Ecological effects on metabolic scaling amphipod responses to fish predators in freshwater springs

Metabolic rate is commonly thought to scale with body mass to the 3/4-power as a result of universal body-design constraints. However, recent comparative work has shown that the metabolic scaling slope may vary significantly among species and higher taxa, apparently in response to different lifestyles and ecological conditions, though the precise mechanisms involved are not well understood. To better understand these under-appreciated ecological effects and their causes, it is important to control for extraneous phylogenetic and environmental influences. We demonstrate how this may be done by comparing the ontogenetic scaling of resting metabolic rate among populations of the same species (the amphipod Gammarus minus) in mid-Appalachian freshwater springs with similar, relatively constant environmental conditions, except for the varying presence of the predatory fish Cottus cognatus. We found that populations of G. minus exhibit significantly lower metabolic scaling slopes (0.54 to 0.62...