Answer:
Simply birds with the right beak shapes for insects and seeds will be naturally selected , and therefore have more population than those with wrong beak shapes.
Explanation:
This detailed the concept of variation, which lead to natural selection against selective pressure, for birds with adaptable beaks for survival.
Since the birds were originally of the same population. Definitely it was the selection pressure(feed types) in their different new environments, that made them to developed different beak size in order to adapt to survive .
In insect dominated environment, birds which populated the habitat must have developed certain traits for this through variation, and those which lack the gene for the beak shape were selected out from the population.<em>Hence, birds with right beak shape for insect will survive, and have more young than the less fitted one.</em>
Likewise, in seed dominated environment, only birds with right beak shape for picking the seeds will dominate the population, because they are well adapted against the selective pressure ,they are the survival of the fittest, and are therefore naturally selected ahead of those with wrong beak.Their young will therefore dominate the population.