Plants and generalist predators as links between the below-ground and above-ground system

This review highlights that the above-ground food web strongly depends on the structure and activity of the below-ground animal community. Two pathways connecting the below- and the aboveground community are distinguished: One functioning via soil animal-mediated changes in plant performance which in consequence affect herbivores and thereby the above-ground community; the second functioning via generalist predators which benefit from below-ground energy supply. The first pathway may be considered as bottom-up control of the above-ground community by belowground animals, the second functions by strengthening top-down forces above the ground when generalist predators switch their attacks from decomposers amongst herbivores. It is assumed that both pathways are of significant importance in many terrestrial systems, surprisingly, so far both are hardly investigated. It is stressed that in the plant pathway microbi-detririvores in soil like earthworms, collembolans and protozoans might be considerably more important than root herbivores which directly affect plant growth. The generalist predator pathway is considered to be particularly important in natural systems like grasslands, however, when employing intelligent management strategies which support microbi-detritivore populations and get generalist predators to switch prey from microbi-detritivores to herbivores this pathway may also help in controlling herbivore pest species in arable systems.