A common belief is that body-mass scaling of metabolic rate results chiefly from intrinsic body-design constraints. However, several studies have shown that multiple ecological factors affect metabolic scaling.  The mechanistic basis of these effects is largely unknown. Here, we explore whether abiotic and biotic environmental factors have interactive effects on metabolic scaling. To address this question, we studied the simultaneous effects of temperature and predator cues on the ontogenetic metabolic scaling of amphipod crustaceans inhabiting two different aquatic ecosystems, a freshwater spring and a saltwater lagoon. We assessed effects of phenotypic plasticity on metabolic scaling by exposing amphipods in the laboratory to water with and without fish-cues at multiple temperatures. Temperature interacts significantly with predator cues to affect metabolic scaling. Our results suggest that metabolic scaling is highly malleable in response to short-term acclimation. The interactive effects of temperature and predators show the importance of studying effects of global warming in realistic ecological contexts.