Thermodynamics of trophic interactions: Toward a reconciliation of energy and elements

• Mark Ritchie

Abstract
Management of the world's ecosystems in the face of changes in climate, availability of carbon, nitrogen and other elements, and invasion of new species will require a much better understanding of trophic interactions. The study of trophic interactions has historically focused on either the exchange of energy or of critical limiting elements, such as nitrogen, phosphorus, or carbon. These separate currencies generally prevent ecologists from fully understanding variation in the magnitude of trophic interactions and element fluxes across environments that receive different amounts of energy. During my proposed Fellowship, I plan to develop a thermodynamic theory of trophic interactions that applies principles of the second law of thermodynamics to interactions between plant resources, plants, herbivores, and predators. Preliminary work suggests a theoretical equivalence rule for energy and element concentrations that successfully predicts previously unrecognized trade-offs in plant nutrient concentrations, water-use efficiency (for terrestrial plants), and tolerance vs. resistance to herbivory. Changes in these plant traits across different environments have potentially profound effects on herbivore abundance and diversity and the likely importance and impact of top predators. To test some of these predictions, I plan to synthesize 15 years of experimental data from my own work on plant-herbivore interactions and extensive data from the literature. This work is likely to lead to several high-profile papers and the identification of critical data needs that might be addressed with a future NCEAS working group.