Prey naiveté alters the balance of consumptive and non-consumptive predator effects and shapes trophic cascades in freshwater plankton

Predators drive trophic cascades by reducing prey biomass and altering
prey traits, selecting 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 ecological and
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. Contrary to expectations, top-down
control of zooplankton and phytoplankton biomass was strengthened by prey
community experience: in systems with experienced relative to naive
zooplankton communities both predation risk (NCEs only) and predation (CEs
+ NCEs) had stronger effects on zooplankton prey biomass and trophic
cascades were twice as strong. These results show that the ecological and
evolutionary experience of diverse prey communities alters the balance of
consumptive and non-consumptive predator effects and influences trophic
cascade strength.