A cross-ecosystem comparison of the strength of trophic cascades

Jonathan B. Shurin*, Elizabeth T. Borer, Eric W. Seabloom, Kurt Anderson, Carol A. Blanchette, Bernardo Broitman, Scott D. Cooper and Benjamin S. Halpern National Center for Ecological Analysis and Synthesis, University of CaliforniaSanta Barbara, 735 State St., Suite 300, Santa Barbara, CA 93101, USA Department of Ecology, Evolution, and Marine Biology, University of CaliforniaSanta Barbara, Santa Barbara, CA 93106, USA *Correspondence: E-mail: [email protected] Abstract Although trophic cascades (indirect effects of predators on plants via herbivores) occur in a wide variety of food webs, the magnitudes of their effects are often quite variable. We compared the responses of herbivore and plant communities to predator manipulations in 102 field experiments in six different ecosystems: lentic ( lake and pond), marine, and stream benthos, lentic and marine plankton, and terrestrial (grasslands and agricultural fields). Predator effects varied considerably among systems and were strongest in lentic and marine benthos and weakest in marine plankton and terrestrial food webs. Predator effects on herbivores were generally larger and more variable than on plants, suggesting that cascades often become attenuated at the plant– herbivore interface. Top-down control of plant biomass was stronger in water than on land; however, the differences among the five aquatic food webs were as great as those between wet and dry systems.