This study demonstrates a fact that should be obvious to most; that all species in an ecosystem, no matter what their size, serve an important function in that ecosystem. This was also the crux of yesterdays article in the Guardian which suggested that we conserve smaller 'useful' species other larger iconic ones, such as tigers (see link below).
A new Yale-led study shows the critical importance of earthworms, beetles, and other tiny creatures to the structure of grasslands and the valuable ecosystem services they provide. During a 3-year study, researchers found that removing these small animals from the soil of a replicated Scottish sheep meadow altered the plant species that grew in the ecosystem, reduced overall productivity, and produced plants that were less responsive to common agricultural management, such as fertilization. The results reflect the long-term ecological impacts of land use changes, such as the conversion of forests to agricultural land, researchers say.