Print PageThe net effect of predators on prey is composed not only of direct consumptive effects (CEs) but also of nonconsumptive effects that result from phenotypic plasticity (NCEs). NCEs are principally due to prey modifying traits in response to changes in abundance of predators. For obvious logistical reasons, the great preponderance of evidence for the impacts of NCEs comes from experimental studies of very simple food webs (e.g., 2-4 species) typically conducted on short-term within-generational time scales of the prey and assessed using individual parameters (e.g. growth rates). Although this body of literature abundantly documents strong NCEs, it leaves open the question whether these NCEs are translated to important effects over longer time horizons (i.e. multiple generations of prey) and in more complex assemblages. Using experimental mesocosms, we examined the nonconsumptive effects of a fish predator, arising from phenotypic plasticity in prey traits, over multiple generations of a diverse zooplankton community.
Results/Conclusions
The nonlethal presence of fish strongly influenced zooplankton community structure, through both direct and indirect pathways, altering the abundance of many taxa by magnitudes as large as 3-10 fold. Fish presence both positively and negatively affected different species of cladocerans and copepods. A particularly striking nonconsumptive effect was the reversal of dominance in copepod taxa: fish presence reduced the ratio of calanoids to cyclopoids from 6.3 to 0.43. Further, the nonconsumptive effect of fish had a strong negative trophic cascade to zooplankton resources (phytoplankton). This experiments shows that nonconsumptive effects can strongly influence the abundance of multiple prey species over time spans of multiple prey generations. Our findings suggest that adaptive phenotypic plasticity of individuals can scale up to affect the structure of ecological communities.
