Seasonal change in species composition and size distribution of epigeic predators in a small field

The predatory arthropod fauna of a small, organic cultivated field in Tyrol (Austria) was sampled by means of pitfall trapping and soil sampling during one year in order to examine the variation in species composition and size distribution at different seasons. The main results and conclusions were: (a) the epigeic predator community constituted of more than 200 species of beetles, spiders and harvestmen. This high number of species reflects the diversity of the surrounding agricultural landscape. Besides the commonly investigated groups like Carabidae, Staphylinidae, Lycosidae and Linyphiidae also Opiliones, Histeridae and Silphidae were caught in high numbers. (b) Juvenile stages of spiders, harvestmen and beetles were active throughout the year. They should receive more attention in further studies, as juveniles may possess interesting predation value and are of great importance for the predator's population dynamics. (c) Predator activity was highest during the growing season, but especially spiders and beetle larvae were also caught from autumn to early spring in sufficient numbers. Predation on overwintering pests by these species would be worth to be investigated in more detail. (d) The extraction of soil samples yielded exclusively beetles. Beetle larvae and adult rove beetles were abundant in June and August/September, respectively, whereas at the end of October predator densities decreased dramatically. This points to a high predatory impact on soil dwelling pests especially during summer. (e) The cold season and July were characterized by a high proportion of small predators, while the activity of large predators increased from April to late summer. Especially during the cold season predation may be high on small sized pest stages, whereas larger pests will be exposed to increasing predation pressure from spring to late summer.