Across the world, plants and animals are silently finding their way into places where they don't belong. These interlopers, called invasive species, have enormous powers — they spread disease, they devour our buildings. Some are destroying the very land under our feet. Odds are these species that evolved in one place and now live destructively in another may have even infiltrated your own backyard.

Around the world, from the forests of Venezuela to Yellowstone’s majestic wilderness to the Caribbean’s coral reefs, researchers are discovering predators play a vital role in the health of our natural systems. Knowing this, should we learn to live with predators? Can we?

Frogs are vanishing in America’s heartland. Canadian beluga whales are mysteriously dying in the Saint Lawrence River. Swarms of sea stars are overrunning parts of Australia's Great Barrier Reef. Are these signals that something is amiss in Earth’s water – from our marshes to the sea? Has water become a massive delivery system for pollutants?