HIERARCHY UNDERLIES PATTERNS OF VARIABILITY IN SPECIES INHABITING NATURAL MICROCOSMS

Relative variability of species has been shown to increase significant ly with a decrease in their ecological range. Similarly, the distribut ion of collapse (e.g., extinctions, disturbances, population declines) magnitudes has also been shown to follow an inverse power-law form de scribed by the 1/f(omega) curve. We hypothesized that the two, possibl y general, patterns associated with ecological systems share a common underlying cause: the hierarchical structure of the system itself. To test the hypothesis we used a model system of 49 natural rock pools in habited by 40 species of invertebrates. Three measures of species vari ability based on changes in abundance, distribution, and persistence i n individual pools conform with the postulated negative exponential cu rves. Correspondingly, frequency distributions of changes of various m agnitudes conform to the 1/f(omega) pattern. Examination of the contri butions of species to the 1/f(omega) pattern revealed that species low in the system hierarchy (habitat specialists in this case) are respon sible for the majority of small variation events (correlations between the ecological range and position on the 1/f(omega) curve range from 0.625 to 0.807 on the three measures of variability). This permits the conclusion that the two patterns are linked and constitute different expressions of the same hierarchical system structure.