In evolution, what does the term "reproductively isolated" imply?

The term "reproductively isolated" refers to populations that cannot interbreed due to various barriers. These barriers can be geographical, behavioral, temporal, mechanical, or gametic, preventing successful mating or fertilization between individuals from different populations. As a result, even though these populations may exist in proximity to one another, they remain distinct evolutionary units.

This concept is fundamental in the study of speciation, as reproductive isolation is often a key factor in the formation of new species. When populations are reproductively isolated, gene flow is restricted, allowing for divergent evolutionary paths whereby each group can adapt to its environment independently. Ultimately, this isolation contributes to the development of unique genetic, morphological, and ecological traits within each population, reinforcing their status as separate species over time.