Ecological physiology (ecophysiology) has transformed thinking about mammal survival beyond an appreciation of the mechanisms of physiology, to an appreciation of the ecological consequences of their physiological constrains and abilities. Ecophysiology has emerged from the long-standing traditions of comparative physiology, but deeper understanding of the contributions of mammalian physiological traits to ecological interactions is scant, and ecological research remains focussed on animal abundance and distribution. Here I describe the role that physiological plasticity of mammals (or lack thereof) may play at finer ecological scales, and argue that such plasticity could be considered as a key factor affecting mammalian survival. This is especially relevant in light of global climate change, but may also be important for understanding and predicting the ecological consequences of invasive mammals, conservation physiology, and factors affecting biodiversity. In this regard, mammals at extreme climates offer opportunity to test hypotheses about the strength of plasticity as a driver or cog for ecological interactions and processes. Mammal abundance and distribution, therefore, may be necessary, but not sufficient, for explaining ecological changes in some systems, and the role of plasticity in affecting mammalian survival and fecundity (and hence abundance) needs to be explored.