FUNCTIONAL COMPLEXITY AND ECOSYSTEM STABILITY

The hypothesis that complexity and stability are positively correlated was experimentally tested at the ecosystem level of organization using intact terrestrial microcosms. Power spectral densities of hourly CO/sub 2/ efflux, from 11 old-field microcosms, were analyzed for the number of low-frequency components. We postulate that the number of peaks is related to functional interactions among system components (i.e., population interactions, physical-chemical reactions, and biological turnover rates) influenced by nonlinearities, feedbacks, and time delays. Thus, the number of low-frequency peaks can be taken as an index of functional complexity. Relative stability was based on the capacity of the system to retain essential nutrients and was measured by net loss of calcium after the system was stressed with a heavy metal, cadmium. Rank correlation supported the hypothesis that increasing ecosystem functional complexity leads to increasing ecosystem stability.