What are the competitors of habitat for checkerspot butterfly?

Depends, I suppose, on which checkerspot you're talking about. It's not so much competition for habitat per se for the Baltimore checkerspot, but deer are notorious browsers of the caterpillar's food plant, turtlehead, and often browse out all the plants unless they are protected. "Competition" for habitat really doesn't rate as a problem for the checkerspot species I'm familiar with.