Final Report Summary - ECOSTRESS (Physiological Reaction to Predation- A General Way to Link Individuals to Ecosystems) The ECOSTRESS project developed and tested a whole new theoretical framework aiming at advancing the integration of food-web interactions to biogeochemical processes in an attempt to explain the unexplored causes of variation in ecosystem functioning. Specifically, in a variety of prey-predator pairs, we tested how prey perceive and respond defensively to the elevated risk of predation, how these changes alter the prey trophic function and consequently regulate key biogeochemical processes such as nutrient cycling at the ecosystem level. We found that prey animals integrate information from various sources, including for the first time cues of non-predatory species, and take deliberate risks to improve their spatiotemporal landscape of fear assessment while minimizing excess costs of defensive overreaction. Our investigation at the individual level revealed that prey animals use various defense reactions that dictated the predator-induced changes in prey nutritional intake target, altering their trophic function. For instance, desert isopods increased their metabolic rate in response to the risk of scorpion predation and consumed less proteins as predicted by our theory. In the field, isopods also consumed more calcium-rich biological soil crust under predation risk to fulfill higher calcium demand. In another example, snails responded to the risk of beetle predation by using avoidance behavior and by increasing their metabolic rate. Evidence showed that these snails altered their nutritional intake target to fulfill those functional changes but the response depended on the food spatial location, revealing a whole new aspect of prey food choice that needs to be considered. Summary of our empirical results at the individual level and those of a comprehensive meta-analysis that used published data suggested that we need to expand our theory to better predict how different types of inducible defenses and the predator traits may affect the prey trophic function. At the ecosystem level, we found that changes in prey trophic function regulated key biogeochemical processes such as the C and N cycling and that these changes were amplified by changes in the soil microbial community function. Our project demonstrated the importance of integrating food-web interactions and biogeochemistry to better explain context-dependency in ecosystem functioning. Yet, we also exposed many methodological limitations and conceptual gaps that need to be adressed before the theoretical framework of ECOSTRESS could reach its true potential.
