Interactions between food-web structure and nutrients on pond organisms

Abstract

THE suggestion that the densities of organisms are regulated by interactions involving entire food chains1 has resurfaced into a new debate about the role of population regulation in environments that vary in productivity2–5. Past work has shown that density responses of organisms to enhanced productivity should be strongly affected by the number of trophic levels in the food chain6–11 but more recent theoretical work on this question has suggested that heterogeneity within a trophic level can be just as important12–15. Here we present direct experimental evidence for such an interaction between environmental productivity and the species composition of herbivores. Our results illustrate that differences in food-web structure similar to those documented in natural communities16,17 can dramatically alter how organisms will respond to abiotic factors such as nutrients that regulate primary productivity.