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A growing body of evidence suggests trophic generalism (feeding on resources from more than one trophic level and/or on different resources of the same trophic level) is a widespread feature among ground beetles (Coleoptera: Carabidae). However, it remains unclear whether trophic generalism applies to single individuals, at the intrapopulation or interpopulation level. Here we present stable isotope data (δ15N, δ13C) of seven common European carabid species on an archipelago of 18 lake islands in northeastern Poland. We found strong differences in isotopic ratios between individuals of the same population as well as between different populations, indicating that carabids are opportunistic feeders and that the degree of opportunism differs between habitats and between islands. Trophic niche breadth as assessed by isotopic ratios was influenced by local habitat diversity. We suggest that opportunistic usage of different local resources results in striking differences between local populations and a very broad trophic niche observed at regional level.

Abstract.We studied the effect of flooding on a carabid community inhabiting grassland in a large river valley (W Poland). We used pitfall-traps to catch beetles from April to November 1999-2001. Some of the samples collected were preceded by floods during the collecting period, which enabled us to evaluate the effects of flooding on species composition and abundance. We collected 17,722 individuals belonging to 108 species. The number of species and individuals per sample differed between plots and showed a nonlinear decrease over time, from spring to autumn. Carabids were more abundant in samples collected after floods than in the control samples. In contrast, the expected cumulative number of species as a function of the number of individuals collected was lower in samples collected after floods than in the control samples. In the case of the most abundant species the species-specific responses in terms of the numbers caught after flooding differed, with those of (e.g. Agonum micans) increasing and those of (Amara plebeja, Epaphius secalis) decreasing. This study shows that floods filter the community with the result that some species increase in abundance but the overall species richness decreases. Therefore natural floods are important in shaping the structure of communities of epigeic carabids on floodplains.

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Ecological intensification of agriculture (e.g., with the use of wildflower strips) is being currently discussed as a mean for gaining high yields, preserving high biodiversity of farmland. The aim of this study was to assess the efficiency of annual wildflower strips (WFSs) established in rye field (RF) in (1) increasing species richness and abundance in terms of beneficial arthropod groups (carabids, ground spiders, plant spiders, butterflies, insect pollinators and plant-dwelling insect predators), (2) decreasing the abundance of insect pests, (3) decreasing damages of the crop, and (4) increasing the yield. The field survey was carried out in 2019, in two WFSs and in the adjacent crop field at the distances of 3, 9, 21 and 45 m. The study was not skewed by pesticide use as it was carried out on an organic farm. Mean “site” species numbers (α-diversity) and the abundance of most groups were found to be significantly higher in WFSs than in RF. A negative relationship was found in most groups between distance from WFSs and species numbers and abundance. The mean total abundance of all observed pest insects was positively related to distance from WFSs and increased by 83% at distances between 3 and 45 m from WFSs. There was a negative exponential relationship between aphid abundance and total predator abundance, which suggests a mechanism reducing aphid abundance resulting from high levels of predator abundance in the nearby WFSs. The study shows that annual WFSs can be an efficient measure for enhancing cropland biodiversity and should be taken into account in agri-environmental schemes in the Common Agricultural Policy after 2020.