This proposal aims to advance a new general theory that links plasticity in prey responses to predation and biogeochemical processes to explain context-dependent variations in ecosystem functioning. The physiological reaction of prey to predation involves allocating resources from production to support emergency functions. An example of such a reaction is an increase in maintenance respiration concomitant with higher carbohydrate and lower N demand. Such changes in prey energy and elemental budget should alter the role prey play in regulating the quality of detrital inputs to soils. Nutrient content of detritus is an important determinant of the way soil communities regulate ecosystem processes. Thus, the physiological reaction of prey to predation can potentially explicate changes in ecosystem functioning. My first empirical examination of a few selected mechanisms of this theory has yielded very promising insights.The main objectives of this proposal are: (1) To systematically test whether prey reactions to predation are consistent with the proposed theory’s predictions across species and ecosystems; (2) to examine the interface between stress physiology and anti-predatory behaviors in explaining predator induced diet shift, and (3) to evaluate how predator induced responses at the individual level regulate ecosystem processes. To address these objectives, I propose combining manipulative field experiments, highly controlled laboratory and garden experiments, and stable-isotopes pulse chase approaches. I will examine individual prey responses and the emerging patterns across five food-chains that represent phylogenetically distant taxa and disparate ecosystems. The proposed study is expected to revolutionize our understanding of the mechanisms by which aboveground predators regulate ecosystem processes. Promoting such a mechanistic understanding is crucial to predict how human-induced changes in biodiversity will affect life-supporting ecosystem services.