ABSTRACT
In terms of ecosystem components being organized in a hierarchical structure, O’Neill et al. (1991) have shown that with respect to the organization of communities of individual organisms, the levels at which different processes occur can be used to dissect out the functional contribution of individual species or groups of species. Using hierarchy theory, they maintain, hypothesis generation can be more accurately achieved. Within ecosystems, organisms of a variety of sizes coexist. We normally identify ecosystems by macroplant community assemblages, but the processes occurring in ecosystems are frequently modified by much smaller organisms. For example, decomposition and nutrient mineralization are carried out by bacteria, fungi, and micro-and mesoarthropods. The immediate effect of any one of these organisms is at the microscale of resolution; however, the combined effects of these organisms are seen at the local, landscape, and whole ecosystem level. One of the most challenging tasks that we face is to create the ability to seamlessly transcend the scales of resolution and convert the processes we observe and measure at one scale to that of the next level up or down. Ecologists thus have taken either a top-down or bottom-up approach to try to understand the complexities of interactions between scales (Parmelee, 1995; Friese et al., 1997; Anderson, 2000). Recently, the idea of reducing ecosystem complexity to its minimum (microcosm approach) has been aided by the development of “mesocosms” (Odum, 1984), in which the degree of complexity of a controlled and contrived ecosystem becomes more analogous to the real world. Here the number of organisms in the ecosy stem is relatively large, and complex interspecific interactions are allowed to develop. Concomitant with this comes a lack of control of changes in the ecosystem, but a more realistic set of dynamics is allowed to develop (Anderson, 1995; Lawton and Jones, 1995). Studying the processes occurring in microcosms, in which almost complete control of the system can be maintained, provides us with limited information. The use of mesocosms that are a nearer facsimile of the “real world” allows us to better understand interactions between organisms and their environment and the functional significance of these interactions. Increasing the complexity of the study system in this way allows us to increase in the functional diversity of the component organisms and to better predict the rate determining factors of environmental processes. As fungal hyphae act at the micrometer scale of
resolution, their species and community effects may extend to the scale of meter and tens of meters, and there is much more use that can be made of studies of the same process at multiple levels of scale.
