Spring wheat, Triticum aestivum (L.), supports a diverse community of ground-dwelling generalist predators, including ground beetles (Coleoptera: Carabidae), rove beetles (Coleoptera: Staphylinidae) and spiders (Arachnida: Araneae). Detritivorous arthropods like Collembola may be an important food source for many of these predators. Several studies have suggested that supplementation of the detrital resource base can result in increases in both detritivore and predator densities. Likewise, I tested the hypothesis that addition of organic matter to the soil in an agricultural ecosystem, will result in increased detritivore densities and could subsequently lead to higher density and diversity of ground-dwelling generalist predators. In 2000 and 2001, experimental plots were established in a wheat field located at the University of Minnesota in St. Paul, MN. Organic matter addition treatments consisting of mixtures of straw and alfalfa, and chopped mushrooms and potatoes were added to the plots early in the growing season. Soil arthropod activity was measured using pitfall traps. Increases in detritivore activity were evident in the treatment plots at various times throughout the growing season compared with the untreated control plots. Slight increases in the activity of ground-dwelling predators were also seen in the treatment plots. These results support the hypothesis that increased resource availability results in increased detritivore activity, and possibly leads to higher predator densities.
Keywords: tritrophic interactions, generalist predator
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