Interactions between granivorous and carnivorous carabids affect weed seed predation

Abstract: Knowledge of biotic and abiotic factors is necessary for optimizing seed predation as a weed control measure. Here, we asked whether carnivorous carabid beetles can affect seed predation. Additionally, weather effects on seed predation were investigated. For this purpose, 1m² enclosures were installed in a winter wheat field in northeastern Germany in early summer. Four treatments were tested: without carabids (0), non-manipulated carabid density and species composition (N), granivorous carabids only (G), and granivorous plus carnivorous carabids (CG). Seed predation was determined daily using seed cards containing Poa annua and Stellaria media seeds. Temperature, relative air humidity and precipitation were measured as covariables. In non-manipulated enclosures, daily seed loss was 9.1/m2 (P. annua) and 7.2 seeds/m2 (S. media). With granivores only, seed predation was 54.3 (P. annua) resp. 14.3 (S. media) seeds/m2 per day. If carnivores were additionally present, seed predation was significantly lower for P. annua (46.6 seeds/m2 d) and equally high for S. media (14.4 seeds/m2 d). The minimum night temperature was the only weather variable that significantly correlated with seed predation rate. This study clearly shows that beyond abiotic factors, multi-species interactions should be considered in order to fully understand biological weed control.