Technology evolution is providing new pervasive service scenarios characterised by a huge number of distributed and dynamic devices. Accordingly, a new generation of services and infrastructures are emerging which support situatedness, adaptivity and diversity. In this paper we model the overall world of services, data and devices, as a distributed computational ecosystem. Each entity will be modelled as an autonomous, spatially-situated individual of the ecosystem, whose existence is reified by an LSA (Live Semantic Annotation). Ecosystem's behaviour is controlled by coordination rules called eco-laws, which are sort of chemical-like reactions evolving the population of LSAs. We describe an architecture supporting this vision along with a model of eco-laws, and show their usefulness in a scenario of crowd steering through pervasive displays.