The Contribution of Microarthropods to Aboveground Food Webs: A Review and Model of Belowground Transfer in a Coniferous Forest

Abstract

Although belowground food webs have received much attention, studies concerning microarthropods in nondetrital food webs are scarce. Because adult oribatid mites often number between 250,000–500,000/m2 in coniferous forests, microarthropods are a potential food resource for macroarthropod and vertebrate predators of the forest floor. Although the contribution of microarthropods to aboveground food webs has received little attention, sufficient data concerning macroarthropods and vertebrate predators were available at the Savannah River Site (SRS, Aiken, South Carolina) to construct a food web model of the various trophic interactions. To supplement this analysis, literature of microarthropod predation by arthropods and vertebrates was reviewed. This information was incorporated with the existing data to produce a model for taxa occurring in coniferous forests at the SRS. Because of the diversity and natural history of microarthropod predators, both vertebrate and invertebrate, the resulting web is quite connected and includes transfers to many trophic levels. The diets of arthropods and vertebrates are variable; yet feeding patterns reflect the relative abundance of prey at a place and time. Also, many predators feed on members of their own group. These factors suggest that belowground transfers are deserved of more attention in these and other forest food webs where substantial numbers of detritus feeding invertebrates inhabit the soil/litter interface and are available as prey items. Moreover, this model can be generalized to describe the dynamics of arthropod and vertebrate communities in other coniferous forests. The functioning of terrestrial ecosystems is dependent upon the interrelationships between aboveground and belowground food webs, and transfers of biotic components of the decomposer subsystem to aboveground consumers connect the two subsystems. It is hoped that those consumers traditionally associated with foliage-based food webs be reconsidered, as they may be gaining a proportion of their nutrition from organisms in the detrital pathway.