The Sierra Nevada yellow-legged frog, a species native to California that was put on the endangered species list in 2014, is making a comeback in the Yosemite National Park.

The amphibian, Rana sierrae, was once found abundant in the western mountain range. It started disappearing during the latter part of the 20th century and was added to the endangered list by the U.S. Fish and Wildlife Service.

Thanks to the diligent efforts of concerned officials, the Sierra Nevada yellow-legged frog population in Yosemite National Park has increased sevenfold over the last 20 years.

Roland Knapp, the lead author of the study that reported the said findings in the Proceedings of the National Academy of Sciences, said that the Sierra Nevada yellow-legged frog is not a rare species of amphibian that became endangered but one that had been present in large numbers. The biologist at the University of California enthusiastically described the recent increase in the frog population as a "dramatic turnaround."

The frog species started vanishing following the stocking up of non-native fish in the park's lakes by the fishermen's organizations. The predatory trout that preyed on the frog's food also feasted on the tadpoles and frogs themselves. In addition, a kind of fungus in the frogs' habitat appeared around the 1970s, which put the species further at risk. The fungus was seen in wet areas where the amphibians lived but not deep under the water that served as the habitat for predatory trout.

The scenario gradually reversed over the past 20 years after the park stopped stocking up non-native fishes in the lakes, reported Knapp and team. As for the fungus threat, it is believed that the frogs are no longer susceptible to the fungal disease because they were able to develop resistance following decades of exposure.

Noah Greenwald, the endangered species director at the Center for Biological Diversity, noted that halting non-native fish stocking up processes didn't just reverse the decline of the frog population. Efforts put in by Knapp in removing such fishes from lakes have a huge role to play in protecting native biodiversity in the park.

"If you take a species that was once so abundant out of a food web, you're going to have a whole series of unintended consequences," Knapp said, in an interview with the Christian Science Monitor. "For example, we know that when the frogs disappear from one of these sites, the garter snakes, which are one of their major predators, also disappear. By restoring frogs to these habitats and to these food webs, we restore the entire food web."

Photo: California Department of Fish and Wildlife | Flickr