Biologists have discovered that many islands contain a variety of unique species. Generally, these species are found nowhere else in the world. A bird species found on an island is similar in appearance to a bird found on the mainland, but the two species cannot produce offspring. Which of the following is a logical conclusion that can be reached regarding these bird species? ( 2 points)
a. Allopatric speciation has occurred as a result of geographic isolation.
b. Hybridization has occurred as a result of reduced gene flow.
c. Reproductive isolation has occurred as a result of prezygotic barriers.
d. Sympatric speciation has occurred as a result of postzygotic barriers.