In 1937, two male and six female ring-necked pheasants were introduced to an island off the coast of Washington state. The pheasants mainly ate wheat. The only known predators on the island were house cats, hawks, and owls. After five years, the pheasant population on the island had increased to 1,325 individuals. The population size then remained stable.
Which of the following most likely explains why the pheasant population size remained stable after five years?