Final answer:
Cryptic species are populations similar in morphology but divergent in specific traits due to geographic isolation leading to unique environmental conditions and evolution.
Step-by-step explanation:
The populations that are similar in morphology but have significant divergence in traits such as songs, temperature, or drought tolerance are known as cryptic species. These species may appear identical at first glance but possess genetic and behavioral differences that prevent them from interbreeding. Cryptic species often emerge as a result of geographic isolation, where unique environmental conditions in isolated areas promote evolution and retention of distinctive traits within species. Examples include differences in warm-blooded animals along a latitudinal cline, flowering plants on a mountain slope indicating an altitudinal cline, and marine species with unexpected molecular divergence indicating the presence of cryptic lineages.