In a previous work on perturbation theory in population dynamics, we showed several plausible situations of preservation of the biodiversity. We give now an improved version of the method exhibiting a phenomenon of emergence of structured diversity. We display several (plausible in ethological or sociological contexts) examples of small modifications of the demographic equations that are emergent, that is, they lead to a limit state (the attractor) where the ‘spectators’ (i.e. to the individuals not concerned with the modification) vanish. In other words, even if the modification involves only a small number of individuals initially, the final pattern involves all the individuals. This behavior is easily understood in cases when the modification is concerned with some kind of symbiotic behavior, as it induces an advantage with respect to the ‘spectators’. But the phenomenon is very much general; we give examples of emergence in other contexts, involving predator/pray relations or other entangled relations, including an experimentally known example of subspecies of Escherichia coli.