Julius-Kühn-Archiv (Feb 2014)
Weed seed predation by granivorous carabids as influenced by carnivorous carabids
Abstract
Weed seed predation is influenced for both biological and abiotic factors. Knowledge about these factors is necessary to optimize seed predation as a biological weed control measure. Here, we asked whether carnivorous carabid beetles can affect the seed predation. Additionally, the effect of weather on seed predation rate was investigated. For this purpose, 12, 1m² enclosures were installed in a field (block design with four treatments and three replications) in northeastern Germany over a period of 23 days. Treatments in the enclosures were 1) without carabids, 2) with a natural density and species composition of carabids, 3) with granivorous carabid beetles (Pseudoophonus rufipes, Harpulus affinis), and 4) as 3) but additionally with carnivorous carabids (Pterostichus melanarius, Poecilus cupreus) Seed predation rate was determined daily using seed cards with Poa annua and Stellaria media seeds. Temperature, relative air humidity and daily precipitation were measured as covariables. In the treatment with granivorous carabids seed predation rate was 54.3 (P. annua) resp. 14.3 (S. media) seeds per enclosure and day. In the treatment with granivorous and carnivorous carabids, seed predation rate was significantly lower for P. annua (46.6 seeds per enclosure and day, paired Wilcoxon-Test, p = 0.04) and equally high for S. media (14.4 seeds per enclosure and day). In enclosures containing non-manipulated carabid densities 9.1 seeds of P. annua and 7.2 seeds of S. media were lost per enclosure and per day, which is significantly higher than from enclosures that were void of carabids. The minimum night temperature was the only weather variable that significantly influenced seed predation rate. This work contributes to a better understanding of the factors influencing seed predation rates in the field.
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