AP Bio test compared to SAT Subject test

How does the AP Biology test compare to the SAT Biology Subject Test in difficulty? I took the subject test last year after Honors Biology and, aside from a bit of plant and animal anatomy that I had to self-study, didn’t find it that hard. Is the AP Bio test significantly more difficult, or are they comparable?

The SAT subject test tests HS biology; The AP test, college biology. You can infer that the AP test is more difficult.