Variations in trophic niches of generalist predators with plant community composition as indicated by stable isotopes and fatty acids

Abstract

Arthropods are a dominant component of biodiversity in terrestrial ecosystems. They are considered pest control agents and drive important ecosystem processes like nutrient cycling. However, such ecosystem effects of arthropods may depend on the environmental context influencing nutrition and behaviour. In the framework of a grassland plant diversity experiment (Jena Experiment), we used stable isotope and fatty acid analysis to investigate intraspecific variations in the diet of two of the most abundant predatory arthropods in grasslands: the ground beetle Harpalus rufipes and the wolf spider Trochosa ruricola. The results show that the diet of H. rufipes varied significantly with plant species diversity, consuming more plant material, probably seeds, at high diversity plots, and in the presence of grasses and small herbs. By contrast, in presence of legumes H. rufipes consumed more animal prey, presumably aphids and/or collembolans. Compared to H. rufipes, the diet of T. ruricola consisted of animal prey only and varied mainly with body size, with larger individuals occupying higher trophic position in the food web. Moreover, the diet of T. ruricola changed in response to summer flooding two months before sampling. Presumably, the availability of secondary decomposer prey as well as intraguild prey was increased in severely flooded plots. As both species are considered pest control agents, the results underline the importance of plant diversity and the composition of plant communities for biological pest control.

Keywords

• spider
• lycosidae
• beetle
• carabidae
• grassland
• diet