“The only thing a predator fears is a bigger predator.”
– Ed, Bill the Vampire
Tome of Bill, by Rick Gualtieri

At this exact moment in the story, the protagonist and his friends are discovering, and marveling, that he is no normal vampire. In addition to being impossible to compel, he can also feed on other vampires without getting sick, the way humans would get sick if they drank human blood. As the other vampires are rather accustomed to being the apex predator, the realization that there’s something above them is due cause for them to fear.

The behavior of predators is a recurring theme in this story. Bill himself, as the narrator, comments how predators pick off individuals instead of charging into the center of the herd. They also don’t make a point of stalking their prey in either metaphorical or literal well-lit, middle-class neighborhoods. No, even the most fearsome predator, no matter their attitude, is, on some level, well aware of their mortality, their vulnerability.

It is, with rare exception, very healthy to practice caution.

So, I would say Ed is correct, but with some slight nuance. Predators don’t fear only “bigger predators” in the literal sense. They fear anything that could successfully hurt them. If they didn’t have that fear, they wouldn’t last very long.

A fearless predator is a dead predator.

Which, actually, also comes into play when Bill the vampire manages to get the advantage over other vampires by biting them, which they weren’t expecting, because they’re fearless… and then, quite suddenly, they know fear again.

In a straight-up fight, the other vampires would absolutely murder Bill, but, because they fear him, they leave him be. And because he fears them, he doesn’t push his luck!

In nature, even an entire pride of full-grown lions will flee from an entire herd of buffalo, an enraged elephant, or an angry hippo. Two grown grizzly bears arguing over a kill will back off and let a wolverine, much smaller than either of them, have the kill instead. An egg-eating monitor lizard will flee the return of an alligator to its nest, as the latter’s head is roughly the size of the former’s entire body. Whenever animals find themselves in a confrontation, they will almost always try to look bigger than their opponent.

And anytime one human bullies or threatens or harms another, the surest way to stop them is to make it too dangerous for them to continue. The smart ones pull back after that, and the not-so-smart ones are left in no position to hurt anyone else. 😉

In short: it pays to be the bigger predator.