When the author is discussing "ecology," he means the environment—and in particular, the people—around an organism. Obviously, in the context of biology, this relationship often involves animals and plants; but in this case, the relation is to other individuals and the society surrounding these "outliers."
In the book, the concept of an "accumulative advantage" involves the idea that, in small groups, certain individuals are encouraged to be better than others similar to them. For instance, several major sports have a surprisingly large number of people from small populations—such as a local region that to produces many high quality players. In these instances, the environment surrounding these individuals encourages a small group (i.e., a microcosm) to become significantly better than average in order to give them a competitive advantage.
If you played soccer, for example, in an area that had significantly better players as well as significantly better coaches, your team would become much better than similar organizations that are not in this environment. This "ecology," which involves the superior coaches and players, gives the entire group an "accumulative advantage"—just like a specialized ecology that caters to the advantages of a certain organism will give that organism evolutionary advantages.