At any given full, or otherwise, speed while maintaining level flight, for any given wing area, for any given airfoil and for any given air-mass-density, there is only one angle-of-attack that satisfies that specific level flight, which is held in position by the force of whatever stabilizing element that the specific aircraft utilizes.
Any variation of any factor disturbs such previously established level flight therefore some item has to be changed to resume the perfect balance.