Final answer:
The reproductive advantage for organisms best suited to their environment is called natural selection, which leads to adaptations and evolutionary changes over time.
Step-by-step explanation:
The reproductive advantage enjoyed by organisms best suited to a specific environment is known as natural selection. This concept is deeply tied to the idea of adaptations, which are heritable traits that enhance the survival and reproduction chances of an organism. Natural selection is responsible for the greater survival and reproduction of individuals within a population that possess favorable heritable traits, leading to evolutionary changes over time. For instance, the webbed feet of aquatic animals are adaptations that enable them to swim more efficiently.