Researchers in astrobiology should develop alternate concepts for the detection of extraterrestrial life. We should search for extraterrestrial ecology, exoecology, as well as for extraterrestrial biology, exobiology. Ecology describes the interactions of living things with their environment. All ecosystems are highly constrained by their environment and conform to well-known and inescapable system design principles. An ecology could exist wherever there is an energy source and living things can employ some method to capture, store, and use the available energy. Terrestrial ecosystems use energy sources including light, organic molecules, and, in thermal vents and elsewhere, simple inorganic molecules. Ecosystem behavior is controlled by matter and energy conservation laws and is described by dynamic systems theory. Typically in an ecosystem different molecules are not in chemical equilibrium and scarce materials are conserved, stored, or recycled. Temporal cycles and spatial variations are often observed.
The general concepts of exoecology can help guide the search for extraterrestrial life. The best strategy for the detection of extraterrestrial life is probably a mixed strategy. We should use detailed assumptions based on terrestrial biology to guide some but not all future searches for alien life. The systems principles of exoecology seem much more fundamental and inevitable than the analogies with terrestrial biology that are usually accepted in exobiology. We should search for exoecology based on general principles as well as for exobiology using familiar mechanisms.