In this paper, we show that the dynamics of homogeneous and isotropic Friedmann-Lema\^itre universes can be studied with population dynamics, in particular with the generalized Lotka-Volterra equation where the competitive species are the barotropic fluids filling the Universe. Without coupling between those fluids, Lotka-Volterra formulation offers a pedagogical way to interpret usual Friedmann-Lema\^itre cosmological dynamics. When the cosmological fluids are coupled however, we establish new dynamical properties of Friedmann-Lema\^itre universes consisting of cycles between its interacting components. This provides a new asymptotic behavior for cosmic expansion in presence of coupled species, beyond the standard de Sitter, Einstein-de Sitter and Milne cosmologies. Finally, we conjecture that chaos can appear for at least four interacting fluids.