A function that by current optimization can describe the succession of an ecosystem. ‘Ecosystems do not, of course, have goals; but their successional development may be described by a goal function’ (Jørgensen and Nielsen (2007) Energy 32, 5). Phillips (2008) PPG 32, 1 reviews theories of evolution and ecosystem development based on goal functions. See F. Müller and M. Leupelt, eds (1998).