Poo makes the world go round ...

Animal waste essential for ecosystem survival.

Take, for instance, salmon. Born in rivers, they head out to sea to fatten up as adults. A couple of years later, they head back inland en masse to mate and die. Their decaying carcasses enrich the rivers and feed, among others, the next generation of salmon. "Salmon fry are literally sustained by their parents," say Wilcove and Wikelski.