Inducible defenses as factor determining trophic pathways in a food web

Abstract

Understanding functional roles of prey defense in biological interactions remains a major task in food web ecology. We investigated the role of an inducible defense as a factor that influences the trophic pathway in an aquatic food web. Quantitative information on food web structure in Lake Suwa (a eutrophic lake in Japan) was provided by carbon and nitrogen stable isotope analyses using samples taken during summer and a structural equation model applied to annual monitoring data. As predicted, there was none or only a weak link detected between the prey with induced defenses (Bosmina fatalis) and its invertebrate predator (Leptodora kindtii). The effects of an inducible defense on the trophic links are based mainly on the mortality or population growth rate of organisms using predation, population (or community) level experiments, field data, and model estimates. However, there was no research linking these different data using stable isotope analyses. Our research provides new evidence supporting previous studies by suggesting the importance of the inducible defense in determining food web structure and function.