Highlight the phrases that provide evidence for the theme “Only the strong survive in the wilderness.”
No more was Spitz a leader greatly to be feared. . . . Buck never came near Spitz without snarling and bristling menacingly. In fact, his conduct approached that of a bully, and he was given to swaggering up and down before Spitz's very nose.
—The Call of the Wild,
Jack London
How does Buck challenge Spitz’s leadership and demonstrate the theme “Only the strong survive in the wilderness”?