Allornetry, biocomplexity, and web topology of hundred agro-environments in The Netherlands

For almost all soil organisms, the logarithm of numerical abundance (N) is inversely related to the logarithm of body mass (M). It is helpful to use allometry and food-web topology to condense environmental information. Using mathematical evidence derived from 99 real webs, a hypothesis is formulated to explain how belowground soil organisms become affected by increasing effects of animal manure and this is discussed in relation to soil productivity. As a matter of fact, the intercepts of allometric correlations change in a highly significant way according to aboveground grazing by mammals. Linear regressions of log(10)(N) values fitted against their log(10)(M) averages show allometric unity (slopes equal to -1) only in one fourth of the webs. Under different levels of taxonomic aggregation, our intercepts remain directly correlated with macroherbivory. Also after removal of bacteria from these real webs, intercepts of the linear regressions robustly fitted on the eukaryotes' M and N reflect the local nitrogen availability from animal manure. Other basic web properties, such as trophic links and structural complexity, display a comparable pattern from nutrient-poor to nutrient-rich ecosystems, in contrast to a rather erratic connectance. Regardless of total soil biodiversity, only in 23 real webs a host of organisms ranging from earthworms and insects to bacterial cells seem to interact in ways beneficial to each other. (c) 2006 Elsevier B.V. All rights reserved.