Spreading life throughout the solar system: "Humanity has the power to fill outer space with life. Today our solar system is filled with plasma, gas, dust, rock, and radiation -- but very little life; just a thin film around the third rock from the Sun. We can change that. In the 1970's Princeton physicist Gerard O'Neill with the help of NASA Ames Research Center and Stanford University showed that we can build giant orbiting spaceships and live in them. These orbital space colonies could be wonderful places to live; about the size of a California beach town and endowed with weightless recreation, fantastic views, freedom, elbow-room in spades, and great wealth. In time, we may see hundreds of thousands of orbital space settlement in our solar system alone. Building these settlements will be an evolutionary event of a magnitude similar to, if not greater than, ocean-based Life's colonization of land half a billion years ago."
This gives a detailed look at the process of colonizing the solar system through orbital space settlements. Although I believe a complete ecological model of space colonization will involve colonizing all bodies of the solar system in addition to orbital space settlements, I agree that the most important form will be the orbital colonies. This is the most universal and portable model here as well as in other star systems.