Predation risk and prey naiveté jointly shape trophic cascades in freshwater plankton

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.