This paper introduces a novel approach to generating audio or visual heterogeneity by simulating multi-level habitat formation by ecosystemengineer organisms. Ecosystem engineers generate habitat by modulation of environmental factors, such as erosion or radiation exposure, and provision of substrate. We describe Habitat, a simulation that runs on a two-dimensional grid occupied by an evolving population of stationary agents. The bodies of these agents provide local, differentiated habitat for new agents. Agents evolve using a conventional evolutionary algorithm that acts on their habitat preferences, habitat provision and lifespan, to populate the space and one another. This generates heterogeneous, dynamic structures that have been used in a prototype sonic artwork and simple visualisation. Keywords. ecosystem engineer, habitat, virtual ecosystem, artificial life, generative art