Physiological ecology combines the study of physiological processes, the functions of living organisms and their parts, with ecological processes that connect the individual organism with population dynamics and community structure. In the past, physiological ecology focused principally on physiological processes in isolation from each other and without strong quantitative connections to ecological processes. That focus is now rapidly changing into a dynamic quantitative and more integrated discipline. Physiological ecology reaches up to population dynamics and community structure and down to genetic phenomena influencing key endocrine functions affecting behavior, energetics, survival, reproduction, and fitness in diverse environments.