Elena Litchman, Mridul K. Thomas 

Warming, the most prominent aspect of global environmental change, already affects most ecosystems on Earth. In recent years, biologists have increasingly integrated the effects of warming into their models by capturing how temperature shapes their physiology, ecology, behavior, evolutionary adaptation, and probability of extirpation/extinction. The more physiologically-grounded approaches to predicting ectotherms’ responses use thermal performance curves (TPCs) obtained by measuring species performance (e.g. growth rate) under different temperatures. TPCs are typically measured while other factors are held constant at benign levels to ‘isolate’ the effects of temperature. Here we highlight that this practice paints a misleading picture because TPCs are functions of other factors, including global change stressors. We review evidence that resource limitation, pH, oxygen and CO2 concentration, salinity, water availability, parasites and mutualists, all influence TPC shape and thermal traits such as optimum temperature for growth. Evidence from a wide variety of organisms – phytoplankton, protists, plants, insects, and fish – points towards such interactions increasing organisms’ susceptibility to high temperatures (reducing it in the case of mutualists). Failing to account for these interactions is likely to lead to erroneous predictions of performance in nature and an underestimation of the risks of warming. We discuss the general patterns and possible consequences of such interactions for ecological communities. But importantly, interactions with TPCs share common features that we can learn from. Incorporating these interactions into population and community models should lead to deeper insights and more accurate predictions of species’ performance in nature – as well as strategies for managing natural and agricultural ecosystems in the face of warming.