Second-Choice Major on Apps

I was wondering whether it would be better to pick second choice majors that are similar or different from the first-choice major. For example, if I pick molecular biology as my first choice, would I have a higher chance of getting admitted if I pick biology (similar), environmental studies (less similar), or something else entirely for my second choice? Does it depend on the school or the competitiveness of the major?

http://admdev.ucdavis.edu/apply/tr_completing_app.cfm
Some information from the UC Davis website: “We also suggest that you include an alternate major in a different field-of-study when you apply; we may consider it if you are not admitted in your first-choice major.” But would that apply only to the most competitive majors?

Some schools do consider alternate majors and some do not even throughout the UC system, each campus may have different criteria.

See link: http://admission.universityofcalifornia.edu/counselors/files/freshman-admission-matrix.pdf