Elements of ecology and evolution

Abstract

Ecological stoichiometry (ES) is the study of the balanceof energy and multiple chemical elements in ecologicalinteractions (Sterner and Elser 2002). This field hasmany roots, but most proximally it has emerged fromstudies of trophic interactions in freshwater planktonand focused primarily on the ratio of carbon tophosphorus (C:P) in the freshwater cladoceran Daphniaand that of their phytoplankton food. Two impor-tant findings emerged from these seminal studies some15 years ago: first, the observation that release of keynutrients like nitrogen (N) and P depended, in apredictable manner, on C:N:P ratios in the zooplanktonconsumer relative to that in its phytoplankton food witheffects on phytoplankton nutrient limitation (Elser et al.1988, Sterner et al. 1992) and, second, the discovery thatof direct elemental limitation, N or P, of consumergrowth due to high C:nutrient ratio in its food (Hessen1992, Urabe and Watanabe 1992, Sterner 1993). Thesetwo observations can be considered two sides of thesame stoichiometric coin and we now appreciate thatconsumers (and especially herbivores and detritivores)frequently have to dispose of excess C from their diets,causing reduced efficiency of growth at the organismsallevel and reduced trophic transfer efficiency at theecosystem level. The validity of these principles hasbeen experimentally verified in an increasing numberof studies. From this small pelagic, freshwater realm,the concept of ecological stoichiometry has expandedto other organisms, other ecosystems, from genes andcells to ecosystems and global regulation of elementalcycles. These developments, at least up until 2001, arereviewed by Sterner and Elser (2002). In this collectionof papers the authors demonstrate the very newestapplications and horizons for stoichiometric theoryand investigation, pointing towards ways that ESmight be more fully elaborated at different levels oforganization and used to understand new questions andproblems.Some words on the process leading up to thiscollection of papers is in order, since they have evolvedin quite an unusual way: in the academic year 2003