The Threshold Elemental Ratio of an ectotherm decreases then increases with rising temperature

Earth is currently facing unprecedented global changes, hurrying scientists to provide predictive tools to explore the futures responses of ecosystems. Among those changes, temperature increase and alterations of nutrient availabilities largely drive consumer performances, yet their interactive effect remains poorly understood. Here we investigate how the dietary C:P ratio that optimizes consumer growth (TER C:P : Threshold Elemental Ratio) changes along temperature gradients by combining a TER C:P model and growth experiments on the model organism Daphnia magna . Both lines of evidence show that the TER C:P responds to temperature in an U-shaped fashion. This shape reconciles previous contradictive observations into a common framework, thereby improving our capacity to forecast the combined effects of nutrient cycle and climatic alterations on ectotherms.