Experimental manipulations of nutrients and trophic structure across ecosystems

Nutrient availability, herbivore grazing pressure, and the indirect effects of top predators control the standing biomass, nutrient content and species diversity of primary producers to varying degrees across global ecosystems. For this comprehensive database, we systematically gathered data from the literature that experimentally manipulated (1) nutrients through fertilization, (2) herbivore pressure through exclusion, enclosion, or removal experiments, (3) predators through similar means, or (4) a combination of these treatment combinations. Special priority was given to studies that factorially manipulated multiple nutrients (especially N & P) or manipulated both nutrients and herbivores (bottom-up and top-down), and which measured species richness, biomass or nutrient content of autotrophic responses at the community level. In addition, the Trophic Cascades database (owned by E. Borer et al.) has been folded into this framework, as well as data from several other published analyses from restricted systems (e.g., H. Hillebrand periphyton database). The goals were manifold; however, the central objective was to compare with meta-analyses the relative effects of these experimental manipulations across global organismal functional groups and ecosystem types. To this end, the database was designed to be general and flexible in order to accomodate varying research questions, methodologies, spatial and temporal scales, and abiotic and biotic covariates reported across different studies. As of this writing (14 November 2006), the database contains nearly 2000 studies across terrestrial, freshwater and marine systems, and well over 10,000 treatment responses. Data are entered into four different tables in a relational design (study-level data, treatment/responses, local biotic covariates of response and manipulated taxa, & general/global taxonomic and functional characteristics of these taxa).