Think about the two words that make up the term reproductive isolation. how do you think reproductive isolation affects the evolution of a species?

Reproductive isolation refers to the inability of an organism or species to breed successfully with other organism or species.

It may arise from various factors such as:

Reproductive and geographical isolations between two populations (of same species) inhibit the flow of genes among them. Slowly, these isolations increase the variations in the gene pools of the two populations.

These genetic variations keep on increasing with time. In addition, as an adaptation to their surrounding or habitat the two populations would develop different behavioral and physiological changes

With time, these differences will increase up to such an extent that the two populations would not be able breed with each other. Hence, it would lead to the evolution of one or both the populations into new species.  

PLATO:

Reproductive isolation refers to populations of organisms that have become isolated from each other. A geographical barrier or a genetic change can cause this isolation. As a result, the organisms are not able to successfully reproduce with each other. The two populations evolve separately from each other, likely developing different frequencies of genetic mutations and possibly selecting different traits.