Stoichiometry of actual vs. potential predator–prey interactions: insights into nitrogen limitation for arthropod predators

William F. Fagan* and Robert F. Denno Department of Biology, University of Maryland, College Park, MD 20742, USA Department of Entomology, University of Maryland, College Park, MD 20742, USA *Correspondence: E-mail: [email protected] Abstract Literature-compiled data sets demonstrate wide interspecific variation in nitrogen content among terrestrial arthropods and raise the possibility of nitrogen (N) limitation for predatory species. It remains unclear, however, whether the same disparities between N supply and demand that appear in literature compilations also exist in particular ecological communities. To address this uncertainty, we compared arthropod predator–prey stoichiometries derived from a compiled database with those from a natural Spartina saltmarsh community. Separate assessments of potential N-limitation were made for arthropod predators feeding on herbivores and for intraguild predators feeding on intraguild prey. Relative to the compiled database, saltmarsh consumer–resource interactions exhibited increased disparity between N-content of herbivores and N-demand by predators. The high N content of saltmarsh arachnids relative to predatory insects at large may contribute to the supply-demand disparity. Whether N-limitation of terrestrial arthropod predators is widespread in the marsh, and in nature in general, depends sensitively on the predatory species gross growth efficiencies for N and carbon. Obtaining hard empirical data for these efficiency parameters should be a research goal.