SOIL INVERTEBRATE MICRO-INVERTEBRATE INTERACTIONS - DISPROPORTIONATE EFFECTS OF SPECIES ON FOOD-WEB STRUCTURE AND FUNCTION

The preservation of biodiversity requires an appreciation of food web structure and an understanding of how disturbance alters their structu re,and function. Theoretical and empirical studies of food webs demons trate that food webs possess a regular structure. Food chain length ap pears limited to three to four transfers, and, complexity and diversit y are constrained. When ecosystem energetics are considered, species w ithin food webs are seen to form interactive assemblages that process matter at different rates and respond to disturbance differently. Dist urbance may affect the diversity of a system, or, may influence the re lative importance of one species assemblage over another. Moreover, pr edicting the impact of disturbance on a system is difficult as species that comprise and process a small fraction of the system's biomass ma y control a disproportionate fraction of the system's biomass and dive rsity. Seven food webs at four sites were used in a modeling exercise to demonstrate this point. Field studies involving the role of mycorrh izal fungi yielded results consistent with the modeling studies as the types of plant species present, the level of production and the diver sity of production were related to the levels of mycorrhizal fungi in the soils following disturbance. The results indicate that all species are important to ecosystem structure and function and that the monito ring of ecosystems and conservation efforts should expand their emphas is to the preservation of ecosystem integrity as well as that of indiv idual species.