Photos: Documenting the world's animals in 'The Photo Ark'

By the year 2100, half of the world's species could be extinct.

Future generations may not even know what they're missing.

But National Geographic photographer Joel Sartore wants to preserve what he can, even if it's only through photographs. In a project dubbed "The Photo Ark," Sartore has set out to document every one of the world's 12,000 captive species — those living in preserves, zoos and other locations under human care around the world.

A selection from his thousands of photographs has been compiled in a new book: "The Photo Ark: One Man's Quest to Document the World's Animals." Four hundred creatures are included: a blue waxbill, a banded sea star, a pileated gibbon, a clouded leopard, a side-striped palm pit viper, a white-bellied pangolin, a spectral tarsier, a veiled chameleon and more.

He started the project 12 years ago and hopes to finish it in another 12. The news often delivers reminders to keep up the pace: Several creatures he's photographed have since gone extinct — and now exist only in records like "The Photo Ark."

Sartore hopes the book will spark action, encouraging people to take steps to preserve the species pictured in the book, and the species in their own backyards.

If you find yourself marveling at the biodiversity that's slipping away, it can be easier to act than you think, Sartore said. Love butterflies? Plant milkweed. Monarch-friendly environments have been decimated, but planting milkweed helps make the monarch migration possible.

Sartore knows his work will outlive him, and he hopes his call for action does too. "Long after I am dead," he writes in the book's introduction, "these pictures will continue to go to work every day to save species."

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