Biodiversity and Complexity of Rice Farm Ecosystems: An Empirical Assessment

Abstract

Modern rice farms are characterized by the use of synthetic agrochemicals, which eliminate a large segment of biodiversity on-farm. In contrast, organic rice farms tend to preserve much of natural biodiversity. While biodiversity- productivity relationship in organic vs. chemicalised rice farms is contested, the relationship of on-farm biodiversity with food web structural properties and ecosystem services remains to be explored. To understand the functional significance of species richness and ecosystem complexity of rice farms, I examine here the architectural properties of rice food webs from West Bengal, based on replicated plots of folk variety (organic) and modern (chemicalised) rice systems. All rice food webs, constructed from observational data collected over three years, show prominent scale dependence of dietary links, link density, web height, diversity of natural enemies to pests, predator-pest ratio, and the numbers of omnivores and omnivory levels. Organic folk rice webs tend to have greater mean species richness, predator diversity, predator-pest ratio and chain length than modern rice farm webs, yet both systems show homogeneity of distribution of the web properties. Analyses of 16,400 computerized analog webs, following non-random rules of species association drawn on real-life, seasonally distinct rice food webs, validate the robustness of conclusions.