L ETTER Predator effects on herbivore and plant stability

Benjamin S. Halpern,* Elizabeth T. Borer, Eric W. Seabloom and Jonathan B. Shurin National Center for Ecological Analysis and Synthesis, 735 State St., Santa Barbara, CA 93101, USA Dept. of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060, USA Dept. of Zoology, Oregon State University, Corvallis, OR 97331, USA Dept. of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, British Columbia, V6T 1Z4 Canada *Correspondence: E-mail: [email protected] Abstract Humans are rapidly altering the diversity and composition of ecological communities by accelerating rates of species extinctions and introductions. These changes in diversity are not random and disproportionately involve the addition or extinction of predators. Theoretical and microcosm studies suggest predator removal may either increase or decrease ecosystem stability. Here we test whether the addition or removal of predators affects aggregate biomass stability in 40 experiments carried out in six different ecosystems. Predators did not alter the temporal variability of autotroph biomass, but significantly destabilized herbivore biomass. The effects of predators on herbivore biomass stability varied significantly among ecosystems, with benthic and pelagic lake systems showing the greatest shifts. Consequently, the addition of predators to communities, as occurs in many conservation efforts, biological control programmes and species introductions, may lead to more variable system dynamics.