The living world is a huge system spread over multiple scales of space and time. Particular aspects of it are addressed with life models: protein interactions, species interplay, developmental dynamics. We are interested in invariant aspects exhibited similarly in various systems regardless of the actual objects they involve: predation, epidemies spread, evolution, cooperation, cheatery, metamorphosis, information transfers. We design an abstract model supporting such invariants. Its statement only relies upon the common properties of biotic objects. We derive it into an abstract biotic simulation engine, useful in both checking validity of the model and animating arbitrary virtual biotic media: multi-agent systems, physical worlds, cellular automata, human languages, stockmarkets, self-reconfigurable robots.