How are cities and companies like ecologies?

Here's an interesting TED talk looking at the relationship between size and success of animals - and cities. There are advantages to scale, he says, but problems like crime also scale up as well.

He also talks about the sigma-shaped growth of companies. They tend to grow rapidly, level off for some time, and then almost without exception disappear and die as well. It is interesting stuff both from an evolutionary perspective and a returns to scale perspective.