National Geographic photojournalist Joel Sartore continues his Photo Ark quest, photographing species around the world that are escaping extinction thanks to human efforts.

Joel Sartore's quest to photograph all the animal species under human care celebrates its 15th year with this collection of photographs. The animals featured in these pages are either destined for extinction or already extinct in the wild but still alive today, thanks to dedication of a heroic group committed to their continued survival. From the majestic Sumatran rhinoceros to the tiny Salt Creek tiger beetle.

Sartore singles out the species most likely to disappear in the next decades, as well as some that have already been lost. Alongside these images are the words of scientists and conservationists who are working to protect and restore populations of endangered species.