<p>I could only find some excerpts of the ecology passage... I think this is the second half of it. Dunno if it'll help any, but here:</p>
<p>The city, in fact, can be thought of as a natural system on at least three different levels, each of which can give us insight into what a city is. At the most obvious level, although we don't normally think in these terms, a city is an ecosystem, much as a salt marsh or a forest is. A city operates in pretty much the same way as any other ecosystem, with its own particular collection of flora and fauna. This way of looking at cities has recently received the ultimate academic accolade -- the creation of a subfield of science, called urban ecology, devoted to understanding it. </p>
<p>At a somewhat deeper level, a natural ecosystem like a forest is a powerful metaphor to aid in understanding how cities work. Both systems grow and evolve, and both require a larger environment to supply them with materials and to act as a receptacle for waste. Both require energy from outside sources to keep them functioning, and both have a life cycle -- birth, maturity, and death. </p>
<p>Finally, our cities are like every other natural system in that, at bottom, they operate according to a few well- defined laws of nature -- laws that are knowable and, indeed, largely known. </p>
<p>So let me state this explicitly: A city is a natural system, and we can study it in the same way we study other natural systems and how they got to be the way they are.</p>