Understanding the impact of trophic cascades across diverse ecosystems

J.B. Shurin¹, E.T. Borer², E.W. Seabloom², K. Anderson³, C.A. Blanchette³, B. Broitman³, S.D. Cooper³, and B.S. Halpern². ¹Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, ²NCEAS, University of California, Santa Barbara, CA 93101, ³Dept. of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, 93106

A meta-analysis of trophic cascade experiments found marked differences in the strength of top-down control over producer biomass among ecosystems. Aquatic systems collectively showed stronger responses than terrestrial, although marine plankton showed weak cascades, on par with grasslands. Interestingly, the strongest effects of predators on lower trophic levels were found in lentic and marine benthos. Stream predators had relatively weak effects on herbivores that translated into disproportionately strong responses by periphyton. Differences in plant responses to predators within and among systems were associated with both biological (e.g., organism size and metabolic type) and methodological (e.g., experimental duration, enclosure size) factors. We discuss theory aimed at elucidating the causes of differences among systems based on plant community turnover rates and nutritional content.