey profiles at different intensities of hunting, related to sequences of overexploitation dependent on species’ vulnerabilities to exploitation. 4. Synthesis and applications. A model is developed to explore the impacts of harvesting on multi-species prey communities. Model predictions can be used to aid the interpretation of incomplete monitoring data, such as snapshots of the species taken by hunters. This will improve our ability to assess the sustainability of multi-species hunting systems using the limited information typically available in these cases. [ABSTRACT FROM AUTHOR]