In а pоpulаtiоn оf birds, there is vаriation in beak size. Birds with small beaks are better at eating tiny seeds, while birds with large beaks are better at cracking hard, large seeds. Birds with medium-sized beaks, however, struggle to eat either type of seed effectively. Over time, the population begins to show an increase in the number of birds with either small or large beaks, while birds with medium-sized beaks become less common. Which type of selection is being displayed in this scenario?