  Using the examples of an excitable chemical system (Belousov-Zhabotinsky
medium) and plasmodium of Physarum polycephalum we show that universal
computation in a geometrically unconstrained medium is only possible when
resources (excitability or concentration of nutrients) are limited. In
situations of limited resources the systems studied develop travelling
localizations. The localizations are elementary units of dynamical logical
circuits in collision-based computing architectures.
