Ecological stoichiometry and nutritional geometry have emerged as two powerful frameworks for studying the flow of energy and nutrients through ecosystems. While often used separately, each framework has strengths and weaknesses at different scales of study. We use experiments on plant-herbivore and predator-prey systems to test the long-held assumption that elements and macronutrients are related and to examine the consequences of these relationships or lack thereof for understanding trophic interactions and their ecological consequences.
In a study of how fertilizer N:P balance affected the elemental and biochemical content of plants, the leaves of plant fertilized with higher N:P had higher N content but lower protein content than plants fertilized with lower N:P. Caterpillars grew best on the plants fertilized with lower N:P, which had both higher P and higher protein. In a study of arthropod predator-prey interactions, elemental and macronutrient analyses resulted in opposite conclusions about the efficiency of predator digestion. Prey remains had high nitrogen content but very little protein content. In addition, understanding the biochemical content of compounds deposited by predators is critical since some nutrients such as excreta are more quickly available to decomposers and plants than other compounds such as undigested parts of exoskeleton, which can take years to decompose. Overall, our results suggest that a genuine synthesis of ES and NG has greater potential to connect physiological mechanisms from the scale of individuals to broader ecosystem patterns than either framework could do on its own.