Predation risk and prey naiveté jointly shape trophic cascades in freshwater plankton
Monday, August 2, 2021
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Henry K. Baker, Stephanie S. Li, Stefan C. Samu, Natalie T. Jones and Jonathan B. Shurin, Ecology, Behavior and Evolution, University of California, San Diego, La Jolla, CA, Celia C. Symons, Ecology and Evolutionary Biology, University of California - Irvine, Irvine, CA
Henry K. Baker
Ecology, Behavior and Evolution, University of California, San Diego La Jolla, CA, USA
Background/Question/Methods Predators drive trophic cascades by reducing prey biomass and altering prey traits. Predators select for prey that exhibit constitutive and induced anti-predator defenses that decrease susceptibility to consumption. These defense traits are often costly, generating a tradeoff between consumptive (CEs) and non-consumptive predator effects (NCEs). The eco-evolutionary experience that prey share with a given predator may determine their position along this tradeoff curve, affecting the nature and strength of top-down control of ecosystems. Conceptual models predict that predator-experienced prey suffer greater NCEs than predator-naive prey, which suffer stronger CEs and total predator effects (CEs + NCEs), but this has not been tested in diverse prey communities. We tested these predictions by comparing the effects of predation (CEs + NCEs) and predation risk (NCEs only) of planktivorous fish on food web structure in pond mesocosms with diverse natural communities of either predator-naive or predator-experienced zooplankton. Results/Conclusions Contrary to expectations, top-down control was strengthened by prey community experience: both predation risk (NCEs only) and predation (CEs + NCEs) had stronger effects on prey biomass and trophic cascades were twice as strong in systems with experienced relative to naive zooplankton communities. These results show that the eco-evolutionary experience of diverse prey communities alters the balance of consumptive and non-consumptive predator effects and controls trophic cascade strength.