The 17,000 islands that comprise the nation of Indonesia stretch more than 3,000 miles along the equator, bridging Asia and Australasia. Indonesia’s natural habitats vary widely. On some islands, tropical forests climb from steamy lowlands to mountain slopes. On others, parched savannah thrives. Coral reefs line thousands of tranquil atolls, while relentless waves batter rocky cliffs on other shores. In Papua, the mountains reach so high that permanent ice caps top their peaks, surrounded by bar...