The length of a hummingbird's beak determines the types of flowers it can feed from. Members of a population of hummingbirds once all had similarly long beaks. Over time, the sizes of the beaks in the population have diversified. Now, some hummingbirds in this population have very short beaks while other hummingbirds in this population have long beaks. Every generation, the proportion of hummingbirds with very short beaks increases in this population. Which of the following best describes this hummingbird population?

A.
Members of the population must compete for resources.
B.
Members of the population exhibit equal reproductive success.
C.
Members of the population have equal chances of survival.
D.
Members of the population do not have any genetic variation.