What was observed to happen to the frequency of small-beak-depth g. fortis on an island when a large-beak-depth competitor was introduced?

The first observation was that, natural selection might itself be variable because it is dependent with the different seasons the environment have. Second, the frequency of small-beak depth Geospiza fortis became lesser on an island when a large-beak-depth was introduced because the large-beak-depth species has greater survival rate especially during dry season were they can eat larger and harder seeds as compare to the small-beak-depth birds.