When the woolly mammoth went extinct thousands of years ago, it did more than just disrupt the food chain—it also decreased Earth’s ability to recycle nutrients. A new study finds that giant animals like woolly mammoths and whales played an important role in the ecosystem through pooping. When a 90-foot-long whale or a massive ground sloth took a dump, it helped spread nutrients from one part of the planet to the other, the study in PNAS argues.
Whales and other marine mammals feed in deep waters and poop and urinate near the surface, which helps spread deep-sea phosphorous. When the animal dies, its decomposing body will also fertilize wherever it ends up. This fecal distribution system moves nutrients from the most productive ecosystems to areas where minerals are less concentrated.
Image Credit: Diagram from PNAS; designed by Renate Helmiss
As the numbers of large animals on the planet started declining around 12,000 years ago and humans took over, this damaged this nutrient cycle. The study’s authors—led by University of Oxford ecologist Christopher Doughty—estimate that with the death of about 150 species of megafauna like ground sloths, mastodons, and mammoths, the capacity of the world’s animal population to move nutrients around the Earth has been reduced to 8 percent of what it once was.
Whales, for instance, annually move about 165 million pounds of phosphorus from the bottom of the ocean to the top, down from about 750 million pounds in the days before commercial hunting devastated their populations. Seabirds and salmon that travel from the ocean up rivers to spawn and die used to move more than 300 million pounds of phosphorus per year, but now they average less than 12 million pounds.
"Phosphorus is a key element in fertilizers and easily accessible phosphate supplies may run out in as little as 50 years," Doughty says in a press release. "Restoring populations of animals to their former bounty could help to recycle phosphorus from the sea to land, increasing global stocks of available phosphorus in the future."