UCLA Major

I am applying to UCLA and UC Berkeley for the fall 2018 semester. I am going to study biology, however, I heard this is a highly impacted major and can effect your chances of acceptance. Is it better to apply undecided and then change your major later?

From the UCLA FAQ:
Q: DOES MY CHOICE OF MAJOR HAVE AN IMPACT ON MY CHANCES FOR ADMISSION?

A: For freshmen applying to a major in UCLA’s College of Letters and Science (L&S), choice of major will neither enhance nor diminish their prospects for admission. In fact, a large number of freshman applicants apply as “undeclared.” Major is a factor for freshmen applying to non-L&S schools at UCLA (Arts and Architecture; Engineering; Nursing; Theater, Film and Television).

SO For UCLA, Biology is in the College of Letter and Sciences and you are not admitted by major. Once you are accepted, the following is what you need to do to declare the Biology major:
All students interested in declaring one of the programs offered by the department must have an established UCLA GPA and be in good academic standing (i.e., not on Academic Probation or STD) at the time of application.

Pre-Requisites for the Majors (Biology; Ecology, Behavior and Evolution; Marine Biology):

For students who entered UCLA as a First-Year college student:

Completion of Life Sciences 1 with a grade of C- or better
Enough units to complete the major without exceeding your current unit maximum
Successful completion of latest attempt of a Life Science Core Curriculum course (C- or better)