Strner isn't so much about predation as he is about acting in one's own interest - his "might is right" philosophy has similarities to Branden's "no one is coming to the rescue" - basically he's saying don't hide behind empty platitudes but instead fight for your rights, property etc, and the preservation of such! If one passively espouses this right or that without upholding it in practice, they've given a certain legitimacy to those with suspect ideas. As is often said, "the surest way for evil to triumph is for good men to do nothing".
The area where he does considerably differ from Rand, apart from his (theoretically) cavalier attitude toward initiation of force, is the rejection of normatives such as "man qua man" which he sees every bit as counterproductive as collectivist ideas of God, State, family, race, etc...