The tallgrass prairie of North American contains a diverse and abundant soil fauna well represented by earthworms, macro- and microarthopods and nematodes. A portion of this fauna representing a large fraction of the animal biomass has been introduced in the last 200 years, and functional roles and regulatory mechanisms may have been altered because of these introductions. Four years of experimental manipulations of plant and fauna variables have failed to establish a definitive net effect of the soil fauna on primary productivity. However, measurable effects of the fauna on nutrient dynamics of the grassland ecosystem have been observed. Experimental manipulations of plant root dynamics and addition of inorganic nitrogen and fixed carbon have demonstrated that both resources quality and resource quantity are factors limiting the size of soil fauna populations