How can effective barotropic matter emerge from the interaction of cosmological fluids in an isotropic and homogeneous cosmological model ? The dynamics of homogeneous and isotropic Friedmann-Lemaˆtre-Robertson-Walker universes is a natural special case of generalized Lotka-Volterra systems where each of the universes fluid components can be seen as a competitive species in a predator-prey model. (Jungle universe : [7]) In addition to numerical simulations illustrating this behaviour among the barotropic fluids filling the universe, we analytically pinpoint that effective time-dependent barotropic indices can arise from a physical coupling between those fluids whose dynamics could then look like that of another type of cosmic fluid, such as a cosmological constant. Since the nature of dark energy is still unknown, this dynamical approach could help understanding some of the properties of dark matter and dark energy at large cosmological scales.