A population of birds colonizes an area in which the insects upon which they feed live inside trees. Which of the following events accounts for an observed increase in average beak size in the bird population over time? a. Decreased fitness of the insects, allowing the birds to catch them more easily
b. Increased fitness of large-beaked birds, leading to natural selection
c. Increased fitness of the large-beaked birds, creating a new species
d. Decreased fitness of small-beaked birds, creating a new species